Can heat-killed Gordonia bronchialis enhance growth and immunity in rainbow trout (Oncorhynchus mykiss)?

In this study, the efficacy of heat-killed Gordonia bronchialis on growth performance, immune system and gastrointestinal structure in rainbow trout (Oncorhynchus mykiss) was evaluated. Fish (mean weight 30g) were fed basal diet (control), or treatment diets containing 2.48x10(8) (low dose) or 1.24x10(9) (high dose) cellskg(-1) feed of heat-killed G.bronchialis on a pulse basis (5days on treatment diet; 10days on basal diet) for 95days. On days 95 and 105, some of the fish were sampled for analysis of mentioned parameters. On days 110 and 120, the remaining fish were injected intraperitoneally with a 20mLL(-1) suspension of chicken red blood cells. Results showed that growth performance was significantly enhanced in both treatment groups compared with the control group. Serum complement and lysozyme activities and hemagglutination antibody titre were higher in both treatment groups compared with the control group. The length of the intestinal and pyloric caeca folds was increased in the high-dose group. Meanwhile, the number of goblet cells was increased in both treatment groups. This study suggests that heat-killed G.bronchialis has the potential to enhance growth, immunological parameters and the gastrointestinal structure in rainbow trout.