Comparative study of growth performance and amino acid catabolism in Oncorhynchus mykiss, Tinca tinca and Sparus aurata and the catabolic changes in response to insect meal inclusion in the diet

This experiment studied the kinetics of three key enzymes involved in the hepatic amino acid metabolism, alanine aminotransferase (ALT, EC 2.6.1.2.) aspartate aminotransferase (AST, EC 2.6.1.1.) and glutamate dehydrogenase (GDH, EC 1.4.1.3.), of three fish species: rainbow trout (Oncorhynchus mykiss), tench (Tinca tinca) and gilthead seabream (Sparus aurata) and their response to two levels (15% and 30%) of fish meal replacement with two different insect meals (Hermetia illucens and Tenebrio molitor). Five iso- nutritional and isoenergetic diets were used; a control diet and four experimental diets by replacing fishmeal with insect meal from H. illucens or T. molitor at 15% and 30%. The daily intake was recorded, and the feeding trial lasted 46 days for trout, 43 days for seabream and 100 days for tench. Initial weight for each fish species was 55.40 g for trout, 17.75 g tench and 6.79 g for seabream. The results showed different percentages of weight gain among species, being 293% for Seabream, followed by trout, 155%. The lowest weight gain was found in tench, 78%, without statistic differences for weight gain among treatment except for seabream feed with H-30 showed the lowest percentage of weight gain. Regarding enzymes activity, the results showed different kinetic parameters for the three fish species according their nutritional needs. A high Vmax, Km and catalytic efficiency for ALT were observed in tench; however, for AST, the highest Vmax was observed in seabream and tench, which also showed the highest catalytic efficiency. Minimal differences in GDH kinetics were found among species; the Vmax in trout was slightly lower than it was in tench. The inclusion of insects affected the different fish species in different ways. In trout, the inclusion of insect meal tended to increase the Vmax of the three enzymes and the Km and catalytic efficiency of GDH. In seabream, the inclusion of insect meal increased the Vmax of ALT and increased the Km of AST However, the catalytic efficiency of GDH decreased with the inclusion of insects, particularly the T. molitor meal. Finally, the tench did not show significant differences with the inclusion of insect meal except a strong interaction for H-30, which could be due an imbalance in essential amino acids/no essential amino acids. Regarding the effect of insect species, in trout AST Km increased with H. illucens meal while in gilthead seabream increased when T. molitor were included. These different metabolic adaptations seem to be consequence of the nutritional habit of each specie in addition with the amino acids bioavailability of each diet.