Hermaphroditic Characteristics of Gonad Morphology and Inferences Regarding Reproductive Biology in Caracanthus (Teleostei, Scorpaeniformes)
Caracanthus typicus and Caracanthus unipinna are small, obligate coral-dwelling, scorpaeniform fishes (F. Caracanthidae). In the majority of individuals in these two species, the male gonad is an ovotestis with several ovarian features, including an apparently nonfunctional gonadal lumen and the frequent presence of healthy-appearing oocytes. In addition, it has a feature typical of secondary testes in the form of peripheral sperm sinuses located within the ovotestis wall. These features collectively suggest that males in these two species arise secondarily from females. Males and females of both species also have an unusual gonad architecture in which the gametogenic tissue is almost entirely surrounded by a peripheral lumen for much of its length. Among females, maturing oocytes project into the ovarian lumen on stalks of stromal tissue and the periphery of the gonadal lumen is lined with a distinctive tall columnar epithelium consistent with a secretory function. Such ovarian features present in three other scorpaeniform species are associated with the release of eggs that are bound together in a gelatinous matrix to form floating egg masses. The presence of such features in female C. typicus and C. unipinna suggests that Caracanthus may have a similar mode of reproduction.Abstract
Ovarian histostructure of Caracanthus typicus. (A) Cross-section of ovarian lobe of an adult female showing a solid gonadal wall (w) and a central compact body of ovigerous tissue (ot) surrounded in its entirety by a gonadal lumen (l); magnification is 50×; (B) higher magnification (95 ×) showing a maturing vitellogenic oocyte (vo) supported by a vessel-bearing pedicel, extending out into the surrounding lumen and directly adjacent to the tall columnar epithelium (e) lining the ovarian wall; also in view are numerous early-stage previtellogenic oocytes (po); (C) collapsed ovarian follicles (f) within the lumen amidst maturing vitellogenic oocytes (vo); magnification is 95 ×; (D) detail of tall columnar epithelium (e), which is in close proximity to a vitellogenic oocyte (vo) and which both lines the ovarian wall (w) and forms the periphery of the gonadal lumen (l) for adjacent ovarian lobes narrowly separated by the abdominal cavity (ac); magnification is 200 ×
Ovarian histostructure of Caracanthus typicus. (A) Detail of a late-stage vitellogenic oocyte and surrounding ovarian follicle (ov) locally extending away from the oocyte and in direct contact with the tall columnar epithelium (e) of the ovarian wall (w); l is gonadal lumen and ac is abdominal cavity; magnification is 300 ×; (B) ovarian wall epithelium (e) showing apparent deterioration in an ovary containing numerous collapsed follicles (f); l is gonadal lumen and ac is abdominal cavity; magnification is 180 ×; (C) cross-section of an ovarian lobe through the anteriormost region where ovigerous tissue (ot) is in direct contact with the ovarian wall (w) and where blood vessels enter and exit the ovary; l is gonadal lumen; magnification is 95 ×; (D)detail of extensive vascularization in the central stromal region (s) of the ovigerous tissue showing numerous thick-walled (i.e., arterial) and thin-walled (i.e., venous) blood vessels (bv) as well as large, thin-walled blood sinuses (bs) filled with blood cells; magnification is 250 ×
Ovotestis histostructure of Caracanthus typicus. (A) Cross-section of ovotestis lobe of an adult male showing a compact body of spermatogenic tissue (ts) consisting predominantly of testis tubules centrally and early-stage oocytes (oc) peripherally; germ cell tissue is surrounded in its entirety by a gonadal lumen (l), which is enclosed by a broad gonadal wall (w) partitioned into numerous longitudinal sperm sinuses (ss) filled with spermatozoa (sp); magnification is 85 ×; (B) detail of peripherally located testis tubules (st) consisting of spermatocysts of male germ cells in various stages of development surrounding a central channel (for transport of spermatozoa) and the frequent presence on the outer margins of early-stage oocytes (oc); l is gonadal lumen; magnification is 130 ×; (C) detail of ovotestis wall consisting of thin-walled sperm sinuses (ss) filled with spermatozoa (sp) and adjacent testis tubules consisting of various developmental stages of male germ cells as well as healthy previtellogenic oocytes (oc); l is gonadal lumen; magnification is 175 ×; (D) cross-section of the ovotestis lobe of a fish from an experimental large-fish pair, showing predominantly ovarian germinal tissue organized in the form of numerous lamellae (gl) projecting into and surrounded by the gonadal lumen (l); the gonadal wall (w) is relatively narrow and contains numerous small-diametered sperm sinuses (ss) containing small amounts of spermatozoa; magnification is 70×