Dietary inclusion of mealworm (Tenebrio molitor) meal as an alternative protein source in practical diets for juvenile rockfish (Sebastes schlegeli)

Abstract

An 8-week feeding trial was designed to evaluate the potential of yellow mealworm (Tenebrio molitor) as a locally available nutrient-rich feedstuff for juvenile rockfish (Sebastes schlegeli). Experimental diets containing elevated levels of mealworm meal (WM) supplemented with synthetic methionine were formulated to be isonitrogenous, isolipidic and isoenergetic to a WM-free fishmeal (FM) based control diet (designated as WM0, WM8, WM16, WM24 and WM32, respectively). To determine the necessity of dietary methionine supplementation at the highest inclusion of WM, a diet was prepared to contain 32% WM without methionine supplementation (WM32-AA). Triplicate groups of rockfish juveniles (Mean ± S.E.; 3.11 ± 0.01 g) were fed one of the experimental diets to apparent satiation twice daily for 8 weeks. Fish growth performance in terms of weight gain and specific growth rate increased with increasing dietary inclusion of WM from 0 to 16% and then tended to decrease with further increase in dietary WM levels to 32%. Protein retention (PR) values followed the same trend as growth rates with the highest values found in fish offered WM16 diet. Although fish fed WM32-AA diet showed significantly lower growth rate and PR values compared to those fed WM16 diet, their performance was still comparable to that of the WM-free control group. Plasma triglyceride level was negatively affected by dietary WM inclusion and the lowest values were observed in the WM32-AA group. Whole-body and fillet proximate and essential amino acid compositions were not altered by dietary treatment and these values were comparable to those of the WM0 group. These findings suggested that WM might prove to be a promising alternative to FM in practical diets for juvenile rockfish and could be used at an inclusion level of up to 32% without having any adverse consequences for the health and performance of the fish. Although the diet containing 32% WM seemed to support a performance similar to that of the control diet, the recommended dietary inclusion level was no more than 16% of the diet dry matter.