Fish spawn in one of two ways:
1. External fertilisation of eggs
This is the most common method and involves either:
- males and females simultaneously releasing eggs and sperm into the water, or
- the female laying eggs onto a surface (gravel or snag etc) which the male then fertilises.
2.Internal fertilisation of the eggs
Cartilaginous fishes such as sharks and rays use this method and lay eggs or give birth to live young. Introduced species such as mosquitofish (Gambusia holbrooki) are the only other species in Australian waters to use this method.
Contrary to popular belief, most popular coastal recreational fish do not spawn in estuaries!
Spawning habitats vary greatly. Fresh and saltwater fish move within and between waters to seek out mates and suitable habitat to spawn. The Australian bass (Macquaria novemaculeata) is the only popular recreational fish that uses estuaries for spawning. The saltwater and estuarine species most fishers are familiar with spawn outside the estuary, usually in in-shore areas.
Freshwater fish such as the crimson-spotted rainbowfish (Melanotaenia duboulayi) lay sticky eggs which attach to fringing vegetation; others such as Murray cod (Maccullochella peelii) seek out clean surfaces of hollow logs upon which to lay their eggs. Australia bass are different: they lay planktonic (tiny floating) eggs in brackish tidal reaches and estuaries that are carried with the tides and currents out to sea.