Sunday 2 June 2013

Cultured Aquaculture Species - Barramundi

 


Information on the culture of the barramundi/ seabass (Lates calcarifer) from the FAO Cultured Aquatic Species Information Programme.




Biological features

Body elongate, compressed, with a deep caudal peduncle. Head pointed, with concave dorsal profile becoming convex in front of dorsal fin. Mouth large, slightly oblique, upper jaw reaching to behind eye; teeth villiform, no canines present. Lower edge of pre-operculum with a strong spine; operculum with a small spine and with a serrated flap above origin of lateral line. Lower first gill arch with 16 to 17 gillrakers. Scales large, ctenoid. Dorsal fin with 7 to 9 spines and 10 to 11 soft rays; a very deep notch almost dividing spiny from soft part of fin; pectoral fin short and rounded, several short, strong serrations above its base; dorsal and anal fins both have scaly sheaths. Anal fin rounded, with 3 spines and 7 to 8 short rays. Caudal fin rounded. Colour in two phases, either olive brown above with silver sides and belly (usually juveniles) or green/blue above and silver below. No spots or bars present on fins or body.

Profile

Historical background

Lates calcarifer, known as seabass in Asia and barramundi in Australia, is a large, euryhaline member of the family Centropomidae that is widely distributed in the Indo-West Pacific region from the Arabian Gulf to China, Taiwan Province of China, Papua New Guinea and northern Australia. Aquaculture of this species commenced in the 1970s in Thailand, and rapidly spread throughout much of Southeast Asia.

Among the attributes that make barramundi an ideal candidate for aquaculture are:
  • It is a relatively hardy species that tolerates crowding and has wide physiological tolerances.
  • The high fecundity of female fish provides plenty of material for hatchery production of seed.
  • Hatchery production of seed is relatively simple.
  • Barramundi feed well on pelleted diets, and juveniles are easy to wean to pellets.
  • Barramundi grow rapidly, reaching a harvestable size (350 g – 3 kg) in six months to two years.
Today barramundi is farmed throughout most of its range, with most production in Southeast Asia, generally from small coastal cage farms. Often these farms will culture a mixture of species, including barramundi, groupers (Family Serranidae, Subfamily Epinephelinae) and snappers (Family Lutjanidae).

Australia is experiencing the development of large-scale barramundi farms that reflect the industrialised style of aquaculture seen in Europe. Where barramundi farming is undertaken outside the tropics, recirculation production systems are often used (e.g. in southern Australia and in the north-eastern United States of America).

Barramundi has been introduced for aquaculture purposes to Iran, Guam, French Polynesia, the United States of America (Hawaii, Massachusetts) and Israel.

Habitat and biology

Barramundi inhabit freshwater, brackish and marine habitats including streams, lakes, billabongs, estuaries and coastal waters. Barramundi are opportunistic predators; crustaceans and fish predominate in the diet of adults.

Spawning seasonality varies within the range of this species. Barramundi in northern Australia spawn between September and March, with latitudinal variation in spawning season, presumably in response to varying water temperatures. In the Philippines barramundi spawn from late June to late October, while in Thailand spawning is associated with the monsoon season, with two peaks during the northeast monsoon (August – October) and the southwest monsoon (February – June). Spawning occurs near river mouths, in the lower reaches of estuaries, or around coastal headlands. Barramundi spawn after the full and new moons during the spawning season, and spawning activity is usually associated with incoming tides that apparently assist transport of eggs and larvae into the estuary.

Barramundi are highly fecund; a single female (120 cm TL) may produce 30–40 million eggs. Consequently, only small numbers of broodstock are necessary to provide adequate numbers of larvae for large-scale hatchery production.

Larvae recruit into estuarine nursery swamps where they remain for several months before they move out into the freshwater reaches of coastal rivers and creeks. Juvenile barramundi remain in freshwater habitats until they are three–four years of age (60–70 cm TL) when they reach sexual maturity as males, and then move downstream during the breeding season to participate in spawning. Because barramundi are euryhaline, they can be cultured in a range of salinities, from fresh to seawater. When they are six–eight years old (85–100 cm TL), Australian barramundi change sex to female and remain female for the rest of their lives. Sex change in Asian populations of this species is less well defined and primary females are common.

Although some barramundi have been recorded as undertaking extensive movements between river systems, most of them remain in their original river system and move only short distances. This limited exchange of individuals between river systems is one factor that has contributed to the development of genetically distinct groups of barramundi in northern Australia, where there are six recognised genetic strains in Queensland, and a further ten in the Northern Territory and Western Australia.

Production

Production cycle of Lates calcarifer

Production systems

Seed supply
While barramundi fingerlings are still collected from the wild in some parts of Asia, most seed supply is through hatchery production. Hatchery production technology is now well established throughout the culture range of this species.

Rearing fingerlings

Barramundi broodstock are held in floating cages or in concrete or fibreglass tanks. They may be maintained in either fresh or seawater but must be placed in seawater prior to the breeding season to enable final gonadal maturation to take place. Barramundi show no obvious external signs of gonadal development and must be examined by cannulation to determine their gender and reproductive status, although milt can be expressed easily from male fish during the spawning season.

Barramundi broodstock are usually fed with 'trash' fish or commercially available baitfish. In order to improve the nutritional composition of the broodstock diet, and prevent diseases associated with vitamin deficiencies, a vitamin supplement may be injected into, or mixed with, the baitfish prior to feeding.

Asian barramundi have been induced to spawn by manipulation of environmental parameters (salinity and temperature) to simulate the migration to the lower estuary, and the tidal regime there at the time of natural spawning. The same techniques have proven unsuccessful with Australian populations of barramundi, which generally require hormonal induction to spawn. Barramundi have been successfully spawned using a range of hormones at various doses, which were administered by techniques including injection, slow-release cholesterol pellets and osmotic pumps. Induced spawning of barramundi is now generally carried out using the leuteinising hormone-releasing hormone analogues (LHRHa) (Des-Gly10)D-Ala6,Pro9-LH-RH ethylamide and (Des-Gly10)D-Trp6, Pro9-LH-RH ethylamide.

Pre-spawning behaviour involves the male fish pairing with a female and rubbing its dorsal surface against the area of the female's genital papilla, erecting its fins and 'shivering'. In the absence of such displays, egg release may occur but they are not fertilised. Spawning occurs 34–38 hours after injection, usually around dusk, and may be accompanied by violent splashing at the water surface. Barramundi will often spawn for up to five consecutive nights.

At spawning, the sperm and eggs are released into the water column and fertilisation occurs externally. Barramundi eggs are 0.74–0.80 mm in diameter with a single oil droplet of 0.23–0.26 mm diameter. The eggs are collected from spawning tanks using fine mesh (around 300 µm) egg collection nets through which tank water is diverted. If barramundi are spawned in cages, the cages are lined with a fine mesh 'hapa' net that retains the eggs inside the cage, enabling their later removal to the hatchery.

Fertilised eggs undergo rapid development and hatching occurs 12–17 hours after fertilisation at 27–30 °C. Newly hatched larvae have a large yolk that is absorbed rapidly over the first 24 hours after hatching, and is largely exhausted by 50 hours after hatching. The oil globule is absorbed more slowly and persists for about 140 hours after hatching. The mouth and gut develop the day after hatching (day two) and larvae commence feeding from 45–50 hours after hatching.
 
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