Effects of butane-defatted black soldier fly larvae meal replace dietary fishmeal on growth, antioxidant capacity and intestine health of rainbow trout (Oncorhynchus mykiss)

Abstract

With the increasing price of fishmeal, the quest for alternative protein sources has become increasingly imperative. Among the potential protein sources, the black soldier fly (Hermetia illucens) has garnered considerable attention as an insect-derived protein source in aquafeed in the recent years. However, in previous studies, the use of full-fat and partly defatted black soldier fly larvae meal to replace a high proportion of fishmeal (more than 50 %) may have negative impacts on the growth of rainbow trout (Oncorhynchus mykiss). Here we provided defatted black soldier fly larvae meal (BSF) using subcritical butane extraction and used it as a protein source to replace graded levels of fishmeal (0, 15 %, 30 %, 45 %, 60 %, 75 %, named CD, BSF15, BSF30, BSF45, BSF60, BSF75) in rainbow trout diet (with white fishmeal content of 42.0 %, 35.7 %, 29.4 %, 23.1 %, 16.8 %, 10.5 % in diets). The initial weight of rainbow touts was 215.16 ± 2.30 g, and the fish were fed for 8 weeks under conditions of 6.7–13.2 °C. The aim of this research was to examine the impact of dietary BSF on growth, antioxidant capacity and intestine health of rainbow trout. The result revealed that the BSF30 and BSF45 groups achieved significantly higher final body weight, weight gain and specific growth rate than the CD group. Further regression analysis of these indicators showed that the optimal replacement level was 36.21 %–37.26 %. The BSF75 group was observed the lowest weight gain and the highest feed conversion ratio in all BSF groups. The activity of SOD was not significantly affected in the liver and intestine among groups. The height of intestine folds was higher in the BSF30 and BSF45 groups than CD group indicated the stronger digestive capacity. Furthermore, the gene expression of myd88 and tnfα were upregulated when 60 % fishmeal was replaced, indicating that high BSF content in rainbow trout diets may stimulated intestine inflammation. Compared to the CD group, the increased expression of atg12 and atg4b, the decreased protein level of p62 and the elevated ratio of LC3B-II/LC3B-I in BSF45 group in intestine indicated its enhanced autophagy activity. Overall, the utilization of 36.21 %–37.26 % BSF in replacement of fishmeal could achieve improved growth performance without causing significant inflammation. Replacing 60 % and greater fishmeal with BSF would reduce the growth rate of rainbow trout which was not recommend.