The stocking of Black Bream into inland water bodies in Southern Western Australia, Aqua info, Technical Aquaculture information, Department of Fisheries, Western Australia, Fish for the Future

The stocking of Black Bream into inland water bodies in Southern Western Australia

This article summarises the key results from a recent two-year study on the performance of black bream (Acanthopagrus butcheri) in inland private dams and describes the goals of a new study which aims to improve growth and survival rates in appropriate dams.

Freshwater fish species for recreational angling

Southern Western Australia has only one native freshwater species suitable for recreational angling, namely the freshwater cobbler which is not a highly sought after species. There are three introduced species that support recreational angling, including two species of trout which generally require regular restocking and are normally restricted to pristine waters in the south-west corner. Redfin perch also occur in waterways used for recreational angling, however this species is considered an unwanted pest which Fisheries Western Australia is concerned will impact on the highly prized marron stocks and non-commercial native finfish species. Only trout are approved for stocking public waterways as they do not usually reproduce in this state. However, fisheries enhancement with native species has potential, especially with black bream (Lenanton et al., 1999).

A number of fish species native to eastern Australia (silver perch, golden perch and Murray cod) have been introduced into farm dams in this state for the purposes of recreational angling and/or aquaculture. Silver perch has been the most successful and is being commercially farmed in Western Australia but only allowed in locations where escape into natural waterways is unlikely. In other locations, it would be necessary to stock such ponds with fish native to Western Australia.

Black bream and aquaculture

One fish that appears to be suitable for stocking into inland water bodies is black bream. Since black bream are native, can be readily cultured, and can seemingly tolerate a wide range of environmental conditions, they appear to be the perfect candidate (Jenkins et al., 1999).

Black bream occur naturally in the rivers and estuaries of southern Australia. Different estuaries represent distinct genetic populations, which indicates the translocation of different stocks into waterways should be avoided until a full understanding of the ramifications of this is known. At present, all of the hatchery production of black bream is from Swan River stock. Over 160,000 fry have been released into approximately 300 fresh and saline private water bodies in the south-west ranging from Carnarvon in the north to Esperance in the east.

In recent years, the success of the breeding and rearing of black bream by the Aquaculture Development Unit at the Fremantle Maritime Centre has generated a great deal of interest from farmers and private industry in the stocking of inland water bodies with black bream for the purpose of recreational fishing. A further interest has been generated in commercial aquaculture. This has all expanded rapidly with limited knowledge of the survival of black bream released into fresh water, the success or failure of past stockings and any real data to support them as a candidate species for aquaculture.

Research projects into stocking black bream

A two-year FRDC (Fisheries Research and Development Corporation) funded research project involving the Department of Fisheries (Research Division), Murdoch University and Fremantle Maritime Centre has recently been completed. The overall aim of this project was to assess the survival of black bream (Acanthopagrus butcheri) that had been stocked into inland water bodies throughout southern Western Australia for the purpose of providing recreational fishing opportunities in this region.

This project had three main aims:

To determine the characteristics of private inland water bodies into which black bream have been stocked. To determine which characteristics of inland water bodies result in a combination of good growth and survival of black bream.
To determine, using laboratory facilities, the influence of salinity and temperature on the growth and survival of black bream.

Survival and growth of black bream in inland water bodies

Results from the surveys of over 150 water bodies in southern Western Australia have shown that the majority of these did not possess the characteristics that are conducive to successful survival and growth of black bream (see below). The most common types of water bodies stocked with black bream were clay dams that are typically used for watering stock. These dams usually contained fresh or very low salinity water that is highly turbid (suspended clay/silt), and were often prone to very low water levels during the summer months. Property owners would therefore be advised to consider other fish species such as silver perch and trout in cooler areas for stocking water bodies possessing these characteristics.

The survival and growth rates of black bream that were stocked into water bodies containing saline water were very encouraging and in a small number of these, the black bream attained sexual maturity. This implies that, provided there is the appropriate habitat and food for the larvae, black bream may breed in some water bodies and establish a self-sustaining population. In several ponds situated on salt-affected land in the central wheatbelt, the survival of stocked black bream has been
> 90% and they have grown from a stocking size of 50 mm total length (4 grams) to over 200 mm (135 grams) in 18 months. However, more information is required on all aspects of production including water quality, growth rates, food requirements and markets before back bream can be considered as a good candidate species for commercial aquaculture.

Laboratory studies on survival and growth

In addition to the data obtained directly from the field, the growth and survival of black bream under various salinity and temperature regimes was assessed in laboratory studies. Trials investigating the effect of salinity found that juvenile black bream were able to survive and grow well at salinities ranging from freshwater to 48 ppt, when grown at a temperature of 22 to 24°C and fed regularly on a high quality ration. Growth was best at 24 ppt, resulting from both food intake and conversion efficiency being maximised at this salinity. Growth was significantly (p > 0.05) reduced at 60 ppt, compared to 24 ppt, and signs of osmotic shock and stress were evident at this salinity.

Trials investigating the interactive effect of temperature and salinity revealed that temperature has a more significant effect on the growth of black bream than salinity. Tested at a temperature range of 16 to 24°C, those fish held at the highest temperature achieved 310% better growth over a 3 month period, compared to those grown at 16°C.

The results from a separate trial on low temperature tolerance revealed that black bream held in fresh water were less tolerant of thermal shock than those held in saline water. Further studies investigating the interactive effect of low temperature, ration (quality and quantity) and salinity may be useful in evaluating the reasons behind the poor performance of black bream held in fresh water in the field.

Farming black bream

The work to date has indicated that the fish have not grown or have died when stocked into fresh water (which is defined as having a salinity of < 1 part per thousand, or < 1000 parts per million, or < 70 grains per gallon). It has also been identified that cormorants (shags) can be a major predator of stocked bream in some areas, particularly if the water is shallow, clear or devoid of cover.

Factors which enhance the survival of black bream in farm dams include availability of cover, such as aquatic vegetation, logs or hides. Juvenile fish must be introduced into a dam or pond carefully (i.e. slowly mixing the fish and ‘new' water) to avoid stress associated with sudden changes in temperature and salinity. The placement of newly stocked fish into a cage or pen has proved successful in assessing losses associated with stocking stress and/or poor water quality before releasing them into the main water body.

The availability of feed, either natural or artificial, is essential if acceptable survival and growth rates are to be expected. Whilst black bream will survive and grow well in some dams with high levels of natural feed, generally the more bream placed into a dam, the greater the need for supplementary feeding.

Site selection is most important. Based on limited experience to date, selected water bodies should:

have a minimum (or winter) salinity greater than 3ppt (210 grains per gallon);
retain adequate volumes of water year-round, i.e. not become very shallow in summer;
incorporate silt traps to minimise deaths due to high organic loads and/or low levels of dissolved oxygen.

Further research

Since black bream are highly regarded for their sporting and eating qualities, they could be used for the stocking of private waters for use as both on-farm recreation and as income-producing fish-out ventures, adding value to what is otherwise valueless salinised inland water. However, the results from the work will provide valuable information to those with commercial aspirations for this species.

The FRDC has recently approved funding to continue this research for a further three years. The ultimate objective of this study will be to determine the suite of conditions required in inland saline water bodies that will enable black bream to be grown to a size suitable for angling. Their suitability as a commercial aquaculture species will not be directly assessed in the coming project.

Aspects of this research will include:

Effectiveness of caging juvenile black bream
Field trials at the Springfield research ponds at Northam will be conducted to determine if stocking black bream fingerlings in floating cages improves survival and subsequent growth.
Evaluation of currently available commercial fish feeds
Laboratory and field trials will be conducted to determine which of six (commercially available) artificial fish feeds result in optimal growth and survival of juvenile black bream. An appropriate large water-stable food brick will be developed for larger black bream.
Elucidation of the growth rates of black bream from different genetic stocks
Black bream larvae will be cultured from two genetically different broodstocks and grown under identical conditions and their growth rates compared. This will provide some insight into the extent to which the genetic stock of black bream influences growth.
Effectiveness of introducing different types of protection to reduce predation on black bream by birds
Effectiveness of using branches, plastic bunting and artificial hides in reducing the predation on black bream by birds such as cormorants (shags).

Conclusion

The initial project was designed to evaluate the success of previous black bream stockings in private waters, and determine some of the environmental parameters required for successful stocking. While more information is clearly required on the optimum conditions for successful aquaculture, the preliminary data collected to date have demonstrated:

Survival and growth rates have been very encouraging in water bodies containing saline water and in several of these, black bream have attained sexual maturity.
Survival of black bream stocked into water bodies containing fresh or very low salinity water has been low or nil.
Small black bream, in some water bodies, can be highly susceptible to predation by cormorants.
Naturally occurring feed in some water bodies may not be adequate for larger black bream and supplementary feeding may therefore be necessary to ensure optimal growth.

Information collected during the study just completed has identified those areas in which further research will be focused during the present FRDC funded project titled "Factors required for the successful culture of black bream in inland waters". This will allow both local and interstate (Victorian and South Australian) farmers to make informed decisions on whether to stock black bream in impoundments on their properties.

The results should also provide the basis for a diversification of farm activities through the provision of on-farm recreational fishing or provide the potential for additional income by identifying water body types that may be suitable for put-and-take fishing. This may have the added benefit of reducing the fishing pressure on natural populations. The information generated will also provide some vital base information relevant to the emerging black bream aquaculture industry, about which information is currently limited.

The Departmenf of Fisheries does not recommend the stocking of black bream in freshwater or low salinity dams (< 3 ppt) in cooler areas of the state.