MEPS 321:245-254 (2006)  -  doi:10.3354/meps321245

Growth-selective survival in piscivorous larvae of Japanese Spanish mackerel Scomberomorus niphonius: early selection and significance of ichthyoplankton prey supply

Jun Shoji1,2,*, Masaru Tanaka1

1Laboratory of Estuarine Ecology, Field Science Education and Research Center, Kyoto University, Sakyo, Kyoto 606-8502, Japan
2Present address: Takehara Fisheries Research Station, Center for Education and Research of Field Science, Hiroshima University, Minato-machi 5-8-1, Takehara, Hiroshima 725-0024, Japan

ABSTRACT: Scombrid fishes are considered to have adopted a survival strategy characterized by fast growth and the ability to consume large prey at an early age. Variability in feeding condition can significantly affect larval growth as early as the post first-feeding stage and may control growth-related survival during the early larval stage. Through otolith microstructure analysis, growth-selective survival was demonstrated for post first-feeding larvae of Japanese Spanish mackerel Scomberomorus niphonius, which exhibit exclusive piscivory, a high growth rate, and low tolerance to starvation. Larvae and juveniles were repeatedly collected in the Seto Inland Sea in June and July from 1997 to 1999. Growth trajectory back-calculated using otolith microanalysis was compared between the survivors (SV) captured in July and the presumed original population (OP) captured in June. Selection for fast-growing larvae was evident during the 5 d after first feeding (Days 5 to 10). More than 90% of the SV had a mean growth rate during Days 5 to 10 (G5–10) > 0.8 mm d–1, and those with G5–10 < 0.8 mm d–1 rarely survived the period. Intensity of selection differed among 3 years. A less intense selection was observed in 1999 when the larval cohort experienced higher prey concentrations and G5–10. Laboratory experiments demonstrated that 1 to 2 d starvation retarded the larval growth during the following larval period, and supported the conclusion that fluctuation in ichthyoplankton prey abundance alters larval survival probability by affecting the larval growth rate within a short period subsequent to first feeding.

KEY WORDS: Scombrids · Spanish mackerel · Scomberomorus · Larvae · Growth-selective survival · Otolith microstructure · Piscivory

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