| Oyster provides much higher annual production than any other marine shellfish in China.It is not only economically important,but also the fundamental species of oyster reefs.It has important ecological functions in purifying water,providing habitat, protecting biodiversity,and biological carbon sequestration.Crassostrea gigas and C.ariakensis are two important oyster species in northern China.In this study,these two kinds of oysters were taken as research objects.1)The physiological response of C.gigas and C.ariakensis to accurate reduced salinity was studied.2)The growth characteristics of clutchless C.gigas in mudflat aquaculture were studied;3)the dynamic energy budget model(DEB)of C.gigas in mudflat aquaculture was established.The main findings of our study are as follows:1. The Metabolic response of C.gigas and C.ariakensis to accurate reduced salinity.The effects of accurate salinity reduction(10 psu and 20 psu,with natural seawater as the control)on the physiological metabolic rate(oxygen consumption rate,ammonia excretion rate,feeding rate and excretion rate)of C.gigas and C.ariakensis were studied by experimental ecological methods.The results showed that accurate salinity reduction had significant effects on the oxygen consumption rate,ammonia excretion rate and feces excretion rate of C.gigas and C.ariakensis(p<0.05),while the responses of the two species of oysters to accurate reduction of salinity were also different.The oxygen consumption rate,ammonia excretion rate,feeding rate and excretion rate of C.gigas are the highest in natural seawater(salinity is about 29 psu),and the accurate reduction of salinity showed detrimental effects on C.gigas.However,C.ariakensis showed better performance on these metabolic parameters at 20 psu than that in the other two groups.To normalize the metabolic rate of oyster with a broad range wet weight,a regression equation for the metabolic rate to wet weight was established,which is fitting Y=a W~b.The wet weight(20 g)was used for the comparison after normalization.At 20 psu,the respiration rate of C.ariakensis is strong,and the respiration energy accounts for 16.1%of total energy consumption,while C.gigas showed stronger oxygen consumption rate in natural seawater(respiratory energy accounts for 7.8%of total energy consumption),and it is lower at 10 psu(respiratory energy accounts for 0.7%of total energy consumption).Our results indicated that the acute lowered-salinity incubation had significant influence on C.gigas than C.ariakensis,and a low-level reduction in salinity can even promote energy metabolism C.ariakensis.2. Effects of accurate salinity reduction on enzyme activity of C.gigas and C.ariakensis.Two kinds of oysters were incubated for 72 hours at different salinity,and the activity of several key enzymes in the gill and digestive gland of oysters under different incubating time(0h,6h,12h,24h,36h,48h,60h and 72h)was studied.Results showed that the tolerance of the two kinds of oyster to accurate salinity reduction was different from each other.A small proportion of C.gigas died at the 10 psu group within the incubation,while C.ariakensis showed no mortality.Accurate salinity reduction had a significant effect on the total protein concentration of the two oysters.At the groups of 10 psu and 20 psu,the total protein concentration of the gills and digestive glands of the C.gigas decreased with the increasing incubation duration,and significant difference(P<0.05)was found between different incubating time.However,the reduction of the total protein concentration of the C.ariakensis was lower than that of the C.gigas.At 10 psu,SOD activity in gills and digestive gland of C.gigas increased with the duration of incubation,while at other salinities(20 psu and 29 psu),SOD activity in gill first increased and then decreased with the increasing incubation time.In digestive gland,the SOD activity showed no change in different incubating time.The change trend of SOD activity in the gills and digestive glands of C.ariakensis was the same under different salinity,and it increased first and then decreased with the increasing incubating time.3. Growth performance of clutchless oyster in tidal flat.Growth performance of clutchless oyster was studied in Laizhou bay from June 2018to November 2019 with the help of shandong Long Wei Group Company.Seedlings cultivated and monitored for growth performance with an initial average shell length of0.5mm.Results show that the shell length of C.gigas increased rapidly from July to October and lowered increasing rate was found from October to December.After six months of cultivation,the shell long of these oysters reached 48.5 mm.Since March 2019,a total of 50 cages of clutchless oyster with a shell length of 36 mm were cultured in the tidal flat,and 150-200 individuals were placed in each cage.Significant increment in shell length was found in April,and higher grow rate was found from May to August.The shell length reached an average of 70mm in August,after this the growth rate slowed down.The growth rates of shell height,shell width and shell length were not consistent,and reached the maximum value in November,which was 49.5mm and 37.9mm respectively.The fastest increasing rate in wet weight was found from June to July,and the growth rate was 0.49g/d.4. Construction of dynamic energy budget model(DEB)of clutchless C.gigas cultivated in tidal flat.In laizhou bay,turbidity meter and thermo-salt depth instrument were used to monitor seawater temperature,salinity and chlorophyll concentration continuously.Allen Newcastle temperature as well as other parameters that was used to determine the shape of the oysters cultivated in tidal flat was measured by simulation in the laboratory.Other parameters was adopted from published literatures.For the DEB model construction,temperature and chlorophyll were taken as fixed parameters and the software of Python3.8 was used to build the model of C.gigas.The model was verified based on the growth data from July 27,2018 to April 28,2019.Results show that the modeled tissue wet weight and shell length simulation value and actual value has significant linear correlation(p<0.01),R~2 of 0.983 and 0.909 respectively.Furthermore high correlation between simulated values and the measured values indicated that the model can reflex the growth performance of clutchless oyster cultivated in tidal flat.The results of our study can be taken as reference data for the oyster tidal flat aquaculture. |
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