Farming Barramundi

The Culture of Barramundi

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.

Flow Chart summarising Barramundi Farming

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.

Figure 2 : typical posture of barramundi when spawning

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 28^o to 29^oC 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).