The Effect of Environmental and Nutritional Manipulation On Year-Round Gonadal Development, Spawning And Recrudescence Of Female Clarias Gariepinus Broodfish.

Abstract

A study was carried out to determine the influence of environmental and nutritional manipulation on cyclical gonadal development, spawning and recrudescence of female pond- bred Clarias gariepinus broodfish. This was aimed at proposing a substitute to chemical/hormonal stimulation for year- round gonadal development and proffering a simple adaptive, cost efficient and effective method of year-round fingerling production, for sustainable Catfish production. A total of 400 hundred adult catfish, weighing between180 and 250grams, measuring between17cm and 20cm were stocked in replicate experimental and control earthen ponds. In the experimental treatment, fishes were fed 40% Crude protein diet, the pond water continually pumped in and the level maintained at 30 cm, whereas water introduction and level in the control pond was dependent on nature (rainfall) and the fishes fed on natural food organisms from the pond waters. Fish were sampled randomly for the 12 months duration, for gonadal development, spawning and recrudescence using standard qualitative and quantitative methods. Qualitative, macro-morphologic assessment showed that, from June to November, both simulated and non-simulated fish groups exhibited a gradual improvement in gonadal development, from Immature Stage I to Fully matured stage IV, and then running ripe Stage V. By November, they all had Spent/Resting Stage VI. This was supported by the quantitative assessment-Gonadosomatic index (GSI), which rose gradually from May, peaking twice followed by a drop in October/November. This trend of gonadal development is natural as fish gonadal development commences and reproduction occurs during the rainy season, and ends as the dry season approaches (Clay, 1979; Legendre, 1986 and Fruend et al, 1995). Subsequently, from November up until January, the non-simulated fish group exhibited mainly the Spent/Resting Stage VI gonads, followed by a gradual improvement from Immature Stage I in February to Maturing Stage II in May. Hyder (1970) and Sikoki (1978) reported that reproductive activity is poor when favorable conditions do not persist. Contrarily, from November, up until May, the simulated fish groups were observed to continually exhibit a steady and stable supply of ready-to-spawn Fully mature Stage IV, and Running ripe Stage V. This was supported by high GSI values of the simulated fish groups as opposed to a drastic drop in GSI of non-simulated fish groups. Subsequently, GSI values of both fish groups showed a gradual rise from February to May, however, the simulated fish groups exhibited higher GSI. In conclusion, the simulated fishes had improved gonadal development as also supported by statistical data (probability of 0.01%). Thus, it is recommended that, further research be carried out on this method, to standardize it for year-round fingerling production and supply, as other forms of stimulants are either in short supply, complex to use for some, too expensive; and even the world at large is going GREEN, and avoiding the use of chemical or biological manipulation/ genetic multiplication of Food organisms.

Key Words: Environmental and Nutritional Manipulation, Clarias gariepinus brood-fish, Gonadal development, Simulated fish, Non-simulated fish.