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The effect of pH and selected chemical variables on the reproductive cycle of Oreochromis mossambicus


, : The effect of pH and selected chemical variables on the reproductive cycle of Oreochromis mossambicus. Water S A (Pretoria) 22(1): 57-66

Adult male and female O. mossambicus from Syferkuil Dam, situated 28 km NW of Pietersburg, were analysed for gonad mass and length, gonadosomatic indices, blood pH and gonad pH over a twelve-month experimental period. Male development seems to be dependant on female development in that it "lags" behind the female by two months. Male GSI reaches a peak of 0.78 +- 0.12% during November as opposed to the female maximum of 3.11 +- 0.72% during September. Blood and gonadal pH show an inverse relationship when breeding is prevalent. Male gonads are more alkaline (7.72 +- 0.29) and females more acidic (6.94 +- 0.16) during September. The chemical composition of the blood plasma and gonadal supernatant varied considerably over the experimental period. Glucose, lipids, lactate and proteins are all involved in energy production or provide a protective function to developing gonads. The presence of urea is indicative of protein metabolism. A breeding, resting and gonadal recrudescent season may be distinguished in both male and female O. mossambicus.

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