Criteria for the Diagnosis of Hermaphroditism in Fishes

TLDR

Hermaphroditism in fish is diagnosed by detecting mature tissues of both sexes within a single gonad or by experimentally inducing self‑fertilization, while sequential hermaphroditism requires multiple indicators such as membrane‑lined testicular cavities, transitional individuals, and specific atretic bodies for protogyny, or degenerating testicular tissue with developing ovarian tissue for protandry, and researchers must exclude alternative explanations because population‑level features like size or sex ratios are unreliable. Experimental manipulation of social systems to produce transitional or sex‑reversed individuals can identify both protogyny and protandry.

Abstract

hermaphroditism can be diagnosed by the presence, within one gonad, of mature tissue of both genders or by experimental induction of self-fertilization. In sequential hermaphroditism (protogyny and protandry), convincing diagnoses will generally require the use of several indicative features. Features strongly indicative of protogyny are: membrane-lined central cavities in testes; transitional individuals; atretic bodies in stages 1, 2, or 3 of oocytic atresia within testes and sperm sinuses in the gonadal wall. The strongest indicators of protandry are transitional individuals whose gonads contain degenerating testicular tissue and developing ovarian tissue. Experimental production of transitional or sex-reversed individuals through manipulation of the social system may identify both protogyny and protandry. Because most indicators may be produced by more than one means, including sequential hermaphroditism, efforts should always be made to exclude alternative explanations for each piece of evidence. Features of population structure, such as bimodal size-frequency distributions with males a different size from females, or sex ratios differing from unity, are not reliable indicators of sexual pattern. Bimodal age-frequency distributions have fewer problems associated with their interpretation than do bimodal sizefrequency distributions.