As sustainability becomes a pressing concern in aquaculture, innovative approaches to enhancing production without depleting natural resources are essential. One such solution is the use of humic acids, which are proposed as additives to promote fish growth and bolster immune defense. Humic acids, naturally occurring in water sources, are organic substances that derived from decomposition of animal or plant material. These substances may be antioxidants with antimicrobial, anti-inflammatory, and immunostimulatory properties. Depending on their structure, humic substances may provide benefits as well as the promotion of growth.
In this current study, 750 juvenile rainbow trout are used in an 8-week feeding trial testing 3 experimental diets formulated with humic substances, as well as control diet. Throughout this period, growth among groups is recorded biweekly through biomass, as well as the individual weights and lengths of 10 fish per tank. At the end of the 8-week period, blood, mucus, kidney, spleen, and intestine are sampled before being challenged with the causative agent of Coldwater Disease: Flavobacterium psychrophilum. These samples are taken again 24 hours, 7 days, and 28 days post-challenge.
Growth metrics, including relative growth, feed conversion ratio, specific growth rate, and weight gain are calculated at the end of the diet trial to determine growth potential of each humic substance. Mortality, and innate/adaptive immune responses are evaluated through challenge survival, antibody assays, and lysozyme activity to determine the impact of the experimental diets on immune function.