Watching fish is probably the most captivating activity that skin divers can engage in. There are hundreds of fish and over 150 species seen regularly by skin divers in Caribbean waters.

Of all the activities snorkelers can enjoy, fishwatching is probably the most enthralling. There are, after all, hundreds of species of fish to observe in Caribbean waters and more than 150 are seen regularly by snorkelers. It’s not that difficult to identify fish but there are a few basic guidelines that can help you get started. Each month, we will present several fish (and other types of marine life), describe their behavior and habitat. This month, we introduce you to fishwatching and present some very common reef fish with uncommon behaviors.

There are distinct day and night shifts on any coral reef. Those fish swimming freely during the day are usually in search of food or protecting their territories. Fish that hide under coral overhangs or crevices during the day are members of the night shift. Dawn and dusk are the “rush” hours of the coral reef, when feeding and reproduction (only at dusk) take place. What a fish does during the day becomes a key behavior point and can help in identifying the particular species.

The second major consideration is shape and body parts. Fish range from long and thin to short and stout. Some are triangular (Trunkfish, for example) and others, such as the Balloonfish, are nearly round. Oval shapes and odd shapes abound. The size of a fish is also important – six inches, a foot or three feet makes a huge difference in species identification.

Long-spine porcupinefish also know as spiny balloonfish - Diodon
Long-spine porcupinefish also know as spiny balloonfish – Diodon

A fish’s color is often the first thing noticed. Color can be misleading, though, since nearly all fish change color during mating, territorial defense, hunting and nesting. Color is just a guideline. Individual markings are more significant and are excellent ways to identify fish. Fish often change both color and markings as they grow from juveniles to adults, adding another layer of complexity to the identification game.

Identification is only the first step in getting to know fish. Learning about a fish’s behavior, especially its diet, is the next step in the familiarization process. Take a look at the four fish on the opposite page. Although they are all approximately the same size and found in the same shallow areas, all have extremely different diets. The angelfish and butterflyfish appear to have the same behavior, swimming around rather majestically and stopping to peck or nibble on parts of the reef. We might assume they eat the same thing. Absolutely not. The angels feast on sponges and the butterflies on tube worms and colonial sea anemones. Likewise, the Blue Tangs only eat algae and the French Grunts (nighttime feeders) feed on small crustaceans on the bottom. When you know what a fish eats, you can start to make sense of when it’s feeding and when it’s defending its territory.

The best way to fishwatch is to study a small section of the reef while staying motionless. Find a particular fish and slowly follow it around. You’ll be fascinated at its range of behaviors. Sometimes it’ll stop at certain areas of the reef and assume a rather rigid posture, with its mouth open. This behavior invites small fish and shrimp to clean parasites off its body. By some unwritten law of nature, the small fish are immune to predators during this activity.

A wealth of fish information is available in the form of slates and books dedicated to fish identification. The bible of fishwatching and fish I.D. is Reef Fish Identification, by Paul Humann and Ned Deloach – a wonderful guide.

[Editor’s Note: Fish are grouped according to family and common name in English. In classic marine biology, there is a family. (shared behavior), genus (shared body characteristics) and species (individual coloration and specific points of physiological difference).!

Foureye Butterflyfish (Chaetodon capistratus). Family: Butterflyfish – Chaetodontidae.

The Foureye Butterflyfish is one of the Caribbean’s most distinctive fish. In addition to its unusual shape, this butterflyfish is easily identified by the ocellus or spot on the rear portion of its body. This false eye is thought to confuse predators, leading them to attack the wrong end of the fish and giving it an easy escape route. Many juveniles have false eyes but they usually outgrow them as they mature – Foureyes keep them for life.

Closeup of Foureye Butterflyfish (Chaetodon capistratus)
Closeup of Foureye Butterflyfish (Chaetodon capistratus)

During the day, Foureyes leisurely cruise the reef in search of food – tube worms and colonial sea anemones. Their odd shaped mouths are perfect for searching crevices to find food.

Foureyes are usually found in pairs and apparently mate for life. During reproduction, the female launches herself toward the surface, followed by the male. At the top of this graceful arc the female releases her eggs, which are then fertilized by the male.

Blue Tangs (Acanthurus coeruleus). Family: Surgeonfish – Acanthuridae.

Blue Tangs

Although these small (six to eight inch) fish are graceful and pretty, all members of the Surgeonfish family have a highly developed natural defense mechanism. The yellow fin at the base of the tail is razor sharp and can extend from the body to slash a predator! Blue Tangs are vegetarians, feeding during the day on algae that grows in dead areas of the reef. They often forage for food in schools.

Queen Angelfish (Holacanthus ciliaris). Family: Angelfish – Pomacanthidae.

These majestic fish are some of the most dramatically colored in the Caribbean. They may appear shy at first but will often observe snorkelers at a close range. These daytime feeders primarily eat sponges. They also eat tunicates and algae. They are usually around a foot long, larger individuals are found on occasion.

Queen Angelfish

Angelfish males are territorial, with the dominant male establishing a courtship area. Males can be identified by their white pelvic fins; the females’ are smaller and yellow. A male may entertain more than one female, suggesting a harem arrangement, but angelfish are often observed in pairs. Eggs are released in mid-water by females and fertilized by the male.

French Grunt (Haemulon flavolineatum). Family: Grunt – Haemulidae.

French Grunts are some of the most common fish found in shallow water. During the day, large schools remain motionless near or under some type of coral shelter. They are wary of snorkelers and will generally keep their distance.

French Grunt

These small fish (six to ten inches) are members of the night shift. At dusk, the schools separate and individuals forage for food, typically crustaceans and invertebrates.

Grunts were named for their ability to grind their upper and lower jaws together, producing an audible “grunt” – a defensive or aggressive behavior.

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