Coral Reef Fish

Coral reef fish are perhaps the most obvious, colorful, and fascinating to watch of all the myriad creatures that inhabit these fascinating ecosystems.

The sheer number and variety in form, coloration, and behavior of these amazing animals provides endless appeal to scuba divers, snorkelers, and underwater photographers like no other members of the reef community.

Hundreds of fish species may occupy a surprisingly small area of the reef. Many of these are small, well camouflaged, or hidden, masking their true numbers at any given location.

Surgeonfishes are common coral reef fishes. Photo courtesy NOAA.

Fishes are dominant animals at the top of the food chain in all three primary coral reef zones, and assessing their true numbers or diversity is a daunting task, even for the most seasoned professional marine biologists.

Adaptations

Coral reefs are uniquely complex and colorful marine environments, with a physical structure radically different than that of the open waters that comprise 99% of the world's oceans. Therefore, it is not surprising that the fishes that live in these ecosystems have developed a number of specialized adaptations for life in such environments.

A. Body Shape

The typical coral reef fish body shape differs substantially from that of most open water fishes. The latter are generally built primarily for sheer speed, and have evolved appropriate torpedo-like shapes that offer low frictional resistance (drag) to movement through water.

In the complex coral reef environment however, a premium is placed upon maneuverability rather than sheer speed. Thus, many coral reef fishes have evolved a body plan that maximizes their ability to make rapid turns, and to stop quickly.

These are highly useful traits for an animal attempting to avoid a swift predator in a physically complex environment.

By quickly dodging into fissures in the reef, swiftly circling around coral heads, or coming to a sudden halt next to a solid object (like a hard coral colony), prey can more readily avoid predators that lack such abilities.

The essence of this design scheme is a deep and laterally compressed body (shaped like a pancake), exemplified by the common angelfish (pictured above).

A less obvious but critical aspect of this altered body plan includes a shift (compared to open water fishes) in the placement and orientation of the pectoral and pelvic fins.

These changes to the main steering fins of reef fishes act in concert with the flattened body shape to maximize maneuverability, including the ability to make sharp turns and sudden stops.

The only way to truly appreciate the combined effects of the adaptive changes in body architecture of reef fishes is to actually witness their ability to escape attacking predators by swiftly and skillfully using the cover afforded by coral reefs.

B. Coloration

Perhaps the most striking feature of coral reef fishes is the variety of brilliant and sometimes bizarre color patterns that adorn them.

In many cases these color patterns contrast starkly with the usual color patterns of open water fishes which typically are monochromatic or silvery, as befits the backgrounds against which they are normally seen.

The reasons for the unusual color patterns seen in coral reef fishes have been debated for some time.

In some cases, the patterns are meant for concealment under certain conditions, as when the fish is resting in particular kinds of places.

In other cases, coloration may be used in species recognition to assure mating success.

Sometimes, fishes possessing venomous spines or flesh display "warning patterns" that enhance recognition by likely predators. Predators are not born with the knowledge that one kind of fish makes a fine meal while another kind will be a most unwelcome surprise if attacked or ingested. However, after experiencing the unpleasant results of attacking such protected prey, predators quickly learn to avoid hunting these species.

C. Feeding Structures

With the unusual variety of prey items available, it is not surprising that many types of reef fishes have evolved highly specialized jaws, mouths and teeth suited to particular kinds of food sources commonly found in coral reef habitats.

For example, the parrotfishes (Scaridae; pictured right) have evolved beak-like mouths suited for scraping algae from coral surfaces.

In contrast, butterflyfishes (Chaetodontidae; pictured above under "coloration") have evolved forcep-like mouths well suited to nipping coral polyps, their primary food source.

Still, many other common reef-dwelling fishes, such as snappers (Lutjanidae) retain a more generalized feeding structure plan that enables them to utilize a wide variety of prey items, including smaller fishes and invertebrate animals.

Feeding Strategies

The feeding strategies of coral reef fishes have been categorized in a number of ways by different researchers, but there remain four basic ways of feeding regardless of the terminology or sub-categories used to describe each of these.

Coral reef fishes may feed primarily as herbivores (plant-eaters), planktivores (plankton feeders), benthic carnivores (predators on animals living on the reef substrate or nearby sea floor habitats), or piscivores (fishes that eat other fishes).

As noted elsewhere, these basic categories are not mutually exclusive in all species. For example, some "herbivores" may occasionally feed on benthic animals, while some "piscivores" may also take larger bottom-dwelling invertebrates. Some species may feed as benthic carnivores when young but as piscivores as adults.

Still, each of the four basic feeding types described require different specialized adaptations, and most reef fishes feed primarily or wholly in one of the four ways described here.

In the remainder of this 5-page section, we devote a separate page to each of these types of feeders (see "Related Pages", below).

Diversity and Distribution

The diversity of fishes associated with coral reef habitats is truly amazing. In the Greater Caribbean region there are some 500-600 species recognized, whereas the Indo-Pacific region as a whole houses perhaps 8-10 times that number.

The reasons for this exceptionally high concentration of fish species in coral reef ecosystems are not well understood, and remain a topic of considerable debate among reef fish ecologists.

Of course, the number of coral reef fish species found in a given area or sub-region within these two primary regions of reef development will predictably diminish with that area's distance from the center of biodiversity for the region as a whole.

Further, the number of coral reef fish species found at any particular reef will usually be considerably smaller than the total found in any of the main regions or sub-regions described.

Economic Value

Coral reef fishes contribute to the economies of many coastal and island nations harboring coral reef ecosystems. The harvest and sale of such fishes provides food and livelihoods for many of the residents of such nations.

Additionally, the colorful and diverse assemblages of fishes found on coral reefs are a major attraction for scuba divers and snorkelers, tourists whose vacation travel expenses often represent a significant contribution to the revenues of island nations.

Related Pages

Planktivorous Reef Fishes
Types and adaptations of coral reef fishes that feed on plankton

Herbivorous Reef Fishes
Information and facts about coral reef fishes that feed mainly on plants

Benthic Carnivores
Carnivorous coral reef fishes that feed by hunting prey that dwell on or close to substrates of coral reef ecosystems

Piscivorous Reef Fishes
Reef fishes whose diet consists wholly or mainly of other fishes