Comparative study on ovarian structures in scorpaenids: possible evolutional process of reproductive mode

Abstract

The reproductive modes of the Scorpaenidae are extremely varied: oviparity, viviparity, and even spawning of internally fertilized eggs or embryos (zygoparity or embryoparity), as in Helicolenus, are known. The ovarian structure of this family is divided into two types by the arrangement of the stroma and the ovarian cavity. One type is the ovary in which the lamella-like stroma develops from the ovarian hilus located on the dorsal side and where the ovarian cavity is located on the ventral side of ovary, classifi ed as "cystovarian type II-1" by Takano (1989). In the other type, the stroma in the ovary develops radially around the blood circulatory system that traverses the center of the ovary, and then the ovarian cavity surrounds all the ovary, classifi ed as "cystovarian type II-3" by Takano (1989). In the present analysis, previous reports about ovarian structure and the relationship to the reproductive mode of scorpaenids were described, and the ovarian structure of eight genera of Scorpaenidae was examined. The ovary of cystovarian type II-1 is seen only in viviparous genera and is not seen in oviparous genera. However, the cystovarian type II-1 is a general structure in other families of Scorpaeniformes, and this structure could be considered a primitive type of ovary rather than that acquired by the process of evolution from oviparity to viviparity. The ovary of cystovarian type II-3 is seen in all six oviparous genera and the one zygoparous genus examined. The ovary of this type is not found in any other family of teleosts, so it could be a structure originally divided in Scorpaenidae. In the genera having the cystovarian type II-3 ovary, there is a common feature of spawning: a fl oating egg mass encompassed by the gelatinous material. We postulate that the evolution of reproductive mode in the scorpaenid fi shes is as follows: Sebastes and Sebastiscus have a primitive ovary in which viviparity has developed, whereas the genera that spawn a fl oating egg mass evolved the ovarian structure from primitive type to cystovarian type II-3, and further zygoparity, such as in Helicolenus, evolved from them.

Life-history traits of the southern hemisphere eastern red scorpionfish, Scorpaena cardinalis (Scorpaenidae: Scorpaeninae)

“…Findings from the present study suggest that S. cardinalis has a similar reproductive strategy. The morphology of the highly specialised cystovarian Type II-3 ovary in S. cardinalis is consistent with that described for other species within the genus that produce gelatinous egg masses (Munoz et al 2002;Koya and Muñoz 2007). The function of the vascularised peduncles that radiate from the central stroma and are attached to each oocyte is to facilitate ovulation of mature oocytes into the surrounding lumen (Munoz et al 2002).…”

“…Reproduction within the genus Scorpaena is characterised by external fertilisation and production of eggs that are embedded in a gelatinous matrix (Wourms and Lombardi 1992;Koya and Muñoz 2007;McMillan 2007). Findings from the present study suggest that S. cardinalis has a similar reproductive strategy.…”

“…The epithelium of each ovary wall secretes a gelatinous mass into the lumen around the mature oocytes, resulting in hollow, bilobed egg masses being produced. This gelatinous mass provides protection and floatation for oocytes (Koya and Muñoz 2007;McMillan 2007).…”

“…Reproduction within the Scorpaenidae is of particular interest because species within this family exhibit a range of reproductive modes (Koya and Muñoz 2007). Most genera within the Scorpaenidae are oviparous (spawning eggs); however, some are viviparous (giving birth to live young) and others intermediate between these two basic forms.…”

“…The intermediate reproductive mode, termed ovoviviparity, includes internal fertilisation and the spawning of fertilised eggs or embryos. Reproduction within the genus Scorpaena has previously been described as highly specialised, with the oviparous species examined (S. porcus, S. guttata, S. miostoma and S. notata) producing floating gelatinous egg masses (Koya and Muñoz 2007). This reproductive mode is thought to represent a shift from a primitive to specialised mode of oviparity (Wourms and Lombardi 1992) and has been used to infer evolution within the larger family Scorpaenidae (Koya and Muñoz 2007).…”