Comparative embryogenesis of Australian and South African viviparous clinid fishes (Blennioidei, Teleostei)

Abstract

The study follows the embryogenesis of 16 species of viviparous clinid fishes (Clinidae, Teleostei), from the Cape south coast of South Africa and from Australia, with comparative remarks on the development of juveniles in oviparous species. The sperm intromitted into the female duct fertilise the eggs within the follicles. The embryos then develop in individual follicles, nourished by nutrients derived from the mother, until they are mature for release. During the reproductive season in the South African genera Clinus and Muraenoclinus, the female's ovaries harbour eggs and embryos at various stages of development, whereas in species of the Australian genera Heteroclinus and Cristiceps, most embryos in each ovary are at an approximately equal stage of development. The ovaries of the studied species fall into two groups: species of Heteroclinus and Cristiceps that produce numerous small eggs, and species of Clinus and Blennophis that produce fewer, larger eggs. As a consequence, Heteroclinus spp. and Cristiceps spp. bear and release high numbers of smaller embryos, of c. 10-13 mm long, whereas others (e.g. Clinus superciliosus, C. cottoides) bear fewer embryos, of up to 22 mm long. The organogenesis of various organs is described, with particular emphasis on chondrification and ossification. The onset of gut, sensory organ and skeletal development in Heteroclinus and related species occurs in embryos of 2.5-3.0 mm, whereas in Clinus spp. organ development starts in 5.0-6.0 mm embryos, and occurs in parallel both in the head capsule and at the caudal ends. Consequently, the pace of embryogenesis in the studied Australian small-egg species is faster in several aspects, and their embryos at the time of release are smaller than those of the large-egg species. The developmental sequences and related phenomena are discussed.

Keywords:

• clinid fishes
• comparative embryogenesis
• intrafollicular gestation
• skeletal ossification
• viviparity