Comparison of the ovaries and oogenesis of some Australian and South African viviparid clinid fishes (Clinidae, Blennioidei, Perciformes)

Abstract

The ovaries of the studied 16 viviparous blenny species of the fish family Clinidae (Teleostei, Perciformes) from Australia and South Africa, are of the cystovarian type and bilobed, ending in a common short oviduct at the gonopore; they are elongated in juvenile fish, becoming bottle-shaped or oval with maturation and onset of embryogenesis, when they comprise 18–20% of the total body weight. The ovarian lumen is covered by the germinal epithelium, resting on a basal membrane. The primordial germ cells are situated along the inner side of each lobe, juxtaposed internally to the lumenal epithelium. Single primary oocytes or nests of such, each in a follicular envelope and covered externally by the lumenal epithelium forming clusters protruding into the lumen, along which the inoculated sperm settle. Two different types of reproductive strategies are demonstrated by the Australian species of Heteroclinus and Cristiceps and the South African species of Clinus and related forms. The Australian species produce high numbers of small (350 ± 50 µm in diameter) eggs that develop synchronously, while the South African species produce much fewer and larger (1.0 ± 0.1 mm) eggs, asynchronous in development. An exception in the latter group is Blennophis striatus, with eggs of ca.1.4 mm that develop synchronously. The Australian species are thus mass releasers that bear and release up to 1000 small (11 ± 1.5 mm in length) embryos/spawn, while the South African Clinus species are discrete releasers that bear eggs of various sizes and small numbers of mature for release embryos that reach up to 22 mm in length, and are released throughout the year. The cytogenesis of the oocytes and surrounding envelopes is discussed.