Effects of diets containing Hermetia illucens and poultry by-products meals on Dicentrarchus labrax intestinal enzymatic activities. Analysis of a commercial production

Aquaculture is facing the challenge of being developed following the circular economy concept; in this regard, the choice of sustainable, nutritious, and non-conventional aquafeed ingredients should answer this need. The SUstainable fiSH feeds INnovative ingredients–SUSHIN project has recently proposed a combination of Hermetia illucens meal (HIM, 8.1 g/100 g as fed) and poultry by-product meal (PBM, 20.6 g/100 g as fed) to substitute up to 40% of vegetable proteins in diets containing low quantity of marine proteins (5.5 g/100 g as fed) for marine species of interest for Mediterranean aquaculture, as European seabass (Dicentrarchus labrax). Thus, the aim of the present trial was to compare the effects of the experimental feed (SSH diet), under commercial conditions (Ittica Caldoli Foggia, Italy). Three thousands mixedsex E. seabass were randomly distributed into three tanks, 1000 fish each and fed a commercial diet. When an average weight of 300 g was reached, fish were fed for 63 days with two different isoproteic (45%) and grossly isolipidic (20%) diets. A control group (CTR) continued being fed the same commercial diet as during the adaptation phase and the two remaining groups were fed with the experimental diet (SSH). At the end of the growing trial, marketable indexes were recorded, then fish intestine and muscle (n=9/group) were sampled. The intestine activity of glutathione reductase (GR), catalase (CAT), glutathione peroxidase (GPX) and lipid peroxidation was measured. In muscle, conjugated dienes and thiobarbituric acid reactive substances were measured as lipid oxidation markers. At the end of the trial, the total length and body weight of fish fed the SSH diet (472.5g) were higher than the CTR group fish (433.9g). The incidence of the intestine on total weight was lower (p=0.05) in SSH than in CTR fish, being 2.18% and 2.38%, respectively. Intestine lipid peroxidation was lower in fish fed the SSH diet than in the CTR ones. Moreover, lower CAT activity and higher GR activity were also registered in the SSH group than in the CTR group, even though not statistically significant. Muscle lipid oxidative status was not affected by the diets. In conclusion, the SSH diet, which in previous trials showed promising results at experimental level, demonstrated to be a suitable alternative to the commercial feed for E. seabass feeding even when administrated in fish farming plant.