Dietary Available Phosphorus Requirement Of Crucian Carp(Carassius Auratus)

A feeding trial was conducted to evaluate the optimum requirement of dietary available phosphorus(AP)for crucian carp(Carassius auratus).Monocalcium phosphorus(MCP)was used to formulate extruded feed containing total phosphorus and available phosphorus of 1.02 % and 0.11 %(D1),1.29 % and 0.36 %(D2),1.49 % and 0.55 %(D3),1.72 % and 0.75 %(D4),1.96 % and 0.98 %(D5),respectively.Each diet was randomly fed to triplicate groups of fish with initial mean weight of 58.33±0.13 g in recirculating tanks,and each tank was stocked with 12 fish.Fish were fed three times daily(07:00,12:00 and 17:00)at feeding rate of 1.5 %,and the experiment last for 9 weeks.Daily accumulation pattern of total ammonia and soluble phosphorus excretion of crucian carp was also measured on day 8 and day 63 during the experiment.The results of the experiment show that the survival rate of each group was 100 %,and the different levels of available phosphorus in the feed had no significient effect on the survival rate of the Crucian carp(p>0.05).During the experiment period,other phosphorus deficiency symptoms were not observed except for the low phosphor feed group(D1~D2),which showed an appetite decline during the later stage of the experiment.Weight gain,specific growth rate,and feed efficiency significantly increased with the available phosphorus increasing from0.11 % to 0.76 % in diet(p<0.05),and then leveled off.The availability of phosphorus levels for different feeds has no significant effect on the amount of condition factor,viscera-somatic index,and hepatosomatic index.The body composition analysis showed that the availability of phosphorus levels for different diets has no significant effect on the whole-body moisture content of the Crucian carp.The whole-body crude protein content and crude ash content increased with the increase of available phosphorus of diet.The whole-body crude lipid content was inversely proportional to the available phosphorus of diet,which reduced from 8.28 % to 6.48 % with the increasingavailable phosphorus of diet(p<0.05).The availability of phosphorus levels in different feeds had no significant effect on the crude protein and crude ash content of the Crucian carp muscle.The crude lipid in the muscle of Crucian carp was decreased sharply,and then increased dramatically with the increasing of dietary available phosphorus.No significance were found in whole-body Fe,Ca,Mg,Cu content among all the treatments.The content of calcium in the spine of the Crucian carp was elevated with the increase of available phosphorus levels in the dietary,and then showed a downward trend.The content of Mg in the spine of the Crucian carp increased with the increase of available phosphorus of diet.The phosphorus content of whole-body(dry weight)and vertebra(wet weight)were significantly improved by dietary phosphorus up to 0.76 % and then leveled off beyond this level.However,no significance were found in muscle(wet weight)phosphorus content among all the treatments.The blood chemistry analysis showed that dietary available P had distinct effects on enzyme activities of alkaline phosphatase,content of triacyglycerol and In-P(p<0.05).The enzyme activities of alkaline phosphatase in the serum was significantly improved by dietary phosphorus up to 0.76 % and then leveled off beyond this level.In contrast,the content of triacyglycerol in the serum was significantly reduced by dietary phosphorus up to 0.76 % and then leveled off beyond this level.The content of In-P in the serum increased(5.76mmol/l~7.49 mmol/l)with the increasing of available phosphorus in the dietary(0.11%~0.98 %).However,no significance were found in serum total cholesterol content among all the treatments.Based on broken-line analyses of weight gain,whole body and vertebrae P content,the requirement of the crucian carp for dietary available phosphorus was estimated to be 0.83 %,0.80 % and 0.78 %,respectively.Based on the determination of soluble phosphate concentration and total ammonia nitrogen concentration of 24 hours,we could found that crucian carp fed at diet with insufficient P(D1、D2)seemed to absorb soluble P from the water.If the available phosphorus level of dietary is lower,the crucian carp will absorp the more soluble phosphate from aquaculture water.When the available phosphorus level of dietary is relatively higher(D3~D5),soluble phosphate excretion of crucian carp increased with the level of phosphorus in feed.When the available phosphorus level of dietary is too high(D5),soluble phosphate excretion of crucian carp will have a significantly increased(D5 is significantly higher than D4),which will cause aquaculture water body pollution,but the total ammonia content was not affected.The main kind of bacteria in the intestine of crucian carp is Proteobacteria,and the following is Firmicutes,Fusobacteria,Actinobacteria.The availability of phosphorus levels in different feeds significantly affect the number of foregut wrinkle wall(p<0.05).However,the different levels of available phosphorus in the dietary had no effect on the number of the midgut and hindgut’s wrinkle wall.The phosphorus level of the dietary can significantly affect the wrinkled wall height,the epithelial cells height and the cross-sectional area of foregut,midgut and hindgut.