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.
Being susceptible to parasites, and due to their limited long distance swimming ability, they will spend significant time at cleaning stations within their home ranges making them more common in shallow water.
Groupers are distinguished by their large lips, stout bodies and the numerous amount of dorsal spines. Most range from 30 to 70cm in length but some are known to grow up to 230cm, like the Giant Grouper. They vary in colours and markings, from browns, deep blues, reds and greens. Some Groupers have a special pigment cell which enable them to change their appearance quickly, allowing them to blend into their surroundings, camouflaging them from their prey or predator.
They are carnivorous diners, hunting smaller fish and crustaceans. Groupers will rest on the reef sitting on their pectoral fins waiting for prey to swim by. Prey is drawn into their gullets by a powerful suction created when they rapidly open their large mouths. It is swallowed whole, secured by hundreds of small rasp - like teeth that cover the jaws and tongue. They also use their mouths to dig into sand to form their shelters under rocks. Their gill muscles are so powerful, it is nearly impossible for a predator to pull them out of a hole, if they feel attacked they extend their gill muscles to lock themselves in.
The brown-marbled grouper has a sharp head profile, big mouth, and a pale yellowish brown body and fins, with many close-set small brown spots. The body has a series of five vertical irregular brown blotchy sections and can be identified by the small dark or black saddle on the tail base. All the fins are large and round.
The brown-marbled grouper is one of the largest fish that we regularly see on almost all of the dive sites around Koh Lanta, particularly around Koh Haa, Hin Muang & Hin Daeng. This stocky and robust species grows to 120 cm, but is usually observed in the 50 cm - 60 cm range. Larger individuals of 60 cm +are sometimes encountered. This is usually a solitary groupe, but occasionally observed in small groups.
This species is an ambush predator and its diet includes fish, crustaceans and cephalopods. It has a well defined territory which it will defend against intrusion from other brown-marbled groupers.
The longfin grouper has an underlying white body colour, covered with close-set polygonal spots (usually five or six sides) in varying shades of brown. There is a broad dark margin on the anal fin, and a brown diagonal band across the breast.
This species can be distinguished for several other similar looking groupers (e.g. honeycomb grouper - Epinephelus merra) by two darkish bands below the pectoral fin base. The tips of the dorsal fin spines are white.
The longfin grouper has large pectoral fins which are used to sit on corals and the sandy or rubble bottom close to the reef.
This solitary species grows to 38 cm, but is often observed smaller, in the 15 cm - 20 cm range. The diet includes shrimp, small fish, worms and crabs.
The Malabar Grouper is a large fish with a generally light brown or olive grey colour and around 5 mottled bars on the body. There are numerous small while spots and blotches on the body and many smaller dark spots.
Larger individuals often have a lighter coloured body with larger pale areas. The tail fin is rounded.
The Malabar Grouper is usually seen in deeper parts of the dive sites, often 20m + and can be observed alone, or in small to medium groups, sometimes resting on the reef or hovering close to it.
The Malabar Grouper grows to 230 cm and is one of the largest fish we regularly see while diving around Koh Lanta.
The diet includes mostly other fishes and crustaceans, and occasionally cephalopods.
The coral grouper has an orange-red to reddish-brown body, usually darker toward the rear. The body and fins (except pectoral fins) are covered with hundreds of dark-ringed, bright blue spots. The pelvic fins are a bright orange-red colour, and there is a narrow blue margin on all fins except pectoral fins. This species may occasionally display pale blue bars.
This is a territorial species where a single male dominates a harem of up to 12 females over a large home territory. Each female guards her individual area of up to 40 square meters against intrusion, and is visited by the dominant male once or more per day.
The coral grouper feeds on small fishes and crustaceans. This species grows to 41 cm, but often observed in the 20 - 30 cm range.
The peacock grouper is typically found sitting on corals and has a brown body, with adults showing five or six pale bars on the rear part of the body.
The body is covered with hundreds of small blue spots with black edges. The rear dorsal, anal, tail and pectoral fins have large blue borders. There is a lighter coloured patch at the pectoral fin base.
The peacock grouper can grow to 55 cm bus is usually observed 25 - 35 cm, perhaps slightly longer.
This species has both a dark and pale phase and can rapidly change between them both. Often found solitary or in small groups, which may include a single dominant male.
The redmouth grouper is a solitary species that grows to 60 cm, but usually observed 25 cm - 35 cm. This species defends its home territory hunting ground against competitors, and employs a slow moving hunting technique.
The grouper swims through shoals of small fish, occasionally swallowing one or more fish from the shoal.
The diet also includes stomatopods and crustaceans which it finds while hiding under ledges or in reef crevices.
The two-banded, or double-banded soapfish is a member of the grouper family, however it does not look, or behave like a grouper. This species has a pale to bright yellow head, body and fins. There is a dark or black eye bar, and a broad dark or black bar from the middle of the dorsal fin to the anal fin. Occasionally this species may have a nearly all-black body.
The two-banded soapfish grows to 25 cm, but usually observed in the 10 cm - 15 cm range. This species is seen solitary, or in small groups, and has a large, expandable jaws, which allow it to swallow surprisingly large prey.
When stressed, the soap fish may release toxins from their skin which can resemble lathered soap.