Title: Preliminary observations on the effect of salinity on the reproduction and growth of freshwater Nile tilapia, Oreochromis niloticus (L.), cultured in brackishwater ponds
Abstract: Abstract. Tilapia, probably Africa's best candidate for aquaculture, is faced by the problems of small size due to overpopulation in culture systems. This paper reports the effect of high salinity on the reproduction of Oreochromis niloticus (L.) while testing the effect of a 20% protein supplemental feed on the growth and survival of this species in brackishwater ponds. The trial was run for 120 days in six 100-m2 ponds with fingerlings having an initial average weight of 2·80g. Salinity in the ponds rose from 25 ppt. to 50 ppt. during the culture period. Sampling for reproduction check was conducted every 2 weeks and 20% of the fish population were weighed to monitor growth changes and adjust quantity of feed fed. A 20% protein feed was fed at the rate of 5% and 3% of the total fish biomass during the first and second, and third and fourth months of the trial respectively. After 120 days the fish in each replicate were counted and weighed in bulk to obtain total weight while 50 females from each replicate were dissected and gonads examined. Results showed that growth was significantly different (P < 0·05) while percentage survival was not significantly different (P > 0·05). 95% of the females were gravid but did not spawn. This suggests that gonadal development and onset of reproduction can be delayed by high salinities, which may be another practical method of population control in the culture of O. niloticus.