Evaluation of mealworm meal as an alternative to fish meal in the diet for giant grouper (Epinephelus lanceolatus) based on the protein level adjusted by the nitrogen content in chitin

The crude protein content of insects may be overestimated due to the nitrogen (N) content in the chitin therein. The present study evaluated the replacement of fishmeal with mealworm meal (MWM) in the diet on the growth performance and body composition of giant grouper, Epinephelus lanceolatus. Before the feeding trial, the chitin and crude protein contents of the MWM were analyzed as 13.21% and 74.63% (N x 6.25), and the corrected protein content of MWM meal was found to be 69.29%. Based on the adjusted protein level, MWM was substituted at the levels of 0%, 10%, 20%, and 30% for the fishmeal protein in the diets. Four experimental diets were each fed to three groups of juvenile giant grouper (initial weight: 20.65 +/- 0.08 g) via a recirculation system for 8 weeks. The weight gain, protein retention, protein efficiency ratio, feed efficiency, survival, and whole-body amino acid and fatty acid profiles were not affected (p > 0.05) by the dietary treatments. The fish in-fish out ratios decreased linearly with increasing MWM inclusion levels. Plasma triglyceride concentration decreased after increasing the replacement levels. The results indicate that the actual protein content in MWM can be adjusted via the nitrogen content in the ingredient, as well as by adjusting the chitin content. MWM can be used to replace fishmeal protein up to 30% in giant grouper diets without any negative effect on growth performance, and this can also reduce the dependence on the marine resources required to provide aquafeed to achieve the goal of sustainable aquaculture.