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<p>Size grading is a common intervention during the planktonic stage of bivalves, yet its impacts on growth and survival lack practical guidance for aquaculture. The purpose of this study was to investigate the effects of size grading on survival, growth, metamorphosis, and thermotolerance in Manila clams (<i>Ruditapes philippinarum</i>) and its congeneric species, <i>Ruditapes variegatus</i>. Clams were subjected to multiple size-based sorting events during the planktonic stage and sorted into size groups (small group “S,” large group “L,” and control group “C”). The results demonstrated an improvement in the specific growth rate (SGR) and survival rate of both clams within 15&#xa0;days post-grading, particularly for “S” group. L3 and L4 of two clams showed similar trends, maintaining the highest final shell length at 40 and 130 days. For metamorphosis, L3 contributed the highest metamorphosis rate (<i>R. philippinarum</i> 62.00%; <i>R. variegatus</i> 62.67%) and the shortest metamorphosis time (<i>R. philippinarum</i> 4&#xa0;days; <i>R. variegatus</i> 5&#xa0;days). L3 and L4 showed the highest survival rates (<i>R. philippinarum</i>: 76.00%, 72.67%; <i>R. variegatus</i>: 74.00%, 72.69%). These indicated that implementing grading at the third and fourth times (from post-umbo stage to early pediveliger stage) is an effective timing. Furthermore, during the thermotolerance assessments, the L3 and L4 groups of both clam species showed the highest survival rates (<i>R. philippinarum</i>: 30.00%, 28.67%; <i>R. variegatus</i>: 74.00%, 76.00%); and the mean SGR (1.52%/day) and the mean survival rate (70.67%) of <i>R. variegatus</i> were higher than <i>R. philippinarum</i>, suggesting that <i>R. variegatus</i> has greater thermal resistance. The implementation of effective grading strategies during the planktonic stage can enhance better outcomes in clam aquaculture.</p>

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Effects of size grading on growth, survival, metamorphosis, and thermotolerance of two venerid clams (Ruditapes philippinarum and R. variegatus) under farmed conditions

  • 期刊论文

  • 发表日期：

    2026年3月23日

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  • Jinlong Li,
  • Shu Xiao,
  • Xiangzhi Lin,
  • Zhaoping Wang,
  • Zongbao Mu,
  • Xiaodong Zheng

摘要

Size grading is a common intervention during the planktonic stage of bivalves, yet its impacts on growth and survival lack practical guidance for aquaculture. The purpose of this study was to investigate the effects of size grading on survival, growth, metamorphosis, and thermotolerance in Manila clams (Ruditapes philippinarum) and its congeneric species, Ruditapes variegatus. Clams were subjected to multiple size-based sorting events during the planktonic stage and sorted into size groups (small group “S,” large group “L,” and control group “C”). The results demonstrated an improvement in the specific growth rate (SGR) and survival rate of both clams within 15 days post-grading, particularly for “S” group. L3 and L4 of two clams showed similar trends, maintaining the highest final shell length at 40 and 130 days. For metamorphosis, L3 contributed the highest metamorphosis rate (R. philippinarum 62.00%; R. variegatus 62.67%) and the shortest metamorphosis time (R. philippinarum 4 days; R. variegatus 5 days). L3 and L4 showed the highest survival rates (R. philippinarum: 76.00%, 72.67%; R. variegatus: 74.00%, 72.69%). These indicated that implementing grading at the third and fourth times (from post-umbo stage to early pediveliger stage) is an effective timing. Furthermore, during the thermotolerance assessments, the L3 and L4 groups of both clam species showed the highest survival rates (R. philippinarum: 30.00%, 28.67%; R. variegatus: 74.00%, 76.00%); and the mean SGR (1.52%/day) and the mean survival rate (70.67%) of R. variegatus were higher than R. philippinarum, suggesting that R. variegatus has greater thermal resistance. The implementation of effective grading strategies during the planktonic stage can enhance better outcomes in clam aquaculture.