What Is an FSA?

Fish spawning aggregations may occur for a number of purposes, including spawning, feeding, or protection from predation. A fish spawning aggregation (FSA) is a group of fish gathered for the purpose of reproduction, with individual densities higher than those normally found during non-reproductive periods1.

Why Do FSAs Occur?

Given that so many different fish species spawn in FSAs, there must be some evolutionary advantage to aggregating. Many hypotheses regarding these advantages have been put forth. Spawning in aggregations may help fish find reproductive mates, may maximize mating and fertilization success,2 and may reduce predation on spawning adults3 and eggs. Some species, such as Nassau groupers, may spawn in very large aggregations during only one or two brief periods each year. The advantage of such a spawning strategy may be to overwhelm egg predators (oophages), and to increase egg and larval survivorship. In fact, we currently do not know the reasons behind the timing (when) and location (where) of aggregations, so precautionary management would suggest managers be particularly careful regarding their maintenance.

It has been hypothesized that reef fish spawn in areas where currents favor offshore egg transport, to carry them away from heavy predation zones3. More recent studies have suggested that FSA sites provide conditions for greater larval retention to promote self-recruitment, or recruitment to natal reefs. Since it is unknown which FSA is supplying eggs and larvae to local populations, all spawning aggregations should be protected.

Dog snapper spawning. Photo © Douglas David Seifert

Which Species Form FSAs?

Species within the following reef fish families have been observed to form spawning aggregations:

Serranidae grouper
Lutjanidae snapper
Caesionidae fusilier
Mugilidae mullet
Labridae wrasse
Scaridae parrotfish
Acanthuridae surgeonfish
Siganidae rabbitfish
Carangidae jacks/trevally
Lethrinidae emperor

Species within the following reef fish families are FSA-forming based on anecdotal evidence:

Mullidae goatfish
Pomacentridae damselfish
Pomacanthidae angelfish
Chaetodontidae butterflyfish
Chanidae milkfish
Ephippidae batfish
Priacanthidae bigeye
Scombridae mackerel
Haemulidae grunt
Monacanthidae leatherjacket


For more information, see The Nature Conservancy’s Working Group Report:

Transforming Coral Reef Conservation: Reef Fish Spawning Aggregations Component (download pdf, 536k)


See Full Citations

1 Domeier and Colin 1997

2 Reaka 1976

3 Johannes 1978


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