Ecological Effects Of Macroalgae And Filter-Feeding Bivalve In Fish Culture

Dissolved inorganic nulrient(DIN) is one of the main pollutions from marine fish culture. In recent years,guided by the "Cleaner Production" and "Ecological culture",integrated culture pattern of fish and other species was paid great attention to. In this paper,different experiments in indoor culture tanks such as:S. schlegeli and G. k'uianeifarmis polyculture,S. schlegeli and A. irradians polyculture were conducted. Through investigations on the variation of physi-chemical and biological factors and growth of the cultural species,the ecological effects of G lenuineiformis and A. iiTdJians in the culture systems were discussed. The main results are following as:In fish monoculture tanks,in Spring,ammonia was the main part of inorganic nitrogen with the contents of nitrate increasing greatly later,and the contents of phosphate were low;while in Autumn,both the contents of ammonia and phosphate were high.G k'maneifornm could effectively remove inorganic nutrients from the water body. In Autumn,compared to monoculture tank,the polyculture tanks had 77.24% ammonia and 65.96% phosphate lower after 23 days,as well as 69.45% ammonia and 26.73% phosphate lower after 40 days. While in Spring tanks with G lenumeifonriis had 90% ammonia lower than monoculture tank after 3 weeks. Temperature had greater effects on the growth of G Lemaneiformis than it did on the nutrient assimilate rate. The average daily growth rate showed that G. lemaneifonnis grew well in spring and poorly in autumn,and had negative growth rate when the water temperature was below I. Besides G. Lemaneiformis may suppress the growth of phytoplankton.The contents of Chla.,POC and PN in the water had obvious relationship either in Spring or in Autumn,but POM had correlation with them only in Spring.Fish and scallop polyculture experiment showed that the contents of Chla.,POC and PN in the water were low while the contents of inorganic nutrient were high,which may caused the large scale death of A. irradicms. In the same time ,food scarcity may be another main reason limiting the growth of A. iiradians.