Effects of high dietary inclusion of defatted mealworm (Tenebrio molitor) meal as a fish meal substitute on growth, histological traits and health performances of rainbow trout (Oncorhynchus mykiss)

Authors: HOSSAIN, MD., SAKHAWAT - Sylhet Agricultural University; Sealey, Wendy; SMALL, BRIAN - University Of Idaho

Submitted to: Aquaculture Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2024
Publication Date: 1/29/2025
Citation: Hossain, Md., S., Sealey, W.M., Small, B.C. 2025. Effects of high dietary inclusion of defatted mealworm (Tenebrio molitor) meal as a fish meal substitute on growth, histological traits and health performances of rainbow trout (Oncorhynchus mykiss). Aquaculture Nutrition. 2025:5568058. https://doi.org/10.1155/anu/5568058.
DOI: https://doi.org/10.1155/anu/5568058

Interpretive Summary: In the last 20 years, efficiency of waste utilization by insects, and increased availability of commercial products have increased interest in their use as animal feedstuffs. Protein meals derived from insects have received substantial attention as novel feed ingredients for aquafeeds due to their high protein content and potential functional properties for supporting fish growth and health. USDA ARS scientists collaborated with colleagues at the University of Idaho to evaluate the effects of high dietary inclusion of defatted mealworm meal as a fish meal substitute on growth and health of rainbow trout. Rainbow trout were provided feeds where defatted mealworm meal replaced 25, 50, 75 or 100% of the fishmeal in the diet for 13 weeks. Results from this study indicate an inclusion level between 20 and 30% (as fed) or 50-75% of fish meal replacement yields the best performance and fish health. These results support the use of defatted mealworm meal as a novel and safe ingredient in rainbow trout feeds.

Technical Abstract: The aim of this study was to evaluate the effects of high dietary inclusion of defatted mealworm (DMW) (Tenebrio molitor) meal as a fish meal (FM) substitute on growth, histological traits and health performances of rainbow trout (Oncorhynchus mykiss). Two separate trials were carried out. In the first, a total of 800 rainbow trout (average initial weight 23 g) were randomly allocated into each of twenty 145-L tanks at 40 fish per tank. A 40% FM control diet (Diet-1) was produced, then 25%, 50%, 75% and 100% of FM from the control diet formulation was replaced with DMW protein for diet groups Diet-2, Diet-3, Diet-4 and Diet-5, respectively. Diets were fed to quadruplicate tanks for 13 weeks. No differences in fish growth and feed utilization performance were detected (P>0.05). Differences in whole body protein, lipid and energy composition were observed in fish fed the highest DMW treatment compared to fish fed Diet-1; however, no differences were observed for fillet composition. Use of DMW meal as FM substitute did not show any significant alteration of measured hematological electrolyte, acid-base, and blood gas parameters, except for a statistically significant (P>0.05) yet negligible increase in sodium (Na) concentration observed in fish fed 50 and 100% DMW as FM replacement. The mean score of measured distal intestinal histopathological characteristics indicated that complete replacement of dietary FM with DMW meal resulted in significantly higher intestinal enteritis. Significantly lower liver inflammation was observed in fish fed Diet 3 and a higher incidence of kidney mineralization was reported in fish fed Diet-5. In a second trial, the apparent digestibility of DMW fed to trout was evaluated using standard practices, and the apparent digestibility coefficient of dry matter, protein, lipid, energy, and phosphorus were 80, 87, 100, 84, and 90%, respectively. All essential amino acids digestibility coefficients were >90%. In total, DMW is highly digestible when fed to rainbow trout and can replace all the FM in the diet, up to 40% as fed, with little to no impact on fish performance, feed efficiency, fillet composition, and health. Based on these results, an inclusion level between 20 and 30% (as fed) or 50-75% of FM replacement yields the best performance and fish health. These results support the use of DMW meal as a novel and safe ingredient in rainbow trout feeds.