Ks. Cole et Df. Hoese, Gonad morphology, colony demography and evidence for hermaphroditism in Gobiodon okinawae (Teleostei, Gobiidae), ENV BIOL F, 61(2), 2001, pp. 161-173
Gobiodon okinawae is a small-sized, obligate coral-dwelling goby. The major
ity of species in this Indo-Pacific genus exhibit an obligatory association
with branching live corals and a number have been shown to be bi-direction
al hermaphrodites in which adults have the capacity to shift between male a
nd female function. Gonadal histology in G. okinawae demonstrated that all
individuals had either an ovotestis or an ovary. Some females had an ovary
with vitellogenic oocytes, indicating adult female function. Hermaphrodites
having an ovotestis were either functionally male, as evidenced by the pre
sence of spermatozoa or, in one instance, functionally female so judged by
the presence of vitellogenic oocytes. No individuals were found to have mat
ure gametes of both sexes, although a number of hermaphrodites had an inact
ive ovotestis with no mature gametes of either sex. Based on size ranges fo
r fish having different gonad morphologies, individuals in this species app
ear to develop first as a female. They then either mature and function sole
ly as a female, or become hermaphroditic. Findings based on experimentally
maintained individuals suggests that adult hermaphrodites can shift sexual
function in either direction. Accessory gonadal structures (AGS) were found
in both sexes. These consisted of two fully differentiated pairs of lobes,
each compartmentalized internally by lumina and containing PAS+secretions.
The secretions of the dorsally located AGS were colloidal while those of t
he ventrally located AGS were fibrillar and granular in nature. The presenc
e of two sets of AGS among males appears to be characteristic of both Gobio
don and its putative sister genus, Paragobiodon. However, the occurrence of
fully developed AGS in both females and males has not previously been repo
rted and may be unique to G. okinawae.