Coryphopterus personatus, a small Caribbean reef goby, is a protogynous hermaphrodite. Unlike the secondarily derived testes of many other hermaphroditic teleost species, those of C. personatus lack a residual ovarian lumen or remnant oocytes, and sperm are produced and
transported through a newly formed, permanent system of anastomosing tubules that comprise the body of the gonad. Functional ovaries have no testicular tissue, but have a small, ventral outfolding situated posteriorly on each gonadal lobe. During sex-change, these outfoldings develop into
apparently secretory structures associated with the newly formed testis. In the laboratory, development of spermiated testes took as little as nine days to occur. In association with gonadal transformation, the genital papilla of sex-changing fish changed in shape, and the second dorsal spine
became greatly increased in length. In natural populations: (1) females outnumber males approximately four to one; (2) male and female size distributions show considerable overlap, but may differ, and; (3) there occur small males which are smaller than the smallest mature females. The testes
of these small males appear to develop from an immature ovariform gonad, and are otherwise indistinguishable from those of males derived from mature females. Sex-change in laboratory groups of females was usually inhibited by the presence of a larger male, but not by the presence of either
smaller males or larger sex-changing females. Multiple occurrences of sex change were frequent in small unisexual experimental groups, and sex-change proceeded most rapidly in the largest female in any group. In all experimental groups, at least one small individual remained female.
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