In the present study, the biofloc supplementation at the 12% level (B12) did not result in proportionate increase in growth rate or improvement of FCR compared with control. Further, the digestive enzyme activities in B12 were not significantly higher than other treatment groups. Earlier, Kuhn et al. (2010) replaced the fish meal by biofloc in L. vannamei diet and recorded significantly higher growth rate at 10 and 15%, and non-significant difference at 21 and 30% dietary inclusion
level of biofloc. The present findings agree in general with those of Wang (2007) and Anand et al.(2013b)who reported that increase in dietary supplementation of probiotic or periphytic algae in shrimpdiet do not increase proportionately the digestive enzyme activities and growth of shrimp.Moreover, reduction in growth rate of fishes was recorded at higher level of microbial supplementation (Ajiboye et al., 2012; Kiessling and Askbrandit, 1993) as microbial products at higher level tend to reduce the feed palatability and digestibility (Kiessling and Askbrandit, 1993). The higher ash level recorded in the B12 diet compared to all other groups also might have influenced the digestibility and growth performance of shrimp. However, the growth performance of B12 was comparable to control suggesting that dietary supplementation of higher level of biofloc do not have growth retardation effects in shrimp juveniles. Seeing the cost-effectiveness, the inclusion of biofloc at 4% level is beneficial in improving growth performance and digestive enzyme activities in shrimp.