A PRELIMINARY SURVEY ON THE BIOLOGY OF MACTRA CHINENSIS IN THE OUTFALL OF YALU JIANG RIVER

Mactra chinensis inhabits in the shallow seas or inter-tidal zones adjacent to riveroutfalls by burrowing into the muddy sand bed 2--7 cm in depth. It can ambulateto some extent and has a great adaptability to the varied environment, such as theannual water temperature varies from -- 1.9--31.5℃, annual salinity varies from8.6--34.8% and also the seasonal dilution of salinity by outpouring of fresh water.The clamr lives chiefly on planktonic diatoms. The amount and components ofthe stomach contents at different sea areas and differant seasons have been observedand it is found to be in accordance with the species which were taken as diet underthese specific enviornments.The clam is gonochorism. It reaches its sexual maturity in a full year term. Theripened sexual cells discharge in batches. Its spawning period starts in late of May atthe water temperature over 14℃. The temperature can be raised by artificial metho-ds. Expediting on parturition can be obtained by induced spawning or by running-w-ater stimulation.The ovum of the clam can be artificially fertilized and normally developed. Thelower limit of temperature for embryonic development lies near 10℃. The larvae livechiefly on small-sized unicellular algae.The clam grows fast in the first three years, especially the first two years, itssize reaches to 3 cm at the end of first year and 4--5 cm in the second year,while inharvesting its size reaches to 5 cm. At the beginning of June, its soft portion (meatportion) becomes fully developed with a most production rats of 40.32%.Appendant formation can be observed at the basal portion of outer gill of theclam.