The potential of rearing juveniles of bluegill, Lepomis macrochirus, in a biofloc system

Abstract

Biofloc technology (BFT) can potentially enhance growth and provide supplemental nutrition to some fish species, but this has not been investigated in bluegill Lepomis macrochirus juveniles. In this study, L. macrochrius juveniles were cultured in a clear-water (CW) system versus BFT when using either corn starch (BFT-Sta) or sucrose-sugar (BFT-Sug) for 32 days at a carbon (C) to nitrogen (N) ratio of 15. After 32 days, water composition of cultivable bacteria were identified using molecular techniques while the survival, growth, histopathology, biochemical composition, and contribution of C and N from bioflocs (based on stable isotope analysis) to L. macrochrius were determined. In the CW system, Escherichia coli was detected but not in the BFT tanks, whereas Aeromonas hydrophila was present in the BFT tanks but not in CW. Fish obtained C and N from bioflocs at 4.11 % and 9.5 % in the BFT-Sta treatment, respectively, and 18.8 % and 1.4 % in the BFT-Sug treatment, respectively. A temporary loss of aeration in the BFT treatments led to dissolved oxygen (DO) plummeting, leading to 50 % mortality, which is indicative of the risk involved when using BFT but also the tolerance of L. macrochrius to temporary low DO. BFT also significantly reduced L. macrochrius growth, which was likely compounded by consistently elevated ammonia and reduced feed intake/feeding activities. The nutritional contribution of bioflocs to L. macrochirus along with no abnormal gill histopathology suggests BFT could have great potential for this species.