Study On Physiological Ecology Of The Undulated Surf Clam,Paphia Undulata

Paphia undulata is an important commercial shellfish in southern China.With the continuous expansion in market demanding for the clam,the aquaculture of P.undulata has developed rapidly in Fujian,Guangdong and Hainan Provinces in the recent decades,which has become the major proportion of benthic aquaculture of muddy beach in the subtidal zone and made full use of the offshore aquaculture environment,therefore there is a very large prospect in P.undulata aquaculture.However,due to a shortage of seedlings and the extensive aquaculture model at present,there are a series of issues in the aquaculture,such as a large of seedlings injured during the long distance transport,a low survival rate and a low yield in culture.At the same time,there are few researches on the physiological ecology of P.undulata.In this paper,we systematically studied the physiological ecology of P.undulata,hoping to provide more theoretical knowledge and basic data for promoting the biology and aquaculture of this species.The main results of this study are as follows:1.The experimental study on the feeding and energy budget responses of P.undulata under different suspended particles showed that the threshold values of pseudofaeces production in P.undulata was 17.00-19.80 mg L-1.The retention of inorganic particles by P.undulata was mechanically screened,which was only related to the particle size.When the particle size was<9 ?m,the retention efficiency increased linearly with the increase of particle size,and when the particle size was>9 ?m,the retention efficiency decreased with the increase of particle size.The retention efficiency of algae was related to the size and concentration,with the increase of concentration,P.undulata tended to retain larger algae.At low concentration(TPM<25 mg L"1)and along the increase of particle concentration and organic content,the feeding rate and SFG of P.undulata increased at a decreasing rate and gradually approached the maximum.At high concentration conditions(TPM>25 mg L-1),the clearance rate and SFG decreased with the increase of organic matter content.2.By studying the effects of environmental factors on the feeding physiology and energy budget of P.undulata,the results showed that the suitable temperature and salinity ranges for feeding and growth of P.undulata were 18-32 ?,25-30,respectively.Exposed to ocean acidification(pCO2>1500 patm)and hypoxia(dissolved oxygen<2 mg O2 L-,),the feeding of P.undulata was significantly inhibited,the feeding rate and SFG decreased significantly.The optimal feeding environmental factors for P.undulata were:28.42 ?,29.29,5.99 mg 02 L-1.3.The lower incipient lethal temperature(26 d LILT50)and upper incipient lethal temperature(8 d UILT50)of P.undulata were 6.76±0.10 ? and 33.49±0.022 ?,respectively,and Arrhenius break temperature(ABT)of cardiac performance was 35.64±0.77 ?,which was the acute lethal temperature of the species.The lower incipient lethal salinity(27 d LILS50)and upper incipient lethal salinity(40 d UILS50)of P.undulata were 17.90±0.40 and 42.06±0.42,respectively.The tolerance of P.undulata to hypoxia decreased with the increased temperature or time.At 25 ?,the lethal dissolved oxygen concentration(288 h LC50)was 0.72 mg O2 L-1 At 30 ?,the 96 h LC50 and 120 h LC50 of P.undulata were 0.49 and 0.64 mg O2 L-1,respectively.The relationship between the lethal time(Lt5o)and temperature(T)of P.undulata exposed to anoxic stress was Lt50=138.31*e-0.124T(R2 = 0.9826).4.The ability of burrowing for P.undulata was enhanced with the increase of the body size.The juvenile P.undulata had a wider selection for sediment size than the adult,which could burrow successfully in the sea mud that the sand content was even up to 80%.Instead,the burrowing of adults was significantly hindered when the sand content was ?40%.The optimum temperature range for juvenile(shell length 5-20mm)was 25-30 ?.When the temperature was<15? or>34?,more than half of 5mm juvenile couldn't complete the burrowing process.The water content and sand content of sea mud affected the feeding and energy budget of P.undulata by altering the burial depth.When the water content was ? 40%or sand content was? 40%,the burial depths of P.undulata were significantly deeper than other sediment conditions,and the shallower and deeper burial depths had a negative effect on feeding of P.undulata.When the burial depth of P.undulata was 6.5cm,the clearance rate and SFG were the largest.5.The survive rate of P.undulata increased with the increase of humidity when exposed to air,and the survival time ofP.undulata was the longest at 15 ?,the lethal time(Lt50)of the species exposed to air was 131 h.After more than 6 h exposed to air,the ability of burrowing of juvenile was impaired significantly.After 48 h,all the juveniles would die.Therefore,during transport of seedlings,the suitable temperature range is 20-24?,the suitable time exposed to air is less than 6 h and it is better not more than 12 h.The survival rate of adults would decrease significantly after recovery when exposed to air more than 24 h,and the survival rate was less than 50%after 48 h.The ability of burrowing for P.undulata wouldn't be impaired when the clam exposed to air less than 24 h,but the feeding and digesting in the recovery were significantly impaired and the values of SFG were negative after exposed to air more than 48 h.Therefore,the suitable transport time for adults is less than 24 h.When exposed to the air,glycogen and pyruvate in.undulata were significantly reduced.Succinate in the foot and mantle were significantly increased after exposed to air more than 12 h,and lactate in foot was significantly increased after exposed to air more than 24 h.The activity of alkaline phosphatase,alkaline phosphatase and catalase in visceral increased significantly after exposed to air for 6 h,12 h and 48 h,respectively.MDA in visceral decreased significantly after 12 h,however,SOD activity significantly decreased after 24 h.6.The burial depth of P.undulata is shallow,therefore the clam couldn't avoid the predation from Portunus pelagicus.The feeding rates of P.pelagicus prey on P.undulata were significantly affected by temperature.When temperature was ? 15 ?,the predator couldn't prey on P.undulata,while when temperature was>20 ?,the feeding rates increased rapidly with the increase of temperature.There were a significant selectivity and diurnal variation on feeding rates of P.pelagicus prey on P.undulata,the predator preferred to prey the juveniles and small-sized adults than the larger clams.However,the existence of P.pelagicus didn't affect the burial depth and filter feeding of P.undulata.