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<p>Japanese temperate bass <i>Lateolabrax japonicus</i> is an euryhaline marine fish of commercial importance, but its feeding habits during the planktonic larval period remained unknown. To reveal feeding habits of <i>L. japonicus</i> larvae, ichthyoplankton was sampled by stratified hauls of a plankton net in Tango Bay throughout the midwinter spawning period from January to March 2020. Water temperature decreased from ca. 14 to 12ºC during the sampling period. <i>Lateolabrax japonicus</i> dominated in the larval fish community earlier, while it was replaced mainly by marbled rockfish <i>Sebastiscus marmoratus</i> later, indicating their respective spawning peaks. Gut contents were removed from each specimen, identified morphologically, and compared between co-occurring <i>L. japonicus</i> and <i>S. marmoratus</i>. In both fish species, feeding habits were not clearly related to vertical distribution but to fish size (i.e., notochord length, NL). Feeding incidence increased progressively from &lt;10% in small larvae (&lt;3 mm NL) to 100% in large larvae (&gt;7 mm NL). Copepods numerically accounted for &gt;95% of prey items identified in both fish species: with increasing NL, copepod eggs decreased, while copepod nauplii remained almost constant and copepodites/adults increased in numerical contribution. Large-sized calanoids dominated in each developmental stage of copepods, possibly indicating selective feeding by the fish larvae on larger copepods. Despite such close similarities, <i>L. japonicus</i> showed a higher dependence on larger prey items (&gt;1 mm) once the larvae started to feed on them at 6.5 mm NL, while <i>S. marmoratus</i> showed no clear dependence on them even though the larvae started to feed on them as early as at 5.0 mm NL. Moreover, although the number of prey items per gut increased continuously with increasing NL in <i>S. marmoratus</i> larvae, it remained one third smaller than what previous studies found in spring. These results may indicate that <i>L. japonicus</i> larvae show a higher dependence on larger prey items as an ecological specialization in winter, although information about prey availability is necessary for further discussion. In contrast, <i>S. marmoratus</i> larvae may have difficulty in demonstrating their best performance under harsh winter conditions, such as low water temperature and low prey availability.</p>

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Midwinter feeding habits of co-occurring planktonic larvae of Lateolabrax japonicus and Sebastiscus marmoratus in Tango Bay, Sea of Japan

  • 期刊论文

  • 发表日期：

    2026年2月4日

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  • Keita W. Suzuki,
  • Manami Hirata,
  • Hiroto Nakajima

摘要

Japanese temperate bass Lateolabrax japonicus is an euryhaline marine fish of commercial importance, but its feeding habits during the planktonic larval period remained unknown. To reveal feeding habits of L. japonicus larvae, ichthyoplankton was sampled by stratified hauls of a plankton net in Tango Bay throughout the midwinter spawning period from January to March 2020. Water temperature decreased from ca. 14 to 12ºC during the sampling period. Lateolabrax japonicus dominated in the larval fish community earlier, while it was replaced mainly by marbled rockfish Sebastiscus marmoratus later, indicating their respective spawning peaks. Gut contents were removed from each specimen, identified morphologically, and compared between co-occurring L. japonicus and S. marmoratus. In both fish species, feeding habits were not clearly related to vertical distribution but to fish size (i.e., notochord length, NL). Feeding incidence increased progressively from <10% in small larvae (<3 mm NL) to 100% in large larvae (>7 mm NL). Copepods numerically accounted for >95% of prey items identified in both fish species: with increasing NL, copepod eggs decreased, while copepod nauplii remained almost constant and copepodites/adults increased in numerical contribution. Large-sized calanoids dominated in each developmental stage of copepods, possibly indicating selective feeding by the fish larvae on larger copepods. Despite such close similarities, L. japonicus showed a higher dependence on larger prey items (>1 mm) once the larvae started to feed on them at 6.5 mm NL, while S. marmoratus showed no clear dependence on them even though the larvae started to feed on them as early as at 5.0 mm NL. Moreover, although the number of prey items per gut increased continuously with increasing NL in S. marmoratus larvae, it remained one third smaller than what previous studies found in spring. These results may indicate that L. japonicus larvae show a higher dependence on larger prey items as an ecological specialization in winter, although information about prey availability is necessary for further discussion. In contrast, S. marmoratus larvae may have difficulty in demonstrating their best performance under harsh winter conditions, such as low water temperature and low prey availability.