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.
These fish are small to medium sized, often 15 to 25 cm. Unusually, scales occur on their dorsal fins and sometimes on the anal fins.
These fish are usually seen in very shallow water, close large rocky ledges, boats, piers and harbours.
The Silver Moonfish, Monodactylus argentus, is a schooling fish often seen in shallow water at several dive sites around Koh Lanta, notably the Bida islands, and to a lesser extent, around the Koh Haa Islands.
Normally around 15 - 20cm in length, the Silver Moonfish is a triangular, bright shiny silver fish with yellowish fins. The dorsal fin is mostly yellow, with a slight black tip, the anal and tail fins are also yellowish with some black colouration.
The Silver Moonfish uniquely adapts to increasing salinity over its lifetime. They are born in brackish estuaries and migrate out into coastal waters as an adult. Juveniles have more yellow colouration and two vertical black bands, one running through the eye and a second across the gill.