The potential role of marine macroalgae Padina pavonica on growth performance, histological status, and resistance of the rabbitfish Siganus rivulatus to Pseudomonas anguilliseptica bacteria

Macroalgae, including Padina pavonica (PP) has recently gained more attention due to their high contents of bioactive components that increase their value as a natural feed additive resource in practical aquaculture. The current study investigated the effect of marine macroalga P. pavonica as a natural dietary feed additive on growth, histological status, and resistance of rabbitfish Siganus rivulatus fry against Pseudomonas anguilliseptica bacteria. Four diets were formulated to contain 0 (control T0), 50  (T1), 75 (T2), and 100 (T3) g PP/kg diet. Rabbitfish fry specimens with an average weight of 1.10±0.06 were divided into four treatments in triplicates. Fish samples were fed experimental diets to apparent satiation three times a day for eight weeks. After the feeding trial, fish were challenged with pathogenic bacteria (P. anguilliseptica) infection. The result revealed that growth performance, feed utilization, and survival (%) significantly improved with increasing PP rate in all experimental fish diets compared to the control. Upon increasing dietary PP levels, total body protein content increased. The opposite trend was observed for total body lipid content. Fish fed on diets containing PP showed protective protection against P. anguilliseptica bacterial infection and recorded a decrease in mortality to 22.5% in a fish-fed diet containing 10 g PP/kg, compared to the control group (72.5%). No histopathological changes were detected in the intestine, liver, and spleen organs in either the control group or the group treated with PP. The results of the current study indicate that S. rivulatus fry-fed diets containing at least 10g/kg of macroalgae, P. pavonica for eight weeks enhanced growth performance, diet utilization efficiency, and histopathological indices of the fish intestine, liver, and spleen.