Barcoo grunter (jade perch) aquaculture

Market and industry

Silver perch farmers that produce Barcoo grunter have found them to be very hardy and are optimistic about their potential. The species are attractive in colour and have a high weight–to–length ratio of the species. Barcoo grunter producers usually target sales to the live fish markets in Brisbane, Sydney and Melbourne.

You should consider economies of scale, marketing strategy and overall profitability before investing in Barcoo grunter aquaculture.

Culture and production systems

Barcoo grunter is farmed in Queensland in either tanks or ponds. To successfully farm Barcoo grunter, carefully manage stocking rates, water quality and diet. Industry evidence suggests you can produce up to 5–10t per hectare in well-managed ponds.

Commercial feedback suggests that Barcoo grunter are suited for production in recirculation tank systems (RAS) with effective biological filtration.

Some commercial production takes place in purpose-built earth ponds. Earthen ponds should:

• vary in size from 0.2–0.5ha in surface area
• have depths of 0.7–2.5m
• be designed so they can be drained easily
• have netting or nylon scarewire placed over them, to protect them from predators.

Water quality

Water temperature and pH levels are key to maximum growth and survival for commercial production:

• use dissolved oxygen (DO) levels of 4mg per litre or greater
• aeration (paddlewheels and/or aspirators) is essential
• increase aeration and water exchanges when pond water temperatures exceed 30°C.

Lower temperatures can seriously affect Barcoo grunter if the temperature is at or below:

• 20°C leads growth rates to decline rapidly
• 17°C, handling fish can cause deaths
• 16°C, farmers often stop feeding
• 13°C, mass deaths can occur.

Barcoo grunter can tolerate a pH of between 6 and 9, but the ideal range is 6.5 to 8.5. Salinity levels of 5g per litre of sodium chloride are acceptable for long-term exposure and can be used to treat ectoparasite and fungal diseases.

Breeding

In their natural habitat, Barcoo grunter spawn during the summer floods, when water temperatures are above 23°C. In captivity, you can induce sexually mature broodstock to spawn with a hormone injection.

First–feeding larvae are about 5mm long and can be reared in a pond environment with a stable zooplankton bloom (rotifers and copepods). Survival rates of 30% or higher are possible. Larvae in ponds metamorphose into fingerlings (15mm long) in 3–4 weeks . When fingerlings grow to 30–50mm at 8–12 weeks, they're ready to be stocked in grow out ponds or recirculation systems.

Chemicals used in aquaculture, including hormones, require veterinary advice and prescriptions before use.

Feeding and growing

Growth rates vary, and depend on water temperature and water management strategies. You should regularly grade (sort) fingerlings into size classes to achieve the best growth rates. Grading prevents large variations in size at harvest and inefficient feeding rates.

You can grade fingerlings in tanks or earthen ponds until they reach 150mm. Grading prevents large variations in size at harvest and inefficient feeding rates.

Stocking density

Industry experience suggests that stocking rates in ponds should be up to a maximum of 15,000 fish p/ha, although no systematic research has been undertaken on husbandry practices. In tanks, the stocking density depends on the capacity of the system but appears to be at least comparable with those used for barramundi.

Careful management of stock density and feed rates prevents excessive concentrations of ammonia. Before stocking, ponds are drained, well dried and, if necessary, limed and cultivated. They are then filled with water that has been passed through a filter screen to exclude predators.

In recirculation systems, Barcoo grunter can reach up to 450g in 4 months, and 800g in 7 months from an advanced fingerling size. Maximum stocking density is usually 40–50kg per cubic metre.

Feeding

Barcoo grunter are omnivores that feed on:

• zooplankton and algae
• small crustaceans
• aquatic insects
• molluscs
• plant material.

Barcoo grunter will also accept commercially-available artificial diets at both fingerling and adult stages. Pellet size varies with the size of the animal. The food conversion ratios (FCR) vary with their stages of development, with a 1.2:1 ratio for fingerlings to 1.6:1 for grow out.

Feeding must be managed carefully, since this fish is voracious and easily overfed.

Harvesting

Ponds are primarily harvested using seine nets, either partially or for a complete harvest.

It is critical to harvest fish in good condition to ensure they aren't stressed during purging and transport to market. Purge the fish in clean water for 7–14 days (depending on temperatures) to remove any off flavours. We also recommend adding salt to the water during purging.