Replacement of Dietary Fishmeal by Black Soldier Fly Larvae (Hermetia illucens) Meal in Practical Diets for Juvenile Tench (Tinca tinca)

The development of specific diets for the juvenile stage is a main target for culture intensification of tench (Tinca tinca). Aquafeeds still rely heavily on the use of fishmeal (FM) but concerns about economic and ecological sustainability make the use of alternative protein sources necessary. Insect meals are considered a promising substitute to replace FM. In a 90-day experiment, 6 diets with different replacement levels of FM by partially defatted black soldier fly larvae meal (BSFLM): 0%, 15%, 30%, 45%, 60% and 75%, were tested on juvenile tench. Survival rates were high (95.8-100%) without differences between treatments. Diet with 45% FM replacement allowed for best growth performance in terms of total length (TL = 66.4 mm) and weight (W = 4.19 g), without differences with 60% and 75% of replacement. A cubic relationship was evidenced between the level of FM replacement and growth. From the regression equations, the estimated optimal level of FM replacement was 47% (356 g BSFLM kg(-1) diet). Externally visible deformities were always under 0.05%. The whole-body lipid content of the fish had a significantly negative linear regression with BSFLM (r(2) = 0.80). The content of the essential amino acids (EAA) arginine, leucine, lysine, phenylalanine, methionine, and threonine in diets decreased with dietary BSFLM inclusion. However, it did not have a negative effect on growth performance, suggesting that EAA requirements were covered. The amount of essential amino acids in whole-body juveniles was similar independently of the diet provided. The results allow considering BSFLM as a sustainable protein source for juvenile tench feeding.