:: Elasmobranch Egg Capsules ::
Elasmobranchs
are cartilaginous fish such as sharks, skates and rays. There
are only about 1,140 species of cartilaginous fish worldwide
compared to the approximately 25,000 species of bony fish which
people are more familiar with.
Elasmobranchs reproduce using internal fertilisation, whereas
most bony fish spawn externally. These two reproductive strategies
differ in that external fertilisation involves a one off injection
of energy to produce millions of eggs and sperm, while internal
fertilisation involves more energy expenditure on less eggs
and sperm. The embryos resulting from internal fertilisation
consequently are better cared for and consequently have a much
higher chance of survival than those that are left to fend for
themselves from day one.
About 43 percent of elasmobranchs lay egg cases whereas the
remaining 57 percent give birth to live young. When the embryos
are developing within a live bearing species there are a range
of ways that the different species nourish their young- from
feeding on egg yolk to feeding on fellow siblings!
Examples of egg cases that are commonly encountered by divers
around the coast of the South Island are those of the carpet
shark (Cephaloscyllium isabellum), rough skate (Raja nasuta)
and the elephantfish (Callorhinchus milii).
