Butterfly fish are a group of tropical marine fish of the family ‘Chaetodontidae’. Butterfly fish are found mostly on the reefs of the Atlantic, Indian and Pacific Oceans. Butterfly fish are small fish and most do not exceed 12 – 22 centimetres in length apart the largest of the species, the Lined butterfly fish (Chaetodon lineolatus), which grows to 30 centimetres in length.
There are approximately 127 species in eleven genera. They should not be confused with the freshwater butterfly fish of the family ‘Pantodontidae’.
Butterfly fish are named for their brightly coloured and strikingly patterned bodies in shades of black, white, blue, red, orange and yellow (though some species are dull in colour). Many have eyespots on their flanks and dark bands across their eyes, not unlike the patterns seen on butterfly wings. Their deep, laterally compressed bodies are easily noticed through the profusion of reef life, leading most to believe the conspicuous colouration of butterfly fish is intended for interspecies communication. Butterfly fish have uninterrupted dorsal fins with tail fins that may be rounded or truncated, but are never forked.
Butterfly fish are pelagic spawners, that is, they release many buoyant eggs into the water which then become part of the plankton, floating with the currents until hatching. The fry go through what is known as a ‘tholichthys stage’, whereby the body of the post larval fish is covered in large bony plates extending from the head. This curious armoured stage is seen in only one other family of fish, the ‘Scatophagidae’ (small fishes native to the Indian and western Pacific Ocean that have become common and popular in the aquarium trade in recent years). The fish lose their bony plates as they mature.
Below are examples of just some of the species of Butterfly fish:
The Copperband Butterfly Fish (Chelmon rostratus), is found in the Indian Ocean, Indo-Pacific and Australia. It is also known as the ‘Beaked Coral fish’. Physically, the Copperband Butterfly Fish is white with copper bands running vertically on the sides of the body.
Copperband Butterfly Fish have a ‘false eye’ towards the back of the dorsal fin and can grow up to about 8 inches (20 centimetres) in length. Primarily carnivorous, they feed on a variety of marine foods, including brine and mysis shrimp. Copperband Butterfly Fish will also eat aiptasia (glass anemones).
In captivity, Copperband Butterfly fish are very sought-after mostly for what it can do rather than for its looks. Copperband Butterfly Fish are known to consume aiptasia, the pest anemones which are not welcome in tanks.
The Longnose Butterfly fish (Forcipiger longirostris), has a very flat body, which allows it to dart in and out of narrow escape routes on the reef, and a very long snout. It is a small fish only growing to up to 6 inches (22 centimetres) long. Longnose Butterfly fish have long thin spines in their dorsal fins (back fins).
Most butterfly fish have an eye band or dark line on their body that runs across the eye. This band masks their eye and confuses predators whose attention is focused on a false eyespot or spot on the fishes tail.
The bright colours of the longnose butterfly fish help it to camouflage in the reefs. Juvenile butterfly fish look different, and in many instances, completely different from their adult form. As they mature, their colours, patterns and even face shape changes.
Their bright colours are muted while they rest at night helping them to hide in the coral and inside reef caves from predators. Longnose Butterfly fish can be found in warm waters on coral reefs in the Indo-West and Central Pacific. In Australia, it is known from waters of north-western Western Australia and from the northern Great Barrier Reef. Longnose Butterfly fish either swim alone or in groups of up to five fish on seaward reefs or reefs near the open ocean and in lagoons at depths of 3 to 380 feet (1 to 114 metres).
Longnose Butterfly fish are diurnal or active during the day. A fussy eater, the Longnose Butterfly fish preys on tiny animals that hide among sea urchin spines and in coral holes and crevices. Their jaws contain slender brush-like teeth which enable them to easily scrape prey off the reef. Longnose butterfly fish eat a wide variety of creatures like fish eggs, shrimp, worms, sea urchins, sea stars, coral polyps and also algae.
Longnose Butterfly fish reproduce with one partner for life and are pelagic spawners, gathering in groups in areas where the fertilized eggs will be taken by the currents. The eggs float in the epipelagic zone or the zone in the open ocean near the surface until the larvae hatch. The larvae live in the plankton layer up to two months. When they reach a certain size, they swim down at night to a reef and join that ecosystem. While floating around, larvae are covered in bony armour, often with serrated or saw-like spines sticking out.
The Yellow tail butterfly fish (Chaetodon xanthurus) is a small fish which grows to around 14 centimetres in length. The main part of its body is white with a black reticulated pattern on the sides and an orange coloured band towards the back of its body. Because of this particular pattern, it is sometimes referred to as the ‘Pearlscale butterfly fish’.
The Yellow tail butterfly fish has a black spot with a white edge on its nape.
The Yellow tail butterfly fish is distributed in Indonesia and the Philippines, north to the Ryukyu Islands in the Western Pacific and is encountered normally along the external reef where it has a maximum depth range of 6 – 50 metres.
Found around stag horn corals, the Yellow tail butterfly fish is the only member of the family with a crosshatch pattern of dark lines on the sides. It is generally seen below 15 metres depth and occurs singly or in pairs. It feeds on small benthic invertebrates and algae.
The Yellow tail butterfly fish is easily confused with the species Atoll Butterflyfish (Chaetodon mertensii) which can be distinguished by the reticulated colour pattern on the sides and by the nape spot with a clear edge.
The Foureye Butterfly fish (Chaetodon capistratus), is a butterfly fish of the family Chaetodontidae.
These fish are found among tropical reefs around the world and particularly in the Indo-Pacific oceanic region.
The foureye butterfly fish is also found in the Western Atlantic from Massachusetts, USA and Bermuda to the West Indies and northern South America.
Foureye butterfly fish are deep-bodied and laterally compressed, with a single dorsal fin and a small mouth with tiny, bristle like teeth. The foureye butterfly fish mates for life and therefore they will often be seen in pairs.
Foureye butterfly fish get their name due to a large, dark spot on the rear portion of each side of the body. This spot is surrounded by a brilliant white ring resembling a false eye. A black, vertical bar on the head runs down the true eye, making it more nondescript and may result in a predator confusing the back end of the fish for the front end. The four-eye butterfly fishes first instinct when threatened is to flee, putting the false eye spot closer to the predator than the head. Most predators aim for the eyes and this false eye spot tricks the predator into thinking that the four-eye will flee tail first.
When escape is not possible, the foureye butterfly fish will sometimes turn to face its aggressor, head lowered and spines fully erect. This may serve to intimidate the other animal or may remind the predator that the butterfly is much too spiny to make a comfortable meal.
Foureye butterfly fish usually frequent shallow inshore waters, where they feed on a variety of crustaceans and coral polyps.
The foureye butterfly fish is known for its uncanny ability to swim in and around coral heads and reefs. The fish is able to find its way through the most intricate passages by swimming on its side or even upside down.
The Raccoon butterfly fish (Chaetodon lunula) also known as crescent-masked or lunule butterfly fish. It is found in the Indo-Pacific oceans from East Africa and also in the southeast Atlantic from East London, South Africa. This fish is usually found at depths down to 30 metres.
The Raccoon butterfly fish can grow up to lengths of 20 centimetres. The Raccoon butterfly fish is a nocturnal species that usually swims in pairs or small groups in warm, shallow reef flats of lagoon and seaward reefs. Juveniles occur among rocks of inner reef flats and in tide pools. Adults feed mainly on nudibranchs (soft-bodied, shell less marine mollusks), tubeworm tentacles (worm-like invertebrates) and other benthic invertebrates including algae and coral polyps.
The Raccoon butterfly fish is generally not aggressive towards other fish, with the exception of lionfish and triggerfish. In captivity, the typical life span of a Raccoon butterfly fish is 5 to 7 years.
Reproduction is oviparous (animals that lay eggs, with little or no other embryonic development within the mother. This is the reproductive method of many fish, amphibians and reptiles, all birds, the monotremes and most insects and arachnids), with pairs forming during breeding.