Preliminary Studies On The Techniques Of Spring Seed Production Of Chlamys Farreri And New Treatment Method For Inducing The Settlement Of Eye-spot Larvae

In the present study,scallops reproduced artificially in spring via promoting water temperature gradually and the seeds were cultivated temporarily in mended shrimp pond. Then the seeds were cultured at sea (Lao shan area) in the same year. The growth process of the seeds was observed and the survival rates were measured in order to testify whether they can survive the high-temperature summer. In addition,the filtration rates of Zhikong scallop larvae and spats was observed and a way of inducing the settlement of eye-spot larvae was summarized.The preliminary results are as follows:1. The artificial reproduction of scallop in springThe artificial scallop reproduction experiment in spring was carried out from February to June of 2007 in Hongdao Clam Original and Eugenic Breed Development Co.Ltd. Under relatively low water temperature (about 6.9℃),by promoting water temperature gradually,the induced maturation was obtained. After 23 days indoor culture,the parents spawned. In a water body of 52m³,1.28×107 seeds with mean shell height 719.58±65.74μm was obtained. After the temporary cultivation in mended shrimp ponds,here were 8.3×106 (4.92×5.66mm)individuals. Because of the suitable temperature and abundance of bait-organism biomass in the shrimp pond,the juvenile had a high survival rate,which can reach 65%.2. The temporary cultivation and cultivation in sea of spring scallopsAt June 28th 2007,the juvnile scallop were transferred from the shrimp pond to the Laoshan area. After temporary cultivation,the scallop were graded into temporary cultivation lantern nets on August 26th which was earlier than the control(that were't graded). In every lantern net,about 387 individuals were put in each layer. On November 8th,they were transferred to the cultivation lantern nets. At November 2007,the average shell length was 19.97 mm and the average shell height was 24.28 mm (the biggest shell length 42.89 mm ,the biggest shell height 46.33 mm). In September 2008,the average shell length and shell height of the scallops were 51.45,56.45 mm,which was bigger than the seed collected from the sea (45.45,50.86 mm). The survival rate was 84.25%,far higher than the control (the seed collected from the sea). In conclusion,the seeds from artficially reproduces scallops successfully survived the summer. 3. Preliminary studies on the new treatment method for inducing the settlement of eye-spot larvaeAfter using benthic diatoms cultch(The benthic diatoms were cultured on the cultch)for the induction of the settlement of eye-spot larvae got successed,a moderate scale experiment was carried out in the water body of 1000m³. The results showed that in the cullth with benthic diatoms on (using palm rope or polyethylene net as the cultch),the settlement and metamorphosis ratea were all increased in different batches although absolute values were not different. The metamorphosis time was also advanced. In the batch of using polyethylene net (with benthic diatoms on),the number of settlement seeds was 6.8 times of the control. In the palm rope group,the number of settlement seeds was 12.3 times of the control and the metamorphosis ratea was increased 3.8 times on average. At the temperature 8-10℃,the benthic diatoms on the cultch were cultured in different time (10 days,7 days,5 days,3 days). The settlement rate of the different culture time of benthic diatoms had no significant difference but the metamorphosis rate had significant difference. In all the treatment groups,the group of 7 days had the highest metamorphosis rate. The groups ranked after the metamorphosis rate were: 7 days>10 days>5 days>3 days.4. Effects of salinities, microalgae densities and diurnal rhythm on filtration rates of Zhikong scallop larvae and spatsAt temperature 24±0.5℃,the filtration rates of Zhikong scallop spats (1.177-2.017 mm in shell length) were determined in (1) different salinities (20,25,30,35) with a microalgae density of 3.0×10⁴ cells/ml,and (2) with different densities of microalgae (Dicrateria zhanjiang gensis) (3.0×10⁴ cells/ml,4.5×10⁴ cells/ml,6.0×10⁴ cells/ml) in a salinity of 30. The static water method was used. The relationship between the filtration rate (FRS) and the salinity (S) can be expressed by FRS = -30.893S2+1691.5S-19610 (r=0.847) (calculated by whole dry weight) , FRS =-0.022S2+1.2236S-14.522 (r = 0.928,calculated by individual quantity). We estimate that at the salinity of 27.8 the filtration rate has the maximum value,of 3.54L/g·dw·h(2.49×10^-3 L/ h·ind). The filtration rate of the scallop spats increased with the salinity when the salinity was lower than 27.8 and decreased when it was more than 27.8. The salinity has significantly influence on the filtration rates of Zhikong scallop (p < 0.05). When fed with Dicrateria zhanjiang in a concentration of 3.0×10⁴ cells/ml,4.5×10⁴ cells/ml,and 6.0×10⁴ cells/ml,the filtration rate of the scallop spats increased and then decreased as parabolic type trend with the microalgae density. We can estimate that it has the biggest filtration rate (0.43×10^-3 L/ h·ind) when the density is 4.7×10⁴ind/ml. The relationship between the filtration rate (FRQ) and the microalgae density (Q) is FRQ=-0.0693Q2+0.6484Q-1.0835(r = 0.722). The diurnal rhythm of filtration rate (FR) of Zhikong scallop spats (1.177-2.017 mm in shell length) when microalgae density is 3.0×10⁴cells/ml at temperature 24±0.5℃,and of the veliger when microalgae density is 1.0×10⁴cells/ml at temperature 18±0.5℃,was determined using a static water method. We surveyed the filtration rate of the veliger and spat at 17:00,21:00,1:00,5:00,9:00,13:00. Analysis showed that the filtration rates of the veliger and spat have the similar diurnal rhythm. They had the lowest filtration rate (veliger: 0.0026ml/h·ind,spat: 0.1231ml/h·ind) in the day (9:00-13:00) and the highest (veliger: 0.0258ml/h·ind; spat: 0.5096ml/h·ind) in the night (21:00-1:00).The analysis shows significant difference.