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Gonad development and evidence of protogyny in the red-throat emperor on the Great Barrier Reef

Authors

  • K. Bean,

    1. CRC Reef Research Centre-Fishing and Fisheries Project, James Cook University, Townsville, QLD 4811, Australia and
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  • B. D. Mapstone,

    Corresponding author
    1. CRC Reef Research Centre-Fishing and Fisheries Project, James Cook University, Townsville, QLD 4811, Australia and
      † Author to whom correspondence should be addressed. Tel.: +61 7 4781 5113; fax: +61 7 4781 4099; email: bruce.mapstone@jcu.edu.au
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  • C. R. Davies,

    1. CRC Reef Research Centre-Fishing and Fisheries Project, James Cook University, Townsville, QLD 4811, Australia and
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    • Present address: National Oceans Office, GPO Box 2139, Hobart, Tasmania 7001, Australia.

  • C. D. Murchie,

    1. CRC Reef Research Centre-Fishing and Fisheries Project, James Cook University, Townsville, QLD 4811, Australia and
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  • A. J. Williams

    1. CRC Reef Research Centre-Fishing and Fisheries Project, James Cook University, Townsville, QLD 4811, Australia and
    2. School of Marine Biology and Aquaculture, James Cook University, Townsville, QLD 4811, Australia
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† Author to whom correspondence should be addressed. Tel.: +61 7 4781 5113; fax: +61 7 4781 4099; email: bruce.mapstone@jcu.edu.au

Abstract

The gonad development in the red-throat emperor Lethrinus miniatus is described and the first detailed evidence for protogyny in this species provided. The identification of transitional individuals, bimodal sex-specific size-frequency distributions and female biased sex ratios suggest that L. miniatus is most likely a protogynous hermaphrodite. Transitional L. miniatus gonads were characterized by the concurrent degeneration of all oocytes and the proliferation of spermatocysts near the edge of the lamellae, an increase in blood vessels along strands of stromal tissue within the lamellae and the formation of multiple sperm sinuses. The sites of oocyte degeneration and proliferation of spermatocysts were spatially segregated. An increase in blood vessels along strands of stromal tissue within the lamellae of transitional phase gonads is likely to assist in the breakdown of oocytes and the proliferation of spermatocysts. Most mature resting females containing spermatocysts occurred within the transitional size-frequency distribution, suggesting that the presence of spermatocysts in these females may be an early sign of sex change. Oocytes within female gonads were interrupted by filamentous strands of stromal tissue within the lamellae. The testis contained a remanent ovarian lumen but no residual oocytes. Three characteristics of transitional L. miniatus gonads were found to be unusual and described for few other species of coral reef fishes. These included the absence of oocytes within testes, increased numbers of blood vessels, and the presence of strands of stromal tissue within the lamellae.

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