Bio-floc technology application in flatfish Paralichthys olivaceus culture: Effects on water quality, growth, hematological parameters, and immune responses

Juvenile Paralichthys olivaceus (mean weight 2.69 ± 0.31 g) were raised in bio-floc and sea water for 4 months. After 4 months, individuals raised in bio-floc (mean weight 296.4 ± 31.7 g and mean length 30.5 ± 2.6 cm) and sea water (mean weight 281.2 ± 30.6 g and mean length 29.4 ± 2.3 cm) were sampled for health evaluation. Growth performance of P. olivaceus raised in bio-floc was slightly higher than that of fish reared in sea water, but the specific growth rate was not significantly different between the two groups. Hematological parameters such as hemoglobin and hematocrit were not significantly different between the two groups. Of the plasma components, glucose, aspartate aminotransferase (AST), and alanine aminotransminase (ALT) in P. olivaceus raised in bio-floc were significantly lower than those of individuals raised in sea water, whereas the other components were not significantly different between the two groups. In regards to immunity, Immunoglobulin M (Ig M) of P. olivaceus raised in bio-floc was significantly higher than those of fish raised in sea water. These results indicate that the bio-floc-rearing system was effective in improving immune function and reducing stress in P. olivaceus without significantly changing its physiology compared with fish in general sea water rearing.