Most fish living in shallow reefs use coloration for protection, predation and intimidation. However, such coloration changes as fish mature. Nonetheless, skin divers can distinguish between juveniles and adult fishes by observing their behavior and color patterns.
The colors created by a coral reef and its myriad inhabitants nearly always leave snorkelers with a dramatic and somewhat blurred first impression. But the coral reef is just like any other neighborhood; spend a little time there and you’ll soon know your way around.
An abundance of reference material and informative courses, available at most popular snorkeling destinations, makes it relatively simple for even casual underwater explorers to delve into the basics of fish identification. The adults of most species are fairly easy to identify; with the juveniles, however, identification is sometimes a little bit trickier.
Quite often the wild and flamboyant markings and color displays of the adults pale in comparison to the outrageous costumes worn by the juveniles. Sometimes the colors remain but the markings and shape drastically change: distinguishable spots and neon speckles move, merge or disappear and, in many species, the brilliance of youth completely fades away. In the most outrageous transformations, the juveniles and adults of a particular species bear no resemblance at all.
Although pretentious outfits appear designed to amuse, the bizarre colorations and outlandish markings are, for many fish, normal and necessary. The fish use these colorful masks for a variety of purposes, including intimidation, protection and predation. As fish age their surroundings and requirements often change. When necessary, pattern and color changes accompany the transition, providing the young fish the camouflage or weapons necessary to ensure its safety and survival.
Before you try to identify juveniles it’s important to familiarize yourself with the body shape, size, habits and characteristics of the fish living in the reef community. Although, in many cases, the form or size of the fins or tail may change, more often than not the overall shape remains the same. Body shape is one of the most reliable features used for identification. Colors and markings are much more subject to change and variation.
If a juvenile resembles the adult in form, the next feature to consider is the size; the juvenile should, of course, be substantially smaller. Next, you need to gather more information so you know what to look for. While many species experience extreme transformations, others retain distinguishing markings throughout their life. Most fish ID books provide fish-watchers all the information necessary to identify both common and unusual juveniles.
Juveniles are actually easy to identify, especially when you know what you’re looking for. In many cases, similar changes occur within each species. Many juvenile butterfly-fish, for example, are cleverly designed with a concealing dark bar to hide behind and a confusing false eye. Rock Hinds and coneys tend to retain their spots but undergo drastic color changes. And parrotfish, perhaps the most amazing quick change artists of them all, undergo dramatic changes in shape, color, size and occasionally, sexual orientation. Infinite variations make parrotfish juveniles among the most challenging to identify.
You can also uncover many clues about both adults juveniles by spending time watching the fish’s behavior: What is it eating? Where does it live? Is the fish exhibiting any unusual or notable behavior? Fish are creatures of habit and their actions and behavior are often keys to identification.
The accompanying photos provide adult and juvenile examples of some common reef species often encountered by snorkelers. The juvenile Trumpetfish (Aulostomus maculatus), is one of the easiest to recognize. The slender trumpet-shaped snout quickly distinguishes it from other reef inhabitants. Being a master of camouflage the Trumpetfish displays a wide variety of color phases, often changing from brilliant yellow to dark brown in seconds. Other distinguishing features are pale horizontal lines, scattered black spots and a black streak on the upper jaw. Except for slight variations in body shape, color and markings, juvenile Trumpetfish are just adults in miniature form.
One of the most gregarious fish on the reef is the French Angelfish (Pomacanthus paru), notorious for boldly approaching divers and snorkelers. The development of the French Angelfish is a dazzling visual display. The juvenile starts life dressed in black, with three bold yellow vertical stripes and a gold band that runs around its lips and down the center of its face. With age the juvenile French Angel’s golden stripes are replaced by stunning gold flecks and a prominent yellow ring around the eyes. Intermediate French Angelfish are identified by two light vertical stripes that fade with age. The only identifiable feature similar in both the adults and juveniles is the slender, disk-shaped body and rounded tail fin. Adults cruise the reef alone or in pairs; juveniles prefer sandy areas and the safety of shady crevices. Juvenile French Angelfish will often act as cleaners for larger fishes, removing debris and parasites. This arrangement provides young French Angelfish protection and easy meals.
The brilliant hues and splashy patterns of most juvenile Damselfish fade with youth, but the striking contrast between young and old makes Damselfish fun to identify and fairly easy to spot on the reef: The metamorphosis of the Threespot Damselfish (Stegastes planifrons) is one of the most drastic; mutating from a golden luminescent hue to drab tan, yellowish brown or gray. The distinguishing feature present at all stages of development is a golden crescent above the eyes, a black saddle on the upper base of the tail and a dark spot on the base of the pectoral fin.
As with most hobbies, the real fun starts when you get past the basics and fishwatching is no exception. When treasure hunting underwater you can only spot the most revered prizes when you know what you’re looking for. Happy hunting.