Reef fishes have developed a diversity of reproductive strategies to maximize survival of their offspring.

They have an enormous fecundity compared to higher vertebrates.
Depending on the species, they can spawn clutches of eggs daily, weekly or monthly or a few times a year. Spawning is secretive and typically only occurs during very specific and brief periods throughout the day.

The majority of reef fishes spawn into the water column (pelagic eggs) or on the bottom (demersal eggs).

Pelagic spawners shed their eggs directly into the water column after rising off the bottom. Such eggs are usually small, transparent and spherical and always slightly buoyant which allows them to be dispersed by currents.

Pelagic spawning is the most taxonomically widespread spawning strategy among reef fishes. It is characteristic of thirty-six reef fish families, including popular aquarium fish groups such as the tangs and surgeonfishes, butterflyfishes, wrasses, hawkfishes, and all marine angelfishes.

Demersal spawners, by contrast, lay their eggs in a pre-selected area on the bottom and care for them until they hatch. The area and nature of the nest depends on the species. The majority, like the damselfishes, blennies gobies attach their nest onto a substrate.

A pair of demersal spawners (Fiji blue devil damsels). As female deposits her eggs the male fertilizes them.

A few groups lay eggs balls (e.g. dottybacks), others build nests to hold their eggs (e.g. fairy basslets), and some even brood their eggs orally (e.g. most cardinal fishes) or in a pouch (e.g. seahorses). In all cases the male incubates and defends the eggs until they hatch. A few reef fishes, like the rabbitfishes, are egg scatterers and spawn sinking (demersal) eggs that are randomly scattered across the bottom.

Fecundity and the survival of reef fish offspring are usually inversely related. Generally, pelagic spawners place their reproductive effort into spawning frequency and/or egg numbers, producing large numbers of eggs with a spawning season.

For example, the pygmy angelfishes spawn every evening each time producing up to 2,000 eggs. Groupers spawn less frequently but when they do they produce millions of eggs.

Pelagic eggs are tiny (less than 1 mm for most pelagic spawning species) and soon after being fertilized (usually within 24 hours). At hatching the larvae are small and poorly developed and therefore have a slim chance of survival. Pelagic spawners therefore reproduce at times when environmental conditions maximize survival of the offspring.

Many spawn at dusk to avoid predators. Others spawn with outgoing tides so that the eggs are rapidly transported from the predacious reef environment. Still others combine this strategy with a full moon to allow the newly hatched larvae to feed at night.

Demersal spawners place their reproductive effort into egg quality and parental care. Generally these eggs are pigmented, have more yolk and take longer to hatch than pelagic eggs. The newly hatched larvae are also more developed and usually go through a shorter larval phase. This gives them a better chance of survival.

For example, clownfishes spawn nests near every two weeks averaging about 600 eggs per nest. The eggs hatch after 7 days during which time the male care for them. Newly hatched clownfish larvae have the physiology (functional eyes, fins, mouth, stomach ect.) to escape predators and can feed within 25 hours. Their larval phase lasts for only 15 days.

Angelfish larvae, by comparison, are in an almost helpless state at hatching, without pigmented eyes, mouthparts and only partially functional fins. These develop for several days (three or more) before the larvae can properly escape predators and start feeding. Angelfish larvae can take anywhere from 35 to over 100 days to become juveniles. (See comparison in figure below).

	Top: A newly hatched clownfish larva
	Bottom: A newly hatched angelfish larva