Influence of humic acids on growth performance, bravery, stress resistance, antioxidant activity, and immune gene expression in male Siamese fighting fish (Betta splendens)

The current study investigated the effects of a humic acid supplement on the growth performance, antioxidant enzyme activity, immune-related genes, behavior and endocrinology of male Betta splendens fish. Fish species that are naturally exposed to high levels of humic substances in their environment are likely to perform better under captive conditions when given these substances. In this study, fish were fed a diet containing 0, 0.5 %, 1 %, and 1.5 % humic acid for six weeks. The results showed no significant differences in growth and feeding parameters between treatments (p > 0.05). The fish with a diet of 1.5 % humic acid showed more aggressive behavior in the mirror test than the control group (p < 0.05). In contrast, the fish fed a diet containing 1 % and 1.5 % humic acid showed a higher level of activity in the test with new objects than the control group (p < 0.05). The testosterone levels after aggression were significantly higher in the fish fed diets containing 1 % and 1.5 % humic acid than in the control group (p < 0.05). In addition, the humic acid-treated fish showed lower oxidative stress and cortisol production in common aquaculture stressors than the control (p < 0.05). Gene expression analysis showed upregulation of immune-related genes, including β-defensin 1, c-type lysozyme, interleukin-1β, and tumor necrosis factor-α, in response to humic acid supplementation compared to control (p < 0.05). Overall, the results of this study indicate that a diet containing 1 % humic acid has a positive effect on the physiology, immunology, and behavior of male B. splendens. •A 1% dietary humic acid positively impacted the physiology and behavior of male Betta splendens.•Fish fed diets enriched with humic acids exhibited increased boldness and stress resistance.•The expression of genes related to the fish immune system was increased in the humic acid-treated groups.•Growth and feed conversion of fish were not influenced by dietary humic acid.