Mass synchronized spawning of Tilapia guineensis D. Campbell., A. T. Mahatane, and S.O. Aleem

AFRICAN REGIONAL AQUACULTURE CENTRE, PORT HARCOURT, NIGERIA
CENTRE REGIONAL AFRICAIN D'AQUACULTURE, PORT HARCOURT, NIGERIA

UNITED NATIONS DEVELOPMENT PROGRAMME
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
NIGERIAN INSTITUTE FOR OCEANOGRAPHY AND MARINE RESEARCH
PROJECT RAF/82/009

July 1986

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MASS SYNCHRONIZED SPAWNING OF TILAPIA GUINEENSIS AFRICAN
REGIONAL AQUACULTURE CENTRE, RAF/82/009

D. CAMPBELL, A.T. MAHATANE* AND S. O. ALEEM

ABSTRACT

A technique for mass synchronized spawning of Tilapia guineensis is described. By introducing a single couple into each of a series of 25,0.4m³ concrete tanks, 102 spawns were obtained from a total of 179 couples with 1355 ± 726 (mean ± SD) fry produced per spawn. Using fish captured from the wild, 64% spawned in 3.3 ± 2.01 days. 48% of the fish that had been previously used and kept in ponds spawned in 8.8 ± 5.75 days. Fish produced during a one week period were of sufficiently uniform size to avoid cannibalism when introduced into ponds.

* Present address: Min. of Natural Resources & Tourism Freshwater Fisheries Institute, Nyegezi, P.O. Box 1213, Mwanza, Tanzania.

INTRODUCTION

Tilapia guineensis (Bleeker, 1862) is a euryhaline species found along the West Coast of Africa from Senegal to Angola (Philippart and Ruwet, 1982). A substratum spawner, the fish will reproduce in ponds. However, the newly hatched fry weigh only about 2mg (Legendre, 1983) and easily fall prey to other species, particularly Sarotherodon melanotheron fry (FAO, 1969; Dadzie, 1981). Although not readily apparent in pond systems, cannibalism by both larger fry and adults of T. guineensis is also a problem, particularly at the yolk sac stage (Campbell, unpubl.). Survival in spawning ponds is very poor, and production of juveniles has been a problem when attempting to culture the species in the Niger River Delta.

A simple means of producing enough seed fish for stocking is necessary for aquaculture development. This paper presents the results obtained from an attempt to produce T. guineensis fry in large numbers and the behavioural differences observed between wild and used broodfish in the degree of synchronization of spawning.

MATERIALS AND METHODS

The work was from September 1985 to April 1986 at the Buguma brackish water fish farm located in the Niger River Delta. 25 separate concrete tanks measuring 65 × 90 × 70cm or 0.4m³ were used to spawn the fish. Each tank was filled to 50cm depth giving about 300 1 volume of water. The water was filtered and pumped from tidal ponds. Salinity was 11 – 20 ppt and water temperature 29–34°C during the period of the experiments. After filling, agricultural lime (CaCO₃) was sprinkled in the tanks to precipitate suspended matter allowing clear observation of the tank bottom. Once the tanks were filled there was no further water circulation or exchange.

A spawning cycle or test began by draining and cleaning all the tanks and filling them with new brackish water. In each test 40 – 50 sexually mature fish with a standard length ranging from 8 – 16cm (15 – 220g) were visually sexed and a male and female of the same size were introduced into each tank. Fish were chosen and paired with no attempt made to ascertain their readiness to spawn. Each spawning cycle lasted 2 – 3 weeks and the fish were not fed throughout the experiment. The tanks were monitored at least 3 times daily for the presence of fertilized eggs. As soon as the eggs were found, the male fish was removed to avoid cannibalism. The female was left to guard and ventilate the eggs. The fry were collected and transferred to a nursery pond when the yolk sack was absorbed.

Broodfish were initially captured by seining fish from unused tidal ponds and were referred to as “wild” broodfish. After completion of a cycle, all fish used in the test were placed in a 200 or 400m² earthen pond with a density of 0.2 – 0.5 fish/m². The ponds were initially limed (CaCO₃) at a rate of 10kg/are and fertilized with inorganic fertilizer (N:P:K 15:15:15) at an initial rate of 5kg/are. Bi-monthly fertilization at a rate of 2.5kg/are continued as long as the fish were in the ponds, and dried brewers waste was given as a supplementary feed. In further spawning cycles, these fish were referred to as “used” broodfish.

In each cycle, some mortality of the broodfish occurred, usually due to poor handling when stocking, but on some occasions fish would jump from the tanks, be killed in fighting, or remove the drain plug from the tank when attempting to build a nest. These fish were not replaced during that particular test, nor taken into account for further calculations.

The time from stocking to spawning was recorded. In each cycle, the percentage of couples spawning was determined from the number of couples which spawned or remained at the end of the cycle, and mortality was not considered. Used and wild broodfish were compared for days to spawning and percentage spawning using Students' t test. To study the relationship between the standard length of the female and the number of fry produced, the result of 35 individual spawns were counted and the female measured.

RESULTS

Nine spawning cycles were completed producing over 120,000 fry. A total of 102 spawns were recorded, with a mean number of 1355 ± 726 fry per spawn. In analysing the results, a difference became apparent in spawning behavior and degree of synchronization between stocks of wild and used broodfish. These differences are presented in Table I.

TABLE I

Results of spawning T. guineensis.

The 3.3 mean days to, spawning of the wild fish is significantly different (P<0.05) from the value of 8.8 days from the used broodfish. Of all the wild broodfish introduced into the tanks, 44% spawned within 3 days, and 62% within the first week. In one instance, the fish spawned only 3 hours after stocking, in another 10 hours.

The spawning rate of the wild fish (64%) was not significantly different (P<0.05 from the value of the used fish (48%). Moreover, with the used fish, the spawning was more protracted and erratic (Fig. 1).

The number of fry produced per female varied substantially (Table II) although all broods counted originated from wild females.

TABLE II

Standard length of female number of fry produced.

Regression analysis gives Y = 219.9 X - 1019.5 (r = 0.635) where X is the standard length and Y the number of fry produced. In terms of the number of the number of fry produced and the lowest mortality, fish of 10 - 12 cm standard length gave the best results although this also have been a function of the tank size as the larger fish were certainly more stressed in the small area.

Fig. 1: Percent of broodstock spawning ‘wild’ and ‘used’ fish

In each spawning cycle, 10,000 - 35,000 fry were produced. Those spawning in the first week, as was the case of almost all of the spawning fish from the wild, produced fish of a relatively uniform size that could be introduced into a single pond with no fear of cannibalism.

DISCUSSION

The method proved to be a viable means of producing large numbers of T. guineensis fry. Using only wild broodfish would be recommended as the time to spawning and the degree of spawning synchronization is significantly better than that of the used broodfish.

The difference may be due to the condition of the fish. Fertilization and supplemental feeding with only dried brewers waste were probably not sufficient to maintain all the fish in good physical condition.

What is more difficult to explain is the degree of synchronization obtained, particularly from the wild fish. In substratum spawners, pair formation, courtship, nest building, and spawning are time consuming and spawning frequency can vary from 24 - 84 days (Fryer and Iles, 1972). Furthermore, the fish were stressed during handling and suffered a complete change of environment. Individuals longer when 15cm standard length would usually die or jump out of the tanks.

With smaller fish, the fact that 44% of the wild fish spawned during the first 3 days, and in some cases in as little as 3 or 10 hours, is remarkable. It could be either that the tank environment stimulates the fish or removes an inhibitory factor present in the wild. The change in substrate, water quality, the absence of predators, or forced association may be the stimulus. Alternatively the stress on the fish during capture and handling might have stimulated the release of reproductive hormones. It was not possible to determine the stimuli involved.

The concrete tanks used on the farm were previously built for other purposes, and were not necessarily the ideal size or configuration. It is quite possible that better results would have been obtained by using larger tanks. Alternatively very small ponds would perhaps be used. What is important is that this proved to be a reliable technique for producing large numbers of uniform size fry for stocking.

REFERENCES

Dadzie, S., 1981. Annual Research Report for 1981. African Regional Aquaculture Centre, Port Harcourt, Nigeria. (Ms.).

FAO, 1969. Report to the Government of Nigeria on experiments in brackishwater fish culture in the Niger Delta, Nigeria 1965-1968. Based on the work of K.K. Nair, FAO/UNDP(TA) Inland Fishery Biologist (Fish Culture). Rep. FAO/UNDP(TA). (2759): 14 pp.

Fryer, G. and Ilos, T., 1972. The cichlid fishes of the great lakes of Africa: their biology and evolution. Edinburgh, Oliver and Boyd, 641 pp.

Legendre, M., 1983. Observations preliminaries sur la croissance et la comportement en elevage de Sarotherodon melanotheron (Ruppel, 1852) et de Tilapia guineensis (Bleeker, 1862) en Lagune Ebrie (Cote d'Ivoire). Doc. Sc. Cent. Rech. Oceanogr. Abidjan Vol. XIV, No. 2, December 1983: 1 - 36.

Philippart, J. and Ruwet, J., 1982. Ecology and distribution of tilapias, p. 15-59. In: R.S.V. Pullin and R.H. Lowe-McConnell (eds) The biology and culture of tilapieas. ICLARM Conference Proceedings 7, 432 p. International Centre for Living Aquatic Resources Management, Manilla, Philippines.