We see damselfishes at all of the dive and snorkel sites around Koh Lanta; They are one of the most common and abundant families on the reef and are usually found in the 2 - 15 m range, though some species can be found in deeper waters.
Damselfishes are small, laterally compressed fish that grow to a maximum length of about 15 cm, however most are usually less than 8 cm. The damselfish subfamilies number over 300 species and are very closely related to clownfish (anemonefish).
Many species can be found near staghorn and branching corals, seeking refuge among the protective branches of acropora corals when threatened.
Coloration varies widely between species, individuals of the same species, and within a locality for the same species.
Damselfishes have evolved into three sub-groups which can be defined by their eating habits.
The first group feeds primarily on small planktonic crustaceans. The second group are grazing species, tending and defending patches of filamentous algae, whilst the third group eat a combination of zooplankton found in coral polyps, small benthic invertebrates and algae in variable proportions.
Damselfish are often territorial and may aggressively defend an area of delicious algae, which they cultivate just as farmers, cutting some algae that they do not like and allow others to grow.
Females leave their territories temporarily during spawning in order to deposit their eggs in male territories, with the males defending the clutches until the larvae hatch.
Adult White Damselfishes have a white body, with variable markings, including 2 or 3 black to dusky spots, saddles or bars on the forehead, mid-back, and rear back. Adults have many small dark speckled spots on the face.
Adult Black Damsels are completely black, with no distinctive markings.
Juveniles are a pale whitish blue with a yellow stripe from the snout to the rear dorsal fin.
The pelvic and anal fins of juveniles are bluish, with a black front margin and there are yellow borders on the tail fin.
The Black Damsel grows to 15 cm, but usually observed around 10 cm. Juveniles are encountered around branching Acropora corals and feed on plankton. As they grow, the diet includes soft coral polyps and later, the waste from Giant Clams (Tridacna).
Juveniles have a black body with tree large white spots, one on each side of the body, and a third on the forehead. The spots will reduce in size as the fish grows, and all the fins are black.
The adult Three Spot Domino Damselfish has a dusky/dark grey body with black scale edges. The fins are dark, except the rear of the dorsal fin, which is translucent. Occasionally has a tinge of yellow or orange on the head and breast.
The Three Spot Domino Damselfish grows to 14 cm. Juveniles can often seen near and in anemones, sometimes mixing with anemonefish. Adults will usually form small groups.
The Blue Damsel, or Sapphire Damsel has a light blue to light green body with vertical dark streaks on the scales. There are scattered blue spots on the head and a dark ?ear? spot. The rear tail and anal fin can be yellowish.
The Blue Damsel grows to 11 cm and is often seen in groups. The diet includes zooplankton and algae.
The Indian Half-And-Half-Chromis has a dark brown to black head, forebody and mid body, with a white rear body and tail.
The Indian Half-And-Half-Chromis grows to 9 cm and is usually seen alone around the reef, close to the bottom, but may gather in larger schools above the reef.
The Indian Half-And-Half-Chromis (Chromis fieldi) commonly seen at the dive sites around Koh Lanta differs from the Red Sea variation (Chromis dimidiata), being identified as a new species by John E. Randall in 2012.