Evaluating Fermented and Hydrolyzed Rice Bran for Improved Biofloc Performance in African Catfish (Clarias gariepinus) Rearing

Abstract

Background: Biofloc system uses the presence of microorganisms in the culture system to generate flocs from nitrogen waste, thus permitting continued water usage. Factors like carbon source, carbon to nitrogen ratio, and stocking density, affect the quality and density of microorganism and the productivity of the biofloc system. This study aims to determine the growth, feed conversion ratio (FCR), and proximate composition of catfish reared in a biofloc system using rice bran (RBB), fermented rice bran (FRB), and hydrolyzed rice bran (HRB) as carbon sources.  Methods: Fingerling catfish of an initial mean weight of 10.55 ± 2.60g were stocked in outdoor 200-liter plastic tanks in a randomized design with the three treatments in two replications. A biomass (g) to volume (l) ratio of 1:2 was maintained throughout the experiment. The carbon-nitrogen contents in the feed, water, and treatment carbon were used to ensure an overall 15:1 C-N content in the system. Results: The weight parameters and FCR at the end of the 8-week rearing trials were significantly higher (P˂0.05) for the catfish cultured in FRB and HRB treatment, with no significant difference between the two. The highest weight gain (46.55g) was recorded in FRB treatment while the lowest value of weight gain (40.50g) was in RBB. The crude protein (65.44%) was significantly higher (P˂0.05) in the FRB and lowest in the RBB, with values of (61.85%). The crude protein and lipid of the biofloc produced in the system were not significantly different (P<0.05) between FRB and HRB treatment. The moisture content was highest in FRB while the ash was lowest in HRB. Conclusions: This experiment showed that acid-hydrolysis and solid-phase fermentation of rice bran could boost its performance as a biofloc carbon source, even though latter has been well reported.