Portions of soybean meal autoclaved at 116°C and 1.2 kg/cm² pressure for 10, 15, 20, 25 and 30 min were used to compound 4 experimental diets appropriately labeled SB₁₀, SB₁₅, SB₂₀, SB₂₅ and SB₃₀ respectively. The experimental diets were fed to Clarias gariepinus female broodstocks intensively for 84 days. During the experimental period, the female fish broodstock growth performance as well as the water and the in-dwelling net microplanktonic quality were monitored. The feed inputs into the different culture media ranged between 13,759 g (SB₁₅) and 15, 649 g (SB₁₀). The highest weight gain was recorded in the female broodfish fed diet SB₂₅. The assayed water quality parameters for the different treatment culture media were not statistically different from each other (P > 0.05). Four (4) phytoplank-tonic phyla containing 7 orders with 30 species were recorded in the various media receiving the different feed inputs. The richest floristic composition with 21 species and a Margalef’s Richness Index (R¹) of 1.66 was obtained in the culture medium that received SB₂₅ feed input. Twenty (20) micro-invertebrate species belonging to 2 phyla and 4 orders were recorded in the various media during the period of study. The rotifers (Order: Ploima) with 16 species dominated the microinvertebrate fauna. Results also showed that the culture medium which received SB₂₅ diet had the highest micro-invertebrate fauna with 19 species.

Key words: Soybean, feed input, Clarias gariepinus, water quality, microplankton.