Investigation of growth and immune responses in channel catfish (Ictalurus punctatus) following feeding of dietary immunostimulants

Abstract

The commercial farming of channel catfish (Ictalurus punctatus) in the United States often faces economic losses due to infectious diseases caused by opportunistic pathogens. Using natural immunostimulants has positively affected aquaculture production, modified hematological and immunological parameters, and enhanced fish response to infectious agents. This study evaluated two immunostimulants, a protease complex (PC) and a humic substance (HS), on the growth, disease resistance, and immune response of channel catfish. In a short-term study, the oral administration of PC and HS enhanced defenses against columnaris disease, Flavobacterium covae, resulting in increased lysozyme activity in the blood and upregulation of proinflammatory immune genes in the splenic tissue. Additionally, these immunostimulants provided protection against columnaris disease. The study also revealed that varying protein concentrations in the diet influenced the growth of channel catfish fingerlings over a short feeding period. However, in a long-term study, prolonged supplementation of PC or HS in channel catfish diets led to positive growth but increased mortality was observed. PC supplementation showed potential for long-term use in commercial production systems and improved feed efficiency. On the other hand, HS supplementation enhanced daily growth but had lower biomass gain compared to the control or PC supplementation. Both PC and HS increased lysozyme activity, indicating immune stimulation, but did not significantly affect immune-related genes after long-term feeding. The reduced survival could be attributed to prolonged exposure to specific dosages of PC or HS and potential interactions with parasitic pathogens. These findings suggest dietary immunostimulants like PC and HS can positively impact channel catfish health and disease resistance. However, their long-term use requires optimization to avoid adverse effects and maximize growth and immunostimulatory benefits in large-scale catfish production. Further research is needed to optimize the inclusion of dietary PC and HS in channel catfish diets and their interactions with pathogens.