BackgroundTwo trials were performed to evaluate a partially defatted Hermetia illucens (HI) larvae meal as potential feed ingredient in rainbow trout (Oncorhynchus mykiss Walbaum) diets. In the first trial, 360 trout (178.9 ± 9.8 g of mean initial body weight) were randomly divided into three experimental groups (4 tanks/treatment, 30 fish/tank). The fish were fed for 78 days with isonitrogenous, isolipidic and isoenergetic diets containing increasing levels of HI, on as fed basis: 0% (HI0, control diet), 25% (HI25) and 50% (HI50) of fish meal substitution, corresponding to dietary inclusion levels of 0, 20% and 40%. In the second trial, 36 trout (4 tanks/treatment, 3 fish/tank) were used to evaluate the in vivo apparent digestibility coefficients (ADC) of the same diets used in the first trial.ResultsSurvival, growth performance, condition factor, somatic indexes, and dorsal fillet physical quality parameters were not affected by diet. The highest dietary inclusion of HI larvae meal increased dry matter and ether extract contents of trout dorsal fillet. The use of HI larvae meal induced a decrease of valuable polyunsaturated fatty acids (PUFA) even if differences were only reported at the highest level of HI inclusion. The insect meal worsened the lipids health indexes of the same muscle. Dietary inclusion of insect meal did not alter the villus height of the fish. No differences were found among treatments in relation to ADC of ether extract and gross energy, while ADC of dry matter and crude protein were higher in HI25 if compared to HI50.ConclusionsThe obtained results showed that a partially defatted HI larvae meal can be used as feed ingredient in trout diets up to 40% of inclusion level without impacting survival, growth performance, condition factor, somatic indexes, dorsal fillet physical quality parameters, and intestinal morphology of the fish. However, further investigations on specific feeding strategies and diet formulations are needed to limit the observed negative effects of the insect meal on the FA composition of dorsal muscle.

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Infection with Lactococcus garvieae is considered the most important risk factor for the European trout industry, and the losses are approximately 50% of the total production. To improve our understanding of the genetic links among strains originating from different countries, we examined the population structure of L. garvieae by comparing 81 strains isolated from different sources and ecosystems (41 farms in six countries) in which the bacterium is commonly found. Genetic similarities (as assessed with molecular tools, including restriction fragment length polymorphism ribotyping with two endonucleases) were compared with serological data. The combined results reveal that in endemic sites the bacterial population displays a clonal structure, whereas bacterial diversity characterizes sites where the infection is sporadic.

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