| Soybean meal is an essential feed protein source for omnivorous fish.Due to the rising demand for soybean meal in aquaculture,the price of soybean meal has soared,which has greatly increased the production costs of aquaculture.The massive use of soybean meal in the aquatic feed also has the food-feed competition problem,threatening national food security.Therefore,it is urgent to find suitable alternative protein sources to reduce the use of soybean meal,which is important for the highquality and stable development of aquaculture.Yellow mealworm(Tenebrio molitor)is a novel insect protein source with abundant nutritional value and environmental benefits.It is suitable for large-scale farming and does not compete with humans for food.In recent years,research on the replacement of fishmeal with yellow mealworm meal has received lots of attention in aquaculture,but whether yellow mealworm meal could effectively replace soybean meal remains unclear.Hence,the present study was conducted by using yellow mealworm meal to replace 0%,15%,30%,and 45%soybean meal to feed Nile tilapia with an initial weight of 70±0.12 g for ten weeks.The feasibility was evaluated from the perspective of growth performance,liver health,intestinal health,and flesh quality.The possible reasons for the effects were also explored.The main results of this study are as follows:1.Effects of yellow mealworm meal replacing soybean meal on the growth performance and whole body composition of Nile tilapiaFinal body weight(FBW),weight gain(WG),specific growth rate(SGR),feed conversion ratio(FCR),condition factor(CF),viscerosomatic index(VSI),and hepatosomatic index(HSI)of Nile tilapia did not show significant changes among the four treatments.The carcass ratio and mesenteric fat index of Nile tilapia increased significantly in YM30,YM30 and YM45 respectively.The moisture,crude protein,and ash contents of the whole body did not change significantly,while crude lipid content was significantly higher in the YM45 group than in the other three groups.From the perspective of growth performance,yellow mealworm meal could replace 45%soybean meal without significant adverse effects on the growth performance of Nile tilapia.2.Effects of yellow mealworm meal replacing high percentage of soybean meal on the hepatic health and intestinal health of Nile tilapiaFrom the perspective of hepatic health,yellow mealworm meal could replace 30%soybean meal in the feed of Nile tilapia.When the replacement ratio increased to 45%,serum alanine transaminase(ALT)activity increased significantly.Liver tissue showed blurred cell boundaries,increased lipid vacuoles,and accumulated lipid droplets and glycogen.Liver lipids,triglycerides(TG),nonesterified fatty acid(NEFA),glycogen content,and glycogen synthase activity increased significantly.Total antioxidant capacity(T-AOC),superoxide dismutase(SOD)activity,and glutathione peroxidase(GSH-PX)activity decreased significantly.Significant accumulation of reactive oxygen species(ROS)and malondialdehyde(MDA)were also found.The liver of Nile tilapia fed with YM45 diets showed significant oxidative stress.From the perspective of intestinal health,yellow mealworm meal could replace 15%soybean meal in the feed of Nile tilapia.When the replacement ratio increased to 30%,the histological morphology of the intestine was altered,as evidenced by the thinner muscular layer,and shorter and wider intestinal villi.A significant decrease in intestinal trans-epithelial resistance was also detected,which indicates an increase in intestinal permeability.The relative mRNA expression of tight junction proteins related genes was significantly up-regulated.When the replacement ratio reached 45%,the intestinal injury was further exacerbated and the intestinal antioxidant status was disturbed.Transcriptome sequencing analysis of the liver and intestine was conducted in YM0 and YM45 and the results showed that the common differential gene klf9(Kruppfel-like factor 9)in the liver and intestine was closely associated with oxidative stress.Meanwhile,the expression of its upstream nrf2(NF-E2-related transcription factor 2)gene,which is related to oxidative stress,was significantly upregulated in both liver and intestine in the YM45 group.It suggested that hepatic and intestinal injury caused by the high percentage of yellow mealworm meal replacing soybean meal might be closely related to oxidative stress.These results suggested that yellow mealworm meal was able to replace 15%soybean meal in the feed of Nile tilapia without affecting the hepatic and intestinal health,but when the replacement percentage reached 30%,it caused damage to the intestinal barrier.When the replacement ratio was up to 45%,the intestinal damage was further exacerbated,and hepatic injury happened.3.Effects of yellow mealworm meal replacing high percentage of soybean meal on the flesh quality of Nile tilapiaFlesh quality determines the acceptance of consumers and the commercial value,thus the effects of yellow mealworm meal replacing soybean meal on the flesh quality of Nile tilapia was investigated.The results showed that the crude protein content of muscle decreased significantly in the YM30 and YM45 groups,and muscular crude lipid content decreased significantly in the YM45 group.The contents of essential amino acids,delicious amino acids,and flavor amino acids were not affected by the substitution.In terms of flesh texture,hardness and gumminess were significantly higher in the muscle of Nile tilapia in the YM45 group than in the YM0.Histological analysis of the muscle revealed that the percentage of small-diameter myofibers was significantly higher in the YM45 group than in the other three groups.Further analysis revealed that the expression of genes related to muscle apoptosis and atrophy was significantly upregulated in the YM45 group,and the muscular antioxidant capacity was significantly reduced in the YM45 group.These results indicated that yellow mealworm meal could replace 30%soybean meal in Nile tilapia diets without substantially altering the flesh quality.When the replacement ratio was increased up to 45%,the fish flesh texture was changed.4.Analysis of possible reasons for hepatic and intestinal injury and flesh texture changes caused by yellow mealworm meal replacing high percentage of soybean mealTo investigate the possible reasons for hepatic and intestinal injury and flesh texture changes in Nile tilapia caused by the high percentage of yellow mealworm meal substitution for soybean meal,several possible causes reported in the literature were analyzed and tested in the present study.The results showed that:(1)Although the replacement of soybean meal with yellow mealworm meal decreased the content of some essential amino acids in the feed,it can meet the needs of Nile tilapia.(2)Analysis of the fatty acid content in the feeds revealed that the changes in the fatty acid composition were not enough to cause hepatic and intestinal damage or change the flesh texture.(3)The fructose content of the feed was tested as well.It showed that the fructose content in the diets decreased gradually as the increase of replacement ratio and it is not the main reason for hepatic or intestinal injury.(4)Since yellow mealworms are rich in polyunsaturated fatty acids and prone to lipid oxidation and deterioration,the acid value of diets was analyzed at the start and the end of the feeding experiment.The results showed that there was no significant difference in feed acid value among the four treatments at the start of the feeding experiment,while the acid value of diets in YM45 was significantly higher than the other three groups after the feeding experiment.It indicated that feed rancidity and deterioration easily occurred when soybean meal was replaced by yellow mealworm meal at a high proportion.We speculate that the rancidity of diets may be the main reason for hepatic and intestinal injury and flesh texture changes caused by the high percentage of yellow mealworm meal replacing soybean meal.In conclusion,this study investigated the effects of replacing soybean meal with yellow mealworm meal on growth performance,hepatic and intestinal health,and flesh quality in Nile tilapia,and found that the negative effects triggered by high percentage substitution might be related to the rancidity of diets.It suggested that more attention should be paid to the storage and processing conditions when yellow mealworm meal was used as a feed protein source. |
