Preliminary Study On The Effects Of Gonads,Substratum And Probiotics On The Hatchling Of Mercenaria Mercenaria

Mercenaria Mercenaria is one of the main economic bivalve shellfish in the shallow sea and mudflat in the west coast of North America Atlantic,and it has become an important animal in culture.Metamorphosis is an important developmental process of clams,the key to artificial seedling rearing,and directly related to population resource changes.The quality of shellfish and external environment have important effects on this process.Good germplasm and suitable external conditions are the key factors to ensure larvae metamorphosis.Therefore,it is of great significance for the development of artificial seedling industry to study the influencing factors of metamorphosis and survival of clams’ larvae.The basic biology of clams was studied from May 2021 to May 2022.The main research results are as follows:1.Changes in biochemical composition of gonads and larval growth of female hard shell clam under cultivation treatmentAfter the treatment of monocystis,there was no significant change in the fertility and macro parameters of eggs,but the triglyceride content in the gonads of female clams decreased by 20% compared with the control group,while the contents of lecithin and progesterone increased by 20% compared with the control group.The metamorphosis rate of juvenile shellfish in breeding group was significantly higher than that in control group(P <0.05),and the metamorphosis rate of juvenile shellfish in breeding group(12-35%)was significantly higher than that in control group(3-14%).The dead shell length(201-333μm)in rearing group was significantly higher than that in control group(196-263μm)(P < 0.05).2.Effects of bait and sediment on growth,metamorphosis and survival of clams larvaeDifferent diets had no significant effects on the metamorphosis rate and survival rate of larvae(P > 0.05).The attachment speed of larvae in sand substrate was significantly higher than that in control group(P < 0.05).The sediment depth of 3mm significantly increased the growth rate,metamortization rate and foot emergence rate of larvae,and the proportion of juvenile larvae buried above 3mm was significantly higher than that at other depths,and the time of diving in sand increased with the increase of the size of juvenile larvae.3.Effects of probiotics on the growth of clam’s larvaeAfter feeding S2 probiotics(compound with metabolites of Clostridium Butyricum),the proportion of small individual larvae decreased,and the growth rate and metamorphosis rate of larvae increased significantly.At the same time,S2 probiotics had a significant effect on the specific growth rate of hard shell clam larvae from different habitats under different temperatures.The specific growth rate of Tianjin experimental group larvae(25℃)was significantly higher than that of the control group(20℃),while there was no significant difference between the Fujian group larvae(25℃)and the control group(20℃).