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Summary
With casein, crystalline cellulose and soybean oil as the main raw materials, the protein content was 39%, 42% and 45%, the cellulose content was 2.5%, 3.5% and 4.5%, and the fat content was 5%, 6% and 7%, and the largemouth bass was fed according to the orthogonal L9 (fourth power of 3) table.
The results showed that there were significant differences in weight gain and protein efficiency between the three levels of protein and fiber (P< 0.05), but there was no significant difference in both weight gain and protein utilization between the three levels of fat (P>0.1).
The authors suggest that the appropriate content of the main nutrients in largemouth bass bait is about 42% protein, no more than 3.5% fiber, and no less than 5% fat.
1 Materials and methods
1.1 Test fish
Taken from Huzhou domesticated perch, the tail weight is 23-29g, a total of 270 tails. They were randomly divided into 9 groups with 30 tails in each group. The pre-test period is 7 days, and the main test period is 30 days.
1.2 Test conditions
9 aquariums, continuous inflation and oxygenation, siphon sewage once a day, and change one-third of the water. The water temperature during the test was 23-28°C.
1.3 Feed preparation and feeding
Nine kinds of feeds were prepared according to the L9 (fourth power of 3) table, and their nutritional levels are shown in Table 1. Casein, crystalline cellulose and soybean oil were used as raw materials and added according to the design requirements (Table 2).
Each group is added with 1% mixed vitamins and 1% mixed minerals. The calcium content is adjusted to 2.5% and 1.5% phosphorus with stone powder and calcium dihydrogen phosphate.
The deficiency share is filled with dextrin and 0.5% Cr2O3 is added. When using, weigh the quantitative premix, stir with water, and use a meat grinder to form ø3.5mm soft particles (about 40% water).
Feeding twice a day, 9:00 a.m. and 4:00 p.m. Since largemouth bass only eat food that moves through the water, they are fed one by one to reduce waste.
The amount of feeding depends on the feeding situation of the perch, and the degree of satiety. The feed intake is calculated by weighing the amount of feed minus the amount of feed remaining (dry weight), and the manure is collected on day 7 for 6 consecutive days.
Fecal samples were dried and stored at 70°C for the determination of protein apparent digestibility. At the end of the experiment, 5 fish were randomly selected at 0, 1, 2, 4, 6, 9, 14 and 18 hours after feeding, and the chemical tract (stomach and foregut) was canceled for digestive enzyme activity measurement.
2 Test results
The basic measured values are listed in Table 3. Intuitively, the combination of group 4 was the best, achieving the largest growth ratio, the highest protein efficiency, and the lowest feed coefficient. The combination of nutrients is 42% protein, 2.5% fiber, and 6% fat.
2.1 Effects of different trophic levels on fish growth
An analysis of variance was performed on the results of body weight gain (Table 4). The results showed that there was a significant difference between the three levels of protein and cellulose (P< 0.05), but there was no significant difference between the three levels of fat (P>0.1).
Multiple comparisons of the mean levels of protein and cellulose (1q test of the least significant range method, see Table 5) showed that there was a significant difference in weight gain between 39% protein level and 42% and 45% protein levels, respectively (P< 0.05), and there was no significant difference between 42% and 45% levels.
There was no significant difference between the fiber level of 2.5% and 3.5%, but there was a significant difference between the two and the 4.5% level (P< 0.05), and the change in growth ratio showed a similar trend to weight gain.
2.2 Effect of different nutrient levels on protein digestibility, protein efficiency and feed coefficient
The results of ANOVA analysis of protein efficiency, apparent digestibility and feed coefficient at different nutrient levels are shown in Tables 6, 7 and 8, and the results showed that there were some differences in protein efficiency and feed coefficient among the three levels of cellulose (P<0.1), while there were significant differences in apparent digestibility (P<0.05).
There was no significant difference between the three levels of protein and fat (P>0.1). The mean of the three levels of cellulose was compared separately (Q-test) (Table 9).
The results showed that there was no significant difference between 2.5% and 3.5% cellulose level on protein efficiency, apparent digestibility and feed coefficient (P>0.05). There was a significant difference between the 2.5% and 4.5% levels (P<0.05).
2.3 Changes in digestive enzyme activity
The results of the measurement of digestive enzyme activity of largemouth bass before and after feeding at 42% protein level and 2.5% fiber level (Figure 1) showed that the activity of pepsin and tryptase gradually increased after feeding, peaked at 4 hours, lasted until 6 hours, began to decline rapidly, and returned to pre-feeding levels at 14 hours.
At the 4-hour peak, trypsin showed an adaptive upward trend with the increase in protein content in the feed (Table 10), while pepsin did not.
The activity of cellulase was low throughout the whole period, and there were only slight changes before and after ingestion. The highest value occurred at 9 hours, and the activity of cellulase did not change with the change in feed cellulose levels.
3.1 Suitable feed protein content for largemouth bass
From the fact that protease activity has an adaptive change in the protein level in the feed, it can be considered that the high level of protein is beneficial to the growth of the fish. However, its effectiveness also depends on the absorption and utilization of the protein.
It can be seen from Tables 3, 4 and 5 that when the fish body gain is taken as the index, the protein content of 42% and 45% is significantly higher than that of 39%, while the difference between 42% and 45% is not significant, indicating that the 42% level is the main level of the difference in fish body gain.
Although the effect of protein level on protein efficiency, apparent digestibility and feed coefficient was not significant in this experiment, the relationship between protein level and growth ratio and protein efficiency (Fig. 2) showed that the growth ratio increased from 39% to 42%, and increased slowly from 42% to 45%.
From the perspective of protein efficiency, with the increase of protein content, there is a rapid upward trend first, peaking at 42% of protein, and then showing a downward trend.
The results showed that although the 45% protein in the feed was beneficial to the growth of largemouth bass, showing a similar growth ratio to the 42% content group, the protein use efficiency was reduced, and the protein overload was present.
The feed coefficient decreases rapidly between 39% and 42%, and increases from 42% to 45%, as well as feed waste. Therefore, it is believed that the appropriate protein content in the feed of largemouth bass is about 42%.
3.2 Effect of cellulose content in feed on nutrient uptake and growth of largemouth bass
The digestive tract of fish does not secrete enzymes that digest cellulose, and some bacteria in the intestines of fish have the ability to produce cellulase, which may have a weak digestive function.
Therefore, fiber has no direct nutritional function for fish, and is only used as a filler or carrier in the bait, which plays a role in helping the digestion and absorption of other nutrients.
Although water-soluble cellulose (e.g., resin) has been shown to convert into gels in the intestine and increase the viscosity of food, thereby delaying the absorption rate of carbohydrates and improving their utilization.
The activity of cellulase in the digestive tract of carnivorous sea bass is very low, which cannot break down cellulose, and at the same time, the utilization rate of carbohydrates in the feed is low, and the high cellulose has a negative effect to some extent.
Within the scope of this experiment, as the cellulose content in the bait increased from 2.5% to 4.5%, it had a certain effect on protein efficiency, apparent digestibility and feed coefficient, and the growth ratio of the bait almost plummeted (Fig. 3).
The protein efficiency decreased slightly in the front segment and increased sharply in the latter segment. The feed coefficient was reflected in the protein efficiency, with a slower increase in the front and a faster increase in the later stage.
Looking at the protein digestibility of the nine feeds (Table 3), the protein digestibility decreased by 12% from 97% to 85% as the cellulose content increased from 2.5% to 4.5%.
This indicates that the cellulose content of the bait as a filler or carrier has exceeded its requirement, which has the opposite effect of hindering the digestion and utilization of protein and slowing down the growth rate.
As can be seen from Tables 5 and 9, there is no significant difference between the cellulose levels of 2.5% and 3.5%, so the cellulose content in the ingredients of largemouth bass should not exceed 3.5%.
3. 3 Fat requirements for largemouth bass
Fat is an important energy source for carnivorous fish with low carbohydrate utilization, and proper addition can have the effect of saving protein.
In this experiment, the oil content increased from 5% to 7%, and there was no significant difference in the weight gain effect between the three levels (P>0.1), and there was no significant difference in protein utilization and growth ratio (P>0.1).
It has been shown that a combination of 5%-7% fat content with several levels of protein is appropriate.
Conclusion The appropriate protein content in largemouth bass bait is about 42%, the fiber is not higher than 3.5%, and the fat is not less than 5%.