3.1 Background
3.2 Research Needs
Countries of the region have particular interest in culturing the following indigenous fishes: Cichla ocellaris, Colossoma bidens, Mylossoma bidens, Pimelodus spp., Prochilodus spp. and Mugil spp. Main problems confronted when their culture has been attempted, and the approach which seems most logical in trying to find solutions that could eventually lead to the development of viable production systems, are summarized below.
3.1.1 Cichla ocellaris
Main utilization of this species has been as a predator for small native fishes and Tilapia sp. in reservoirs and ponds. Although the species breeds freely even in small ponds, difficulties arise when trying to produce large amounts of fingerlings for stocking farm ponds. Its highly territorial behaviour during spawning and parental care, together with, its predacious nature and the cannibalistic habits developed mostly when fingerlings are crowded, result in low survival rates when the simple methods of breeding and nursing currently in use are practised.
The species has shown ability to control the population density of Tilapia in ponds when stocked at the right proportion and time; however, the standardization of this technique for those Tilapia species considered most promising for Latin American fish farming has to be worked out. Predator-prey ratio and time of stocking should be standardized for each combination.
On the other hand, it is well known that when a predator is stocked for the prevention/control of overpopulation arising from the excessive reproduction of the prey species, an upgrading of energy takes place at the cost of some loss in yield. This should be quantified for the combination Cichla-Tilapia, and comparisons experimentally made with other production systems utilizing different methods to prevent the breeding of Tilapia, in order to clearly determine the applicability of each system to specific conditions found in the region.
The following topics were therefore identified as candidates for consideration as part of a research programme with this fish:
(i) reproductive potential under conditions at the Centre;(ii) development and standardization of breeding techniques for mass production of fingerlings;
(iii) nursing, holding and feeding of large numbers of fingerlings;
(iv) management of brood fish;
(v) best size, proportion and time for stocking Cichla ocellaris fingerlings to prevent overpopulation of Tilapia in ponds. Predator-prey relationships;
(vi) yield of Cichla-Tilapia combinations under different management schemes, including organic and/or chemical fertilization of the ponds and the use of supplementary feeds for the Tilapia; economics of each combination/treatment;
(vii) growth rate of Cichla ocellaris under each management scheme;
(viii) the effect of predation (by Cichla on Tilapia) on the yield, as compared to yields obtained in the culture of Tilapia using other population density control methods in ponds, such as monosex culture through hybridization, visual sexing, or sex reversal.
3.1.2 Colossoma bidens and Mylossoma bidens
Good growth and yield under different pond conditions were attained with these two species in preliminary small-scale experiments run at the Pentecoste Station in northeast Brazil (Lovshin et al., 1977a). The species demonstrated a good ability to digest plant protein when given a pelleted feed containing 29 percent protein, 8 percent of which was of animal origin. In nature, Colossoma is a filter feeder but also eats larval shrimp, insects, and terrestrial fruits when available, while Mylossoma appears to thrive mostly on local fruits.
Fingerlings for these trials had to be captured in the natural environment, since these fish do not breed freely in ponds. Partially positive response to the injection of hormone extracts prepared with pituitaries from Prochilodus caerensie was obtained but either no fecundation of the ova was possible or the embryos did not complete their development (Bezerra-da Silva, 1975). Both species are reported to mature late (3-4, 5 years old).
In order to develop a system for culturing these species, the focus of studies should be on the following aspects:
(i) development and standardization of a breeding technique through the use of natural and/or synthetic hormones; reproductive potential of each species;(ii) development of nursing methods, including the feeding of fry and fingerlings;
(iii) development of a nutritionally complete feed formula, based if possible on ingredients widely available in the region or easily substituted by local products. Cost should be, of course, a very important consideration. The formula already developed at the Pentecoste Station must be carefully studied.
Once these fundamental objectives are attained, production systems could then be worked out, paying special attention to the following:
(i) highest stocking rate compatible with good average growth and yield, under a monoculture scheme using organic manuring and chemical fertilization of ponds, plus feeding;(ii) yield and interspecific relationships under a simple polyculture scheme with secondary species occupying a different niche, i.e. Prochilodus sp.;
(iii) a programme of selection for lines with earlier maturation age than the wild stock.
Before designing a detailed research programme for Colossoma and Mylossoma at the Centre, information should be obtained on recent studies, if any, being carried out at the Pentecoste Station.
3.1.3 Pimelodus spp.
Little information is available on the breeding habits of these catfishes in nature. A study by Godinho et al. (1974) shows that maturation of the ovaries in P. maculatus begins in October and reaches a peak in December, when spawning probably occurs.
Similarly, information on food preferences is scanty, the most detailed research report available showing P. clarias and P. albicans from the Paraná river basin to be omnivorous (Bonetto, Pignalberi and Cordiviola, 1963). Local small-scale studies report P. maculatus as primarily insectivorous (Jensen, 1977), while P. clarias and P. grosskopfii are considered omnivorous in Colombia.
The fact that a good percentage of fish was found in the stomachs of P. clarias and P. albicans during the study by Bonetto, Pignalberi and Cordiviola (1963), points toward the possibility that these species might act as predators of Tilapia sp. in ponds. This and the omnivorous habits shown by Pimelodus should enable the combination with Tilapia to have wide-applicability to small-scale fish farming in vast areas of the region.
Useful basic information appears to be available on the Pimelodus species from the Mogi-Guassu river bordering the Centre site (Godoy, 1975). If this particular species can attain an acceptable adult size, it should be selected for research for the development of culture systems; otherwise another species with a wide distribution in Latin America should be chosen for this purpose.
The main problems identified for experimental work were the following:
(i) induced breeding through the use of natural and/or synthetic hormones; standardization of techniques; reproductive potential;(ii) incubation of eggs; adaptation of methods applied to other catfishes, or development of special techniques;
(iii) nursing and feeding of fry and fingerlings; growth rate, and survival;
(iv) development of a nutritionally complete feed formula.
It is likely that enough numbers of Pimelodus fingerlings can be captured in the wild from the Mogi-Guassu river basin at certain times of the year for the applied studies suggested above, to be carried out simultaneously. This approach could mean a saving of time in the development of culturing systems for this fish. Subjects to be dealt with might include the following:
(i) response of the fish to organic and/or chemical fertilization of the pond, as measured by growth rate and yield;(ii) highest stocking density compatible with good fish growth;
(iii) simple polyculture with each of the following species: Tilapia sp., Prochilodus sp., Triurobrycon lundii; interspecific relationships; best stocking densities and proportions; the combinations Pimelodus-Tilapia and Pimelodus-Prochilodus appear particularly interesting for semi-intensive fish farming;
(iv) management schemes: fertilization, feeding, harvesting;
(v) economics of both the intensive and semi-intensive systems.
3.1.4 Prochilodus spp.
Techniques for the induced breeding of this fish were developed long ago and are currently applied in the production of fingerlings for stocking both natural lakes and artificial reservoirs. These techniques could, no doubt, be improved; similarly, the nursing methods could be upgraded to allow for mass production of fingerlings and larger fish. P. reticulatus has shown acceptable growth rate under an extensive type of culture when the population density is kept at a low level. Substantial increase of growth rate was also observed when this species was stocked along with Tilapia rendalli, which in the experiments was fed leaves of Alocasia macrorhiza (Araceae).
As in the case of Pimelodus, the Prochilodus species initially selected for research at the Centre should be the one inhabiting the Mogi-Guassu river (P. scrofa), for which the complete life history and ecological requirements are known.
Research topics for the development of a system for culturing this fish should include:
(i) growth and yield under a monoculture scheme; response to organic manuring and/or chemical fertilization of the pond, as measured by these parameters;(ii) acceptance of supplementary or complete feeds; development of a feed formula; feeding techniques;
(iii) simple polyculture with the following species: Tilapia sp. (or Tilapia hybrids), Colossoma bidens, Mylossoma bidens, Triurobrycon lundii; the combination with Tilapia should be tried in small ponds, since it seems particularly interesting for small-scale fish farming suited to rural development projects in the region.
3.1.5 Mugil spp.
One of the constraints to the development of grey mullet culture systems has been that they do not breed freely in ponds. For experiments run in Latin American countries, finger-lings have had to be captured in seaside lagoons or along the coastline where they abound at certain times of the year.
Techniques for the induced breeding of certain species of Mugil have been developed. The applicability of these techniques for the breeding of local species has to be tested. Problems for research that might be considered with the local species at the Cananeia Sub-Centre include:
(i) induced breeding, through the adaptation of techniques developed elsewhere for grey mullets;(ii) nursing and feeding of fry and fingerlings;
(iii) salinity ranges in which they can be raised.
If enough numbers of fingerlings for experimentation can be captured in the neighbourhood, as appears most likely, the following lines of research might be carried out simultaneously with the studies suggested above:
(i) feeds for fry and adult fish in brackishwater ponds;(ii) maximum population density which, under conditions of extensive culture, permit good fish growth;
(iii) response to organic manure and/or chemical fertilization of the pond, as measured by fish growth and yield; management of the ponds to produce pastures for grey mullet (Mugil) feeding;
(iv) engineering aspects relating to the design of brackishwater ponds and water control structures for effective use of tidal flows; optimum pond depth for water exchange under local conditions;
(v) comparative economics of mono- and polyculture;
(vi) diseases of fish in brackishwater ponds.
3.1.6 Other indigenous fishes
The Characinid sub-family Bryconinae comprises a widely distributed group of Latin American freshwater fishes living both in warm- and medium-temperature ranges. They spawn only in running waters, but appear to be susceptible to spawning techniques similar to those currently applied in trout culture.
These fish are more or less omnivorous. Triurobrycon lundii eats leaves, flowers and fruits (Godoy, 1975), while Brycon dentex has been classified as omnivorous with a tendency to be predatory (FAO/UN, 1975). B. atrocaudatus and B. moorei include fruits in their diet, while B. henni is basically insectivorous. All species are quite appreciated locally for the flavour of their meat, and also as sport fish.
Brycon spp. can be easily adapted to pond life, and accept pelleted feeds. They show excellent potential for intensive culture, particularly in places with abundant running water. Species living in medium-altitude zones (1 000 - 1 700 m above sea-level) such as B. oligolepis and B. henni, appear quite promising for culture under highly intensive systems similar to those adopted for rainbow trout.
It is suggested that a couple of these fishes, one from the warmer temperature range, like Triurobrycon lundii from the Mogi-Guassu river, and the other from cooler waters, like B. henni, be included among the species for which a culture system should be developed at the Regional Centre. Research topics identified by the Task Force with this aim included:
(i) artificial breeding; reproductive potential; age at maturity;(ii) incubation and nursing techniques; feeding of fry and fingerlings;
(iii) temperature tolerance; dissolved oxygen requirements; effects of crowding;
(iv) development of a nutritionally complete feed formula for intensive monoculture;
(v) engineering aspects related to the adaptation or design of facilities such as raceways for culturing medium-temperature species under highly intensive conditions;
(vi) simple polyculture of the warm-water species with Prochilodus scrofa; use of cheap agricultural by-products, fruits of the season, or wastes from animal industries/processing should be considered as supplementary feeds;
(vii) response of the fish to organic manuring and/or chemical fertilization of the pond, as measured by growth and yield.
On the basis of this review of information gaps and on the basis of higher probability for obtaining positive results in a short period of time with wide regional applicability, the Task Force identified the following priorities for consideration within experimental development programmes with indigenous fishes at the Centre. Special precautions must be exercized during all introductions of fish selected for experimentation to ensure that they do not introduce undesirable parasites or infectious diseases to the Centre.
(i) Development of nutritionally complete feed formulae, utilizing ingredients widely available in the region or easily substituted by local products (needless to say, these feeds should be as simple and economical as possible); a chart of available ingredients with their nutritional composition should be worked out;(ii) simple polyculture of the combination Prochilodus scrofa and hybrid Tilapia;
(iii) artificial breeding of Triurobrycon lundii, Brycon henni (or a similar cool-water Brycon species), Pimelodus clarias and Mugil sp.; incubation techniques; nursing and feeding of fry and fingerlings;
(iv) monoculture of Triurobrycon lundii under intensive conditions; simple polyculture of the combination T. lundii and P. scrofa;
(v) monoculture of Pimelodus clarias under intensive conditions; simple polyculture of the combinations P. clarias and Tilapia sp., P. clarias and Tilapia hybrids, and P. clarias and P. scrofa;
(vi) highly intensive culture of Brycon henni or a similar cool-water Brycon species, adapting systems currently in use for the commercial culture of rainbow trout.
