Effects of partial or total fish meal replacement by agricultural by-product diets on gonad maturation, sex steroids and vitellogenin dynamics of African catfish (Clarias gariepinus)

The establishment of the first sexual maturation was characterized in African catfish (Clarias gariepinus) in order to study the efficiency of replacement of fish meal (FM) by diets composed of local vegetable ingredients. Four diets were formulated containing decreasing levels of FM (50-0% for diet 1 to diet 4) and increasing proportions of vegetable ingredients (50-100%). Gonadosomatic index (GSI), diameter and percentages of developmental stages of oocytes, plasma sex steroids and vitellogenin dynamics were investigated from February to June using one-year-old fish. Fish were individually tagged, and 12 individuals from each diet were investigated monthly. Replacement of FM with plant ingredients did not affect the GSI neither in males, nor in females. All males were spermiating, and no abnormal gonads were found. In females, GSI and percentages of advanced stages of oocytes decreased during the dry season, indicating seasonal changes in gonad development. Moreover, oocytes were in late exogenous vitellogenesis, but no final maturation stages were observed, whatever the diet. Higher plasma levels of E2 in females and of androgens (T and 11-KT) in both sexes were observed in fish fed diet 4 than in those receiving diet 1 depending on the season. Levels of plasma E2 and ALP (indicator for vitellogenin) in males did not differ among treatments and seasons suggesting no phytoestrogenic activity. The results showed that total replacement of FM by vegetable diets composed of groundnut oilcakes, bean and sunflower meals has no deleterious effect on the onset of sexual maturation in African catfish but, may stimulate the sex steroid production and in turns may potentially exert some positive actions on reproductive success.