Dietary Tenebrio molitor Larval Meal Enhances Chitinase Activity in Yellowtail Lambari (Astyanax bimaculatus)

The increasing demand for sustainable aquafeeds has stimulated the evaluation of insect meals as alternative protein sources. Among these, Tenebrio molitor larval meal (TMLM) contains chitin, a structural polysaccharide that may modulate digestive enzyme activity in fish. This study evaluated the effects of dietary TMLM on chitinase activity in yellowtail lambari (Astyanax bimaculatus). A total of 400 fish (2.53 ± 0.13 g) were distributed in a completely randomized design with five dietary treatments and four replicates. Fish were fed isonitrogenous (320 g kg⁻¹ crude protein) and isoenergetic (3,200 kcal kg⁻¹ digestible energy) diets containing 0, 30, 60, 90, or 120 g kg⁻¹ TMLM for 56 days. At the end of the experimental period, chitinase activity was determined in digestive tract samples. Data were subjected to analysis of variance (ANOVA), and significant responses were further evaluated by polynomial regression at a 0.05 significance level. Dietary TMLM significantly affected chitinase activity (P < 0.001). Fish fed the control diet exhibited the lowest activity (13.00 ± 0.41 IU × 10⁻⁴), whereas fish receiving 30, 60, 90, and 120 g kg⁻¹ TMLM showed significantly higher values of 47.25 ± 0.25, 47.00 ± 0.41, 47.75 ± 2.75, and 55.00 ± 2.45 IU × 10⁻⁴, respectively. Regression analysis revealed a positive linear response (ŷ = 16.65 + 8.45x; R² = 0.65; P < 0.05), indicating that increasing dietary inclusion of TMLM progressively enhanced chitinase activity. The elevated enzyme activity suggests an adaptive digestive response to the higher chitin content provided by insect meal, demonstrating the ability of A. bimaculatus to utilize chitin-containing feed ingredients efficiently.