Australian Barramundi Farmers Association

Among our native Australian fishes, the barramundi has a national and international reputation as a splendid sporting fish with premium eating qualities. Stocks of the fish support important commercial fishing, tourist and aquaculture industries in Queensland. Because of its complex life cycle, the barramundi also holds considerable scientific interest.

While barramundi have long been regarded as a highly prized fisherman's catch, surprisingly little was known about its biology and exploitation in Queensland. The Department of Primary Industries in 1978 initiated research investigations to gather this information. Studies commenced in the north-east part of the State and in 1981 were extended westward into the Gulf of Carpentaria and south along most of the east coast.

Distribution

Scientifically named Lates calcarifer, the barramundi belongs to the perch family of fishes, and indeed was once known as the giant perch. Several other species of Lates inhabit Africa, but the barramundi is the only representative in Australia. It is distantly related to the Australian bass and the yellowbelly perch - popular sports fish of more temperate, southern waterways.

Barramundi live in rivers and estuaries in tropical and subtropical countries - from southern China to the Persian Gulf and across the equator to northern Australia, where its range extends from the Ashburton River in central coastal Western Australia, to the Mary River in southern Queensland.

Barramundi prefer slow-moving or still, muddy water in rivers, creeks, swamps and estuaries, but are adaptable and may often be found around nearshore islands and reefs. In Queensland, the fish are most abundant in the large meandering rivers of the east-coast and the Gulf of Carpentaria, where there are extensive swamp and lagoon systems.

Colour forms and genetic variation

There are well-marked differences between barramundi taken from saltwater and those taken from freshwater. Saltwater specimens are coloured bluish or greenish-grey on the upper body surface, silver on the lower body, have yellowish fins and an elongated general body shape. Usually there is no trace of fatty tissue internally.

Freshwater barramundi have a much darker upper body, a golden underbody, and dark fins with a deep girth and thick tail. The body cavity contains fat deposits, and may be practically full in specimens from land-locked lagoons. The flesh of such fish when cooked often has a muddy or earthy flavour.

Juveniles have the structure and form of the adult fish. The only distinguishing juvenile colouration present in specimens longer than about 100 mm, is a white dorsal head stripe, the intensity of which varies with the physiological state of the fish. This stripe can be seen in excited barramundi up to 500 mm long.

Recent genetic investigations suggest at least seven distinct varieties of barramundi occur in northern Australian river systems. Five varieties are presently identified from Queensland: two in the Gulf of Carpentaria and three along the east coast. All differ slightly from one another in growth, breeding, and life span. Slightly different strategies are required to manage each stock in the best possible manner.

Breeding

Barramundi is a catadromous fish species. This means it grows to maturity in the upper freshwater reaches of rivers and then moves downstream each year (often aided by floodwaters) to breed in estuaries and coastal shallows. High salinities are required for egg fertilisation and larval survival.

The timing and duration of the breeding season vary between regions, rivers and from year to year, but generally breeding is synchronised so that larval and juvenile barramundi can use nursery swamps that form during the monsoon season. Breeding usually starts after the first heavy rainstorms before the main wet season (mid-October to January).

Barramundi land-locked in lagoons and swamps move out when floodwaters connect these areas with an estuary or the open sea, and usually spawn from January to March. Generally these later spawnings are of little significance in terms of producing large numbers of viable offspring.

In a normal season, the juvenile barramundi produced by late-breeding adults have low survival in nursery swamps already occupied by larger fish from earlier spawnings. If the monsoon rains are delayed or interrupted and the swamp habitat forms later on, then significant recruitment can result from the spawning of formerly land-locked fish.

Spawning activity peaks during new and full moon periods on evening tides. On the spawning ground, fertilisation occurs outside the body when eggs and milt are shed synchronously into the water. After reproducing, many adults swim back upstream but some remain in saltwater.

Eggs, larvae and juveniles

Female barramundi can produce more eggs than almost any other fish species in the world. A 20 kg Queensland specimen produced 46 million eggs. Larger female barramundi produce more eggs than smaller fish. High levels of egg production are often associated with poor survival expectations in the young of a species. Barramundi may produce many eggs as an adaptation necessary for maintaining populations in the harsh conditions of the estuarine and nearshore environments.

After spawning, fertilised barramundi eggs spend 15 to 20 hours among the plankton before the larvae hatch out at an average size of 1.5 mm. For the first week or so the larvae bear little resemblance to the adults. Their fins are poorly developed and they drift with tides and currents into the river and adjoining mangrove swamps. At 20 mm length, the young fish have the adult shape and show conspicuous dark vertical bands on the body. By 80 mm length the juveniles have the silvery colour of the adult. These juveniles disperse among mangroves swamps, into tidal creeks, and upstream into freshwater.

Figure 1. Life Cycle

Age and growth

After one year, young barramundi are about 300 mm long. Growth is most rapid during the wet season months. Sexual maturity (usually as a male) does not normally occur until three to five years of age. Adults can grow to 1500 mm, weigh 55 kg and live over 30 years. Anglers usually catch fish of around 500 to 700 mm length (about two to four years old).

Sex change

An interesting feature of their life cycle is that barramundi change sex. Most start life as males, and breed at least once (usually more often) as males before changing into females. Very large fish are almost exclusively females. Sex change normally occurs at about seven years of age (around 900 mm length). Stunted, early-maturing populations live in far northern Cape York Peninsula rivers. Such populations occur where alluvial deposits of bauxite are also present, but the effect of bauxite on stunting and early sex inversion has not yet been investigated.

Sex change provides a method whereby the larger, more successful individuals (the female fish) are able to make the greatest contribution to the genetic material (inheritance) of a stock. Female barramundi are the older, surviving individuals and are therefore better adapted to local conditions. The females are able to pass on this trait by each producing many eggs and having a number of male fish fertilise them.

Diet

The food of barramundi is varied. It is a dominant predator of the estuaries, tidal creeks and lower freshwater reaches of rivers. Generally barramundi prey on smaller fish or crustacean (eg prawns, crabs) species. They are also cannibalistic and capable of eating smaller barramundi up to half their own body length.

Movements

Studies where fish are marked with tags for individual recognition, set free and then recaptured after a time interval, have shown that barramundi do not move far along the coastline, but may travel great distances in a particular river system from freshwater and estuarine environments to marine habitats during the breeding season. At this time they are especially vulnerable to fishing pressure.

Fishery and Management

Northern Australia's barramundi resource supports a multi-million dollar commercial inshore gillnet fishery. Queensland's limited entry gillnet fisheries in the Gulf of Carpentaria and on the east coast annually gross about $6 million. The Queensland recreational angling and sportfishing industry centred on the species is conservatively valued at $8 million.

The Queensland Fisheries Management Authority administers the regulatory and control measures for the state's fisheries. Commercial fishermen's activities are governed by seasonal and area fishing-closures, gear restrictions and stringent licensing provisions. Line fishing with artificial lures and live baits are popular angling techniques. A bag limit applies to east-coast anglers. A closed fishing season on barramundi operates from November through January each year, with the exception of Lake Tinaroo on the Atherton Tableland.

A minimum size restriction of 580 mm applies to barramundi catches. Fisheries reserves, where declared, offer protection to barramundi populations from the pressures of development and fishing exploitation. Through its ongoing research programmes, the DPI's Fisheries Group is helping to provide the information needed for effective management of the stocks.

Aquaculture potential

Barramundi's ready market acceptance and the high price it commands make its culture an attractive proposition. Restocking depleted populations in various water systems is supported by stocking Groups and DPI.

DPI has successfully developed production techniques for barramundi at Northern Fisheries Centre, Cairns and Freshwater Fisheries and Aquaculture Centre, Walkamin using south-east Asian aquaculture technology as a starting point. This, and planned future research programmes, will ensure that DPI continues to play a significant advisory role in developing a barramundi aquaculture industry in Queensland.

Facts About Barramundi

Introduction