Why release so many eggs?

External fertilisation depends on eggs and sperm meeting in the water. Releasing them together can improve the chances and temporarily change the risk of predation. For the same reproductive investment, producing more eggs generally means putting fewer reserves into each one.

Follow the egg. Its fate depends on what it carries and where the water takes it.
Three stages from fish egg to larva.
The sequence runs from the first cell divisions to the hatching of a larva with a yolk sac. © dive.explo360.fr — All rights reserved. Reproduction requires permission.

Inside the egg

Cell division begins before the body axis and organs take shape. Yolk supplies energy to the embryo. Temperature, salinity and oxygen affect its development, and currents carry pelagic eggs through the water. This transport is known as advection.

The first meal

As yolk reserves run out, a larva needs prey it can catch and swallow. The match–mismatch hypothesis proposes that recruitment depends partly on whether suitable prey is abundant at that critical stage.

A fish larva and small prey in the plankton.
The larva approaches a young crustacean. The jellyfish in the background represents a potential predator. Sizes are schematic. © dive.explo360.fr — All rights reserved. Reproduction requires permission.

Larvae can influence where they go

A small shift in depth can bring a larva into water moving in a different direction.

Dispersal reflects both currents and larval behaviour. Some larvae change depth or respond to chemical or acoustic cues. An experiment can show that a larva responds to a cue. How much the cue changes its route at sea is a separate question.

Finding shelter in an unfamiliar habitat

At settlement, the young fish enters a different habitat and faces different risks. In flatfish, one eye moves as the skull is remodelled. A larva that swims upright in open water becomes a juvenile that rests on one side on the seabed.

A young fish near branching coral beside exposed sand.
At settlement, a young reef fish may shelter between coral branches. Different species use different refuges. © dive.explo360.fr — All rights reserved. Reproduction requires permission.

Continue reading

AMIGANSEAU CONTENT

The rest of this article is for subscribers

Log in with your AMIGANSEAU licence to continue reading.

All active AMIGANSEAU licences give access to the full article.

Explore the same world

Explore further