Effects of Stocking Density and Diets on Growth, Survival, Settlement and Metamorphosis of Ruditapes philippinarum Larvae

To explore optimal large-scale breeding conditions of artificial Manila clam (Ruditapes philippinarum) seedlings, the effects of different stocking density and diet species on the growth, survival, and attachment metamorphosis of R. philippinarum larvae were investigated. Four cultivation density gradients (5, 10, 15 and 20 ind./mL) and four groups of diets (Group A Lsochrysis galbana, Group B Chaetocerossp, Group C Lsochrysis galbana + Chaetocerossp 1:2, Group D Lsochrysis galbana + Chaetocerossp 2:1) were set up. The larval shell length and survival rates were measured on the 3rd, 9th, 18th, and 27th days. The larval settlement and metamorphosis rates were evaluated on the 27th day. The results indicated that the larval shell length of (0.968±0.002) mm in diet group A was the largest on day 3. The shell length of (0.102±0.013) mm in the medium density group (10 ind./mL) was the largest, which was significantly higher than that of other density groups (P < 0.05). The survival rate of bait group A (26.67%) on the 18th day was the lowest, which was significantly lower than that of the other groups. There was no significant difference in the survival rates between group C and group D, but the survival rates of group C and group B were significantly higher than those of group A and group B. There was no significant difference in the survival rate between the density groups of 5 ind./mL and 20 ind./mL; however, they were significantly lower than those of density groups of 10 and 15 ind./mL. In terms of settlement and metamorphosis, the mixed diets groups of C and D were significantly higher than those of diet groups of A and B. The density group of 15 ind./mL had the highest settlement and metamorphosis rate (17.38%), followed by 16.65% in density group of 10 ind./mL. For larval settlement and metamorphosis rates, there was no significant difference between density groups of 15 and 10 ind./mL, but significantly higher than those in density groups of 5 and 20 ind./mL. The results showed that larvae fed at early opening with Lsochrysis galbana had the highest survival rate, and larvae fed with the mixed diets showed the highest growth and metamorphosis rates. Therefore, the culture density of larvae should be maintained between 10–15 ind./mL. In summary, artificial seedling rearing of R. philippinarum, larval density should be maintained at 10–15 ind./mL. To obtain the most suitable condition for larval growth and survival, a Lsochrysis galbana diet should be selected for the early development stage and mixed diets should be adopted for the late development stage. These results provide the necessary scientific basis for the environmental factors of R. philippinarum larval growth and development and have important guiding significance and application value for improving the seed yield per water unit and stable production of seedlings of clams.