Commencing Hatchery Production 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 s ufficient 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 o C 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). Larval Rearing Control is required because of geographical location (i.e. the hatchery is situated in an area where barramundi are not normally found). The majority of barramundi farms in northern Australia use extensive larval rearing procedures (Barlow et al., 1996). Barramundi laveae hatch in about 17 hours at 28 o C, live on their yolk sac for the first 40 to 44 hours and then feed on microscopic zooplankton. They continue to feed on zooplankton for a number of weeks, moving on to larger prey as they rapidly grow. Barramundi larvae and fingerlings are cannibalistic so grading is vital until fingerlings reach 80-100mm total length (TL) (Schipp 1996, Barlow 1998). There are three culture systems currently used in Australia for producing barramundi fingerlings: Each system has its own merits with hatchery site characteristics usually dictating the type of system used. In South-East Asia, barramundi larvae are mainly reared intensively, whereas in Australia only a few hatcheries use this technique, usually in situations where environmental control is required because of geographical location (i.e. the hatchery is situated in an area where barramundi are not normally found). The majority of barramundi farms in northern Australia use extensive larval rearing procedures (Barlow et al., 1996). Informtation courtesy of the WA Department of Fisheries | 