The sheer number and variety in coral reef fish form, coloration, and behavior provides endless appeal to scuba divers, snorkelers, and underwater photographers like no other members of the reef community.
This group of animals includes members of two different classes of vertebrates: the bony fishes (Cl. Osteichthyes) and the "cartilaginous fishes" (sharks and rays; Class Chondricthyes). The vast majority of fishes dwelling on coral reefs 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 seen among coral reef fishes are not well understood, and remain a topic of considerable debate among reef fish ecologists.
While entire books can (and have) been written about these animals, here we provide an introduction to two major aspects of of coral reef fish biology and ecology :
General adaptations for life on the reef
Feeding strategies
General Adaptations For Life On The Reef
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 many of the fishes that live in these ecosystems have developed a number of anatomical and other specialized adaptations for life in such environments.
The basic body plan of fishes twhat dwell in reef habitats differs in a number of crucial ways from the basic fish body designs that originated in far different kinds of habitats. The three most notable and common such adaptations are discussed below.
Body Shape
The typical body shape of reef dwelling fishes 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 reef dwelling fishes have evolved a body plan that maximizes their ability to make rapid turns and stop quickly, highly useful traits for an animal attempting to avoid predators in physically complex habitats.
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 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 cumulative effects of the referred adaptations in body architecture is to actually witness the ability of these fishes to escape attacking predators by swiftly and skillfully using the cover afforded by coral reefs.
Adaptive Coloration
Perhaps the most striking of all the adaptations of fishes inhabiting coral reefs is the variety of brilliant and sometimes bizarre color patterns that adorn these animals.
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 dwelling fishes have been debated for some time.
Many reef fish color patterns are intended to make the bearer less conspicuous to predators or potential prey. Coloration may also be used for species recognition, to facilitate mating success.
Sometimes, territorial reef fishes or those possessing venomous spines or flesh display "warning patterns" (see photo, left) that enhance recognition by likely enemies or competitors.
Reef fishes are not born with the knowledge that one kind of fish makes a fine meal while another kind will mean trouble if attacked, ingested, or even approached too closely. However, after experiencing the unpleasant results of an encounter or two with such "protected" species, other fishes quickly learn to avoid them.
Common adaptive coloration in nocturnally active fishes generally consists of uniform reddish hues, which appears very dark under low light.
Feeding Structures
With the unusual variety of prey items available, it is not surprising that the adaptations found in reef-dwelling fishes include highly specialized jaws, mouths and teeth suited to particular kinds of food sources commonly found in coral reef habitats.
Not surprisingly, eating and digesting plant material requires specialized feeding structures and digestive systems that differ considerably those of meat eaters (carnivores).
For example, the parrotfishes (Scaridae; pictured left) have evolved beak-like mouths perfectly suited for scraping algae from hard coral surfaces.
In contrast, butterflyfishes have evolved forcep-like mouths armed with numerous fine teeth well suited to nipping exposed coral polyps.
Still, many other common reef 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.
Other Adaptations
The number and complexity of adaptations found in fishes inhabiting coral reefs is far too great to even begin to approach on a single web page; indeed, that topic alone could fill a sizeable entire web site. Here, by way of concrete example, we present just one such case of an adaptative response of these fishes to deter predation - in this case, both chemical and behavioral.
Anemones are common coral reef animals, equipped with a formidable defense mechanism - tentacles bearing stinging cells called nematocysts. Some coral reef dwelling anemones form close symbiotic relationships with other animals, most notably certain fishes as well as some shrimps and others.
The clownfish (left) is a coral fish that has adapted to shelter among anemone tentacles. It does this by first performing a ritualistic "dance" with a potential host anemone, lightly brushing up against the tentacles to initiate the relationship.
Special chemical contained within the mucus layer enveloping the skin of the clownfish have the capacity to block anemone nematocyst stings. Because the anemone host normally feeds on fishes, the clownfish thereby gains protection from predators. In exchange, the clownfish cleans its host from parasites.
Coral Reef Fish Feeding Types
Feeding types among reef fishes have been classified in various ways, but here we will consider four basic types of feeders: herbivores, planktivores, benthic carnivores, and piscivores.
These categories are not mutually exclusive. For example, many so-called "herbivores" sometimes feed on small animals, while some "piscivores" may also occasionally take larger invertebrates. Some species may feed as planktivores while young but switch to a piscivorous lifestyle as adults.
Herbivores
Herbivorous fishes are those that feed mainly or entirely on plant material. 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 coral reef herbivores. Their name stems from the brilliant hues and beak-like mouths that characterize the group. The cutting edges of the beaks of these herbivores are used to scrape algae from coral surfaces. In so doing, some coral tissue is also ingested.
Surgeonfishes and the closely related rabbitfishes (see below) are the mid-size models of herbivorous coral fishes. The name "surgeonfish" stems from the retractable scalpel-like spines at the base of each side of the tail. These are formidable defensive weapons that can deliver serious wounds.
Rabbitfishes are named for their blunt, elongated snouts. These herbivores are closely allied with the surgeonfishes, and are common members of reef fish assemblages throughout the Indo-Pacific region from Hawaii to the Red Sea. However, they are entirely absent from coral reefs of the Greater Caribbean region.
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 - even against much larger fish foes. 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 fish consists of a hodgepodge of species of diverse heritage, including specialized genera and species of damselfishes (see Chromis, left), wrasses, snappers, sea basses, and surgeonfishes.
Benthic Planktivores: A diverse group of small daytime plankton feeders - such as the jawfish - hunt their tiny prey while remaining close to the safety of the reef or other nearby benthic habitats. The price of such security is less food, since the incoming plankton concentrations have been diminished by other predators.
Nocturnal Planktivores: As darkness falls, the "day shift" of planktivores seeks shelter within the reef and are replaced by a "night shift" of species adapted to low light conditions. These night hunters include cardinalfishes (Apogonidae), along with 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 animals living on or near the sea floor. As a group, benthic carnivores make up the majority of fish species associated with coral reef ecosystems.
Butterflyfishes are among the most ubiquitous and colorful of daytime reef benthivores. Their forcep-like mouths armed wih fine comblike teeth serve them well in browsing on exposed coral polyp tentacles and other tiny reef invertebrates. Their flattened bodies are highly manuverable in the complex reef environment. 
Triggerfishes (pictured left) are members of a reef fish order (Tetraodontiformes) that has evolved to become masters of this hunting strategy. Also included in this group are the filefishes, trunkfishes, and puffers. All are slow swimmers, but possess effective anti-predator defenses like stout spines or toxins.
Trunkfishes: Few benthic carnivores have the capacity to hunt in safety by day out in the featurelss sand and seagrass expanses far from the reef. The heavily armored trunkfishes are an exception. These fearless predators are often seen hunting for shelled benthic invertebrate prey far from nearby reefs.
Many species of Grunts shelter on the reef by day and venture out into sand plains and seagrass meadows distant from their "home" reef to feed under the cover of darkness. On Caribbean reefs, some species perform a nightly migration to foraging areas up to half mile from their "home reef" where prey is more plentiful.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 fish 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. These fishes have streamlined bodies, and are capable of extremely fast attack speeds. Examples include the jacks (Carangidae, pictured left), mackerels, and many sharks. 
Stalking Predators utilize stealth to approach their prey before striking. Common coral reef fish 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.
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 stray into striking range. Common ambush piscivores include frogfishes, lizardfishes (pictured left), flatfishes, groupers, and scorpionfishes.