Fish
Malaysia's freshwater ecosystems can be divided into two distinct types: lentic (still water) and lotic (running water). They support a great variety of animal life. In the broadest sense, Malaysia's aquatic animals represent all groups of animals, from protozoans to mammals. They can be divided into surface dwellers (such as water skaters and whirligig beetles), floating forms (zooplankton, such as water fleas, rotifers and copepods), swimmers (fish, amphibians, reptiles, birds and mammals), stone and weed dwellers (insects, snails and shrimps), and burrowers or bottom dwellers (annelid worms and clams). However, many of these animals (for example, mammals and reptiles) are covered in other parts of this volume and this section concentrates on fish, crabs, prawns and snails.
While some of the freshwater fishes of Malaysia are highly prized by the restaurant trade for their delicious flavour, others, such as the golden dragon (kelesa) (Scleropages formosus), fetch high prices in the aquarium fish trade for their beauty. Although not of economic importance in Malaysia, another family of fishes, the mudskippers, are endlessly fascinating to visitors to the mud flats, with their ability to travel across land and to survive out of water for long periods.
Also very noticeable in the mangroves at low tide are the fiddler, soldier and hermit crabs, especially the very colourful species, and their distinctive burrows. Most striking are the male fiddler crabs with one extra large claw, which they use for signalling females and for fighting to defend their territory. Now confined to only a few islands is the very large hermit crab, the coconut or robber crab (Birgus latro).
Crabs of a different type inhabit the rivers of Malaysia. More than 90 species have already been identified, and others are still awaiting discovery. Some members of this very diverse group must return to the sea to breed. Others complete their life cycle entirely in fresh water. Yet others have adapted so well that they have become completely terrestrial; some live in caves.
Similarly, some of Malaysia's freshwater prawns must return to the sea to complete their life cycle, while others spend their entire life in fresh water. The large Macrobrachium prawns with very long pincers are considered a gourmet delicacy, and are being cultivated on a large scale in aquaculture projects for export as well as to fulfil the insatiable demand from local restaurants.
Freshwater snails are also marine creatures which have adapted to life in fresh water. Although some freshwater snails act as biological control agents, others are seen in a less favourable light. The golden apple snail (Pomacea canaliculata) is a pest in the paddy fields, while a number of species are of public health importance as the hosts of parasites from which people can contract diseases.
Characteristics
Common external features of a fish.
Reproduction
Fish reproductive organs include testes and ovaries. Over 97% of all known fishes are oviparous, that is, the eggs develop outside the mother's body. However, a few oviparous fishes practise internal fertilisation, with the male using some sort of intromittent organ to deliver sperm into the genital opening of the female, most notably the oviparous sharks, and oviparous rays. In these cases, the male is equipped with a pair of modified pelvic fins known as claspers.
Life Cycle of A Fish
Diagram of The Fish Life Cycle
Habitat destruction
A key stress on both freshwater and marine ecosystems is habitat degradation including water pollution, the building of dams, removal of water for use by humans, and the introduction of exotic species.
Here are some pictures of the fish in Malaysia.
