Marine Fishes of South-East Asia. Gerry Allen

      INTRODUCTION

      There are approximately 22,000 types of fishes inhabiting our planet, including approximately 13,500 marine species. Seas encompassing northern Australia and the tropics that lie immediately northward are inhabited by the richest fish fauna on earth. Official counts are lacking, but an estimated 4,000 species occur in the region, or about 30 per cent of the world’s total marine fishes. For most families of tropical marine organisms there are more species represented in this area than any place on earth. For example, among the reef-dwelling damselfishes, a family containing about 330 species worldwide, about 175 species or over 50 percent of the world’s total inhabit the region sometimes referred to as the Indo-Australian Archipelago.

      Why is this region populated by so many species? No doubt a combination of several factors are responsible. Certainly among the most important are a lengthy history of favourable climatic conditions (ie., warm water), a diversity of habitat types, and a tumultuous geological and hydrological past. In the latter category events such as sea level changes, ocean current shifts, volcanism, and continental drift have created isolating barriers that greatly enhanced the speciation process.

      One of the most significant factors responsible for the region’s great plethora of fishes and other marine organisms is its vast tropical shoreline with an array of diverse habitats. Coral reefs are the most complex habitat system. They provide abundant living space and seemingly endless “survival opportunities” for a wealth of creatures. Spires of tabular and branching corals are the reef’s equivalent of multi-story tenements. Not only do they house thousands of living polyps, they also serve as a retreat for legions of brightly coloured fishes that swarm above. Ledges, caves and crevices form the inner sanctum of the reef city, which is populated by shy, seldom seen fishes that may only emerge for night-time feeding patrols.

      The sand and rubble fringe surrounding individual reef complexes appears devoid of fish life. But first impressions are deceptive. Close inspection reveals an entire community of specially adapted species. Although this habitat contains far fewer fishes than nearby reefs, its inhabitants are equally interesting. Common adaptations include camouflage colouration and burrowing behaviour. Other major habitats in the region include inshore coastal environments - vast stretches of sandy or rocky shores, interspersed with estuaries and coastal mangroves - and open offshore oceanic habitats. All of these zones are populated by distinct fish communities.

      The book contains nearly 2,000 hand-painted illustrations featuring 1,635 individual species. The paintings were completed over a 3-year period and are primarily based on photographs or colour transparencies of either live fishes taken underwater or freshly caught specimens. In many cases preserved specimens at the Western Australian Museum have been consulted to ensure accuracy of detail and proportions. The end result is a colourful and highly comprehensive guide to the sea fishes of northern Australia and the adjacent South-east Asian region.

      AREA OF COVERAGE

      This book provides coverage of tropical Western Australia, Northern Territory, Queensland, and the region immediately north of Australia encompassing Malaysia, Indonesia, Philippines, New Guinea, and Solomon Islands. The main emphasis is placed on reef and shore fishes - relatively good coverage is provided except for gobies (Gobiidae) and threefins (Tripterygiidae). Both of these families contain small, cryptic, seldom seen species, whose classification has not been satisfactorily studied - many of the species are difficult to identify, even by trained specialists.

      Relatively good coverage is also extended to families containing species of interest to anglers. Foremost in this respect are the trevallies and their relatives (Carangidae), tunas and mackerels (Scombridae), and billfishes (Xiphiidae and Istiophoridae). Less than full coverage is given to families containing cryptic, hence seldom encountered species (Antennariidae for example), or species living in deeper sections of continental shelves. Excluded from coverage are the true deep sea fishes which for the most part, live well offshore, below 200 m depth (although some make daily migrations to the surface).

      A diver inspects a colony of anemonefishes (Amphiprion melanopus) in the Coral Sea off Australia's north-east coast. (R. Steene)

      FAUNAL COMPOSITION

      Most of the region’s reef and shore fishes can be broadly described as being of Indo-Pacific origin. In other words, they belong to the overall reef fish community that ranges across the vast reaches of the tropical Indian and Pacific oceans. Although individual species, and particularly the mixture of species present, vary greatly from one locality to the next in this huge region, there is a general faunal theme that pervades. Nearly all families and many genera are widely distributed throughout the region. Also the dominant (i.e., most speciose) families tend to be the same regardless of locality. Dominant groups across this region usually include such families as gobies, wrasses, damselfishes, gropers, moray eels, cardinalfishes, and surgeonfishes.

      The reason for the region’s relative homogeneity in faunal composition is at least partly explained by examining the life cycle of reef fishes. With few exceptions most species have a pelagic larval stage which is transported by ocean currents for variable distances depending on hydrological conditions and duration of the larval period. Until recently the length of larval life for most fishes was an unknown factor, but thanks to otolith aging techniques our knowledge in this area is rapidly expanding. Essentially this technique consists of counting daily microscopic growth rings that appear on the bones of the inner ear (otoliths). We now know that the larval duration is highly variable, ranging from just a few days up to nearly two months, with an average length of about 3-4 weeks. Although the adults of most reef fishes are highly home-ranging or territorial, a homogeneous gene-pool is maintained over a broad area by the dispersal capabilities of the larval stage.

      Many Indo-Australian reef fishes are distributed widely across the Indian and West and Central Pacific oceans. Species such as the Racoon Butterflyfish (Plate 55-13) and Pacific Gregory (Pl. 66-12) range from the shores of eastern Africa to the Hawaiian Islands and a few others such as the Moorish Idol (Pl. 92-9) and Longnose Hawkfish (Pl. 67-18) extend even farther, to the coast of the Americas. Indeed, throughout the Indo-Pacific region a significant segment of the fauna consists of similar widespread species. Another important component of the fauna consists of species that have more limited regional distributions. A number of species such as the Honey-Head Damsel (Pl. 61-8) and Rainbow Monocle Bream (Pl. 51-12) are mainly confined to what biogeographers refer to as the Indo-Australian Archipelago, which encompasses the Malay Peninsula, Indonesia, Philippines, northern Australia, and Melanesia. At the bottom end of the scale, a few species such as the Banggai Cardinalfish (Pl. 34-7) have an extremely limited range. It is only found among a small group of islands off central-east Sulawesi. This fish, and others that are similarly restricted, usually lack a pelagic larval stage, which prevents their dispersal.

      BIOLOGY OF

       REEF FISHES

      The region’s tremendous diversity of inshore fishes is reflected in a wide variety of reproductive habits and life history strategies. The following discussion is intended to give an overview of the most common patterns. More detailed information is available in the scientific literature or semi-popular works such as Thresher’s (1984) Reproduction in Reef Fishes. The majority of reef fishes are egg layers that employ external fertilisation. Relatively few species bear live young that are prepared to fend for themselves at birth. Included in the latter category are sharks, rays, and cusk eels. Basically two patterns of oviparous or egg-laying reproduction

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