Histological evaluation in sturgeon's gut fed Hermetia illucens meal

For many years fishmeal (FM) was the first protein source in carnivorous fish diets. Currently, FM is often replaced by vegetable protein meal (VM) even if high levels of substitution often lead to intestinal and hepatic damage that compromise animal health and reduce performances. Recently, studies have been conducted evaluating the effects of insect meals as FM replacer on performance, but only a few have investigated the histological effect. Moreover, no study has been done on sturgeon. The aim of this study was to evaluate the effect of inclusion of highly defatted Hermetia illucens (HI) larvae meal on liver and spiral valve histology of Acipenser baerii juvenile. Four diets were formulated: a control diet (HI0), in which FM was the main protein source, two diets containing respectively 18.5% (HI1) and 37.5% (HI2) of HI and a VM-based diet (CV) (with 49% of VM and without HI). At the end of the performance trial (data not shown), 12 fish per treatment were sacrificed by over anaesthesia. Samples of spiral valve and liver were taken, subsequently fixed by immersing in 10% neutral-buffered formalin and processed by standard paraffin wax techniques. Samples were stained with haematoxylin-eosin and Periodic-Acid Schiff. Liver was evaluated for hepatic degeneration on 12 samples. Morphology (length and integrity) and number of goblet cells, on 25 villi per 5 samples/treatment, were evaluated in spiral valve. Regarding hepatic degeneration, the Kruskal-Wallis test didn't show significant differences among groups; likewise, linear regression didn't show significant differences in spiral valve evaluation. At microscopical level, HI0 and HI1 spiral valves showed a better preservation of absorption epithelium and villus structure, and a lowest mucus quantity than HI2 and CV. The hepatic accumulation of lipids showed an increasing pattern among groups: lowest in HI0 and HI1, highest in HI2 and CV.