Specific enzyme activities for protease across all treatments were presented in Fig. 2. At early larval stages (Z3 and M3), specific protease activity in shrimp was not significantly different between probiotic treatment and control. In contrast, at the subsequent ontogenetic stages (PL1–2 and PL7–8), the highest protease activity (0.21 ± 0.02 U mg− 1 protein and 0.26 ± 0.02 U mg− 1 protein, respectively) was observed in T-2 and there was a significant difference (P < 0.05), as compared with the control (0.16 ± 0.02 U mg− 1 protein and 0.17 ± 0.01 U mg− 1 protein, respectively). Similar results were also observed in T-3 at the PL7–8 stage (P < 0.05). However, there was no significant difference among all treatments (T-1, T-2 and T-3) in protease activity. T-1 showed no significant difference (P > 0.05) in protease activities of shrimp larval compared with that of the control during the whole trial