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Coral Reef Fishes

Coral reef fishes are perhaps the most obvious, colorful, and fascinating of all the myriad creatures that inhabit the coral reef biome.

Queen angelfish. © Fotolia.com

This group of animals includes members of two different classes of vertebrates: the bony fishes (Class Osteichthyes) and the "cartilaginous fishes" (sharks and rays; Class Chondricthyes). The vast majority of common coral reef fishes are bony fishes.

In the Greater Caribbean region some 500-600 species of fishes associated with coral reef ecosystems are recognized, whereas the Indo-Pacific region as a whole houses perhaps 8-10 times that number. The reasons for the extraordinarily high diversity among coral reef fishes are not well understood, and remain a topic of considerable debate among reef fish ecologists.

Coral reef fishes are perhaps the most obvious, colorful, and fascinating to watch of all the myriad creatures that inhabit these amazong marine ecosystems. The sheer number and variety in form, coloration, and behavior of these fishes provides endless appeal to scuba divers, snorkelers, and underwater photographers like no other members of the reef community.

Coral Reef Fish Feeding Types

A common and useful (from an ecological perspective) way of analyzing the highly diverse fish assemblages inhabiting coral reefs is by categorizing the many species into a few basic groups based upon feeding habits.

Feeding types of coral reef fishes have been classified in various ways, but we will herein discuss four basic types: herbivores, planktivores, benthic carnivores, and piscivores.

The four basic feeding strategies described below are not necessarily mutually exclusive; some "herbivores" may sometimes feed on small animals, while some "piscivores" may also take larger invertebrates. Some species may feed as planktivores or benthic carnivores while young, but switch to a piscivorous lifestyle as adults. Larval reef fishes that have yet to settle on reef habitat often have a very dirfferent feeding mode than they will after achieving reef residency.

Herbivores

Herbivorous coral reef fishes are those that feed mainly or entirely on plant material found within coral reef ecosystems. Most of the biomass of herbivorous fishes found within coral reef ecosystems is distributed among only a few major groups in both the Indo-Pacific and Greater Caribbean regions. These are discussed below.

Parrotfishes are the largest and most colorful of herbivorous coral reef fishes. Their name is derived from the brilliant hues displayed by many species, and the beak-like mouths that characterize the group. The cutting edge of the beak is used to scrape microscopic and macroscopic algae from coral surfaces. At night, parrotfish secrete a protective mucous envelope that surrounds their bodies as they sleep within reef crevices. The "cocoon" is believed to deter detection by predators.

Surgeonfishes and the closely related rabbitfishes (see below) are the mid-size models of herbivorous coral reef fishes. The name "surgeonfish" is derived from the retractable scalpel-like spines located near the base of each side of the tail. These are formidable defensive weapons. Surgeonfishes browse the reef in search of suitable algae during the day, but retreat to reef crevices after dark. Some species feed in mainly in schools, while others roam the reef to feed as solitary individuals.

Rabbitfishes are named for their blunt snouts.. They are common members of coral reef fish assemblages throughout the Indo-Pacific region from Hawaii to the Red Sea, but are entirely absent from coral reefs of the Greater Caribbean region. Although rabbitfishes they lack the retractable tail spines of the surgeonfishes, they are still well-armed. Numerous strong spines and dorsal and anal fins connected to venom glands are capable of delivering a painful toxin.

Dameslfishes: Unlike the parrotfishes, surgeonfishes, and rabbitfishes that are wide-ranging nomadic browsers, small herbivorous damselfishes are more sedentary territorial "farmers" that maintain and vigorously guard small patches of algae on the reef. They seldom stray more than a few feet from their homes and will aggressively attack any fish, regardless of size, who has the audacity to intrude upon their territories. Even large parrotfishes retreat from such attacks.

Planktivores

Planktivorous coral reef fishes are those that prey upon small animal plankton (zooplankton). There are several widely used strategies to this mode of feeding.

Open Water Plankton Feeders: The daytime open-water plankton feeding "fraternity" of coral reef fishes consists of a hodgepodge of species of diverse heritage, including specialized species of damselfishes, wrasses, snappers, sea basses, and surgeonfishes. These fishes have adapted to an atypical lifestyle and bear little superficial resemblance to most other members of their respective groups (compare the blue chromis pictured left with the territorial herbivorous damselfish pictured above).

Benthic Planktivores: A diverse assemblage of small daytime plankton feeders do so while remaining close to the reef or other nearby benthic habitats. In such places, plankton concentrations have already been diminished by other predators. But this drawback is compensated for by the safe retreats afforded by nearby reefs or tunnels. Among this group are the jawfishes (pictured left), which feed by day on passing plankton while peering from the safety of their tunnels.

Nocturnal Planktivores: Opportunities to feed are not wasted in on coral reefs. As darkness falls, the "day shift" of planktivorous coral reef fishes (see above) takes shelter within the reef and are replaced by a "night shift" consistings of different species with adaptations appropriate to low light conditions. The masters of this nocturnal feeding strategy are the small cardinalfishes (Apogonidae) and larger squirrelfishes and soldierfishes (Holocentridae, pictured left).

Benthic Carnivores

The term "benthic carnivores" (also sometimes referred to as benthivores) is used here to describe fishes that prey on a variety of invertebrate animals (and sometimes small fishes) living on or near the reef substrate or nearby sea floor habitats. As a group, benthic carnivores make up the majority of fish species associated with coral reef ecosystems. Below, we present but a few representatives of this highly diverse group of hunters.

Butterflyfishes are among the most common of daytime coral reef benthivores. Most reef benthivores feed by day, and for good reason. During daylight hours, most of their invertebrate prey are motionless and well concealed. Thus, keen eyesight and precise attack movements - abilities only possible under daylight conditions - are a basic necessity for locating and capturing such prey. Such daytime hunters are generally inactive and hidden in the reef after dark.

Triggerfishes (pictured left) are members of an entire order (Tetraodontiformes) of coral reef fishes that has evolved to become specialized masters of this hunting strategy. Also included in this group are the filefishes, trunkfishes, and puffers. All have the keen eyesight, precise movements, and specialized mouths needed to excel at this lifestyle, as well as formidable defenses (e.g., stout spines, toxins) that prevent them from becoming easy prey themselves as they hunt.

Trunkfishes: A relative few benthic carnivores have the capacity to hunt in comparative safety by day out in the featurelss sand and seagrass expanses far from the reef. The heavily armored trunkfishes (pictured left) are one such group. These fearless predators are often seen hunting far from nearby reefs during daylight hours. Their size and covering of thick bony plates rather than ordinary fish scales provides safety from all but the largest of piscivores.

Grunts (pictured left) and certain snappers shelter on the reef by day and venture out into sand plains and seagrass meadows distant from the reef to feed under the cover of darkness. On Caribbean reefs, some species of grunts perform a nightly migration to select foraging areas as far as half mile from the home reef. They disperse to feed as solitary hunters throughout the night, then reassemble and follow underwater trails back to the home reef just before dawn.

Some other common daylight benthic carnivores that hunt and feed on or near the reef include the blennies (Blennidae), gobies (Gobiedae), wrasses (Labridae), and goatfishes (Mullidae).

Piscivores

Piscivorous coral reef fishes are those that prey mainly or entirely upon other fishes. There are three different basic hunting strategies employed by such predators, each requiring different physical adaptations and behaviors. These may be defined as pursuit, stalking, and ambush.

Pursuing Predators are those that rely on sheer speed to run down prey in open water. They are capable of sustained high speed swimming, and bursts of extremely fast attack speeds. Examples include the jacks (Carangidae, pictured left), mackerels, and many sharks. These fishes typically have streamlined torpedo-shaped bodies, sickle-shaped tail fins, and very narrow caudal peduncles (the body area just forward of the tail fin) equipped with lateral keel-like projections.

Stalking Predators utilize stealth to approach their prey before striking. Common coral reef fishes employing this strategy include barracudas, needlefishes, and trumpetfishes. All have slender, elongated bodies that present a minimal profile to the prey when seen head-on, just prior to attack. Their symmetrical posterior fins function like the vanes of an arrow to ensure an accurate strike. These predators also have oversized caudal fins used to quickly accelerate from a hovering position.

Ambush Predators: rely on disguise and stillness to hunt. Their coloration and shapes make them virtually invisible as they wait motionless for unsuspecting victims to wander within striking range. Attacks are generally made at very close range, often less than a body length. Most have very large upturned mouths that can inhale their luckless victims in a single swift gulp. Common ambush piscivores include frogfishes, lizardfishes (pictured left), flatfishes, groupers, and scorpionfishes.

Further Reading

Coral Reef Fishes: Indo-Pacific and Caribbean

Fishes of the Great Barrier Reef and Coral Sea

Caribbean Reef Fishes