| Largemouth bass(Micropterus salmoides),a carnivorous fish,is one of the important freshwater cultured fishes in China.They mainly feed on chilled fish and mixed fish in aquaculture.However,in the recent years,wild resources of wild fish have been declining,and the price of chilled fish has been rising,causing the cost of culturing largemouth bass to be increased year by year.At the same time,the feeding of wild fish imposes a great pressure on natural resources and the ecological environment,which seriously affects the further development of the largemouth bass breeding industry.Researchers in China and other countries have carried out a lot of researches on the nutrition and digestive enzymes of the largemouth bass,and have made some research achievements.However,these researches have been mainly focused at the laboratory level,and there have been no reported studies on the activities of various enzymes in the digestive tract and intestinal morphological structure of largemouth bass cultured into commercial specifications.At the same time,as a carnivorous fish,largemouth bass is lack of amylase,and this leads to the unsatisfactory feeding effect of formulated feeds on largemouth bass,and in particular,it is not possible to consume artificial feeds with higher plant-based feedstuffs.The feeds that fish consume must be digested by physical digestion of the digestive tract and digestion by various digestive enzymes secreted in the stomach,intestine,and pancreas,and they are decomposed into small molecules,such as amino acids,small peptides,monosaccharides,and fatty acids within digestive tracts to meet the energy needed by the fishes during their growth process.The digestion and absorption of various substances by fish depend,to a large extent,on the fish's diets,digestive characteristics,and the amount and activity of digestive enzymes in each part of the digestive tract.Therefore,in this study we investigated the effects of feeding different feeds on the amylase activity of largemouth bass,analyzed the morphological structure of the intestine of largemouth bass fed with different diets,and studied the digestibility of digestive enzymes on several feed ingredients in vitro.This study provided basic data and theoretical references for the development of artificial diets for largemouth bass.The main findings are as follows:1.Effects of different feed on digestive tube index and amylase activity of Micropterus salmoidesTo study the effect of different diets on digestive tract index and amylase activity of largemouth bass,digestive tract index and amylase activity of largemouth bass raised the formulated feed(feed group)and the ice fish(chilled group)were analyzed comparatively.The results indicate that the intestinal weight/body weight,hepatopancreas weight/body weight,splanchnic weight/body weight in feed group were significantly higher than those of the chilled group(P<0.05).The amylase activities in different organs were sequenced as follow: hepatopancreas> pyloric caeca> intestine> stomach in two groups.The amylase activities in hepatopancreas were significantly higher than those in other organs(P<0.05).For the amylase activities in the chilled group and feed group,the optimum pH were 7.2 and 6.8,6.4 and 6.8,6.4 and 6.8,6.8 and 6.8 in stomach,hepatopancreas,pyloric caeca and intestine,respectively.The optimum temperature were 30? and 30?,35? and 30?,50? and 55?,60? and 60?,respectively.The concentration of starch were 8% and 8%,0.5% and 2%,8% and 8%,8% and 8%,respectively.The amylase activity of digestive organs in the feed group was significantly higher than that of the chilled group under same temperature and concentration of starch(P<0.05).The results provide reference for adding enzyme preparations and optimizing artificial feed formulation in the process of artificial feed preparation.2.Effect of different feeds on the morphological structure of intestineIn order to study the effects of feeding feeds on the largemouth bass of the intestine,largemouth basses were fed with compound feed and chilled fish,their intestines were sliced and examined.The results showed that their mucosal thickness and villus height of the anterior and posterior intestines in the feed group were all lower than those of the largemouth in chilled group while the mucosal thicknesses of the anterior and posterior intestines were significantly decreased by 13.71%(P<0.05)and 22.73%(P<0.05),respectively.It was significantly decreased by 22.49%(P<0.05)and 20.51%(P<0.05);the thickness of the mucosa of the midgut and the height of the villus were higher than those of the chilled group,which were significantly increased by 19.07%(P<0.05)and 10.72%(P<0.05),respectively.In the feed group,the intestinal muscle thickness,villi height/crypt depth(V/C)values were lower in the anterior,middle and posterior groups than those in the chilled group,and the muscle thickness,which were decreased by 47.40%(P<0.05)and 7.40%(P<0.05),22.66%(P<0.05)respectively,V/C ratios were significantly decreased by 42.7%(P<0.05),8.7%,(P<0.05),and 56.5%(P<0.05).The crypt depth of the intestine in the feed group was higher than that that in the chilled group,which was significantly increased by 20.49%(P<0.05),19.36%(P<0.05),and 39.98%(P<0.05),respectively.Compared with chilled fish,the digestive and absorption function of the largemouth bass fed with the compound feed was reduced,the thickness of the mucous membrane and the height of the villi were decreased,the depth of the recess was deepened,the V/C value was decreased,and the health of the intestine was damaged.3.In vitro digestibility of five common feed ingredients by digestive enzymes from different organs of largemouth bass fed with two feedsTo investigate the effects of digestive enzymes on the in vitro digestibility of five feed ingredients and the effect of different temperature on the in vitro digestibility of feed ingredients,the in vitro digestive method was used to determine the crude enzyme solution of four each digestive organ of largemouth bass.The in vitro digestibility of Peruvian fish meal,domestic fish meal,corn meal,soybean meal,and vegetable meal,and the in vitro digestibility of Peruvian fish meal and corn meal by the crude enzyme solution of each digestive organ at different temperatures were measured.The experimental results showed that the in vitro digestibility of dry matter and protein of five feed ingredients by digestive enzymes of the feed group were significantly higher than those of the chilled group(P<0.05).At 20-30°C,the in vitro digestibility of Peruvian fishmeal and corn meal increased with the temperature increasing.The total digestibility of dry matter in the feed group of stomach,liver,pyloric caeca,and intestine for five feed ingredients was as follows: 22.81% for Peruvian fishmeal,21.01% for domestic fish meal,20.22% for Chinese cabbage,19.78% for soybean meal,and 17.63 for corn meal.The total digestibility of dry matter of 5 feed ingredients by the corresponding organs of the chilled group was as follows: 18.64% of domestic fishmeal,16.45% of Peruvian fishmeal,14.05% of Chinese cabbage,13.09% of soybean meal,and 6.21% of corn meal.The total digestibility of protein in the feed group for five feed ingredients was as follows: 24.42% for Peruvian fishmeal,21.12% for domestic fishmeal,20.22% for Chinese meal,12.19% for soybean meal,11.33% for corn flour,and 17.08% for Peruvian fishmeal.16.93% of fishmeal,14.79% of rapeseed meal,11.86% of soybean meal,and 6.33% of corn meal.These results indicated that the activities of the digestive enzymes of the feed group were higher than those of the chilled group in vitro;the in vitro digestibility of feed was affected by temperature,the feed and chilled groups have better digestion effects on animal protein feeds than on plant protein feeds.Both the chilled group and the feed group had the best in vitro digestion of Peruvian fishmeal and domestic fishmeal,followed by rapeseed meal,soybean meal,and corn meal. |
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