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Aspects of the reproductive biology of Gonostoma bathyphilum (Gonostomatidae)
Author(s) -
Badcock J.
Publication year - 1986
Publication title -
journal of fish biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.672
H-Index - 115
eISSN - 1095-8649
pISSN - 0022-1112
DOI - 10.1111/j.1095-8649.1986.tb04975.x
Subject(s) - biology , sexual maturity , sexual dimorphism , zoology , mating , reproductive biology , population , sex ratio , ecology , mating system , demography , fishery , embryo , sociology , embryogenesis
Protandrous hermaphroditism among deep‐sea fishes is known only within one family, Gonostomatidae, and therein restricted to a few species of two genera, Cyclothone (C. atraria, C. microdon) and Gonostoma (G. elongatum, G. gracile). Gonostoma bathyphilum , the deepest dwelling (700–2700 m depth) of Gonostoma spp., is also protandrous and shares with Cyclothone spp. an expression of sexual dimorphism manifested by the excessive development of olfactory structures, including the olfactory lobes, in ripe males. Sex‐reversal in ripe males, therefore, involves a regression of these structures. The relationships apparent between sex, maturity and olfactory development, and those between animal size, maturity and depth of occurrence, indicate that whilst protandry is an integral component of the species' reproductive strategy some individuals develop directly as females and that among males (max. size 150 mm S.L.) sex‐reversal is not obligatory. Primary females, together with those derived from prematurely reversing males, may form an early maturing female group, spawning for the first time at about 110–120 mm S.L. Most hermaphrodites were < 100 mm S.L., and within the 70–99 mm S.L. size‐range a significant proportion had mature male characters. Since males of this size were all found to be immature, this suggests that these hermaphrodites are derived from a precocious element within the initial male population, and, by virtue of size‐stratification by depth, are responsible for mating with the early‐maturing females. The lack of a marked seasonality in the sexual cycle implies an ever presence of all sexual categories within the population. It is conjectured that sex‐reversal of ripe males is a response to critical population density levels of ripe females and that the smaller, precocious males would be more prone to sex‐reversal than the larger, later‐maturing ones. In some respects protandry in G. bathyphilum is similar to that in G. elongatum. In the latter, however, the reproductive cycle is seasonally linked and sex‐reversal in males is probably obligatory. Even so, critical density levels of ripe females can still be invoked as being causal to sex‐reversal.