Effect of mealworm (Tenebrio molitor L.) larvae meal on amino acid composition of gilthead sea bream (Sparus aurata L.) and rainbow trout (Oncorhynchus mykiss W.) fillets

To date, the insect Tenebrio molitor (TM) seems suitable for partial replacement of fish meal (FM) in aquafeeds for a variety of marine and freshwater fish species, considering fish growth performance and diets nutrient utilization. Nevertheless, very few studies were conducted to evaluate the effect of the inclusion of TM meal, as alternative protein source, on total and free amino acid (TAA and FAA, respectively) composition of gilthead sea bream (Sparus aurata L., SB) and rainbow trout (Oncorhynchus mykiss W., RT) muscle. Three isonitrogenous and isocaloric diets were formulated both for SB and RT and tested in two separate trials: a control diet (TM0), and two diets in which TM larvae meal was included at 25% (TM25) and 50% (TM50) as fed as substitute of the conventional protein source (FM and corn gluten meal in SB feed; FM, corn gluten and wheat meal in RT feed). Thirty-one specimens of SB and 15 RT were randomly killed after 163 and 90 days of growing trials, respectively. Then, fish fillets were subdued to TAA and FAA analyses together to TM and feed samples. The TAAs composition of TM was mainly characterized by alanine (Ala), glutamine (Glx), glycine (Gly), asparagine (Asx), and leucine (Leu), being their sum almost 52% of TAAs. Contrariwise, TM was deficient in arginine (Arg). The fish diets were also affected by TM inclusion, as well as TAA and FAA profile of SB and RT. For instance, Ala, Leu, and Lys as TAA were higher in SB-TM50, while histidine (His) and phenylalanine (Phe) were lower in SB-TM25 and SB-TM50 than in SB-TM0. RT-TM50 group had a significantly higher level of total Ala, taurine (Tau), tyrosine (Tyr), cysteine (Cys), Leu and proline (Pro) than RT-TM0 group while Glx, His, Met, and Thr declined in RT-TM50 compared to the other two groups. Even the FAA profiles of the diets and fish muscle were affected by TM inclusion. In the present study, SB-TM50 contained higher Arg, valine (Val), Leu, Phe, Gly, His and Pro than SB-TM0. In addition, both SB-TM25 and SB-TM50 were poorer in Tau than SB-TM0. Concerning RT, we observed an overall significant reduction in the essential AA (Ala, Ile, Leu, and Lys) in RT-TM50. Moreover, the RT-TM50 had the lowest Gly and His content among the tested diets. Since the relation among AA profile of the diet and fish digestion is not still clear, further investigation should be done in order to confirm these preliminary data.