Chitin digestibility and intestinal exochitinase activity in Nile tilapia and rainbow trout fed different black soldier fly larvae meal size fractions

Abstract

Black soldier fly (Hermetia illucens) larvae meal (BSFLM) is a novel fish feed ingredient with a high crude protein content (~40% dry matter, DM). However, BSFLM also contains chitin, which might impair nutrient digestibility. To investigate the effect of chitin on nutrient digestibility and chitinase activity in fish, BSFLM with different chitin contents were tested as feed ingredients for Nile tilapia (Oreochromis niloticus) and rainbow trout (Oncorhynchus mykiss). BSFLM was sieved into three size fractions obtaining different chitin contents: 0-200 μm (fine), 200-400 μm (medium), >400 μm (coarse), 1.8, 2.7 and 15.4% chitin on a DM basis, respectively. Four isoenergetic and isonitrogenous diets were formulated for each species including an experimental reference diet and three diets replacing 25% of the experimental reference diet matrix with one of the three BSFLM size fractions. Dietary inclusion of the coarse BSFLM fraction resulted in significantly lower apparent digestibility of DM, crude protein, nitrogen-free extract and chitin when compared with the other treatment groups in both fish species, which supports the hypothesis that chitin might act as an anti-nutrient. However, it was also found that both species could digest chitin but its digestibility decreased with a higher dietary chitin inclusion level. Furthermore, β-N-acetylglucosaminidase activity (exochitinase) increased with higher dietary chitin inclusion in the proximal and distal intestine of both fish species suggesting that exochitinase production can be upregulated depending on the dietary chitin intake. Overall, the results corroborate that chitin could act as a nutrient source as well as an anti-nutrient in both Nile tilapia and rainbow trout.

Potential of shrimp waste meal and insect exuviae as sustainable sources of chitin for fish feeds

“…However, it is also true that chitin has been hypothesized to have a potentially negative impact on fish performance and nutrient digestibility. For instance, it was recently found in both Nile tilapia (Oreochromis niloticus) and rainbow trout that chitin can act as a nutrient source as well as an antinutrient because its digestibility is negatively related to dietary inclusion levels (Eggink et al, 2022). The indications that chitin, as a nondigestible fiber, negatively influences the digestibility of lipids and proteins have led to a tendency to remove chitin from food and feed.…”

Biowaste and by-products as rearing substrates for black soldier fly (Hermetia illucens) larvae: Effects on larval body composition and performance

“…The amino acid contents of substrates and larvae and chitin content of larvae were quantified by HPLC and spectrophotometry, respectively, as previously described by Eggink et al [ 31 ].…”

Growth performance and economic analysis of Nile tilapia (Oreochromis niloticus) fed on black soldier fly larvae (Hermetia illucens)

“…This in turn causes lower FCR, low weight and smaller-sized fish in turbot, pacific white shrimp, yellow catfish, Nile tilapia and rainbow trout. The amount of chitin in BSF-containing diets appears to have a deleterious influence on feed intake, growth, and digestibility (Kroeckel et al, 2012;Cummins et al, 2017;Xiao et al, 2018;Eggink et al, 2022). However, the FCR obtained in this investigation suggests that O. niloticus may have a high efficacy in digesting chitin or tolerating specific levels.…”