Tuesday, 20 September 2016

Aquarium 4: Flame Angelfish

  There are two species of marine angelfish currently on show in the aquarium. The smallest, and the most vividly coloured fish in the tank, is a Flame Angelfish, Centropyge loricula.

Currently there are over 30 species of Centropyge, commonly referred to as Dwarf Angelfish, found in warmer waters and reefs all over the world. Most live in fairly shallow water, but some deep water species are known.  They are all fairly small species, with C. loricula at over 10 cm being one of the larger species. It has a wide range in the Pacific, from the Australian Great Barrier Reef to Hawai’i. It tends to live in the deeper parts of the outer reef, where it shelters in crevices in the rubble.

The diet in the wild has a large component of filamentous algae, supplemented with crustaceans and other invertebrates. The social structure is a harem of a single male with up to 10 females in a shared territory. Although during the day they range over the reef in search of food, during the breeding season they transition at dusk to the spawning routine.

Spawning begins with each female seeking out their own spawning station, which is a coral head or similar landmark. The male begins patrolling around the territory, visiting females to determine whether they are ready to spawn. As he approaches he may produce a grunt, which may be responded to by the female. The female will eventually follow him in response to his signals, sometimes all the way to the next female station, in which case a male may spawn with several females simultaneously. Spawning is initiated by the partners changing colour and swimming 3ocm up into the water column to release their eggs to be fertilized by the male. The eggs are rendered buoyant by an oil droplet which takes them up to the surface where they join the plankton.

The floating eggs hatch in around 15 hours into larvae about 3mm long. They begin to feed after 48 hours, by which time the mouth and digestive system have developed. The larvae require extremely small live food such as the nauplii of copepods at first and take a long time to reach metamorphosis, 80 days for C.loricula. As a result, at present there are no commercial suppliers I am aware of for Centropyge species, although they have been spawned and raised in captivity. As techniques improve it will hopefully become commercially viable to produce these for the aquarium trade, and some expert hobbyists have raised them at home.

Captive breeding of various marine angelfish is aided by their reproductive strategy. All individuals start off as females, and the dominant fish will change sex to a male, which in C.loricula can be identified by additional blue in the dorsal and anal fins as well as size. As with other marine fish with this biology, to obtain a pair it is only necessary to obtain two of different sizes and a breeding pair will result. They are however very territorial, so a large tank is required to house them despite their comparatively small size. In addition, there must be sufficient depth for the spawning rise into the water column to take place. Of course, once fertile eggs have been obtained, the really difficult part starts.

Next week, the other Pomacanthid currently on show, the Yellow Faced Angelfish

Images from wikipedia

No comments:

Post a Comment