Studies On Settlement And Metamorphosis Of Larvae And The Growth Of Shellfish Larvae In Paphia Undulata

This paper introduces the effect of salinity、pH and photoperiod on settlement and metamorphosis of larvae in Paphia undulata. The results showed that the effect of salinity and pH was significant, but the photoperiod was not. When water temperature was25.6℃, salinity was in the range of24-33‰, the average survival rate of larvae could reach more than60%, the settlement rate was more than30%; Salinity was in the range of30-33%o, the metamorphosis rate reached46.33%, the average growth rate of larvae was the highest while salinity was33‰. Temperature was25.6℃and salinity was32.7%o, pH was in the range of7.5-8.5, the average survival rate of larvae could reach more than60%, the settlement rate was more than45%; While pH was8.0, the highest metamorphosis rate was39.33%and the optimum pH ranged from8.0to8.5, the metamorphosis rate of control group was the highest in photoperiod experiments, it reached44.3%. The settlement and metamorphosis of larvae were inhibited when the normal rhythm was changed.The Paphia undulata larvae were induced to metamorphose by5different kinds of chemical cues, including three neurotransmitters and two chemical ions, the order of settlement rate was that L-noradrenalin (NE)> Levodopa (L-DOPA)>g-aminobutyricacid (GABA), the order of metamorphosis was that L-noradrenalin (NE)>□-aminobutyricacid (GAB A)> Levodopa (L-DOPA). The concentrations of three chemical drugs were difference. The effective induction concentration of NE was10-500μmol·L-1, the optimum concentration was50μmol·L-1.The effective induction concentration of GABA was0.1-100μmol·L-1, the optimum concentration was10μmol·L-1. The effective induction concentration of L-DOPA was0.01-1μmol·L-1, the optimum concentration was1μmol·L-1It found that NH4+could not improve the settlement rate during the chemical ions research. The higher concentration of NH4+could reduce the metamorphosis rate. Treated with K+(10-20mmol·L-1), the larvae had the most effective metamorphosis, the metamorphosis rate increased by16.34%which the concentration of K+was20mmol·L-1, but the improvement of settlement rate was not obvious. The suitable temperature for young growth ranged from18℃to32℃, and the optimal temperature ranged from26℃to30℃. The suitable salinity ranged from20%o to40%o, and the optimal salinity ranged from28%o to32%o.The young mollusk tolerated with high-salt stronger than low-salt. The death rate was not effected with high density breeding, but it effected significant to the growth rate. High density breeding reduced the average individual food intake. The growth of individual was influenced directly. It found that substratum which was mud mixed sand was suitable to the young mollusk. Silt content got at about50%, the silt deeper, the more conducive to the growth.Response surface methodology is used to analyze the conditions of growth, it found temperature and salinity, salinity and density impacted on the growth significantly, but the effect of temperature and density were not significant, the salinity was the most critical to the growth. Optimum environment combination was that temperature was26.93℃, salinity was31.39%o, the density was1.12ind/cm2. The theoretical optimal growth rate was41.47%, after the experiment, the growth rate was42.30%.The experimental results conform to predicted value.