Diving with Ray-finned Fishes

Lanta Marine Life | Actinopterygii

There are many hundreds of species of tropical fish found at all the dive sites around Koh Lanta, and many species can even be spotted while snorkeling off the beach in front of our office.

Tropical fish are all types of ray-finned fishes, a subclass of the bony fishes. The fins are constructed from webs of skin supported by bony or horny spines, hence the name 'Ray-finned fishes'.

Ray-finned fishes are the dominant aquatic vertebrates today, making up about half of all vertebrate species known. Any animal with a back-bone is called a vertebrate.

Ray-finned fish are found in every aquatic habitat from the deepest depths of the ocean to freshwater streams and ponds; a few can even crawl on land for short periods of time (we have mudskippers around the mangroves here on Koh Lanta).

Moray Eels

Yellow-edged Moray (Gymnothorax flavimarginatus)

There are over 200 species of morays found worldwide ranging in size from 10 cm to 3 m in length, with many species preferring to live in warm tropical waters. Several species of moray eels are found at the dive sites around Koh Lanta, often found hiding in reef crevices between rocks, rubble, and hard corals with only their heads protruding. Some species of moray love to settle inside giant barrel sponges.

There are 35 species of Garden Eels in the family Heterocongrinae, most of which are found in the Indo-Pacific region. The garden eels have long, slender bodies, with both the pectoral and caudal fins being reduced or absent. These eels have no scales.

Crocodile Needlefish (Tylosurus crocodilus)

Needlefish (sometimes called long toms) are long, slender fish, up to 1.5m in length and comprise up to 34 individual species. Their most distinctive feature is their long, narrow beak, which houses multiple sharp teeth.

Variegated (Sand) Lizardfish (Synodus dermatogenys)

Lizardfish are part of the Synodontidae family and are commonly called 'Grinners' due to their large smiling mouths. Most species are found around shallow rocks and reefs or on sandy bottoms in tropical waters.

Doubletooth Soldierfish (Myripristis hexagona)

The family Holocentridae has 2 subfamilies, Holocentrinae typically known as squirrelfish, and Myripristinae, typically known as soldierfish. Members of these families are usually reddish with robust fin spines, and spines on the gill cover.

Chinese Trumpetfish (Aulostomus chinensis)

As a member of the pipefish and seahorse order of ray-finned fishes (Syngnathiformes), Trumpetfishes are a generally slow-moving fish, active in the day-time and often found singly around the reef. This is a poorly studied fish, with little known about their behaviour.

Bluespotted Cornetfish (Fistularia commersonii)

There are only 4 species of cornetfish which are found worldwide in tropical and subtropical areas. Cornetfish have a very long and slightly depressed body, with a long tubular snout.

Ornate (Harlequin) Ghost Pipefish (Solenostomus paradoxus)

Ghost pipefish are a member of a small group of tropical fish belonging to the Solenostomidae family, a relative of the True Pipefish and the Seahorse, the Syngnathidae family.

Seamoths are a very unusual family of small, bottom dwelling fish. Seamoths have flattened bodies, large, wing-like pectoral fins, a long snout and the body is completely encased in fused, bony plates.

Seahorses are a family of small fish with some unusual features. With a head, snout and neck resembling a horse, seahorses also have a fully enclosed brood pouch, an upright posture and a curled tail which has evolved to grasp and hold objects.

Short-Tailed Pipefish (Trachyrhamphus bicoarctatus)

Pipefishes are a subfamily of small fishes closely related to seahorses, indeed they look like straight seahorses, and have a long tube-like snout which ends in a small, toothless, narrow mouth which opens upward. The body in encased in bony rings, similar to a seahorse tail.

Razorfishes are a small family of unusual shaped species which are normally found in shallow tropical waters. The long thin bodies have sharp dorsal and lower body edges and a straight profile with a long snout. The very small mouth has no teeth.

The waspfishes are a family of small fish related to the scorpionfishes, and as their name suggests they are often venomous, having poison glands on their spines.

The scorpionfishes are a large super-family of venomous fish, including the lionfish. stonefish, waspfish and velvetfish. Among divers, the word scorpionfish commonly refers to the genus scorpaenopsis, and here we also include the subfamily pteroinae which includes the lionfish.

The Stonefish family are so called due to their ability to camouflage themselves as rocks. There are two subgroups (genus) within the Stonefish family.

Velvetfish are a family of small fish with a velvet-textured skin. They are generally compressed with small pelvic fins and some also have venomous spines.

Blue Ring Angelfish (Pomacanthus annularis)

The 96 species of angelfish are some of the most colourful and noticeable fish found on a coral reef. Oblong or oval shaped, deep-bodied and highly compressed fish, this family also have short snouts, small mouths and bristle-like teeth.

Andaman Butterflyfish (Chaetodon Andamanensis)

Butterflyfish, with their wonderful display of colours and patterns, are a common sight on the reefs around Koh Lanta. The family Chaetodontidae has over 100 species of Butterflyfish including Coralfish and Bannerfish.

Two-Lined Monocle Bream (Scolopsis bilineata)

There are around 70 species of threadfin breams, also known as false snappers. The bodies of threadfin breams are long, oval-shaped and are have large scales. They have small mouths and some species have a spine located below the eyes.

There are around 40 species of goatfish, all characterised by two long barbels on the chin which are used to forage for food in sediment. Once the prey is located, the fish often roots into the sediment with its barbels and snout for small crustaceans and worms.

Groupers are one of the most recognisable members of the of the Sea Bass family, Seranidae. They are commonly seen inhabiting the reefs and dive sites around Koh Lanta.

Rabbitfish are a colourful and easily identified family of 29 species. The name rabbitfish is derived from their peaceful temperament, rounded blunt snout, and rabbit-like appearance of the jaws.

The Carangidae family comprises around 200 species of medium to large sized fish, and includes the trevallies, runners, jacks, pompanos, mackerels and scads. Body shape varies greatly, from elongated and streamlined to very deep-bodied and thin.

The family Rachycentridae contains a single genus, Rachycentron, of which there is a single species, Rachycentron canadum. The single member of this family is often referred to as a Cobia, however other common names include Black Kingfish, Black Salmon, Ling and Lemonfish.

The moonfish are a small family of 6 species of very laterally compressed (thin) fish with disc shaped bodies and tall fins. Due to their silvery colour, they are often referred to as moonfish, however they can also be referred to as fingerfish.

Sister family to the fusiliers, snappers are seen at every dive site around Koh Lanta, sometimes in very large schools numbering many thousands of fish. Snappers are a small to large family (from 15 - 20 cm to 1.5 m +) and have a single dorsal fin and two nostrils on either side on their snout.

Vanikoro Sweeper (Pempheris vanicolensis)

Sweepers are a family of small to medium sized fish with 26 members. Reaching up to 22 cm for some species, they have compressed (flat), elongated (stretched relative to width) and deep (high) bodies.

Gold-spotted Sweetlips (Plectorhinchus flavomaculatus)

Sweetlips are a genus of 31 fish in the genera plectorhinchus, subfamily plectorhynchinae of the grunts and are easily identified from their small mouth, big, fleshy lips and distinctive colour patterns. Their colours and patterns are highly variable, ranging from uniformly coloured to spotted, blotched, banded and striped.

Emperors are a family of around 30 different species, sometimes also called emperor breams. Features common to this family include thick lips, strong jaws, and cheeks without scales. Emperors live on or close to coral reefs and are found only in coastal tropical waters.

Intermediate Cardinalfish (Cheilodipterus intermedius)

Cardinalfish are a large family of generally small fish, with almost 350 known species. The length of most species is in the 4 - 17 cm range, though typically they are less than 10 cm. Cardinal fish have large eyes, large mouths, and the dorsal fin is divided into two separate fins with short bases. The lower jaw is often protruding and the tail fin can be either rounded or forked.

Wide-Band Fusilier (Pterocaesio lativittata)

Fusiliers (Caesioninae) are closely related to tropical snappers (Lutjaninae). Although they share a number of similarities with snappers, they are generally more slender and have a small and distinctly different jaw. Fusiliers often congregate in large zooplankton feeding schools in mid-water over the reef.

The 54 species of sea chubs have short heads, blunt snouts, and small mouths. They have strong, close-set teeth which are strangely shaped like hockey sticks and a single, continuous dorsal fin which can be folded into a scaly groove. They have a forked tail and are usually a drab colour and may have some bluish or yellowish stripes.

Blue Blanquillo (Malacanthus latovittatus)

Tilefish are mostly smaller fish, often found in sandy areas close to coral reefs where they construct burrows in coral rubble, in small holes, caves or piles of rock.

Coral Hawkfish (Cirrhitichthys oxycephalus)

The Hawkfishes are a family of 38 small species, with big heads, slightly elongated bodies, and short, rounded tail fins. Hawkfishes range from 8.5 to 30 cm in length, and are only found in tropical waters, down to around 50 m.

False Clown Anemonefish (Amphiprion ocellaris)

Clownfish or anemonefish are the sister family to the damselfishes, comprising 30 species. With adults reaching 15 cm, this is a family of small fish which display a very unusual partnership with some sea anemones.

Three Spot Domino Damselfish (Dascyllus trimaculatus)

Damselfishes arevery closely related to clownfish (anemonefish). Damselfishes are small, laterally compressed fish that grow to a maximum length of about 15 cm, however most are usually less than 8 cm. Coloration is variable between individuals and within a locality for the same species.

Brothers and sisters to the parrotfishes, wrasse are a large and very diverse group of fish, many of which have thick lips, long, slender bodies, a pointed snout and often brightly coloured.

Greenthroat Parrotfish (Scarus prasiognathos)

Parrotfish are closely related to the wrasse family and with around 95 species, they are one of the most commonly seen and most important fish on a coral reef. Parrotfish are easily identified by the tightly packed teeth on the external surface of their jaw bones, forming a parrot-like beak with which they scrape algae from coral and other rocky substrates.

Barracudas are found world-wide in all warm and tropical waters, and are usually spotted in shallow water close to coral reefs and seagrass beds. Here around Koh Lanta we have 4 species of barracuda often observed on all of the coral reefs and dive sites. Fast, powerful, and known for their often fearsome appearance, barracudas have long, thin, elongated bodies, with some species growing up to 2 m.

Grey mullets often have longish bodies, broad, flat heads, two well separated dorsal fins, small mouths and few or no teeth. The pectoral fins are set high up on the side of the body and the scales are rough and medium to large in size. The tail fin is concave or may be weakly forked.

Speckled Sandperch (Parapercis hexophtalma)

Sandperches are a family of small to medium sized fish, generally ranging between 12 and 28cm, with a few species slightly smaller or larger than this. Sandperches have long bodies which are flattened toward the rear and more rounded towards the head.

Combtooth blennies have with comb-like teeth lining their jaws. Generally small, typically under 15cm, this fish often has a blunt head, large eyes located high on the side of the head and a wide mouth low on the head.

Tripplefin, or threefin blennies have a dorsal fin which is separated into three parts, and the family name Tripterygiidae is derived from the Greek word 'tripteros' which means 'three wings'.

Gobies are one of the largest families of fish, representing almost 10% of all known fish species, with 10 - 20 new species discovered each year.

Surgeonfishes, tangs, and unicornfish have deep compressed bodies with the eyes high on the head. Members of the genus Naso, commonly known as unicornfish, have a horn-like projection in front of the eye.

Found on almost all coral reefs and sometimes on sandy bottoms, the Moorish Idol is one of the most widespread fish in the Indo-Pacific region.

The family Ephippidae includes the reef-dwelling genus Platax, the batfishes, which are often seen at dive sites around Koh Lanta, sometimes alone, sometimes in small schools of 20 - 40 fish. With a maximum size of 50 - 60 cm, these can be curious fish and sometimes approach and follow divers.

Lefteye flounders are a family of very flat fish which lie on the seafloor on their right sides, with both their eyes on their left sides. It is possible, but highly rare, that this is reversed in some specimens.

Horn-nosed Boxfish (Ostracion rhinorhynchos)

Boxfish are, as the name implies, box-shaped, with an armored and rigid body which in most cases would inhibit locomotion. This disadvantage is offset by the boxfish's shape which has led to the evolution of an unusual swimming style.

Filefish are rhomboid-shaped fish with with deep keeled bodies and can appear very similar to triggerfish, their close relatives. Filefish have very thin (laterally compressed) bodies, small snouts and mouths with projecting incisor teeth.

Pufferfish are a common sight on all of the coral reefs around Koh Lanta. They typically have round faces, tapered bodies and big eyes, ranging in size from 2 cm to around 1 m in length.

Closely related to pufferfish, porcupinefish are medium to large sized fish with short, wide bodies, and large eyes. The mouth contains teeth which are fused to form a strong, beak-like crushing structure which can give a nasty bite. Just like pufferfish, porcupinefish have the ability to inflate their bodies by swallowing water or air, making themselves up to twice as big when feeling threatened.

Clown Triggerfish (Balistoides conspicillum)

Triggerfish are seen at all dive sites around Koh Lanta, many of them brightly coloured. Growing to a maximum 80 cm, they have a flattened body, small mouth and 8 very strong outer teeth adapted for crushing shells and crunching coral.

Freckled Frogfish (Antennarius coccineus)

Frogfish are unusual, short, stocky, well camouflaged fish, with no scales, ranging from 2.5 - 38 cm in length. Their mouths point upward, and many species can change colour and are sometimes covered in short spines and other appendages to aid camouflage.

Scuba Diving & Snorkel Trips

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Find Out More

Indo-Pacific Marine Life Guides

Allen, G., Steene, R., Humann, P., DeLoach, N. (2003) Reef Fish Identification, Tropical Pacific. Jacksonville, FL., USA: New World Publications, Inc., ISBN 1-878348-36-1.
Humann, P., DeLoach, N., (2010) Reef Creature Identification, Tropical Pacific. Jacksonville, FL., USA: New World Publications Inc., ISBN 978-1-878348-44-9
Debelius, H. (2013) Indian Ocean Reef Guide. Frankfurt, Germany: IKAN - Unterwasserarchiv, ISBN 978-3-939767-52-7.
Debelius, H. (2004) Nudibranchs and Sea Snails, Indo-Pacific Field Guide. Frankfurt, Germany: IKAN - Unterwasserarchiv, ISBN 3-925919-51-1
Erhardt, H., Knop, D. (2015) Corals Indo-Pacific Field Guide. Frankfurt, Germany: IKAN - Unterwasserarchiv, ISBN 3-925919-69-4.
Veron J.E.N., Stafford-Smith M.G., Turak E. and DeVantier L.M. (2016). Corals of the World

More Marine Life References and Further Information

Diving with Ray-finned Fishes

Lanta Marine Life | Actinopterygii

Moray Eels

Garden Eels

Needlefish

Lizardfish

Soldierfish and Squirrelfish

Trumpetfish

Cornetfishes

Ghost Pipefish

Seamoths

Seahorses

Pipefishes

Razorfishes

Waspfishes

Scorpionfish & Lionfish

Stonefishes

Velvetfish

Angelfishes

Butterflyfishes and Coralfishes

Threadfin Breams

Goatfishes

Grouper & Sea Bass

Rabbitfish

Jacks, Runners & Trevallies

Cobia

Moonfishes

Snappers

Sweepers

Sweetlips

Emperors

Cardinalfishes

Fusiliers

Sea Chubs

Tilefish

Hawkfishes

Clownfishes

Damselfishes

Wrasse

Parrotfishes

Barracudas

Grey Mullets

Sandperches

Combtooth Blennies

Triplefin Blennies

Gobies

Surgeonfishes & Tangs

Moorish Idols

Spadefishes (Batfishes)

Lefteye Flounders

Boxfishes

Filefishes

Pufferfishes

Porcupinefishes

Triggerfishes

Frogfish