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Official account
In this experiment, grass carp was used as the research object, and 0, 0.15, 0.3, 0.6, 1. 2, 2.4, 4.8 mg/kg selenium, the effects of different concentrations of sun on the growth, nutritional composition and digestive enzyme activity of grass carp were studied, aiming to further understand the mechanism of action of sun and provide a theoretical basis for the rational application of drying in grass carp compound feed.
The experimental fish were grass carp species of the year, with a body length of (10.16±0.14) cm and a weight of (21.20±0.24) g;
After purchase, disinfection with 3% salt solution, pre-test period of 10 days, first 3d feeding bait, then with bait with basic diet, after all can better feeding, take strong individuals, consistent specifications, according to the random grouping method, record the initial weight, transfer to their own numbered cages, for formal testing.
During the breeding experiment, feeding was carried out daily (9:00 13:00 17:00), the feeding rate was 3% -5%, and the feeding amount was adjusted according to the water temperature and the size of the fish. Daily observation and recording of water temperature, grass carp bait and death, and timely picking up and weighing of dead fish found, and making records. The trial lasted 84 days (12 weeks).
During the test, the water temperature was 24~30 °C, the pH value was 5.5~7.0, the dissolved oxygen was 5 mg/L, the ammonia nitrogen level was < 0.5 mg/L, and the aquaculture water contained selenium (0.055 +0.07) mg/L.
Fifteen fish were taken as initial fish composition assay samples prior to the test. At the end of the test, the fish were accurately weighed after 24 hours of starvation, and growth rate, feed utilization efficiency, physical indicators (including body weight/body length, visceral weight/weight, liver and pancreatic weight/weight, spleen weight/weight), fat fullness and shell rate were determined.
The nutritional components of feed, whole fish and muscle were determined by conventional nutrient composition analysis methods, and the water was dried at 105 °C by constant weight method.
The determination of crude protein content was determined by Kjeldahl method; The determination of crude fat content was carried out by Soxhlet extraction; Crude ash was determined by incineration in a digester (550 °C).
Results & Analysis
Effects of selenium on the survival and growth of grass carp: The effects of selenium addition to feed on the survival and growth of grass carp are shown in Table 3.
It can be seen that the survival rate of grass carp in all groups is high, above 95%, and the difference in statistical analysis is not significant (P >0.05). In terms of growth, the specific growth rate, weight gain rate, feed efficiency, protein efficiency and feed protein deposition efficiency of grass carp after the addition of selenium to the feed were significantly higher than those of the control group (P < 0.05).
When the amount of feed selenium was 0.6 mg/kg, the feed efficiency was the highest and the growth promotion effect was the most obvious, and the specific growth rate and feed efficiency were increased by 28.37% and 38.30%, respectively, compared with the control group.
When the amount of selenium added was greater than 0.6 mg/kg, the added amount increased and the growth slowed down.
Effect of selenium on the shape index of grass carp: In this test, the physical index (weight/body length, visceral ratio, liver and pancreatic ratio, spleen index), fertility and empty shell rate were determined, and the results are shown in Table 4.
Effects of selenium on the nutritional composition of whole fish and muscle of grass carp
The nutritional composition of whole fish and muscle of grass carp (including water, crude protein, crude fat and crude ash) is shown in Table 5.
Whether it was whole fish or muscle, the addition of selenium to diet had a significant effect on protein content and fat content (P<0.05), and there was a negative correlation between protein and crude fat, that is, when the amount of addition was 0~0.6 mg/kg, with the increase of the added amount, the protein content increased and the lipid content decreased;
When the amount of addition is 0.6~2.4 mg/kg, with the increase of the amount added, the protein content decreases and the fat content increases.
When the dosage was 0.6 mg/kg, the contents of whole fish and muscle protein were the highest, which were 8.6% and 5.9% higher than those in the control group, respectively. The fat content was the lowest, 15.62% and 9.95% lower than the control group, respectively.
Effect of selenium on digestive enzyme activity of grass carp
The effect of selenium addition on the activities of grass carp liver, pancreas and intestinal digestive enzymes is shown in Table 6.
It can be seen from Table 6 that the addition of selenium to feed has significant effects on the protease, amylase and lipase activities of grass carp (P<0.05).
The enzyme activity in the addition group was higher than that in the control group (except for the 4.8 mg/kg hepatic and pancreatic amylase).
With the increase of selenium added in feed, the activity of digestive enzymes showed a trend of first increasing and then decreasing.
When the addition amount was 0.6 mg/kg, the activities of three digestive enzymes of grass carp liver, pancreas and intestine reached the maximum, and the lipase activity increased the most.
Hepatopancreatic and intestinal lipase activities increased by 205.55% and 249.33%, respectively, compared with the control.
Intestinal protease and amylase activity is generally higher than hepatic trypsin activity; The intestinal lipase activity is weaker than that of the liver and pancreas.
Evaluation of the effect of selenium on the growth performance of grass carp
Selenium is an important element necessary for the growth of fish and has a growth-promoting effect on aquatic animals.
Hua Xueming et al., Wei Wenzhi et al. on the study of heterogeneous Yinqing, Wang Anli's research on Chinese shrimp all proved that selenium can increase the rate of weight gain and specific growth rate;
The results of this experiment showed that the addition of selenium to feed had a significant effect on the growth of grass carp, and the growth performance of the group with an added amount of 0.6 mg/kg was the best, and the specific growth rate, weight gain rate, feed efficiency, protein efficiency and feed protein deposition efficiency reached the highest.