Effect of Protein Level on Gonadal Development of the African Catfish

Abstract

A study was carried out to determine the effect of protein level, on the gonadal development of the African catfish, Clarias gariepinus, broodfish, using regularly recommended 31% and 40% crude protein (CP) diets. This was aimed at determining, the best level of crude protein inclusion in their diets, capable of enhancing gonadal recrudescence, maturity and spawning, and yet ensuring cost-effective feeding of pond-bred Clarias gariepinus broodstock. Juveniles weighing 5gms to 8gms with lengths ranging from 6cm to 9cm, were reared on the diets, for six months. Gonadal development (using Qualitative (Macro-morphological gonad examination) and Quantitative (Gonadosomatic index– GSI) methods), and Fish condition (using the Condition factor – K) were assessed at the third and sixth months. At the third month, qualitative gonad assessment revealed low gonadal development for all fishes though that, of the fishes (females and males) fed the 31% CP diets were 100% immature stage I gonads, whereas the 40% CP diet fed fishes were 70%immature stage I and 30%maturing stage II for males, and 80%immature stage I and 20%maturing stage II for females.. At the sixth month however, qualitative gonadal assessment revealed that, fishes fed 40% CP had 30% of the females spawning, and 30% of the male fishes attained full maturity, but amongst the fishes fed 31% crude protein, 30% of females and 20% of males were about attaining maturity. This was supported by higher GSI ranges of 25.5% - 39.1% for females and 0.17% - 0.22% for males fed 40% CP, as compared to lower GSI ranges of 20.5% - 28.6% for females and 0.11% - 0.14% for males fed 31%CP diet. The condition factor-K values were generally high at the third month (1.46 -1.90 and1.25 to1.68, for females and males fed 31%CP respectively; and 0.12 to2.16, and1.28 to1.95 for females and males respectively, fed 40%CP) but fell at the sixth month (0.57 - 0.75 and 0.59- 0.84, for females and males fed 31% CP; and 0.59 – 0.73 and 0.74 to 0.92 for females and males respectively, fed 40%CP). This down-ward trend indicates loss in condition related to gonadal development. However, the loss exhibited by fishes fed40% CP was less and their condition were better .The observed differences in GSI between 30% and 40%  CP diets fed-fishes were significant at P<0.05% for females and P<0.01% for males. Also,  the condition of females fishes fed 31% and 40% crude protein were not significantly different, but the males fed both experimental feeds were significantly different at P<0.05%. It could thus be inferred that, the 40% CP diet gave better results than 31%CP diet.  It is therefore recommended that, aquaculturist utilize 40% crude protein- inclusion for enhancing broodfish condition, gonadal recrudescence and spawning, for year-round seed production and cost effective  Clarias gariepinus broodfish management.

Keywords: Clarias gariepinus, Crude protein, Gonadal development, Fish condition.