or on coral- burrowing molluscs. The coral reef offers numerous examples of fishes that have similar narrow habitat and feeding requirements. Water depth is also an important partitioning factor, and again there are numerous examples of coral reef fishes that have well defined depth ranges. In the very broadest sense there are three main depth categories for reef fishes: shallow (0-4 m), intermediate (5-19 m), and deep (20 m+). The depth limits of these zones may locally vary depending largely on the degree of shelter and sea conditions. The shallow environment is typified by wave action which in highly protected areas such as coastal bays or lagoons may exert its effect down to only a few cm. On the contrary in exposed outer reef structures the effect of surface waves may sometimes be felt below 10 m. The intermediate zone harbours the greatest abundance of fishes and live corals. Here wave action is minimal, although currents are often strong, and sunlight is optimal for reef-building corals. The deep outer reef slope is characterised by reduced light levels, hence fewer corals and fishes. Although species numbers are reduced the species that occur in this habitat are among the most interesting of coral reef fishes. A high percentage of the new fishes that have been discovered on coral reefs in the past three decades were collected on deep reefs by SCUBA diving scientists.
The region’s reef environments can be broadly classified into two major categories: sheltered inshore reefs or lagoons and outer reefs. Under optimum conditions both of these environments can support extensive beds of nearly 100 per cent coral cover. Inshore or coastal reefs may be strongly influenced by freshwater runoff and resultant siltation. Underwater visibility on these reefs is often greatly reduced, particularly during the wet season when rivers are flowing at their maximum. Coastal reefs and lagoons are further characterised by extensive sand or silt bottom areas that may support broad seagrass beds. In most coastal reef or lagoon situations the maximum depth seldom exceeds 25 m and due to heavy siltation coral growth is usually sparse below 15 m depth.
Outer reefs often have a classical reef structure consisting of a broad shallow reef flat, a raised algal ridge, reef front zone of surge channels, and a steep outer slope. But on some islands the bottom plunges into the depths directly from the rocky shore. The clearest waters are found on outer reef slopes and underwater visibility may sometimes exceed 30 m. Coral growth is most abundant between about 5 and 15 m depth, although in some areas appreciable growth may extend well below this limit. In shallower water corals are inhibited by the pounding surge, and in deeper water by the much reduced penetration of light. Although most reef-building corals do not thrive below 30-40 m, certain reef fishes may penetrate well below these depths. Observations made in research submarines at Hawaii and Enewetak Atoll indicate that reef species, including some damselfishes, butterflyfishes, and squirrelfishes, may occur to depths approaching 200 m.
A perfect day on Australia’s Great Barrier Reef. (R. Steene)
CLASSIFICATION OF
FISHES
Although the fundamentals of biological nomenclature and classification are common knowledge to many, it is my experience that the average non-biologist frequently has little idea of the basis of scientific names or how fishes are classified. It therefore seems worthwhile to include a brief section on the rudiments of this subject.
Every described organism, be it a single-celled amoeba, crab, bird, fish or mammal has a scientific or Latin name. It is composed of two parts and is generally italicised. The first part is the genus or generic name and the second is the species or specific name. For example the Five-lined Seaperch is Lutjanus quinquelineatus. The generic name Lutjanus pertains to a group of closely related species which share a number of common features related to general shape, scalation, type of teeth, fin-ray counts, etc. The specific name quinquelineatus applies only to a single entity that is distinguished from its relatives by a unique set of characteristics, often including colour pattern. Related genera (plural of genus) are grouped together in a family, whose spelling always ends in - idae. An illustrated list of families is presented on pages 9-18. Worldwide there are about 450 families - more than 300 are represented in Australia and surrounding regions. A group of similar families is placed in one of the 35 orders of fishes whose spelling always ends in -iformes. The highest rungs on the ‘ladder’ of classification pertain to class and phylum. The class Myxini contains the jawless hagfishes and lampreys (no species included in this book); Chondrichthyes contains sharks and rays; and the third class Osteichthyes contains the majority of fishes. All fishes, as do other higher animals including amphibians, reptiles, birds and mammals, belong to the phylum chordata. Therefore, in summary the classification of the Five-lined Seaperch can be represented as follows.
Phylum - Chordata (all animals with notochord)
Class - Osteichthyes (all bony fishes)
Order - Perciformes (most reef fishes)
Family - Lutjanidae (seaperches and relatives)
Genus - Lutjanus (closely related seaperches)
Species - quinquelineatus (5-lined seaperch)
Characters that are most often used to separate species, and often genera, include external features such as the number of fin rays, size and number of scales, ratio of various body proportions, and colour pattern. For higher classification at levels above genus internal structure, particularly those pertaining to skeletal elements, are often indicative of relationships.
Many species previously unknown to science have been found in our region over the past few decades. When a new fish is discovered it is given a scientific name by the researcher who formally publishes a detailed description in a recognised scientific journal. Scientific names are frequently descriptive. For example quinquelineatus is Latin for five lines and is therefore appropriate for the Fivelined Seaperch (see Pl. 42-7 in species section). New fishes are sometimes named after the locality from where they are collected, for example japonicus (Japan) or novaeguineae (New Guinea). A third category of specific names are based on the names of people, often the person who first discovers the fish (respectable researchers never name fishes after themselves). Fishes named after a male end in - i, those after females in - ae.
PRESERVING FISHES
It is sometimes desirable to preserve specimens, particularly if a positive identification by museum authorities is required. Also small, unusual or rare fishes can be kept as curios or as teaching aids for children. The recommended method of preservation in any case is exactly the same one that is employed by fish biologists in museums. The basic ingredient is full strength formalin which can be obtained from a pharmacy. The preserving solution is made by diluting one part of formalin with nine parts of water. The fish should be fully immersed in the solution. If larger than about 15-20 cm a slit along the side of the belly will facilitate preservation of the internal organs. For long term storage it is desirable to transfer the specimen to a 70 per cent ethyl alcohol solution (70 per cent ethanol, 30 per cent water) after the fish is fully fixed in formalin (i.e. after several weeks). However, the fish may be held in the initial formalin solution for several years without deleterious effects.
Unfortunately colours fade rapidly in preservative. Therefore photography (see below) is a valuable method of accurately recording the colour pattern.
SENDING SPECIMENS
TO THE MUSEUM
Although most of the specimens in the reference collections of the various museums around Australia and South-east Asia are collected on special expeditions by museum staff, occasionally valuable fishes are donated by the public. Also it may be desirable for people living far from their local museum
