Murray Cod

Aquaculture status in Victoria Hatchery and juvenile production Growout systems Water quality parameters Marketing attributes Scientific name: Maccullochella peelii peelii (Mitchell, 1838) Environment and Status Native (demersal) - freshwater, threatened. Distribution Naturally found north of the Great Dividing Range throughout the tributaries of the Murray River and the Murray Darling Basin.

Figure 1: Murray Cod

Aquaculture Status in Victoria

There are currently 35 commercial producers in southeastern Australia of which 15 are producing fingerlings for stock enhancement and aquaculture. To date, 16 have produced table fish both in ponds and in recirculation systems.

Production and Value Production of Murray cod in Victoria has increased rapidly over the past 2-3 years, primarily due to the success of one large recirculation system (Figure 1). In 1998/99, Victoria produced approximately 20 tonnes of Murray cod and 162,000 juveniles with a value of $559,000 (O’Sullivan and Dobson, 2000). Estimates for the 1999/2000 production year have been put at 80 tonnes with a market value of around $1.5 million. It is expected that production will continue to increase over the next few years as a number of hatcheries and growout systems are under development. Broodstock Murray cod broodstock are usually wild-caught due to the fact that there is currently no supply of mature farmed broodstock. Procuring broodstock is likely to become more difficult in the future as there is no commercial fishing permitted in NSW and Victoria. The industry is trialing the use of domesticated broodstock and in time this should improve the genetic quality and disease status of juveniles.

Figure 2: Murray Cod Production 1997 - 2000

Broodstock are kept in small static ponds and fed yabbies, goldfish, trout or ox liver. The fish spawn in nesting boxes in the pond. The eggs are removed from the boxes and transferred to the hatchery. Smaller fish can be induced to spawn using hormones.

Hatchery and Juvenile Production

In recent years, techniques have been developed to enable large-scale hatchery production of Murray cod juveniles, however juvenile production is still largely seasonal. The fish spawn between October and January each year. The eggs are incubated in tanks and take about 6-11 days to hatch. The fry are then transferred to outdoor fertilised earthen ponds (stocking density approximately 35 fry/m²) where they feed on natural food. Alternatively, techniques have been developed to wean juveniles directly onto commercial diets (Ingram et al, 2001). At 30-50 mm (8-10 weeks old), the juveniles are ready to be transferred to growout systems.

Page Top

Grow-out Systems

Intensive
The most popular growout systems for Murray cod in Victoria are intensive recirculating tank systems (RAS). Murray cod have proven to be very tolerant of high stocking densities (80-150 kg/m³) but oxygen injection is required with very high stocking levels. Murray cod display efficient food conversion (<1.5:1) in these systems with medium-fast growth rates (2g to 500-1000g in 12 months). Survival rates are >80%, but this is dependent on the management of water quality and good fish husbandry techniques. Smaller recirculation systems have stocking rates of 30-40 kg/m³, FCRs of 1.5-2.0 and fish reach market size in around 12-18 months. However, lower stocking densities generally reduce the risk of system failure, as there is a lower load on the biological filter.

Semi-intensive
The most common semi-intensive systems for rearing Murray cod are ponds. These systems are stocked as highly as the RAS systems, but can only produce up to 14 tonnes/ha/year. Water is not exchanged regularly in these systems, but is added to the pond on a regular basis to compensate for evaporation and seepage losses. It takes longer for fish grown in ponds to reach market size; up to 24 months in northern Victoria. Cage culture is another semi-intensive culture option, however there is limited information on the performance of Murray cod in cages. Trials are being carried out to determine optimal stocking densities and culture methods. There are restrictions on stocking Murray cod in ponds and cages south of the Great Dividing Range.

Extensive
Extensive grow-out in farm dams and ponds is commonly undertaken at stocking rates of 300-500 fish/ha. These fish feed on predominantly natural feeds and have growth rates of 2-3 kg in about 3 years.

Table 1: Water Quality Parameters for Murray Cod Culture

Parameter	Lower Level	Upper Level	Optimal Range
Water temperature (oC)	9	34	20-25
Salinity (ppt)	-	-	<6.0
Dissolved oxygen (mg/l)	4.0	-	>5.0
pH (scale)	5.5	-	6.5-8.0

Culture Attributes

• Existing juvenile production
• Relatively tolerant to water quality conditions
• Commercial diets are being developed for the species
• Medium-fast growth rates
• Efficient food conversion

Marketing Attributes The eating quality (firm white flesh) of Murray cod is highly regarded by both domestic and export markets and is suitable for Asian and Western cuisine. Recently, a taste-testing study was undertaken with representatives from four Asian countries with the fish very well received in terms of flavour, texture and colour (DNRE, 2001). The Murray cod aquaculture industry is still in its infancy in Victoria and production from this sector is expected to grow significantly over the next few years. Market development is currently being undertaken by the existing industry to build demand for the fish in the domestic market and overseas. It is thought that there is significant demand for the product to be exploited in both the domestic and international markets. Preferred sizes vary with markets and the time of year and may range from 500g to 3.0kg. Larger Murray cod are also in demand, however the economic viability of growing these fish must be considered.

Figure 3: Average Price of Murray Cod at the Sydney Fish Market 1999 - 2001