Marine fish - aquaculture prospects

Introduction

Despite having the third largest fishing zone in the world, Australia’s fisheries resources are not as abundant or productive as those in many other parts of the world and many fish species have been heavily exploited by human activity.

Not surprisingly there is a growing interest in aquaculture and the development of marine finfish farming. Over the last decade the industry has grown moderately and well within its potential with total production estimated to be about 9,500 tonnes per annum in the latter part of the 20th century, valued at around $96 million.

The successful farming of marine fish on a large scale may also serve to reduce the fishing pressure on wild stocks of inshore species currently being over-exploited. There is also increasing interest in enhancement of wild stocks through release of hatchery reared juvenile fish.

Aquaculture Research Information Sheet: Marine Fish Breeding

Industry in NSW

The temperate coastal waters of NSW are too cold for commonly farmed tropical species like barramundi and too warm for salmonids like Atlantic salmon which are farmed in Tasmania. Nonetheless, marine fish farming for commercial market and stock enhancement has potential for significant growth in NSW. However, in the past a number of technical impediments have limited expansion, including the lack of a consistent supply of juvenile fish for stocking, a scarcity of suitable sites for marine fish farming along the coastal zone and the expense of suitable feeds.

NSW Fisheries are undertaking research to overcome these impediments and have selected, bred and reared native fish species for farming and stock enhancement. Although a number of marine finfish species are considered to have potential for aquaculture in NSW, two species, snapper (Pagrus auratus) and mulloway (Argyrosomus japonicus) have been singled out for investigation at the Port Stephens Research Centre (PSRC) as species having the best potential. NSW Fisheries has been conducting research into the breeding of marine fish at PSRC since 1990 with significant advances in farming techniques.

The commercial (wild catch) snapper fishery is the third most valuable NSW finfish resource after sea mullet and bream. The annual NSW commercial snapper catch in 1997 was about 300 tonnes and had a wholesale value of about $2.6 million. More than half the snapper sold at the Sydney Fish Market is imported from other Australian states or New Zealand. Over 1300 tonnes were imported from New Zealand in 1999. Both snapper and mulloway command high market prices (about $10-15 per kilogram). The growing demand for high quality finfish is making the aquaculture of marine fish more economically feasible.

Mulloway were bred for the first time at PSRC in 1992. Eight years of intensive research by NSW Fisheries, supported by grants from the Fisheries Research and Development Corporation (FRDC) and through collaboration with the Co-operative Research Centre

(CRC) for Aquaculture, resulted in successful pilot-scale breeding and growout in sea cages of snapper and mulloway.

NSW Fisheries is currently undertaking research which could prove critical to the future development of a marine fish farming industry in New South Wales. Research is being carried out to develop commercial hatchery techniques for snapper and mulloway to allow sustainable production of high quality and inexpensive fingerlings.

Hatchery and nursery techniques for snapper have now advanced to the stage where commercial quantities of fingerlings should be available to industry. A private company is also having considerable success at their hatchery in northern NSW, raising juvenile snapper for sea cage growout.

Currently, there is a commercial snapper and mulloway farm in Botany Bay, Sydney, utilising floating mesh cages. NSW Fisheries has also granted a lease for a snapper farm near Port Stephens, in ocean waters 3 kilometres off the coast. The project is designed to test the feasibility of a full-scale commercial snapper farm. The future expansion of the marine finfish farming industry in the short term will be dependent on the outcome of a rigorous environmental monitoring program that has been established for both commercial operations. A trial period of two years was allowed to assess the feasibility of sea cage farming in New South Wales.

Inland saline research project

NSW Fisheries is involved in a research project to assess the suitability of saline groundwater for growout of snapper and mulloway. Inland Australia has huge quantities of saline groundwater. At Wakool, near Deniliquin in south-western NSW, Murray Irrigation Limited (MIL) manages approximately 60 ponds (each 20 hectares in size) used to evaporate saline water which has been pumped to the surface from shallow water tables. This is done to prevent the saline water table from rising into the root-zone of irrigated agricultural crops. In many of the ponds the salinity is similar to ocean water, which presents an excellent opportunity to investigate whether the saline groundwater can support marine fish. Initial results indicate that water chemistry needs to be slightly adjusted and this can be done economically. Pending the outcome of additional experimental work, this project may lead to the development of management strategies for large-scale inland marine fish culture in saline groundwater.

Distribution and similarity to other species

As stated, snapper and mulloway have been identified as having significant aquaculture potential. Red sea bream – a closely related species to snapper, was first artificially bred in Japan where it forms the basis of a significant aquaculture industry and has been farmed for about 25 years. There is also an independent and reproductively isolated population of red sea bream in China. In Australia, snapper are found in temperate waters in all states and New Zealand. Juveniles are found in estuaries, while adults inhabit coastal and offshore waters.

Mulloway are found in all states of Australia as well as in Africa, Madagascar, Mauritius and India. In Australia, juveniles of the species commonly inhabit estuaries and inshore reefs. Adults occupy similar environments and tend to move to deeper inshore waters and ocean beaches. In America, two species similar to the mulloway, the white sea bass (Gynoscion nobilis) and the red drum (Sciaenops ocellatus) are being reared in large numbers. These fish are mostly used to enhance wild stocks and enhance catch rates in recreational fisheries.

Growth and production

Consequent to the well established red sea bream aquaculture industry in Japan, biological and nutritional requirements of snapper have been extensively studied. The aquaculture of marine fish closely related to Australian snapper and mulloway is well advanced overseas.

Reproduction

The rearing of marine fish usually involves collecting broodstock, hormone treatment to induce spawning, incubating fertilized eggs and nurturing yolk-sac larvae, culturing and feeding live food to larvae and final growout of juveniles to market size.

The spawning period of snapper varies with latitude but appears to occur when surface water temperatures exceed 18° C. Snapper from the Sydney region spawn in spring and early summer. Snapper are serial spawners and depending on the size and age of the female, they can produce up to six million eggs each season. Snapper broodstock held in tanks in controlled environments can be induced to spawn all year round by manipulating temperature and photoperiod (day-length).

Established hatchery techniques exist for the same species in Japan. Research has shown that these techniques also work with snapper in Australia but improvement in growth and survival of fingerlings is necessary to reduce the cost of production.

The egg and larval development of snapper closely follows that described for red sea bream. Of particular relevance to their aquaculture potential is their small size at metamorphosis (8-9mm).

Less is known about the reproduction of mulloway in the wild. A highly fecund species they are believed to spawn offshore in late summer and early autumn. Wild-caught broodstock have been successfully induced to spawn following hormone induction with hCG (100 iu/kg). Captive broodstock have also been induced to spawn several months earlier than wild fish by manipulation of temperature and photoperiod.

Large numbers of mulloway fingerlings have been successfully produced by NSW Fisheries using intensive and extensive, fertilized pond techniques. Similar techniques have been used to breed other species in the same family (Sciaenidae) such as red drum (Sciaenops ocellatus) overseas.

Growth

The growth rate of snapper in the wild is relatively slow; they take 3-5 years to reach the market size of 28cm (measured from snout to tip of tail) and an average weight of 400g.

In the Sydney area, snapper can be grown to this size in tanks and seacages within 21 months at ambient water temperatures. Snapper reared in captivity do not have totally uniform growth with varying sizes of fish increasing the likelihood of cannibalism and territorialism.

Mulloway grow faster in the wild than snapper. In the Clarence River, wild mulloway grow to 25cm total length by the end of their first year, and to 60cm by the end of their second year. The total weight of a 60cm mulloway is around 2kg.

Mulloway grown in seacages in the Sydney area reached legal-size of 45cm (total length) and approximately 1.1kg within 26 months at ambient water temperatures. Juveniles are very cannibalistic and regular size grading is necessary to prevent large losses of fish at the hatchery. However, the cannibalistic behaviour becomes less of a problem when fish are around 80mm total length.

Growout Densities and Behaviour

Marine fish can be grown-out at high densities in seacages if the cages are located at sites with good water quality and circulation. In Japan, red sea bream are usually raised at densities of 6-8kg per 1000L. In Europe, sea bass and gilt-head sea bream are fed pellets and kept at densities of 22-40kg per 1000L.

Snapper and mulloway have good attributes for growout in cages such as their preference for forming schools and ability to adjust to captivity, which makes inspection for diseases relatively easy. Mulloway tend to spend long periods of time ‘hovering’ rather than swimming. The energy saved by this behaviour may result in faster growth.

NSW Fisheries successfully grew snapper and mulloway to market-size in the pilot scale seacage trial in Botany Bay. The density of fish at final harvest was 10kg per 1000L for snapper and 15kg per 1000L water for mulloway.

Diet

When reared intensively, there is a high mortality rate in red sea bream and snapper when they are about 12-17mm (about 30-40 days after hatching). This appears to be related to a deficiency in their initial diet, usually rotifers or artemia, or both. The production of these live foods is expensive and preliminary research by NSW Fisheries on early weaning of snapper with artificial pellet diets formulated for Red sea bream have been successful. Mulloway larvae have not shown the same early mortality syndrome as snapper when fed nutritionally enhanced rotifers and artemia.

Feed is the most costly item in rearing marine fish. Extensive literature is available on how to optimise growth. NSW Fisheries has completed preliminary research on dietary requirements of snapper based on information for red sea bream. A pellet diet has been developed which has a high percentage of protein (up to 50% by dry weight), highly unsaturated fatty acids and a low-fibre content. It also contains a range of vitamins and minerals.

Hatchery reared juveniles can be weaned readily from live food, to high quality pellet diets. Growout trials have shown that snapper can convert pellets with 42% fishmeal protein, to flesh at a ratio of 2:1. The ease with which snapper take pellets provides the opportunity to vary the composition of the diet. Another attractive feature of formulated diets is that snapper raised to market size on fishmeal pellets are as acceptable to consumers as wild snapper.

Wild mulloway feed mainly on live food. In captivity, they can be weaned onto dead fish, squid and prawns. Hatchery reared mulloway larvae readily accept artificial diets at an early age (about 20 days after hatching) and learn quickly to feed from automatic feeding devices.

Diseases

Epidemic diseases caused by organisms such as ciliated protozoan and monogenean trematodes, have killed juvenile and adult snapper and mulloway. The behaviour of heavily infested fish often changes rapidly and may include loss of appetite, ‘flashing’ or rubbing their bodies on tank surfaces, slow swimming, loss of flight response when attempts are made to catch them and rapid or laboured gill movement. Control of ciliated protozoans is achieved best with prophylactic treatment of formalin at 150-200mg/L – 1 for one hour over three consecutive days once every two weeks. Control of trematodes is achieved best with treatment (with active ingredient, Trichlorphon) at 0.5 – 1mg/L – 1 every third day for 12 days. Heavy mortality can occur if diseases are left untreated and during weaning and at other times when fish are stressed.

A small percentage of broodstock either collected from traps or held in tanks may develop gas bubble disease which is presently untreatable and blinds the fish in the infected eye.

Hardiness

Juvenile snapper are reasonably tolerant to handling and overcrowding although their eyes can be easily damaged if handled roughly or with nets. Adult broodstock readily acclimate to captivity. Mulloway juveniles are more delicate than snapper and their tails may erode quickly after handling if water quality is not optimal. Adult mulloway adapt readily to captivity, however, the time taken to resume ‘normal’ behaviour in tanks is reduced if several fish are held together.

Research has shown that snapper which were reared from eggs to maturity in hatchery tanks or cages (first generation: G1) are less stressed and reproduce high quality eggs and larvae more easily than broodstock fish collected directly from the wild.

Site selection

The artificial propagation of juveniles using intensive rearing techniques needs relatively small areas of land; access to suitable water at potential sites may present a problem. However, a major limitation on marine fish farming in New South Wales is the likely scarcity of suitable sites in sheltered embayments for the growout of fish to market size.

Marine fish could be on-grown to market size either in sea cages in territorial waters or in land based, outdoor pond or intensive tank systems. A number of important criteria need to be met in order to establish a suitable site for sea cage farming. Sites would need to have moderate currents, be secure from vandalism and damage by storms, be close to shore-based support operations, have adequate water depth and excellent water quality. Sites in sheltered embayments with these characteristics are relatively sparse in NSW, due to existing demand from a variety of other interest groups (population pressure on coastal zone, recreational anglers and boaters). Adverse weather conditions also have the potential to create challenging working conditions for sea cage operators offshore.

Using land-based culture, abundant amounts of high quality seawater is necessary and coastal sites are favoured where clean water can be accessed and pumped ashore. The extensive rearing of marine fish in earthen ponds needs large areas of land. Suitable coastal sites need to be carefully evaluated for snapper, as they do not tolerate large reductions in salinity. Mulloway tolerate low salinities and it would be possible to rear them in brackish water in ponds such as those already constructed for prawn farming on the north coast.

A site selection process has been conducted in the North Coast Aquaculture Strategy that identifies potential land based aquaculture sites on the NSW north coast. This strategy also sets out design and operational performance standards together with other useful information for potential investors and establishes a streamlined approval process for new enterprises.

Markets

Snapper are relatively easy to market and NSW is a relatively big net importer of snapper. The majority of the existing demand is for plate-size fish (400g), which are sold and served whole. In Japan, Red Sea bream are highly prized as sashimi and for the live fish market. There are a number of ways to expand the high value market for Australian snapper. One is to export live and sashimi-quality snapper to Japan. Technology has been developed in New Zealand to export live wild snapper. Another is to develop a local market for live and sashimi snapper.

Marketing mulloway is a different proposition. Unlike snapper, large mulloway (more than 2.5kg) currently fetch the best price. Wild-caught smaller mulloway (soapies) have poorer consumer acceptance, however informal taste tests of 1kg mulloway grown in seacages were very favourable and pond rearing trials have also produced a high quality product. Little is known of the export potential for mulloway.

Conclusion

Marine fish farming is developing in NSW but continued research and capital investment is needed before the industry will expand. The limited number of suitable sites for marine finfish farming may restrict the size of the industry initially. If inland saline groundwater is suitable for marine fish, then a new industry could develop very quickly.

An assessment of the environmental performance of the two commercial seacage operations (Botany Bay and Port Stephens) over the last two years will affect the future feasibility of offshore seacage farming. Land based marine fish farming on the coastal zone has significant potential for expansion in the short to medium term.

* commercial farming of market-size fish well established
† commercial farming of market-size fish developing
‡ commercial farming of fingerlings for stock enhancement in freshwater impoundments

Further information

For further information, call NSW Fisheries; Port Stephens: 02 4916 3900.

References

NSW Fisheries, September 1998. Information Sheet: Marine Fish Breeding

NSW Fisheries. Fishnote DF/6 "Aquaculture Prospects for Marine Fish in New South Wales"

Stewart Fielder, Scientific Officer, NSW Fisheries, Port Stephens Research Centre (Personal Communication).

Fielder, S. 1998 "Salted Fish." In Fisheries New South Wales – The Journal of Sustainable Fishing. Summer 1998/99 edition.