Effects of dietary Lactobacillus plantarum C20015 on growth, immunity, and disease resistance in koi carp

Koi carp (Cyprinus carpio) are well-known and highly valuable fish in the international ornamental fish community that have been plagued by Aeromonas veronii infections in recent years. Some A. veronii infections are serious enough to cause death. Lactobacillus plantarum, a probiotic, is one of the most environmentally friendly and safe alternatives to antibiotics for use as a feed additive for aquatic animals such as fish. The present study investigated the effects of L. plantarum C20015 on growth performance, immune responses, and eradication of A. veronii infection in koi carp. During a 6-week feeding experiment in an indoor aquarium and a 14-day A. veronii artificial infection experiment, a control diet group was fed with untreated feed twice a day, while experimental groups were given different concentrations of L. plantarum in their feed. The results indicated that the specific growth rate and percent weight gain of fish were significantly higher in the experimental groups than in the control diet group (P < 0.05). The activity of superoxide dismutase (SOD), peroxidase (POD), and lysozyme (LZM) and the levels of IgM antibody were significantly higher in the L. plantarum–supplemented groups than in the control diet group, and the enzymatic activity in the 108 CFU/g C20015 group was higher than that in the 107 CFU/g C20015 and 109 CFU/g C20015 groups (P < 0.01). In contrast, alkaline phosphatase (AKP) activity in the experimental groups was the highest at 42 days. All fish in the control diet group died 7 days after A. veronii infection. After 14 days, the relative percent survival (%, RPS) of the fish in the L. plantarum–supplemented groups was significantly higher than that of the fish in the control group, and the 108 CFU/g C20015 group had the highest RPS. Therefore, we first reported that fish fed with 108 CFU/g of L. plantarum C20015 could promote food intake and growth for koi carp.