| The effects of stocking density in recirculating aquaculture systems on growth performance, body composition, digestive activity, and blood biochemical parameters of marbled eel(Anguilla marmorata) were investigated in a 71-d experiment. The study stocked the fish in triplicate in 1.0 m3 tanks at densities of 12, 20, 28 kg/m3 nominally indicated as the low density group(LD), medium density group(MD) and high density group(HD), which up to 20.72±1.13, 32.51±0.70 and 43.76±0.79 kg/m3, respectively. The mean individual weight was from 169.72±2.75 g at the beginning reached to 314.81±20.37, 285.31±8.38 and 272.95±9.16 g in LD, MD and HD respectively. The fish survival rate was 100% during the experimental period.Moreover, fish were displayed an improved(P<0.05) growth performance, including final weight, growth efficiency and feed intake. There were no significant differences of specific growth rate, feed conversion ratio, protein efficiency rate, hepatosomatic index, moisture content and crude protein content of fish back muscle among different density groups. Fish of LD and MD showed a higher(P<0.05) ash content compared to that of HD. Crude lipid content of MD and HD was significantly(P<0.05) lowered in fish of LD. The activities of protease in the stomach and intestine showed no differences among all stocking densities, whereas the activity in intestine of MD was significantly lower compared to other experimental densities. There was no significant difference(P>0.05) between MD and HD in the level of serum cortisol, total cholesterol, triglycerides, urea, and alkaline phosphatase activity, whereas fish of LD showed significantly(P<0.05) higher glucose contents and albumin. And the levels of total protein and aspartate aminotransferase were higher in LD than in MD(P<0.05), but not statistically significant in HD. The level of alanine aminotransferase was significantly higher in HD than in LD. The results showed that the growth with a limited increasing in stocking density treatment, but turn into a stress when excess. In summary, the optimum growth rate of Anguilla marmorata can be achieved at 20 kg m-3 in RAS.Under the experimental model of the circulating water aquaculture, feeding frequency on the Anguilla marmorata growth performance, body composition, digestive enzymes and serum Health indicators, test period of 90 days. This test each processing aquaculture cylinder volume is 1 m3, experimental stocking density is 20 kg m-3, have three feeding frequencies were fed 2 times/ 2d(S1 group, interval 1d), 1time/d(S2 group), 2 times/1d fed twice(S3 group). Quality start of the test fish from 261.17 g, at the end of the test three feeding frequencies quality treatment group were 440.99 ± 10.49,447.83 ± 10.83 and 463.00 ± 9.19 g. Test cycle flower eel survival rate was 100%.Effect of different feeding frequencies Anguilla marmorata growth, Anguilla marmorata weight and body length with increasing feeding frequency increases. There are different feeding frequency of Anguilla marmorata end weight, specific growth rate, food consumption and liver body weight ratio was significant difference(P<0.05), feeding frequency of 2 times / d at the end of body weight and food intake was significantly higher. Feeding frequency was no significant difference in weight gain and feed conversion. Anguilla marmorata body composition, feeding frequency was no significant difference(P>0.05) on the moisture content of the flower eel muscle and organic carbon content. Feeding frequency of 2 times / ash content of the test when the end of the flower eel d was significantly higher than the other two groups(P<0.05), crude protein content was significantly lower than the other two groups(P<0.05). There was no significant difference(P>0.05) fat content end of the test. For the activity of digestive enzymes, trypsin activity in different frequency groups of similar activity and trends intestinal lipase, there was no significant difference(P>0.05) between the different feeding frequency active trypsin treatment groups at the end of the test, feeding frequency 1 time / d intestinal lipase activity was significantly higher than the other two groups(P<0.05), and pepsin activity was significantly lower than the other two groups(P<0.05), while the remaining two intestinal lipase activity and pepsin There was no significant difference(P>0.05) activity. For flower eel serum biochemical parameters, similar to the different feeding frequency on blood glucose and urea influence trends with increasing content of farmed time to increase further reduced, the low end of the trial feeding frequency 2 times/ 2d blood glucose concentration was significantly higher than the other two groups(P<0.05), feeding frequency of 1 time/d of high urea content. At the end of the test, serum total cholesterol treatment groups at different frequencies and total protein concentration was not significantly affected(P<0.05). Feeding frequency of 2 times/d concentration of serum triglycerides were significantly lower(P<0.05), alkaline phosphatase was significantly higher than the other two groups(P<0.05). Different feeding frequency of Anguilla marmorata aspartate aminotransferase activity and alanine aminotransferase activity no significant effect(P<0.05). With the increase of the frequency of feeding, the number of Anguilla marmorata satiation increases, nutrients and energy intake of a substance that regulates the metabolism of fish blood sugar, protein and triglycerides, growth performance Anguilla marmorata well, so the Anguilla marmorata optimal feeding frequency of 2 times/d. |
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