Glossary

yolk sac

A membranous sac containing yolk attached to the ventral surface of embryos and early larvae in some fishes. Retained for a period post-hatching in those species which form yolk sac larvae.

Related terms

embryo
A young, unborn or unhatched organism in the process of development.
larvae
Plural of larva.
membranous
Relating to, composed of or similar to a membrane.
oil globule
Small, spherical droplet of oil found within the yolk sac of fish larvae. There may be one or more present and the size, positioning, and colour are also variable meaning they can be useful in terms of taxon identification.
ventral
Of, on, or relating to the underside of an animal or plant; abdominal.
yolk
Substance in an animal egg consisting of protein and fat that nourishes the developing embryo.
yolk sac larva
Post-hatching larval stage occurring in many fish species whereby the yolk sac remains attached to the ventral surface for a period. The larva does not feed normally until the yolk is fully-absorbed.
yolk sac viviparity
Form of livebearing in which the larvae are mostly nourished by a yolk sac which is fully-absorbed prior to birth.