Mealworm (Tenebrio molitor) as a potential ingredient in practical diets for rainbow trout (Oncorhynchus mykiss)

The sustainability of the aquaculture industry greatly depends on the ability to find good replacements for fish meal, characterized by the same nutritional quality, cost and market availability, and easily manageable for the requested uses [1]. Nowadays there has been a growing interest in animal protein sources from insects. Recent experimental trials showed the possibility to use insect meal as alternative source of protein and fat in aquafeeds for cultured fish, without negative effects on growth performances [2-3]. Among insect meals, mealworm (Tenebrio molitor) (MW) is a good candidate as raw material for fish nutrition due to its high protein and lipid content. The aim of this research was to evaluate MW as a potential substitute for fish meal in rainbow trout diets. The MW was characterized on the basis of proximate analyses, fatty acid profile and amino acid composition and then two experimental diets were formulated to be isonitrogenous (crude protein 45%) and isoenergetic (21.5 MJ kg-1 dry matter) with increasing levels of MW (25%, and 50%, respectively) tested against a control diet without MW (MW0). A feeding trial was performed on quadruplicate groups of 30 rainbow trout (mean initial weight: 115.9 g) fed experimental diets for 75 days. At the end of the trial, the growth performance traits were determined and viscera and hepatosomatic indexes were calculated on nine fish per each treatment. Moreover, dorsal muscle tissues were sampled and analyzed for their proximate composition. Statistical differences did not appear for any of the growth performance traits considered, while as far as the somatic indexes are concerned, fish fed the 25% and 50% MW diets showed the lowest hepatosomatic index values (1.80 and 1.62, respectively). Fish proximate composition did not show any statistical difference among treatments. In conclusion, the main result of this study is that the MW can be used at an inclusion level of up to 50% without a growth performance reduction in rainbow trout feedstuffs, leading to a saving on fish meal protein.