EFFECT OF ELEVATED TEMPERATURE TREATMENT AND PAWPAW SEED POWDER ON PRODUCTION OF STERILE MONOSEX NILE TILAPIA

Abstract

Nile tilapia is the most widely cultured fish species in Kenya. The greatest problem with tilapia is its prolific breeding due to mixed sex, resulting in stunted growth of the fish. Therefore, there was a need to employ simple techniques that embrace use of locally available materials for ease of implementation, which previous methods did not fully consider. This study therefore investigated the effect of high temperature treatment and pawpaw seeds powder on production of sterile monosex Nile tilapia (Oreochromis niloticus). The effect of high temperature treatment on sex differentiation and survival rate at different larval stages was studied; as well as the effect of pawpaw seeds powder on the histological structure of gonads, growth performance and proximate composition of O. niloticus. The research was carried out in two phases with 12 glass aquaria in each phase. In Phase 1 temperature treatment at 36 oC was done for 10 days at different days post-fertilization (dpf) of 1 dpf, 6 dpf and 10 dpf. The control was kept at 28 oC from the egg stage to the end of the experiment. In Phase 2 administration of pawpaw seeds powder to the fish from the best result of Phase 1 in terms of highest male ratio which was 10 dpf was done at 0g, 4g, 8g and 12g PSP/kg feed for a period of 60 days. Male percentage ranged from 45.56-82.22% while female percentage ranged between 17.78-54.44%. The control group had the least percentage of males (45.56%) while swim-up fry had the highest percentage of males (82.22%). Percent Survival was lowest at egg stage (43%) and highest at control group (80.7%). In Phase 2, histology of gonads of fish treated with different levels of PSP revealed that ovaries and testes of 0g PSP/kg feed were normal. Ovaries subjected to 4g PSP/kg feed had degenerative stromas while testes had scanty spermatozoa. At 8g PSP/kg feed, the ovaries showed increased atretic follicles and testes had degeneration of spermatozoa. Treatment with 12g PSP/kg feed resulted in severe atretic follicles of the ovaries and deformation of seminiferous tubules and erosion of spermatozoa of the testes. Proximate composition of the fish carcass showed that the 8g PSP/kg feed had the highest values (mean ± SE) of CP and ash (53.97 ± 0.094 and 20.05 ± 0.35) respectively. Body weight gain and Specific growth rate was highest at the 8g PSP/kg treatment level, but this treatment level had the lowest Feed Conversion Ratio. This study recommended the use of high temperature treatment of 36 oC to yield a high male percentage and this technique can be combined with the administration of pawpaw seeds powder to control the breeding of O. niloticus in production units.