Blue faced angelfish with its characteristic gill spine easily visible.
Some fishes like sharks and puffers are easy to recognize, as are the food fishes we eat regularly. Others often look alike and it's not easy to tell them apart. This section provides tips to identify fishes. A knowledge and appreciation of reef fishes will help make the underwater experience much safer, educational, exciting and enjoyable.
Top: Different parts of a fish.
Bottom: Body shapes and profiles of common fishes.
The simplest way to identify fishes is by their physical shape and appearance. Everyone can easily recognize a shark because of its distinctive shape. Different species have different profiles when viewed from the side, top or front. Some are slim and elongated, others fat and rounded. Many have characteristic fins, tails, bumps or curves. Look at the diagram showing the different parts of the fish and observe how these parts differ across species. To help with your identification, observe the body shape or profile, size, colour and markings, the number of fins and fin shape, location and size of mouth and eyes, and the shape of the tail. Even if you do not recognize the fish, taking note of these characteristics will help you identify it later when you are thumbing through fish reference books.
Note that the young (juvenile) of some fish species like the batfish and sweetlips may look different from the adults. Some fishes also mimic other species, like the bluestriped fangtooth blenny mimicking the cleaner wrasse, which make identification more difficult.
Observe the habitat that the fish lives in. Some, like scorpionfish, goatfish, lizardfish, gobies and flounders, live on the seabed, reef flats or reef wall. Others, like jawfish, soldierfish, cardinals and eels, like to live in holes or crevices. Others, like jacks, trevallies and wrasses, prefer to swim around in the open.
Finally, observe the behaviour of the fish. Some, like lizardfish and hawkfish, sit motionless on coral. Others like snappers, fusiliers and cardinals prefer to congregate in schools. Some swim in a peculiar fashion, like wrasses 'flapping' their pectoral fins like a bird and gobies 'walking' on their pectoral fins. Others sleep in the day and are active mainly at night like soldierfish and cardinalfish.
Many colourful reef fishes are adorned with pretty patterns and markings on the body. Often, their common names include the kind of marking found on them. For example, the 'six-bar regal angelfish' has 6 vertical bars on its body. The 'chevron barracuda' has visible chevron markings. The 'saddled butterflyfish' has saddle markings while the 'banded wrasse' has bands. Some of these markings act as camouflage to break the outline of the fish, while others like the false eye spot are used to confuse predators.
The size and position of mouths of fishes differ and there can also be differences in the relative sizes of their upper and lower lips. The mouth can be right at the front or at the bottom of the head. They can be elongated or protruded, making the fish appear to have a long nose. Lips can be thin or thick, sometimes one lip might be bigger than the other, or one lip may protrude more than the other. Groupers and rock cods are easily identified by their superior mouths, where the lower lip or jaw protrudes. Sharks have inferior mouths, while parrotfishes have terminal mouths. Needlefish have elongated mouths, while goatfishes have barbels (whisker-like appendages) under their mouths.
Although most fishes have the usual set of fins at the top (dorsal fin), side (pectoral fin) and bottom (pelvic and anal fins), the size, shape and number of fins may differ. Groupers, damsels, wrasses, surgeonfish and angelfish have one continuous dorsal fin, while barracuda, goatfish, gobies, soldierfish and cardinalfish have 2 dorsal fins.
The tails of fishes also come in a variety of shapes. Fusiliers, jacks, soldierfishes and cardinal fishes typically have forked tails, while wrasses and parrotfishes typically have truncate or rounded tails. Lunate tails are crescent shaped while lanceolate tails look like a lance or arrow head.
Sometimes, at first glance, it is hard to tell two similar looking fishes apart. In such cases, look out for distinguishing features that may be present in one species and absent in the other, such as barbels (whiskers), spines and fin arrangements. On tiny fishes, these features may be harder to see so you'll have to study the fish carefully. Shown below are distinguishing features between some common fishes that appear similar.
Gill spines on blueface angel (left) and regal angel.
Angelfish have a clearly visible spine on the gill cover which is absent in butterflyfish. In general, butterflyfish are smaller and many species are predominantly yellow in colour.
Bannerfish (left) and moorish idol.
Bannerfish have yellow tails while moorish idols have black tails. In addition, moorish idols have a predominantly black face and a tubular white nose with a yellowish-orange patch. The character 'Gill' in the movie 'Nemo' is a moorish idol.
Gobies (left) have 2 distinct dorsal fins; 'eyelashes' on blenny.
These fishes can be tiny and often partially hidden, making identification difficult. Gobies have 2 distinct dorsal fins while blennies have 1 continuous dorsal fin. Many blennies also appear to have 'eyelashes' or small feelers near the eyes and faces that resemble grasshoppers. The pelvic fins on gobies are joined at the base forming a little cup for support, while the pelvic fins of blennies are separate and located clearly behind their pectoral fins. Prawn gobies are easier to identify as they live with a prawn as a housemate, the goby standing guard at the entrance to the hole while the prawn cleans out their living quarters.
Napolean wrasse (left) and bumphead parrotfish.
Both of these large fishes have pronounced bumps (or humps) on their heads especially in mature adults. The bump on the Napolean (or Humphead wrasse) is located on the forehead while the bump on the parrotfish appears at the top of the head. The Napolean has a longer protruding jaw with subtle striped patterns on its face while the parrotfish has a beaked mouth and light stripe running down its nose.
Smooth pufferfish (left); spines on porcupinefish.
Both can inflate their bodies by sucking in water but the porcupinefish has many small spines all over its body while the pufferfish has a smooth body. When the spines are folded flat against the body, they look like little uneven bumps on the body of the porcupinefish.
Gill spine on squirrelfish (left), none on soldierfish.
Both are predominantly red, have large eyes and large scales, but only squirrelfish have a visible spine on the gill cover. Many squirrelfish species also have horizontal stripes running across the length of the body.
Stonefish (top) and scorpionfish (below).
Both look like stones or corals and are very well camouflaged. The stonefish has a short and wide upturned mouth which gives it a distinct grumpy appearance and eyes set deeper into the head. From the top, it also looks rounded with the head and torso looking top-heavy, and a tail that is often curled slightly to one side. The scorpionfish looks more slender and fish-like with a longer snout and a mouth that is angled but not grumpy.
Folded tail spines on surgeonfish.
Surgeonfish have a scalpel-like spine at the base of the tail which is absent in other fishes. When folded, the spine may not always be clearly visible and sometimes appear as a fine horizontal line. The character 'Dory' in the movie 'Nemo' is a palette surgeonfish.
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