Phytogenic feed additives, derived from plant-based sources like essential oils and extracts are increasingly utilized in aquaculture. They have the potential to bolster immune responses, enhance disease resistance and improve growth performance in fish. The study investigates the effect of commercial phytogenic feed additives (Actifor Pro, Actifor Power, Fresta Protect, Syrena Boost, and Enviro QS) on disease susceptibility, immunity, and growth performance of juvenile channel catfish (Ictalurus punctatus) within an indoor recirculating system. Over six weeks, 750 juvenile channel catfish (14.8 ± 0.4g) were stocked in 30 tanks and fed either a control diet or the phytogenic-supplemented feed. Following the feed trail, fish were immersion-challenged with virulent Aeromonas hydrophilia (vAh; ML09-119; 1.86 × 109 CFU mL-1), a pathogen that causes considerable losses in the catfish industry due to motile Aeromonas septicemia (MAS).
Growth performance, including weight gain, survival and feed conversion ratio, was similar among treatments, with no statistically significant differences (P > 0.05). After exposure to A. hydrophilia, for 7 days, cumulative precent mortality (CPM) was higher in the control diet (60%) compared to the phytogenic treated fish. Notably, fish fed with Fresta protect exhibited the lowest CPM (19.6%), while other treatment groups had CPM ranging from 45% to 58%. Survival analysis indicated improved survival probability in the phytogenic-treated groups (p= 0.009). Sera lysozyme activity was significant differences across the groups, (P= 0.009), moreover, the catfish fed with Fresta protect had higher sera lysozyme activity than the control group.
This study concluded that phytogenic feed additives enhance juvenile channel catfish disease resistance and aspects of innate immunity. Specifically, Fresta Protect showed the most promise toward improving channel catfish survival against vAh. Incorporating phytogenics could be a viable alternative to antibiotic uses in U.S catfish aquaculture.