Primarily Study On Ecological Prevention And Control Of Enteromorpha Prolifra With Siganus Guttatus And Its Physiological Basis

With the development of fisheries economy, the environmental problems also gradually increases in recent years, such as water degradation and great economic losses caused by overgrowth of Enteromorpha prolifra. Chemicals are often used for keeping E.prolifra down.But at the same time chemical drugs cause side-effects which have bad influence on the culture water.Siganus guttatus ingest E.prolifra and it may become a new method to control E.prolifra growth. In order to provide reference for the technique that uses S.guttatus to control overgrowth of E. prolifra,living habits,feeding rhythm,daily food intake,growth characteristics,digestive enzyme activity,serum biochemical and antioxidant enzyme indices of juvenile S.guttatus were studied. According to the results above,culture mode of S. guttatus and E. prolifra were studied.1.Feeding habits on E. prolifra and of juvenile S. guttatusS.guttatus living habits and feeding rhythm were studied by means of underwater photography and direct observation.The results showed that the fish inhabited in the middle and low layer and liked to move around in groups.They distributed dispersedly in water and liked to gnaw the attachment on cages,such as microalgae and detritus.S.guttatus had strong stress reaction.They were easily scared by surround sound and vibration caused by breeders.The fish swam quickly away when they sensed danger.S.guttatus was accord with the daytime feeding type.There were three apparent feeding peaks in daytime.The first apparent feeding peak appeared at 5 a.m. Besides this peak,the juveniles had another two feeding peaks around 9:00 and 14:00. Unlike the peaks around 9:00 and 14:00,the formation and decline of the peak around 5:00 took shorter time.They seldom fed from 19:00 to 20:30 and had no feeding behavior from 20:30 to3:00, indicating that light intensity could affect their feeding activity.In order to investigate the daily food intake and growth characteristics of juvenile S. guttatus,90 fish were cultivated from June 24 to September 19 in three2.5m×1.5m×1.5m cages(30 fish per cage) which mesh size were 0.5mm.The fish average body length(BL) was(39.9±2.3) mm and average body weight(W) was(2.1±0.2) g.Collected and weighted the residual feed every day at 5:30(summer),and fed the fish with enough fresh E. prolifra(500.0g) concurrently.The results showed that the average body length and weight of the experiment fish increased from(39.9±2.3) mm to(66.0±5.8) mm,and(2.1±0.2)g to(9.8±2.2) g,respectively,after 90 days culture.Daily body adding length was 0.29 mm and daily body weight gain was0.09 g.A linear relationship between total length(TL) and body length(BL) could be indicated as TL=1.1439BL+2.1082(R2=0.9449),and a power function relationship could be indicated as W=0.000024TL2.9387(r2=0.9543) between body weight(W) and total length.The power index was nearly 3,so S. guttatus grew at a uniform velocity.The average daily food intake of 30 fish(average body length was(64.5±5.6)mm and average body weight was(7.6±1.3) g) was 260.3g E. prolifra(wet weight),8.7g feed per fish,1.1 body weight.2.Growth performance and digestive enzyme activity of juvenile S. guttatus fed with artificial feed and E. prolifraThe growth performance and digestive enzyme activity of juvenile S. guttatus fed with artificial feed and E. prolifra were studied.The results showed that the weight gain rate, specific growth rate, relative growth rate, crude protein and crude fat contents, ratio of viscera and hepatopancreas weight to body weight of juvenile S.guttatus fed with artificial feed were significantly higher than that fed with E. Prolifra(P < 0.05), while the crude ash, ratio of intestine gut weight to body weight and ratio of intestine gut length to body length of juvenile S. guttatus fed with artificial feed were significantly lower than that fed with E. Prolifra(P < 0.05). Pepsase activity in stomach, trypsin activity in foregut and midgut, lipase activity in pyloric caeca, gut and liver of juvenile S. guttatus fed with artificial feed were significantly higher than that fed with E. Prolifra(P < 0.05), while amylase activity in pyloric caeca and gut of juvenile S. guttatus fed with artificial feed were significantly lower than that fed with E. Prolifra(P < 0.05). According to the results, the growth performance of juvenile S.guttatus fed with E. Prolifra was not as good as the fish fed with artificial feed. But the amylase activity, the ratio of intestine gut weight to body weight and ratio of intestine gut length to body length of juvenile S. guttatus fed with E. Prolifra were significantly higher than that fed with artificial feed. S. guttatus showed good feeding and digestion ability to E. prolifra, which can satisfy the growth need of S. guttatus,and the fish was easily raised.3.Serum biochemical and antioxidant enzyme indices of juvenile S. guttatus fed with E. prolifra and artificial feedThe serum biochemical and antioxidant enzyme indices of juvenile S. guttatus respectively fed with E. prolifra and artificial feed were studied.The results showed that the total protein(TP), urea nitrogen(UN) and alkaline phosphatase(AKP) of juvenile S. guttatus fed with E. Prolifra were significantly higher than that fed with artificial feed(P <0.05), while the glutamic oxalacetic transaminase(AST/GOT) and glutamic-pyruvic transaminase(ALT/GPT) of juvenile S. guttatus fed with E. Prolifra were significantly lower than that fed with artificial feed(P < 0.05). SOD, GPX and anti-superoxide anion radical activity in liver, kidney, gill and muscle of juvenile S.guttatus fed with E. Prolifra were higher than that fed with artificial feed, and these antioxidant enzyme activities in kidney of juvenile S. guttatus fed with E. Prolifra was significantly higher than that fed with artificial feed(P < 0.05), while CAT and inhibiting hydroxyl radical activity in liver of juvenile S. guttatus fed with artificial feed were significantly higher than that fed with E. Prolifra(P < 0.05). According to the result of the experiment, the juvenile S. guttatus fed with E. Prolifra showed better antioxidant defense system. And the fish was easily raised and has stronger ability of digestion and absorption of E. Prolifra. The technique that uses S. guttatus to control E. prolifra deserves deeply study, probably S. guttatus could realize an important role in the matter.4.Construction of culture model of S.guttatus and sea cucumberThe experiments was carried out from 2014 April 14 to 2015 October 1 in sea cucumber aquaculture ponds which affected by E. Prolifra for the third time in three years.According to the growth of E. Prolifra and water temperature, S. guttatus were cultured in diffreent stocking densities in different ponds.The results showed that local daily minimum temperature stabilized at 16 ~ 17 ℃ and above from lata May to early June.Aquiculture water contained high amounts of nutrition for crops, such as nitrogen and phosphorus. E. Prolifra coverage percentages riesd from to 1% to 30%from late April to late June.The relationship between S. guttatus daily food consumption(FD) and body weight(BD) could be indicated as FD = 184.28ln(BW)-379.71(R2 = 0.9933).The fish average body length(BL) was(15.35±20.54) cm and average body weight(W) was(135.04±37.43) g and there was no significant difference in different experiment groups.The culture model could be constructed asfollows:stocking density of S. guttatus(ind/mu) =132.95 × the highest E. Prolifra coverage in previous years(%) — 0.2609 × fish body weight(g) + 37.0296(r2=0.9924),and S. guttatus stocked into sea cucumber aquaculture ponds when water temperature stabilized at 16 ~ 17 ℃ and above.