Effects Of Breeding Mode And Density On The Growth And Physiology Indexes Of Sinonovacula Constricta

Razor clam（Sinonovacula constricta）is a shellfish that lives and camps in the mudflat.It has the characteristics of simple breeding technology and a wide variety of seed sources.It is an earlier shellfish cultured in our country.There are many modes of shellfish pond culture.Now multi-trophic ecological comprehensive aquaculture has become the mainstream.Compared with monoculture,ecological comprehensive aquaculture improves the utilization rate of water bodies and obtains higher economic and ecological benefits.Cultivation density is one of the important environmental factors in pond ecological aquaculture.In order to increase the profit of breeding,increasing the breeding density of species is an inevitable choice.However,too high stocking density will cause stress to the breeding species,causing a series of negative effects such as growth retardation,metabolic disorders,and decreased immunity.This thesis studies the effects of different shellfish on the water quality of cultured waters and the effect of different shellfish on the removal of nutrients in the cultured waters,and analyzes the changes in pond water quality under different shellfish culture modes,and finally the growth of Sinonovacula constricta,Physiological and water quality indicators were studied.This study provides reference materials for the water purification effects of different shellfish in artificial culture ponds and the optimal culture density of Sinonovacula constricta under the pond culture mode,and provides a theoretical basis for the reasonable and sustainable culture of shellfish.1.The research objects of this experiment are Razor clams,green clams（Cyclina sinensis）,clams（Ruditapes philippinarum）and scapharca subcrenata（Scapharca subcrenata）.Pond culture is simulated under laboratory conditions to explore the impact of different shellfish on the water quality of the culture system.The effect of different shellfish on the removal of nutrients in aquaculture water.In addition,the water quality changes of four artificial breeding ponds（No.1,No.2,No.3,and No.4）under different cultivation modes were compared.The results of the simulation experiment showed that the total phosphorus（TP）removal rate of the four shellfishes had no significant difference（P>0.05）;the removal rate of total nitrogen（TN）by clams and constrictor clams was significantly higher than that of larvae（P<0.05）;There was no significant difference between the COD removal rate of clams and the COD removal rate of Sinonovacula constricta（P>0.05）,but it was significantly higher than the COD removal rates of clams and cockles（P<0.05）.There was no significant difference in the removal rate of COD between clams and cockles（P>0.05）.There was no significant difference in the removal rate of ammonia nitrogen（NH₄⁺-N）among the four shellfish（P>0.05）.The experimental results show that the four kinds of shellfish have a certain removal effect on different nutrients.The water quality test results of artificial breeding ponds showed that the NH₄⁺-N content of the No.4 pond of the monoculture of shrimps and crabs was significantly higher than that of the three ponds（P<0.05）,ponds with monoculture of shrimps and crabs often have higher nutrient content,and the water quality in ponds with shellfish and shrimps and crabs polyculture has improved to a certain extent.2.The research object is Sinonovacula constricta.There are three breeding density groups,100 grains/m²（G30）for low-density group,200 grains/m² for medium-density group（G60）,and 300 grains/m²（G90）for high-density group.Three repetitions,the experiment period was 60 d,and the cultured Sinonovacula constricta in each experimental group were randomly excavated at 15 d,30 d,45 d,and 60 d to determine their growth,survival,and related physiological and biochemical indicators.The water quality at different time points（0 h,3 h,6 h,12 h,24 h and 48 h）during the breeding process was also tested.The results showed that the specific growth rate of the shell length,shell width,shell height and body weight of the low-density G30 group were significantly higher than that of the G60 and G90 groups（P<0.05）.There was no significant difference in the specific growth rate of shell length,shell height and body weight between G60group and G90 group（P>0.05）.As the breeding density increases,the survival rate of Sinonovacula constricta shows a downward trend.After the breeding,the glutathione peroxidase（GSH-Px）activity of the three density groups all increased to a certain extent compared with the initial value.The activity of GSH-Px in the G90 group was significantly higher than that of the G30 and G60 groups（P<0.05）.Both superoxide dismutase（SOD）and total antioxidant capacity（T-AOC）have a certain degree of decline compared to the initial values.The activity of lactate dehydrogenase（LDH）in the hepatopancreas tissue of Sinonovacula constricta in the G90 group was significantly lower than that in the G30 and G60 groups（P<0.05）,and both decreased compared with the initial value.The phosphofructokinase（PFK）activity of G60 group was significantly lower than that of G30 and G90 groups（P<0.05）.The water quality measurement results showed that the high-density G90 group had significant differences in the nutrient content in the water at the end of the test compared to the other two groups.3.The research object is Sinonovacula constricta,with three density gradients of300 per m²（G1）,450 per m²（G2）,and 600 per m²（G3）,four repetitions,and one repetition to supplement the density.Samples were taken at 0 h,6 h,24 h,48 h and 72 h to determine the oxygen consumption rate,ammonia excretion rate,enzyme activity and other physiological indicators of Sinonovacula constricta and the water quality indicators of the aquaculture water.The results showed that the oxygen consumption rate of the G3group increased gradually within 48 hours,and then dropped sharply;the oxygen consumption rate of the G1 and G2 groups fluctuated little.The oxygen consumption rate of G3 group was significantly higher than that of G1 group and G2 at 48 h（P<0.05）.There was no significant difference in the ammonia excretion rate between the G1 group and the G2 group at each time point（P>0.05）;the ammonia excretion rate of the G3 group increased first and then decreased,with a peak at 24 hours.The SDH activity of the G1group was significantly higher than that of the G2 and G3 groups（P<0.05）,and the difference between the three groups at 48 h and 72 h was not significant（P>0.05）;the effects of different densities on the serum blood glucose of Sinonovacula constricta were not significantly different（P>0.05）).The changing trends of NH₄⁺-N,NO₂^--N,TN and TP in the waters of Sinonovacula constricta culture under different densities are the same,and they all increase with time.The higher the density,the faster the accumulation of nutrients in the water.