Barramundi (Lates calcarifer)
Commercial Fishery & Aquaculture

A total of 16 genetically distinct stocks of barramundi in various major river systems throughout Australia have been identified, although populations in WA have not been studied exhaustively (Makaira 1999). This has caused problems in developing barramundi aquaculture, particularly in WA, due to the variation in maturation and spawning stimuli between these genetically discrete populations.

As barramundi farming is well established in the Eastern States, the production phases and options for farming are well known. The flow chart on the preceding pages summarise these phases which are discussed in detail within this document. Initial attempts to induce spawning with WA-caught barramundi using Eastern States techniques were unsuccessful (Lawrence, 1995). It appears that current Australian spawning induction methods will require further modification before WA barramundi can be induced to spawn in a captive environment. The following description of spawning techniques are therefore based on techniques currently used by farmers in other States.

Hatchery production of barramundi commences with the spawning of captive breeding fish or 'broodstock' and is completed when the small fish or 'fingerlings' are 20 to 25mm long (Schipp, 1996). In preparation for examination of the spawning condition of the fish, the broodstock must first be caught and anaesthetised. Once anaesthetised, barramundi broodstock are cannulated to assess gonadal development (using a piece of silicon tubing, a small sample of eggs or sperm (milt) are removed from gonads and examined microscopically). Only animals with sufficient egg and sperm development are capable of being stimulated to complete their gonadal development and spawn. Suitable female fish should have a majority of tertiary yolk eggs with diameters of >0.4mm (400 microns), while male fish should produce at least a bead of milt when gently test stripped or have a 5mm milt plug in the catheter tube.

Captive barramundi broodstock that are held in recirculating systems (20 to 80t) and conditioned to a constant environment of salinity 30 to 36ppt, temperature 28o to 29oC and summer photoperiod (13 hour day length) are able to be induced to spawn using hormones year round (Garrett & O'Brien, 1994). For detailed instructions on the preparation and administration of hormones for barramundi broodstock please refer to Schipp (1996). Generally, a commercial barramundi hatchery holds between 25 and 70 brood fish, ranging in size from 3 to 20kg. Excess broodstock are preferred to ensure egg supply but the actual number required depends on the performance of the fish (i.e. fecundity, ease of spawning, regularity of spawning etc.), with the cost of holding broodstock requiring consideration.

Maintenance of genetic diversity in farmed populations is facilitated by use of large numbers of broodstock.

Eastern States barramundi spawn naturally in tanks following injection of luteinizing hormone-releasing hormone analogue (LHRH-a) at 19 to 27 micrograms per kilogram (µg/kg) of body weight. Each female releases 3 to 6 million eggs and the males immediately 'pirouette' around the females' tail, releasing their sperm (Figure 2). Males do not require hormonal stimulation as they receive visual cues from the female to release sperm (Garrett & O'Brien, 1994).

Barramundi are reared on progressively larger pellets as they grow from fingerling to market size. Most farmers prefer to use semi-floating extruded pellets as they float about 20cm from the water surface. Barramundi are reluctant to feed from the water surface or the pond or tank bottom. Diets produced by Australian fish feed manufacturers give good food conversion ratios (FCR) of 1.6 to 1.8:1 under commercial farm conditions (Barlow et al., 1996).

Recent research has shown use of high protein (> 55%) and high energy (> 18% fat) diets for juvenile and plate-sized barramundi can greatly improve growth, FCR (< 1.0 in experimental systems) and profitability of barramundi farming. Formulated feeds need to be stored correctly to avoid loss of nutrients, this is particularly important in the tropics where fats will quickly go rancid and vitamins break down if not stored in an air-conditioned room. Pelleted feed should not be stored for extended periods (Schipp, 1996).