Improving greater amberjack (Seriola dumerili) defenses against monogenean parasite Neobenedenia girellae infection through functional dietary additives

Abstract

The main objective of this study was to determine the effect of two feeding additives (cMOS: Actigen®, Alltech Inc., USA) and a phytogenic specifically designed for reducing ectoparasite incidence, combining garlic and labiatae herbal extracts (HERB; Delacon, Austria) on growth performance, stress and immune response of greater amberjack (Seriola dumerili) before and after an experimental parasitization with the skin ectoparasite Neobenedenia girellae, a monogenean with high incidence on Seriola cultured in sea cages. Two parallel trials were conducted in order to determine the effect of 70 days of functional diets supplementation (0.2% cMOS and 200 ppm HERB) on greater amberjack: a) Growth performance and stress resistance and b) disease resistance against N. girellae. Additionally, in order to evaluate the effects of the dietary supplements pre- and post- parasitization challenge against N. girellae, the expression of some immune-related genes was evaluated. The relative expression of Il-1β, piscidin, hepcidin, IgT, tnf-α, muc-2, cathelicidin, complement c3, cd8, and caspase-3 was determined in skin. The activity of protease and lysozyme in serum and skin mucus were also evaluated, as well as parasite load and parasite total size. The use of both functional additives did not affect fish growth performance. However, the dietary supplementation of HERB significantly (p<0.05) reduced circulating cortisol levels after the stress challenge, whereas dietary cMOS significantly (p<0.05) reduced the parasite load and total parasite size. When comparing pre and post parasitization challenge, skin mucus protease activity was significantly (p<0.05) higher in all the treatments before parasitization, while the use of both functional additives increased skin mucus lysozyme activity after challenge. From the eleven immune genes studied, only piscidin was significantly (p<0.05) up-regulated by HERB supplementation before challenge, whereas after parasitization, muc-2 and piscidin were significantly (p<0.05) up-regulated by HERB and tnf-α, il1-β, hep, c3, cd8 and casp3 were up-regulated by both functional additives. Moreover, hep, IgT, cath, c3 and cd8 expressions were negatively correlated with the parasite load. In general, greater amberjack supplementation with cMOS and HERB at the dose used in the present study was effective for reducing stress and for increasing the skin associated lymphoid tissue (SALT) immune response against N. girellae during the infection process.