Other techniques associated with fertilization not discussed in this review appear limited in Africa. Although widely practised in Asia, the use of sewage in fish culture is not practised in Africa as noted by Bardach et al. (1972). Drying ponds for release of nutrients from bottom muds is used rarely in most countries at present, but most authors agree this technique would be beneficial in the tropics. During the 1950's this practice was widely used. It appears that the use of green manures is not practised either in Africa and that benefits to be obtained from this technique are minimal.
The efficiency of most fish cultures in Africa may be considered poor. Much work remains to be done on improving the methods of tilapia culture. Productivity is often high in ponds in Africa, and monocultures of tilapia-the dominant system of culture- cannot efficiently exploit all natural foods present in such rich ponds. Techniques of polycultures need to be developed using locally available species. Such techniques cannot be developed without preliminary research.
A comparison of various fertilizers and feeds used in Africa is presented in Table XI. This table is an effort at comparing possible production, incidence of cost per kg of fish produced and profit index. In composing this table the author assumed: 1) the full crop was harvestable; 2) the price of one kg of fish was CFA.F. 200; 3) all costs are based on current prices in Bangui except where indicated; 4) the profit index was based on the following:
and 5) the incidence of cost was based on the following formula (Vincke, 1969):
The figures in the table have limitations and may be considered “ideal” in some cases. However, in most cases calculations were based upon actual results obtained by the C.T.F.T. in the Ivory Coast and Malagasy Republic and past and current FAO/UN projects in the Central African Republic, Gabon, Congo and Cameroon. The costs of fertilizers include inland transport to Bangui, thus, fertilizer costs in other countries may be less. Other figures may represent unique situations as well - such as the cost of beer waste and spoiled foods used by the FAO/UN project in Bangui being CFA.F. 4/kg. The only cost of this particular ration is transport and labour.
Van der Lingen (1967) calculated the profit index for fertilizers and feeds as 7.5 and 2.0 respectively. Current data as presented in Table XI indicate the lower profit index obtainable with fertilizers (mean 5.73) due to greatly increased costs and the higher profit index obtainable with feeds (mean 6.06).
In the final analysis, the choice of fertilizers or feeds for use in fish culture in Africa is based upon availability and cost. Fertilizers have greatly increased in price in recent years, but they still offer promise for use in fish culture in Africa as shown in Table XI. Availability, though, of large quantities of fertilizers required for commercial-scale fish culture presents a serious problem in many countries.
Feeding of fish can be expected to increase in popularity with development of other agricultural endeavours. But the use of pelleted feeds and other feed technology will probably remain restricted to research for several more years.
It appears that associated animal husbandries such as the raising of pigs in pens beside or over fish ponds may prove to be more practical and economical for commercial fish production in, at least, parts of Africa. Such fish culture systems are based on continual organic fertilization and appear to work very well with tilapia species.
TABLE XI
A comparison of various fertilizers and feeds including possible fish productions,
incidence of cost/kg of fish produced and profit index
| Fertilizer or Feed | Application Rate (kg/ha) or Feeding Rate (% body weight) | Frequency of Application | Expected Production (kg/ha/yr) | Incidence of Cost/kg of Fish (CFA.F.) | Profit Index | Cost/kg (CFA.F.) |
| Inorganic Fertilizer | ||||||
| Triple superphosphate | 25 | monthly | 1 400 | 18.21 | 10.98 | 85.00 |
| Triple superphosphate | 60 | monthly | 1 600 | 38.25 | 5.20 | 85.00 |
| Double superphosphate | 56 | monthly | 1 100 | 70.00 | ||
| Lime | 1 680 | initially | 193.96 | 1.03 | 33.00 | |
| 280 | monthly | |||||
| Organic Fertilizers | ||||||
| Chicken manure | 8 000 | monthly | 2 300 | 32.97 | 6.06 | 0.79 |
| Feeds | ||||||
| Rice bran | 10% | daily | 300 | 45.40 | 4.40 | 10.00a |
| Corn meal | 10% | daily | 350 | 77.09 | 2.59 | 20.00a |
| Cassava flour | 10% | daily | 325 | 79.49 | 2.50 | 17.32a |
| Cooked corn | 10% | daily | 430 | 57.71 | 3.46 | 15.98a |
| Cooked cassava | 10% | daily | 300 | 73.44 | 2.72 | 15.30a |
| Ration A - Tilapia | 4% | daily | 5 000 | 37.52 | 5.30 | 32.07 |
| Ration B - Tilapia | 4% | daily | 6 000 | 62.88 | 3.18 | 38.58 |
| Ration A - Clarias | 4% | daily | 18 000 | 115.45 | 1.73 | 32.07 |
| Beer waste + spoiled feeds of 20% protein | 33% | daily | 5 000 | 50.80 | 3.93 | 4.00 |
| Ground cotton seed (coarse) | 10–15% | daily | 4 200 | 40.14 | 4.98 | 4.50 |
| Feed + Fertilizer | ||||||
| Beer waste + | 33% | monthly | 4 300 | 49.10 | 4.07 | 4.00 |
| Chicken manure | 500% | monthly |
a Prices from Malagasy Republic, 1970
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by
Yoel Pruginin
FAO Consultant
FAO/UNDP The Promotion of Integrated
Fishery Development Project
P.O.Box 593
Lilongwe, Malawi
Abstract
Guidelines for species selection and stock manipulation in pondfish culture in Africa are reviewed and possible approaches suggested. It is felt that despite the spread of pondfish culture to many countries in the continent, the lack of standard record practices hinders comparative evaluation of results so far obtained. The tilapias are the principal cultivated fishes in the African continent; their culture requires special management techniques aimed particularly at density control - monosex culture and density control by selected predator(s). Polyculture of tilapia and carps, the need for hatcheries and the relationship of pond carrying capacity and feeding practices to stocking rates are discussed. The establishment of standard recording procedures in fish culture is recommended.
Résumé
Les directives pour le choix des espèces et l'aménagement des stocks, propres à la pisciculture africaine, sont passées en revue. Des solutions possibles sont suggérées. Malgré le développement de la pisciculture en étangs sur le continent, il semble que l'absence de méthodes normalisées pour l'enregistrement des données de base empêche de comparer les résultats obtenus à ce jour. Les tilapias sont les poissons les plus cultivés en Afrique; leur élevage requiert des techniques spéciales d'aménagement orientées d'abord vers le contrôle de la densité de peuplement - élevage monosexe et contrôle par un prédateur déterminé. Sont également discutés l'élevage mixte de tilapias et de carpes; le besoin en centres d'alevinage; les relations existant entre d'une part la capacité de charge de l'étang et les types d'alimentation et d'autre part le taux de charge. L'établissement de procédures normalisées d'enregistrement des données sur la pisciculture est recommandé.
Fish farming has spread to many countries in Africa during the time between the two world wars. The practices and status of fish culture are described in several books by Hickling (1962), Maar et al. (1966), Huet (1970), and Bardach et al. (1972). The Cichlidae, mainly species of the genus Tilapia, are the predominant cultivated finfish in African aquaculture. Predatory species from the families Bagridae, Centrarchidae, and Centropomidae are stocked in combination with Tilapia spp., primarily for density control. The introduced species Cyprinus carpio is also cultured in combination with the tilapias. Among other species, silver carp (Hypophthalmichthys molitrix) and grass carp (Ctenopharyngodon idellus) have been introduced to some countries and may be suitable for use in polyculture (see section 5). The CIFA Working Party on Aquaculture (1974) recommended a list of species for large-scale aquaculture in CIFA member countries in which the tilapias are the most important group.
Yields of 200–6 000 kg/ha/annum have been reported. Most of the publications, however, lack quantitative data on stocking and feeding rates as well as rates of growth that could help fish farmers in drawing up guidelines. Maar (1966) recommends species combinations based on different feeding habits, without giving details of each species in the combination.
2.1 Stocking of Breeding Fish in Ponds
The bigger fish from the pond are cropped while the smaller fish are restocked. Most fish produced by this method are small.
2.2 Monosex Culture of Tilapia
This culture method is used in places where bigger fish are preferred. Only the males are cultured and are obtained in one of two ways: (a) hybridization of two Tilapia species producing 100 percent males in F1 - e.g., Female T. nilotica x Male T. aurea: and (b) sexing Tilapia spp. fingerlings (at a size at which their sex can be distinguished by the appearance of the genital papilla) and discarding the females. Pruginin and Kanyike (1965) and FAO (1967) have shown that in addition to the advantage of monosex culture, the male hybrid of Female T. nilotica x Male T. hornorum has shown a clear advantage over the parent species cultured in the same ponds as demonstrated in Table I. When stocking this male hybrid at 1 000 and 4 000/ha, the higher stocking rate resulted in an increased yield and a reduced food conversion ratio.
Table I
Growth Potential of a Tilapia Hybrid
(Pruginin, 1967)
| Duration of Observation (Days) | Average Wt Gain | Daily Wt Gain per Fish (g) | |
| Hybrid | 126 | 118.00 | 0.92 |
| T. nilotica | 126 | 82.75 | 0.63 |
| T. hornorum | 126 | 75.00 | 0.55 |
These results were obtained from ponds fed with maize. Elsewhere, e.g., Israel, Tilapia spp. hybrids raised in polyculture with carp gained up to 3 g/day when fed with sorghum and up to 8 g/day when fed pellets containing 25 percent protein.
Monosex culture experiments with T. shirana and T. mossambica, both sexed by hand, are presently being carried out in the Malawi Kasinthula Fish Farm (FAO/UNDP project). Preliminary results (Pruginin, unpublished data) have shown a considerable increase in yield compared to bisex culture of the same species at a stocking rate of 3 000/ha. Increasing the rate of stocking from 3 000/ha to 10 000/ha (monosex) did not affect the individual gain and increased the daily gain per hectare from 3 kg to 10 kg (Mseska and Arad, personal communications). In these ponds a predator (Serranochromus robustus) was added in various ratios to control wild spawning due to sexing errors and the incursion of wild fry through the water supply.
2.3 Density Control by Predator
In Uganda, Tilapia sp. and Lates niloticus were stocked at a rate of 2 000 Tilapia and 30 L. niloticus/ha (FAO, 1965). This pond produced about 600 kg/ha and 95 percent of the fish cropped were of marketable size. Similar results were obtained by using Bagrus docmac as a predator. These species are used in several countries, but lack of quantitative data makes it difficult to evaluate the results. The introduced species Micropterus salmoides is also used as a predator in tilapia ponds in some countries.
Poor results from many ponds throughout Africa may be a result of ignoring the relationship between the physical and chemical condition of the ponds and the feeding habits of various species. In Tanzania, T. rukwaensis from Lake Rukwa, which is warm and alkaline, were stocked in ponds in the Njombe region which is a typical tea-growing area with a water and soil pH of five and a low temperature during part of the year. It is not surprising that the ponds in this area yielded less than 100 kg/ha. Similar results were obtained from C. carpio introduced into Uganda in silty water; it was found that the higher the percentage of silt in the water, the lower the yield of carp (FAO, 1961). It has been reported that the pH in pond bottoms in Kajansi (Uganda) is 4.3–5.4 at which very little benthic fauna develops (FAO, 1968). As the carp is primarily a bottom feeder, the yields obtained were only 200–400 kg/ha/annum. The daily gain in weight ranged from 0.09 kg/ha to 1.78 kg/ha and the food conversion ratio ranged to as high as 8:1. With excessive feeding, the yield was increased to 1 000 kg/ha, but feed costs made the economic feasibility of this approach questionable.
In more favourable conditions in Lesotho, the same species (C. carpio) in ponds with a pH of 7–8 yielded up to 2 200 kg/ha/annum, with a daily gain of 10 kg/ha. According to Bar-David (personal communication), with advanced feeding methods (using demand feeders), the daily gain reached 38 kg/ha with food conversion ranging from 2.7 to 3.1. The estimated annual yield was 7.8 tons/ha.
Ponds whose soil pH is low can be filled with water with a higher pH, e.g., in Kajansi, pH of the soil is 4.3–5.4 and the pH of the water is 6.8–7.2. In these ponds a dense phytoplankton develops which can support a population of planktophagic fishes.
The carrying capacity of ponds varies according to the species and the rate of growth. The rate of growth depends on three factors: rate of stocking, rate of feeding, and quality of feed. Daily weight gain of Tilapia spp. when fed with bran or maize was 1–3 g, and 6–8 g when fed on pellets including 25 percent protein. Afterwards the carrying capacity of the pond, i.e., 1 000 kg/ha, and the ultimate size of the fish desired for market, i.e., 250 g, were determined. The proper rate of stocking may be estimated by dividing the carrying capacity by the required weight of fish, e.g.
Observation on polyculture of common carp (an introduced species to African countries) with Tilapia spp. has shown that the species grow better when stocked in combination. However, it was concluded that due to the poor production of natural food for carp (bottom fauna) that the rate of stocking of carp should not exceed 500–1 000/ha. The actual stocking rate for each species should be determined after considering the available supply of the required natural food.
It is possible to compensate for a lack of sufficient natural food by adding balanced supplemented feeds. The economic feasibility of this practice should, however, first be carefully examined, e.g., carp could be given feeds with a high protein content in ponds deficient in natural food, but in many cases this would result in non-competitive production costs.
Availability of hatchery facilities or their absence may influence the decisions concerning species selection and stocking rates. A hatchery-produced supply of seed is required in the case of:
Hybrids of Tilapia spp. It is necessary to maintain pure strains of the desired parent species.
Introduced species, e.g., common carp, silver carp and grass carp. Although the common carp will spawn freely in ponds, in many African countries special nursing ponds must be provided to protect the fingerlings against predation, especially by frogs of the genus Xenopus. It is believed that this predation has prevented the establishment of the common carp in natural bodies of water. The silver carp and grass carp require induced spawning under hatchery conditions.
Indigenous species, primarily Tilapia spp., required for high density and especially monosex culture (sexing by hand). The supply from wild spawning in rearing ponds is usually inadequate and requires hatchery and nursery pond facilities.
The above data are not given as formulae to be implemented but are mainly provided as examples to show the importance of various factors to be considered in species selection and stock manipulation.
Factors which influence the decisions fall into three main categories:
Environmental considerations, e.g., water and soil pH, temperature, salinity; biological factors such as suitability of the species to be cultured, natural food produced in the ponds, predators, parasites, etc.
Market requirements and economic feasibility, i.e., species and size preference, marketing possibilities, seasonal considerations, production costs in comparison to other protein foods, cash crop or subsistence farming, etc.
Farming activities and methods, e.g., species ratios, availability of feeds, hatchery services, fertilizing and manuring, cropping, and economic feasibility of each farming method.
To enable comparison and evaluation of various methods used in different locations, it is necessary to establish a standard criteria index which will cover the above mentioned aspects with agreed parameters and standard recording procedures of farming activities - rate of stocking of each species, feeding techniques, sampling frequency, fertilizing and manuring, daily gain per fish and per hectare, cropping (interim skimming) and final harvesting by drainage, crop analysis (size of fish according to species), food conversion ratio and cost of input.
Bardach, J.E., J.H. Ryther and W.O. McLarney, 1972 Aquaculture. The farming and husbandry of freshwater and marine organisms. New York, Wiley - Interscience. 868 p.
FAO, 1967 Report to the Government of Uganda on the experimental fish culture project in Uganda 1965–66. Based on the work of Y. Pruginin. Rep.FAO/UNDP(TA), (2446):16 p.
FAO, 1968 Report to the Government of Uganda on fish culture development. Based on the work of K.M. Apostolski. Rep.FAO/UNDP(TA), (2575):11 p.
FAO/UN, 1961 Report to the Government of Uganda on an experimental fish culture project in Uganda 1959–60. Based on the work of A.G. Wurtz. Rep.FAO/EPTA, (1387):32 p.
FAO/UN, 1965 Report to the Government of Uganda on the experimental fish culture project in Uganda 1962–64. Based on the work of Y. Pruginin. Rep.FAO/EPTA, (1960):25 p.
Hickling, C.F., 1962 Fish culture. London, Faber and Faber. 295 p.
Huet, M., 1972 Textbook of fish culture. London, Fishing News (Books) Ltd. 436 p.
Maar, A., M.A.E. Mortimer and I. Van der Lingen, 1966 Fish culture in Central East Africa. Rome, FAO. 158 p.
Pruginin, Y. and E.S. Kanyike, 1965 Mono-sex culture of tilapia through hybridization. Paper presented to Symposium on Fish Farming, O.A.U., Nairobi
by
L.L. Lovshin2 and A.B. Da Silva
Centro de Pesquisas Ictiológicas
Convênio DNOCS/SUDENE/USAID
Fortaleza, Brazil
1 Contribution from the International Center for Aquaculture, Auburn University
Contract AID 1152 TO 2 ICA
2 USAID/Auburn University fishery adviser
Abstract
Tilapias have been cultured for many years with limited success because uncontrolled reproduction in growing ponds results in stunted populations. Two of the most promising methods of controlling tilapia reproduction are the selection of only the faster growing males for culture and the hybridization of two species of tilapias to produce 100 percent male offspring. Experiments demonstrate that the monosex culture of male tilapia or the culture of all-male hybrid tilapias has vast promise in tropical areas where protein deficiency is endemic. High yields of male tilapias can be cheaply and easily produced using organic and inorganic fertilizers and a wide range of agricultural waste products as feeds.
The potential of all-male tilapia culture has been experimentally proven. Now it must be shown that tilapia culture is both technically and economically feasible if these fishes are to alleviate protein deficiencies. Lack of knowledge concerning the large-scale production of all-male tilapia fingerlings is the major barrier to the realization of this goal.
Résumé
Pendant des années on a pratiqué la pisciculture des Tilapia avec un succès limité à cause de la reproduction incontrôlée dans les étangs d'élevage qui a donnée des populations mal venues. Deux des méthodes les plus prometteuses pour contrôler la reproduction des Tilapia sont la sélection des mâles à croissance plus rapide pour l'élevage et l'hybridation de deux espèces de Tilapia pour donner une progéniture à 100 pour cent de mâles. Des expériences montrent que l'élevage monosexe de Tilapia mâles ou l'élevage de Tilapia hybrides tous mâles a un grand avenir dans les régions tropicales où la déficience en protéines est endémique. On peut obtenir des rendements élevés de Tilapia mâles à bas prix et facilement en utilisant des engrais organiques et minéraux et une large gamme de déchets de produits agricoles comme nourriture.
Les possibilités de l'élevage de Tilapia tous mâles ont été démontrées expérimentalement Maintenant, il faut montrer que l'élevage du Tilapia est faisable à la fois techniquement et économiquement et ces poissons doivent compenser les déficiences en protéines. Le manque de connaissances concernant la production à grande échelle d'alevins de Tilapia tous mâles est le principal obstacle pour atteindre ce but.
Fish of the genus Tilapia are endemic to Africa but are presently found in most tropical and sub-tropical areas of the world where water temperatures are suitable for growth and reproduction. Once promoted as the “miracle fish”, several species of Tilapia were widely distributed around the tropical world during the 1950's as the answer to man's protein problems. The original high expectations for Tilapia turned to disillusionment as the problems with husbandry of this fish became apparent to inexperienced fish culturists. The tilapia's ease of culture, resistance to poor water quality and diseases, and ability to efficiently convert organic material, animal and agricultural waste products into high quality protein could not offset their principal fault of excessive reproduction in culture ponds. This fault resulted in large numbers of small, unmarketable fish. The lack of knowledge for controlling unwanted reproduction discouraged most tilapia farmers and thousands of fish ponds built throughout Africa and Asia for tilapia culture were later used either to raise other species of fish or abandoned.
Several researchers, recognizing the potential of tilapia culture continued to study methods of reducing or eliminating unwanted reproduction in tilapia cultures throughout the 1960's and early 1970's. Efforts to control tilapia numbers in growing ponds soon centered on the following techniques:
Use of a predator species to consume young tilapia.
Establishment of a monosex culture by separating the sexes on the basis of secondary sex characteristics.
Establishment of a monosex culture by hybridization of certain species or strains.
Sex reversal by administration of a hormone treatment.
Elimination of reproductive capability by physiologically altering the gonads by means of chemo-sterelants or irradiation.
While the use of a predator species to control reproduction has met with various degrees of success, the most promising methods of reducing reproduction appear to be the monosex culture of male tilapia, the crossing of two species of tilapia to produce “all-male” hybrids or hybrids that yield a high percentage of males, or sex reversal by means of hormone treatment.
2.1 Monosex culture
The monosex culture of tilapias has normally been done by selecting the faster growing males for culture while females are discarded. While any species of tilapia that has external sexual characteristics that can be identified can be used in monosex culture, the most popular species appear to be T. aurea, T. mossambica. The sexing of males and females of most Tilapia species is a relatively simple procedure if fish of a minimum size of 50 g are used. With a few exceptions, male tilapias can be distinguished either by the size and shape of the genital papilla or by the fact that the genital papilla contains two orifices. The female tilapia often has a smaller genital papilla and the papilla contains three orifices (Fig. 1).
Early methods of monosex fingerling production simply consisted of seining a pond containing Tilapia sp. and sorting out the males for transfer to growing ponds. Chimits (1957) cited early attempts by workers to develop a feasible method of producing monosex fingerlings based on the more rapid growth of the males. Brood stock were placed in small spawning ponds and the fry from these spawns were captured when 5 cm in length and stocked into nursing ponds at 2 500/ha. After three months, the fish had reached an average size of 10 cm and the difference in total length between the males and females was approximately 2 cm. Theoretically, all the larger fish were males and could be transferred to growing ponds. Planquette (1974) elaborates in more detail upon the method of producing monosex hybrids. Brood stock at the ratio of 1 male to 3 females are placed in 50 m2 spawning ponds. After two months, the fry averaging 4 g each are captured and transferred to nursery ponds. Each female parent produces an average of 750 fry. The fry are stocked into the nursery ponds at the rate of 10/m2 or 100 000/ha and after 35 days have reached a size of 20 g to 40 g with the feeding of high rates of agricultural wastes. At this time, the larger males can be selected and transferred to growing ponds. Bard (1974) mentions a similar process for monosex fingerling production but instead of manually sexing, he suggests the use of graders or separators for mechanically separating the larger males.
The culture of monosex tilapias is practised on a commercial scale in Israel; consequently, a great deal of research has been carried out on production of tilapia fingerlings in the country. Unfortunately, much confusion exists as to the exact species being cultured and hybridized. The principal species used in monosex culture in Israel is T. aurea.
Here again, the process for production of monosex tilapia fingerlings is very similar to that employed in Africa but is modified slightly because of climatic conditions. Mires (1969) states that fry of 4 g to 5 g are removed from spawning ponds in early summer and transferred to nursery ponds. The tilapia fry are often stocked in association with carp fry or adults. In the fall, the fingerlings are removed from the nursery ponds and sexed.
The sexed males range in weight from 60 g to 200 g depending on the stocking density and pond fertility. These selected males are overwintered in deep ponds where warm water can be added on especially cold days. The following spring, the males are transferred to growing ponds and are fattened together with carp.
2.2 Hybrid culture
A hybrid is the offspring of male and female animals or plants of different races, breeds, species or varieties. Some tilapia crosses result in the production of 100 percent male offspring while other crosses result in only a higher percentage of male than female offspring. Also, some crosses may give a normal sex ratio. The production of 100 percent male offspring has a great advantage in that fingerlings can be stocked without sexing.
Hybrid crosses that result in less than 100 percent males, in most cases, must undergo a sexing process to remove the females. Therefore, the work required in a monosex culture of a pure species and the culture of hybrid crosses giving less than 100 percent male is nearly equal.
The hybrid cross usually produces a higher than normal proportion of males to females and the hybrids often show hybrid vigor. However, the steps involved in producing less than 100 percent hybrid fingerlings are the same as for the production of monosex tilapia fingerlings. Mires (1969) reported results of nursing the hybrids of male T. aurea and female T. nilotica to stocking size. In one 4.1 ha pond, 12 g hybrid fry were stocked at 8 800/ha. After 86 days, the fish were harvested and sexed. The hybrids were 61 percent males with an average weight of 179 g while the remaining females had an average weight of 119 g. A second pond of 4.5 ha was stocked with 5 g hybrid fry at the rate of 11 350/ha. After 104 days, the fingerlings were harvested and sexed with 62 percent being males. The male hybrids averaged 86 g while the females averaged 70 g. Mires states that fish of this size were easily sexed by hand on a sorting table. The average number of males separated per work day, out of a 60 percent male population, was 2 000. Sarig and Marek (1974) report some interesting experimental results in raising tilapia fry to 10 g size at extremely high densities. Two earthen ponds of 0.15 ha and 0.12 ha were stocked with 0.8 g tilapia fry at the rates of 900 000/ha and 500 000/ha respectively. With aeration and pelleted ration containing 25 percent protein the larger pond yielded 700 000/ha, 8 g fingerlings in 47 days while the smaller pond yielded 460 000/ha, 24 g fingerlings in 72 days. Survival was 78 percent and 92 percent respectively. The amount of food added per day in the larger pond was 240 kg/ha and resulted in a feed conversion of 1.9 to 1 while the smaller pond received 320 kg/ha/day and resulted in a feed conversion of 1.8 to 1. No mortalities were noted due to poor water qualities. Unfortunately, the authors do not state the species of tilapia used or the numbers of these small fingerlings stocked into nursing ponds for producing a fingerling of sufficient size to be sexed and stocked into fattening ponds.
Work done in the U.S.A. by Avault and Shell (1968) resulted in the production of 70.6 percent males when male T. nilotica1 was stocked with female T. mossambica. The reverse cross of the above two species resulted in 71.6 percent males.
A number of hybrid crosses are known to give 100 percent male offspring. The first all-male hybrids were produced in Malacca, Malaya in 1960 by Hickling (1968). Hickling crossed the male T. mossambica2 (Zanzibar strain) with the female T. mossambica (Java strain) and obtained all male offspring. Hickling noted that the hybrids are fertile and will backcross with either female parent resulting in offspring with a sex ratio of 50 males to 50 females. In West Africa, Lessent (1968) crossed T. macrochir males with T. nilotica females, producing 100 percent male offspring; however, the cross could not be regularly produced under natural conditions.
1 This Tilapia, originally from Israel, has been re-identified as Tilapia aurea.
2 This subspecies has since been reclassified and is now called Tilapia hornorum zanzibarica.
In Uganda Pruginin (1968) obtained 100 percent male hybrids by crossing male T. hornorum with female T. nilotica. This cross was produced by stocking 25 to 30 female T. nilotica per 1 000 m2. Males were stocked in the proportion of two males for every three females. Pruginin also noted that the male hybrids reached sexual maturity in five to six months and could back-cross with the female parents producing fry with the normal 50:50 sex ratio. He concluded that the brood fish should be removed from the spawning ponds before the male hybrid reached sexual maturity and back-crossing could occur.
In Brazil, studies with the all-male hybrid of male T. hornorum and female T. nilotica have been in progress the past two years. Da Silva, et al. (1973) reported that 9 female T. nilotica with an average weight of 45 g and 3 T. hornorum males with an average weight of 90 g were stocked into each of three earthen ponds of 350 m2. After 71 days, the ponds were lowered and the parents removed. The ponds were refilled and the hybrid fry allowed to grow for another 63 days at which time the ponds were completely drained. Pond one contained 2 007 hybrids with an average weight of 7 g, pond two contained 2 517, 8 g hybrids, and pond three yielded 3 639, 6 g hybrids. Average number of fry per female was 223 for pond one, 280 for pond two, and 404 for pond three. No spawns were found in production ponds when these same hybrids were raised for eight months.
Lovshin, Da Silva and Fernandes (1974) elaborated further on the method used in Pentecoste, Brazil to produce all-male hybrids for experimental studies. Ponds of 355 m2 are stocked with 10 to 30 female T. nilotica and male T. hornorum at the rate of 1 male to 3 females. The spawning ponds are fed and fertilized and after three months, the parents are removed to prevent back-crossing with hybrid off-spring. The parents can be removed by one of two methods. Spawning ponds can be lowered, and the parents removed with a seine, the spawning ponds then being refilled and the fry allowed to grow for another month or two at which time most hybrids will be of stocking size (20–30 g). The second method involves complete draining of the spawning ponds, the hybrid fry being removed and placed in nursing ponds where the fry are grown to stocking size of at least 20 g.
Lovshin et al. (1974) emphasized the extreme care that must be taken in isolating parent stocks so that pure lines of brood stock are maintained. Any contamination of the brood stock through back-crossing will result in loss of the parents capability to produce offspring which are 100 percent male. At Pentecoste, pure stocks are kept in 36 m2 concrete tanks which are relatively isolated from other ponds and have the inlets filtered with fine, saran screen sacks. The tanks are also covered with nylon netting to prevent the entrance of predator birds and animals. Pure tilapia stocks to be raised as broodfish are held in 355 m2 ponds. If contamination occurs in these ponds, they can be drained and all fish killed. Brood stock ponds can then be restocked using fry from the pure strains held in the concrete tanks.
Lovshin and Da Silva (unpublished data) report further on hybrid spawning work carried out in Brazil. Twelve ponds of 355 m2 were used of which 6 were divided by a fence in the shallow end of the pond to facilitate the removal of brood stock after 3 months. The area enclosed by the fence was 100 m2. Brood stock were placed within the enclosed area; the mesh of the fence was of such size that fry could pass to the other side of the pond but the brood stock were held captive when the pond was lowered. Two treatments, fence and no fence, were tested at two levels of stocking, 10 T. nilotica females and 5 T. hornorum males versus 6 T. nilotica females and 3 T. hornorum males. Each level of stocking was replicated three times. No significant difference was found in the number of hybrid fry between treatments. The ponds with the fence produced an average of 2 133 fry per pond while the ponds without a fence produced an average of 1 985 fry per pond. Interestingly, no significant difference was found between levels of stocking. Ponds stocked with 10 females had an average of 2 165 fry while ponds with 6 females had an average of 1 985 fry. The range in numbers of fry per pond for those ponds stocked with 10 females was from a high of 2 981 to a low of 93 while ponds with 6 females ranged in numbers from a high of 3 619 to a low of 580. The reason for this large variation in numbers of fry per pond is not understood. The average weights of the male T. hornorum parent and female T. nilotica parent at draining were 436 g and 617 g respectively. The average number of fry per female for all females was 271. In 11 of the 12 spawning ponds, 100 percent male offspring were found. The reason for female offspring that occurred in one pond could not be determined. The use of a fence to facilitate the removal of brood stock was very effective and did not appear to harm hybrid fry production at the rates the brood fish were stocked.
All ponds were fertilized with triple superphosphate and fed a ration of wheat bran or cottonseed cake. Considering feeds, fertilizer and labour the calculated price per hybrid fingerling was U.S.$ 0.006.
The production of all-male hybrid tilapia is a relatively simple process if pure strains of brood fish are used, male T. hornorum and female T. nilotica are properly sexed, and the female parents are removed from the spawning ponds at three months to prevent back-crossing.
Studies carried out by St. Amant (1966) in southern California showed that the all-male hybrids from male T. hornorum and female T. mossambica are easily produced in aquaria. The minimum recommended size of aquaria is 20 U.S. gal (76 l). The aquaria are checked every 10 days and females carrying eggs are placed in separate aquaria while in the case of females carrying fry, the fry are removed and placed in aquaria. Adequate protection should be provided for the females in a confined environment as agressive males in spawning condition will often kill females not yet in spawning condition. Free swimming larvae and fry should be separated from the parents as it is suspected that the parents are predatory on the young hybrid fry in confined environments.
Malcolm C. Johnson (personal communication) reports that two more crosses have been reported in Israel that give 100 percent male offspring. There, Y. Pruginin has succeeded in crossing T. vulcani males with T. aurea females and T. zambia males with T. aurea females, both crosses resulting in all-male broods.
3.1 Monosex production
Shell (1968) tested the growth of monosex male T. nilotica at three rates of stocking. Males stocked were one-year old fish with an average weight of 100 g. Three earthen ponds of 2.02 ha each were stocked at rates of 2 519, 3 804 and 5 039 fish per ha. The fish were fed a pelleted ration containing 45 percent protein, 6 days a week. Highest production of 2 152 kg/ha in 163 days was found in the pond stocked with 5 039 fish per ha. No difference was found in average weight per fish between the three stocking rates indicating that fish density probably could have been increased without affecting growth. Lovshin, Da Silva and Fernandes (1974) reported that monosex culture of male T. nilotica resulted in a production of 2 839 kg/ha in 180 days when 63 g fingerlings were stocked at 10 000/ha. The earthen ponds were fertilized biweekly with triple superphosphate and ammonium sulfate and the fish were fed rice bran at 3 percent of their body weight, 6 days a week. Average weight of the male T. nilotica was 236 g. This experiment was a comparison in growth of the male T. nilotica with growth of the all-male hybrids of male T. hornorum and female T. nilotica. No significant difference (P<.05) was found between the growth of male T. nilotica and the all-male hybrids.
Sanchez (1974) reported a net production of 2 160 kg/ha of male T. aurea in 60 days (12 960 kg/ha/yr) in El Salvador. He stocked 40 000 males/ha with an average weight of 113 g. Ponds were fertilized with ammonium sulfate three times over the 60-day period at the rate of 10 g/m2 and fish were fed a pelleted ration containing 30 percent coffee pulp daily at 3 percent of their body weight. Average weight of the male T. aurea at harvest was 143 g. T. aurea reproduction was found in the experimental pond at termination of the experiment.
Yashouv and Halevy (1967), Yashouv (1969), and Yashouv and Halevy (1972) have written a series of papers describing their work with the culture of male T. aurea, male T. vulcani, and hybrids produced by these two species. The production and growth of T. aurea males and T. vulcani males, and their hybrids were compared along with the roles these tilapias play in mixed fish culture with carps and mullets. It was concluded that there was no difference in the growth between all-male cultures of T. aurea and T. vulcani and their hybrids.
T. aurea males had a positive effect on the production of carps when these two species were cultured together. Best growth was attained when male T. aurea or T. vulcani were stocked at the rate of 5 000/ha along with mirror carp Cyprinus carpio at 2 000/ha and silver carp (Hypophthalmichthys molitrix) at 1 500/ha. Ponds were fertilized weekly and a pelleted ration with 25 percent protein was fed. Average weight of males stocked was 20 g and after 104 days, 1 366 kg/ha of male tilapias were harvested with an average weight of 334 g. The production of tilapia males represented 29 percent of the total weight of fish produced.
Sarig and Marek (1974) reported the results of the highly intensive culture of male tilapias. Unfortunately, the species of tilapia cultured was not specified. Male tilapia were cultured in ponds with aeration and fed a pelleted ration containing 25 percent protein at extremely high daily rates. Highest production resulted when males with an average weight of 260 g were stocked at 60 000/ha. After 67 days, 25 000 kg/ha of fish were harvested with an average weight of 420 g. Net production was 9 600 kg/ha in 67 days. The feeding rate was 415 kg/ha/day without fish mortality.
3.2 Hybrid production
Pruginin (1968), working with the all-male hybrid of male T. hornorum and female T. nilotica in Uganda, reported yields of 800 kg/ha/yr when 1 500 hybrids/ha were stocked. When hybrids were stocked at 8 000/ha the rate of growth up to 50 g did not differ from that of fry stocked at lower rates. After reaching 50 g, hybrid fry previously maintained at high densities were then transferred to growing ponds at the density of 1 000–1 500/ha. Under these conditions, daily weight gain of hybrids was 1.5 to 3.0 g per fish and individual fish reached a weight of 200 to 450 g after a period of 100–150 days. It was not stated if feeds or fertilizers were used in these trials. All-male hybrids stocked with T. nilotica had a growth rate over a 100-day growing period 20 percent higher than T. nilotica stocked alone. Hickling (1962) reported that all-male hybrids produced at Malacca, Malaya, reached weights of about 450 g in six months, giving a total production of 1 365 kg/ha, with production ponds receiving nothing more than 46 kg of triple superphosphate/ha.
Pond experiments in Ivory Coast by Lazard (1973) resulted in the production of 1 396 kg/ha/yr of male hybrid Tilapia using triple superphosphate as fertilizer. The all-male hybrids resulting from the male T. hornorum x female T. nilotica cross were stocked at 10 000/ha with an average weight of 2 g and after 180 days the hybrids reached an average weight of 98 g. Fertilizer was applied at the rate of 13.5 kg/ha every two weeks.
Lovshin, Da Silva, and Fernandes (1974) also studied the growth and production of the all-male hybrid of male T. hornorum and female T. nilotica. Experiments were performed in 355 m2 earthen ponds. Water entering the ponds had a pH of 7.8–8.3 and total alkalinity of 140–150 ppm. An early experiment tested three treatments at two levels of stocking, 5 600/ha and 8 960/ha. The treatments were a control, culture with cattle manure, and culture with supplemental feed. The ration was composed of 50 percent castor bean meal and 50 percent wheat bran fed at 3 percent of the fish's body weight, 6 days a week. Ponds receiving cattle manure were fertilized once a week with 840 kg/ha. Tilapia hybrids with an average weight of 7 g were stocked to determine growth during a 253-day period. Average total productions for ponds stocked at 5 600/ha were 330 kg/ha, 804 kg/ha, and 980 kg/ha for the control ponds, cattle manure ponds, and fed ponds, respectively. Average total productions for ponds stocked at the rate of 8 960/ha were 277 kg/ha, 1 016 kg/ha, and 1 778 kg/ha for control ponds, cattle manure ponds, and fed ponds, respectively. The average weight per fish for the best treatment was 229 g from ponds stocked at 8 960/ha and receiving supplemental feed. The conversion rate of feed to fish was 2.7 to 1. There was a significant difference (P>.05) in total of fish production between the two levels of stocking and a significant difference between treatments. Higher fish production was obtained with a higher rate of stocking and with the use of feed.
A second experiment was performed on the production of tilapia hybrids using different methods of culture over a one-year period. Methods of culture tested were: organic fertilizer, chemical fertilizer, and organic fertilizer plus feeding, all with one level of stocking, 8 960/ha. Ponds in one treatment received 1 400 kg/ha/week of cattle manure, while ponds in a second treatment were given bi-weekly applications of triple superphosphate and ammonium sulfate at a rate of 28 kg/ha each. Ponds in the third treatment were fertilized with 1 400 kg/ha/week of cattle manure and received a ration of 50 percent castor bean meal and 50 percent wheat bran fed at 3 percent of the fish's body weight, 6 days a week. The experiment lasted 356 days.
Ponds receiving organic fertilizer had an average total production of 1 341 kg/ha, ponds receiving chemical fertilizer had an average total production of 1 856 kg/ha, and ponds receiving organic fertilizer plus feed had an average total production of 4 883 kg/ha. Tilapia hybrids at stocking averaged 21 g in weight. At the termination of the experiment average weights of 154 g, 215 g, and 565 g were noted from organic fertilizer, chemical fertilizer, and organic fertilizer plus feed, respectively. Significant differences (P>.05) in production existed between treatments. Total production with feeding and fertilizer was 163 percent and 264 percent more than with chemical or organic fertilizer respectively.
A tilapia hybrid culture mixed with mirror carp (Cyprinus carpio) was tested to determine if the addition of mirror carp would increases total production. Mirror carp were stocked into ponds at the rate of 2 240/ha, tilapia hybrids were stocked at the rate of 8 960/ha, and tilapia hybrids and mirror carp were combined in ponds at the rate of 8 960/ha and 1 400/ha respectively. All ponds received applications of cow manure at 1 400 kg/ha/week for five months after which applications were suspended. Ponds were fed rice polishings 6 days a week at 3 percent of the body weight of fish in the ponds. After 245 days, total production for carp ponds only averaged 812/kg/ha, for hybrids only 3 993 kg/ha, and for the mixed culture 3 567 kg/ha.
No significant differences (P<.05) in total production existed between treatments with tilapia hybrids and hybrids and carps mixed. However, these two treatments had total productions of harvestable fish significantly different from the treatment with carp only. Although there was no significant difference in total production between the treatments with hybrids, and hybrids plus carp, 105.9 kg of hybrids and carp were raised on 295.1 kg of feed while 107.9 kg of hybrids stocked alone were raised on 440.6 kg of feed. Thus, less feed was required to raise an equal weight of hybrids and carps than was needed to raise hybrids alone. Average weight of hybrids raised with carps was 285 g while average weight of hybrids cultured alone was 353 g.
Da Silva and Lovshin (unpublished data) tested the culture of all-male Tilapia hybrids in conjunction with the fattening of pigs. Three ponds of 1 000 m2 were stocked with 25 g hybrid fingerlings at the rate of 8 000/ha. Pig sties were constructed on the margins of three ponds and 7 pigs (70/ha) averaging 17 kg were placed in each sty. The pigs were not allowed to enter the ponds. The sties were cleaned daily and all waste products washed into the ponds. The pigs were fed a daily ration at 5 percent of their body weight consisting of manioc- 35 percent, wheat bran- 20 percent, corn- 15 percent, babacu cake- 15 percent, and grass- 20 percent. The ration contained 10 percent protein. After 189 days, 1 490 kg/ha of tilapia hybrids with an average weight of 205 g were harvested. Pigs averaged 60 kg each. Conversion rate of feed to pigs was 7.1 to 1 and the conversion rate of feed to pigs and fish combined was 5.9 to 1.
Three ponds of 1 000 m2 were also stocked with 25 g fingerlings at the rate of 8 000/ha and fertilized with chicken manure. These ponds received 50 kg/week (500 kg/ha/week) of chicken manure taken from a commercial chicken farm. The chicken manure contained 16 percent protein and consisted of 79 percent organic matter. After 189 days, 1 350 kg/ha of tilapia hybrids with an average weight of 186 g were harvested. Conversion rate of chicken manure to fish was 10 to 1.
Experimental studies on the production and growth of several Tilapia hybrids produced in Israel which were not 100 percent males were reported in works by Chervinski (1964; 1967), Yashouv and Halevy (1967; 1972; 1973), Yashouv (1969), and Mires (1969).
3.3 Other methods for controlling tilapia reproduction
Mention should be made of the experimental attempts by several workers to eliminate tilapia reproduction by methods other than sex selection or hybridization.
Pagen (1969) noted that all T. aurea reproduction was eliminated when this species was raised in floating cages. T. aurea was unable to reproduce in cages. Apparently the eggs fell through the bottom of the cage and even if fertilized, the lack of parental care precluded their normal development. However, to obtain maximum yields, a complete ration must be fed as tilapias are unable to fully utilize natural foods in such a confined environment. The production of a complete, pelleted ration is often expensive to produce in developing countries.
Experiments were conducted by Al Daham (1970) in attempts to sterilize Tilapia using chemical sterilants, X-rays and gamma-rays. Preliminary tests gave promising results using chemical sterilants to eliminate reproduction.
Guerrero (1974) did experimental sex reversal with T. aurea. By feeding T. aurea fry of 9–11 mm with an inexpensive, commercially available sex hormone, androgen, female T. aurea fry were transformed to functional males, thus, creating all-male tilapia populations. Continuing this research in the Phillipines, Guerrero (personal communication) demonstrated the feasibility of all-male tilapia production by feeding 9–11 mm T. aurea fry, measured amounts of the sex hormone methyl testosterone for a four-week period. Collection of fry for treatment was facilitated by pairing the brood fish in hapas located in the spawning ponds.
Chervinski and Yashouv (1971) raised T. aurea in saltwater ponds with salinity ranging from 36.6 to 44.6 percent. Results demonstrated that T. aurea grew almost as well in saltwater ponds as in freshwater ponds but did not reproduce in saltwater ponds. This is an important discovery as pure strains of T. aurea can be stocked into saltwater growing ponds without the worry of unwanted reproduction interfering with growth. This method shows great potential and warrants further study.
4.1 Fingerling production
In Northeast Brazil, the biggest problem facing government biologists trying to promote the culture of all-male Tilapia hybrids among the private sector is the lack of sufficient numbers of hybrid fingerlings for distribution. It is an interesting point that for years, the major problem with tilapia culture has been uncontrolled reproduction in growing ponds. Yet, in all-male hybrid cultures, the lack of fingerlings is a principal concern.
Preliminary studies in Brazil have shown that an average of about 300 all-male Tilapia hybrid fry can be expected per female per spawn. Of course, the number of fry will vary with the size of the female tilapia. If we assume that a female can spawn about 6 times a year in the tropics, one female can produce approximately 1 800 fry/yr. This means that to stock 1 ha of water with 10 000 fingerlings, approximately 5 to 6 females will be needed. If this stocking rate is increased to 20 000 Tilapia hybrid fingerlings/ha/yr, then 11 females are needed. In terms of a 50 ha commercial operation, approximately 550 females would be needed to provide 1 000 000 hybrid fingerlings necessary to stock the production ponds.
Special culture techniques and installations will have to be developed for working with the large numbers of brood stock needed to produce all-male Tilapia hybrids on a commercial scale. Experimental ponds at the fish culture research station in Pentecoste, Brazil were not constructed specifically for producing Tilapia hybrids. Efforts to produce Tilapia hybrids in earthen ponds of 355 m2 have met with several problems. Presently brood stock are placed and maintained in the ponds for three months. Then the ponds are lowered and the brood stock removed by seining. Care must be taken to remove all female parents. The ponds are subsequently refilled and the fry allowed to grow for one or two months longer. The only drawback in this method is that the female T. nilotica are extremely difficult to remove from a 355 m2 pond because they lie on their sides in the mud and pass under a seine. It is extremely difficult to ascertain whether a missing female has been left in the spawning pond or has died. This uncertainty necessitates repeated passes with the seine which is time consuming. Excessive seining also muddies the water, often causing mortality to young fry. An alternate method is to completely drain the spawning pond after three months removing all adults and fry. The fry are then placed in a nursery pond where they are grown to stocking size. This second method also has the following drawback: the female T. nilotica spawn intermittently over the three-month period, resulting in many small fry at draining. These are often lost in the mud and cannot be recovered or may be killed due to handling. To facilitate the removal of brood stock from spawning ponds, several spawning ponds were divided in the shallow end with a wood frame fence covered with nylon netting. The brood stock were placed in an enclosed area of about 100 m2. After three months the ponds were lowered and the fry passed through the fence while the brood stock were retained and removed. The ponds were then refilled and the fry allowed to grow another month after which they were of a size large enough to be netted and transferred to other ponds without excessive mortality. This latter method proved to be the most successful of the three. However, even the use of a fence has a drawback, as hybrid crosses cannot be reinitiated until the ponds are drained, all fry removed and ponds allowed to dry. For each 4-month fry production period consisting of 3 months of spawning and 1 month of additional growing time, one month of spawning time is lost while the fry are growing. To eliminate this delay in restocking the brood stock so that the hybridization can be more continual, 2 types of experimental spawning ponds were designed and are under construction (Fig. 2). Spawning ponds of two elevations will allow the fry to pass from the upper elevation to the lower level with a minimum of handling. The division between the two ponds can then be closed allowing the reintroduction of the brood stock into the upper unit while the fry are growing in the lower unit. This system should allow for continual production of all-male hybrids. Model B of the spawning ponds which provides spawning compartments has the added advantage of allowing for the genetic selection of T. nilotica females and T. hornorum males. Those females that most readily hybridize with T. hornorum males and produce the largest and most frequent spawns can be selected. Fry can also be taken from the females at an early age which should increase the frequency of spawning. It is felt that the smaller size ponds with two elevations will allow for a greater control of brood stock and less handling of fragile fry until they are of sufficient size to be transferred to nursery ponds. As these spawning ponds are now under construction, the exact impact they will have on hybrid fry production is not known.
Our experience indicates that the biggest problem facing the aquaculturist producing all-male Tilapia hybrids is that of maintaining brood stock of pure lineage. Only pure stocks will produce 100 percent male offspring. The fish culture research station in Bouaké, Ivory Coast has given up working with all-male Tilapia hybrids because they can no longer be produced with any regularity because of contaminated parent stocks (Jacques Bard, personal communication). This also appears to be the case in Malacca, Malaya where the all-male hybrid once produced by Hickling is no longer cultured (Lui, personal communication). After three years, pure strains of T. hornorum and T. nilotica are still available at the Pentecoste research station and all-male hybrids are produced with a high degree of success. Good isolation techniques, filtered water supplies, constant vigilance on the part of research station biologists are essential ingredients for maintaining pure tilapia strains over time.
The production of male tilapias for monosex culture and less than 100 percent male hybrids is a simpler cultural process but not necessarily more economical of time or labour. The fear of contaminating pure lines of brood stock is decreased especially in the production of male fish for monosex culture. However, male fish must be hand sorted which is very time consuming and labour intensive. Even with trained workers, it is almost impossible to separate the males with complete accuracy and usually a few females are accidentally included. Furthermore, only the male tilapia are used for stocking and the females are discarded, resulting in a loss of 50 percent of the fingerlings produced.
4.2 Production of monosex and hybrid tilapias
Tilapias possess excellent culture characteristics. Tilapias spawn all year round in tropical regions providing a constant supply of fingerlings. Spawning is easily accomplished in a wide range of environments and installations. Many species of tilapias are highly resistant to poor water quality and diseases. Even in ponds receiving high levels of feed and fertilizer, some tilapias are able to survive periods of extremely low dissolved oxygen levels by coming to the water surface and utilizing atmospheric oxygen. Parasites and diseases have caused very few problems in tilapia culture even when pond waters are very fertile. At the Pentecoste research station, no T. hornorum, T. nilotica, or all-male hybrid has ever been killed due to low dissolved oxygen or diseases to this date. The hardiness of many tilapias is a distinct advantage when working with farmers in developing countries who lack a technical knowledge of fish culture. If a farmer can follow simple fertilizing and feeding instructions, he can raise good crops of tilapia hybrids or monosex males with very little effort. Farmers raising 100 percent male hybrids in North-east Brazil generally visit their ponds once a day for 15 minutes to feed the fish. This is all that is really needed and makes raising tilapias a simple chore. There is no need for early morning visits to ponds to check dissolved oxygen or costly treatments for parasites and diseases.
Most tilapias are able to utilize inexpensive agricultural waste products or organic manures as feeds. Developing countries usually have some sort of agricultural waste products available at relatively low cost that can be fed to tilapias. Raising tilapias in combination with pigs, chickens, or ducks is one of the most economical and efficient ways to culture fish. Profit can be made from the pigs, chickens, or ducks as well as the fish. Sources of enrichment, such as run-off from feed lots, thirdstage sewage from municipal treatment plants, or treated organic garbage from cities can be used to raise tilapias. The only limiting factor seems to be man's imagination. For example there is a farmer in Brazil raising all-male tilapia hybrids in a one-ha pond. On a hill overlooking the pond, he has a feed lot for milk cows. The waste products from his feed lot are washed into the pond daily. The milk from the cows is used to make cheese. The wastes from the cheese processing operation are fed to pigs which are located in a sty on the pond margin. The wastes from the pigs are also washed into the pond. A recent fish sample taken from the pond showed the tilapia hybrids to be 300 g average weight after five months of growth. This is a calculated production of 3 000 kg/ha, which should result in a healthy profit for the farmer as he invested no money in feeds for his fish.
Sarig (1974) reports that 1 112 tons of tilapias were raised in ponds in Israel in 1973. These fish were marketed at a size range of 400 g to 750 g and sold for about U.S.$ 0.80 per kg. The Israeli fish farmers raise tilapias in mixed cultures with other species of fish. Tilapias have the role of a pond cleaner, maintaining the water in good culture condition by consuming organic material and waste feeds that would otherwise decompose and pollute the pond environment. With fishes of lesser tolerance to poor water quality than tilapia, the production of fish is usually limited by the amount of feed that can be added to the pond without causing depletion of dissolved oxygen. With the tilapias helping to keep the pond clean, higher rates of feeding can be used resulting in high productions of the primary culture fish. Tilapias were found to have a positive effect on carp production (Yashouv and Halevy, 1967).
It is believed that the secret to successfully culturing tilapias is high water fertility and that there is little profit in raising tilapias unless the ponds can be heavily fed and fertilized. Unfortunately, in some developing countries feeds and fertilizers are not readily available. Under such conditions grass and leaves could be used to increase pond fertility but not with the success of concentrated feeds and fertilizers. Existing evidence shows that with high levels of pond fertility and agricultural waste products, culture of male tilapias should result in productions of 2 000 to 5 000 kg/ha/yr depending on water quality and type of culture. With the use of higher stocking rates, high protein pelleted feeds, and continuous harvesting techniques, even higher productions can be expected.
Our experience also suggests that high yields of marketable size tilapias can be produced without the total elimination of tilapia reproduction in culture ponds. This is especially true where fish of 100 g to 300 g are readily marketable as is the case in many developing countries where a protein shortage exists. Jacques Bard (personal communication) states that T. nilotica males and females can be raised in the same pond to a size of 100 g and 80 g respectively in 3- to 5-months yielding a total production of 2 000 to 3 000 kg/ha/yr. Tilapia fry of the same age class are raised with high levels of fertilization and feeding, and reproduction is not a major influencing factor in this short period of time. In many areas of the world, fish from 80 to 100 g in weight are acceptable. Where larger fish are desired, however, some kind of sexing or hybridization must be done to eliminate a majority of the female fish.
The addition of a few female fish in ponds has had little influence on the growth of male tilapias in intensive culture over a 3- to 5-month growing period. Male tilapias of 200 to 300 g can be grown in this period of time from 20 g fingerlings even with a few females present in the growing ponds. If large fish of 500 g are desirable, then females must be completely eliminated or predator fish used to control unwanted reproduction. In Brazil, reproduction in our male hybrid ponds begins to affect the growth of the hybrids after approximately 5 months. Bar Ilan (personal communication) states that it is common to encounter tilapia reproduction in growing ponds but that the growth of carps and tilapias is not adversely affected by this reproduction in intensive culture over a short period of time.
Where feed and fertilizers are not readily available or larger fish are required for the market, it is necessary to eliminate all females through hybridization, manually selecting male fish or stocking a predator with the predominantly male tilapia stock to eliminate reproduction.
There can be little doubt that the elimination of reproduction in tilapia culture ponds is a goal that should be investigated. However, culturists should not be discouraged from raising tilapias because some reproduction is encountered in growing ponds. Short term, intensive cultures still allow for good crops of tilapias to be raised where feeds and fertilizers are readily available.
There is a definite need for good research to be performed on all aspects of tilapia culture. Some of the past research with tilapias has not been of high value because results were not properly reported. Researchers must be trained and installations built and adequately financed that allow them to carry out meaningful trials.
In our opinion, researchers should begin thinking in terms of commercial scale production of monosex male tilapias and tilapia hybrids. Our experience in Brazil suggests that the area in need of the most research at the present time is propagation of seed stock.
There is more information available on the production of male tilapias than on any other phase of their culture. Still, much remains to be done. Questions requiring solutions include: How many female brood stock per unit of area should be used? What is the optimum age and length of time males and females should be used before being replaced? What is the optimum period of time that brood stock should be left in spawning ponds before being removed? Is there an advantage to holding the female tilapia and the male tilapia to be hybridized in separate ponds before placing them together in spawning ponds?
Another area of research priority should include genetics. Why is it that when some species of tilapias are crossed, all-male offspring result? What is the exact genetic mechanism at work? Are there other species of tilapias not yet known that, when crossed, will produce all-male offspring? For example the production of all-male herbivorous tilapia would be an important discovery. Studies should be done to select those males and females that most readily hybridize naturally. Selection for tilapia females that give large spawns, spawn with increased frequency or produce offspring with increased growth rates would also be of value.
Work also needs to be done on predators that can be used in male tilapia cultures to control reproduction when females are accidentally introduced into the ponds. Fish should be found that are not only effective predators but can be easily reproduced in controlled environments and are resistant to poor water quality.
Another area in need of experimentation is nutrition. It is known that supplemental feeding will increase tilapia production. However, what are the dietary requirements of tilapias? What are the most economical and efficient rates of feeding tilapia? Is there sufficient increase in efficiency of food utilization to economically warrant the use of pelleted rations instead of simple rations? What would be the effect of adding various levels of an animal protein to the ration; would this practice be economically feasible? The use of coffee pulp in El Salvador is just one example of an underutilized agricultural waste product that served to increase tilapia production. There must be many other cheap locally available agricultural by-products that could be used to increase tilapia yields.
The culture of tilapias in association with other animals holds great promise and biologists should begin working with these combinations. What are the best methods and installations for raising pigs, ducks, and chickens in conjunction with fish? What are the numbers of livestock animals needed per unit area of pond for high production of tilapias? What effect does the level of protein in the ration fed to these animals have on the growth and production of tilapias?
In the field of water quality, the principal question yet to be answered is just what are the requirements in terms of aquatic parameters for various species of tilapias? How long can tilapias continue to grow and survive in water with low levels of dissolved oxygen?
These are typical questions that remain to be answered and as fishery research biologists probe deeper into the culture of tilapias, many more will be suggested. Even with existing limited knowledge, tilapias have shown a potential for producing large quantities of cheap animal protein that few other culture fish known today can match. In a world where the scarcity of animal protein is becoming more critical every day, the culture of tilapias can aid in reducing this protein deficit. It remains for a fishery programme to be developed which will provide the methodology needed to lift the tilapia from the subsistence level of culture found in most areas of the world today into a modern aquaculture system reflecting present knowledge along with extending this base through sound research and extension programmes.
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Figure 1. The genital orifices of the female (left) and male (right) Tilapia nilotica. Adapted from Bard, Lemasson, and Lessent (1971).
FIG-2. DESIGNS OF TILAPIA HYBRID SPAWNING PONDS
MODEL — A
MODEL — B
CROSS SECTION, MODELS “A” AND “B”
