Effects of 5-aminolevulinic acid on the growth performance, immunity and stress resistance of juvenile large yellow croaker (Larimichthys crocea) fed low-fishmeal diets

A 60-day feeding trial was conducted to evaluate the effects of dietary 5-aminolevulinic acid (5-ALA) on the growth, immunity and stress resistance of juvenile large yellow croaker ( Larimichthys crocea) with 17.33 ± 0.10 g of initial body weight. Seven experimental diets were designed. The diet with 40% fishmeal and without 5-ALA supplementation was used as the positive control (A1). The diet with 30% fishmeal and without 5-ALA supplementation was used as the negative control (A2). Based on the negative control diet, the other five experimental diets were formulated with 3 mg/kg (A3), 9 mg/kg (A4), 27 mg/kg (A5), 81 mg/kg (A6) and 162 mg/kg (A7) of 5-ALA, respectively. There was no statistically significant difference in the survival rate of large yellow croaker among the treatments ( P > 0.05). The A2 group had the significantly reduced weight gain rate (WGR) ( P < 0.05). Supplementation with 9–81 mg/kg 5-ALA into diets significantly increased the WGR. In the A5 and A6 groups, WGRs had no significant difference with that in the positive control of A1 group ( P > 0.05). The A2 group had significantly decreased acid phosphatase (ACP) and alkaline phosphatase (AKP) activities, as well as increased aspartate aminotransferase (GOT) and alanine aminotransferase (GPT) activities ( P < 0.05). However, dietary 5-ALA supplementation significantly enhance the ACP and AKP activities, and reduce the GOT and GPT activities ( P < 0.05). The A2 group had significantly up-regulated expressions of apoptosis-related genes ( bax and caspase3 ) and decreased antioxidation enzyme activities ( P < 0.05), and these effects were alleviated by dietary 5-ALA supplementations (≥3 mg/kg). Supplementation of dietary 5-ALA more than 9 mg/kg significantly increased the contents of porphobilinogen, heme, and the activities of HO-1, ferrochelatase and δ-aminolevulinic acid dehydratase in liver. Meanwhile, this supplementation level of dietary 5-ALA also significantly increased the resistance of large yellow croaker to air exposure stress. Overall, based on the weight gain rate of large yellow croaker, the optimal supplementation level of dietary 5-ALA was estimate as 85.29 mg/kg for large yellow croaker.