ANEMONEFISHES
CLASSIFICATION
Anemonefishes are members of the Pomacentridae, one of the largest families in order Perciformes, with approximately 325 species. Members of this family, commonly known as damselfishes, are almost entirely marine (three mainly brackish water species sometimes occur in fresh water), and most species occur in tropical, and to a lesser degree, subtropical latitudes. About 70% of damselfishes, including anemonefishes, are restricted to the vast Indo-West Pacific region.
Amphiprion and Premnas constitute the Amphiprioninae, one of four pomacentrid subfamilies. The only other damselfishes that sometimes dwell with anemones are Dascyllus trimaculatus, and D. albisella, which belong to another subfamily, the Chrominae.
IDENTIFICATION
Colour pattern is the most important feature for identifying an anemonefish in the field. Other useful characters, which include tooth shape, scalation of the head, and body proportions, are mainly of value to laboratory workers identifying preserved specimens. Correct identification of juveniles is often difficult, due to great similarities among many species and to the colour patterns of many differing from those of adults. The easiest juveniles to identify are those that resemble the adult and that mostly have either no bars or a single white bar: A. akallopisos, A. leucokranos, A. nigripes, A. perideraion, and A. sandaracinos. Distinctive shape and colouration make the young of A. latezonatus, A. ocellaris - A. percula (which, however, are difficult to distinguish from one other), A. polymnus, A. sebae, and P. biaculeatus relatively easy to identify. More difficult to separate are the red-finned species, whose adults possess a single bar (A. frenatus, A. melanopus, A. rubrocinctus, and A. ephippium), for juveniles generally have two or three white bars, which they lose sequentially from the tail end as they grow. Perhaps most difficult to distinguish are juveniles of species that possess two or three bars as adults and have variable amounts of yellow or orange on body and fins. Curiously, juveniles of these fishes frequently have one bar to begin with, developing the other(s) as they grow. For many such species, it may be necessary to observe a transitional series of progressively larger fish in order to link the smallest young with adults. Fortunately, in field situations this is often possible, as "family" groups of a single species composed of individuals of increasing size usually occur with larger anemones.
Individual species accounts provide information on important colour pattern features, including an underwater photograph, means of distinguishing similar species, anemone host(s), and details of distribution. Several "species pairs" share nearly identical patterns: for example, Amphiprion allardi - A. chrysopterus, A. chrysogaster - A. tricinctus, and A. akindynos - A. chagosensis. Fortunately, the members of each pair have widely separated geographic ranges. Thus, knowledge of the distribution of a species may be very useful in identifying it correctly. Dascyllus trimaculatus, juveniles of which are often encountered with anemones, is also included among the species accounts.
COLOUR VARIATION
The colour of anemonefish of one species sometimes varies. Geographic variation is most common among widely distributed species. For example, A. clarkii, which has the broadest distribution of any anemonefish, is exceedingly variable over its range. Another type of variation is melanism (black pigmentation), which is somehow induced by the host anemone. This topic is discussed in more detail in Chapter 5.
Other categories of variation are related to sex (see Chapter 4), are due to hybridisation, or are purely random. Hybrid crosses between closely related species have been produced in aquarium conditions, and at least one probable cross, involving A. chrysopterus and A. leucokranos, has been observed by us in Papua New Guinea. The most common sort of random variation involves irregularities in the shape of the white bars displayed by most species, particularly the head bar. In some cases, one or more bars may be absent or greatly abbreviated.
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