ALMOST two-thirds of Australian households own a ‘barbie’, making Australia somewhat of a ‘barbecue Mecca’, and showing how central having a barbie is to the nation’s identity. When it comes to what people like to throw on those millions of barbecues, the iconic prawn is usually near the top of the list.
The stats on prawns in Australia are perhaps even more impressive. Between 2014 and 2015, Australia produced 5,282 tonnes of farmed prawns and 19,777 tonnes were wild-caught. Around 6,491 tonnes of high-value prawns were exported, while a whopping 32,286 tonnes of prawns were imported as frozen, or prepared and preserved product (Australian fisheries and aquaculture statistics 2015, DAFF).
You may have seen or heard some of the news recently about a possible shortage of prawns[Link will open in a new window] expected this Christmas, with suppliers urging seafood lovers to get their orders in now or risk missing out. Understandably, prawns normally cost more at this time of year because of the demand, but this year prices for the best and biggest local prawns may surge. The reason for the shortage is a combination of domestic disease outbreaks and floods last year, import restrictions and overseas demand for high quality premium Australian prawns.
In this context, it is clear prawn aquaculture will play an important role in meeting the insatiable demand for high-grade Australian prawns, both domestically and internationally. Keeping this supply sustainable will require higher productivity and more efficient prawn aquaculture in Australia. Optimising the feeding of the prawns and their nutrition is essential to achieving these goals, with feed being the major running cost of prawn aquaculture.
A short history of prawn aquaculture
Large scale commercial prawn (penaeid shrimp) farming began in the 1970s and global production grew quickly to meet an ever increasing demand for the tasty critters. All farmed prawns are dominated by just two species, Litopenaeus vannamei (whiteleg shrimp) and Penaeus monodon (black tiger prawn) (see Figure 1). The rapid global growth in the prawn industry since 2000 has been mainly driven by the production of the smaller and cheaper whiteleg shrimp.
To put the Australian industry in perspective, production only started here in the 1980s and represents a tiny 0.1% of the global industry. The black tiger prawn and the banana prawn, Fenneropenaeus merguiensis, are the only two species farmed in Australia, with small volumes of kuruma prawn, Penaeus japonicus, having been farmed in the past.
The shift from small family farm prawn production towards the larger commercial intensive systems of today has driven a shift from reliance on natural food organisms to more dependence on formulated aquafeeds to provide the bulk of the nutrition required by the prawns.
That’s where the problem is—the aquafeeds used for farmed prawns still contain wild fish resources, which is widely recognised as unsustainable.
Reducing wild-caught ingredients
Fishmeal is a crude by-product produced from wild-caught fish and their remains from processing. In 2010, the aquafeed industry used 73% of all fishmeal harvested, with prawn aquafeeds accounting for 26% (Davis, 2015).
A significant, but declining, proportion of fishmeal is used as raw material for farmed aquaculture as it is considered one of the most palatable, nutritious and digestible ingredients due to its high protein content, excellent amino acid profile and micronutrient value. Because of this, fishmeal is heavily relied upon for optimum growth and health of farmed prawns. In addition to fishmeal, wild-caught marine invertebrates such as squid, polychaetes, shrimp, krill and molluscs are often include in aquafeeds as they contain ‘unknown growth factors’ for prawns (Williams et al., 2005).
In an attempt to improve the sustainability and productivity of their feeds, much of the aquaculture industry’s focus has gone into finding ways of reducing fishmeal use through intensive nutrition research. This involves quantifying dietary requirements for digestible energy, amino acids and other micronutrients, as well as a rigorous evaluation of potential alternative ingredients.
Other feeds, such as oilseed meal, are used by the industry but the availability and price of oilseed meal and other plant ingredients are dependent on external factors and there is competition for them from other livestock industries, as well as human consumption. Successfully using these ingredients without reducing feed quality is dependent upon knowledge of the nutritional requirements of the cultured species. And unless inexpensive ingredients could readily be sourced, nutritionally complete alternative feeds would not be feasible.
Nutritional research for prawns lags that of other cultured animals, like pigs, poultry and trout, which have been intensively studied (see Figure 2). Improving our knowledge of the nutrient requirements of prawns not only offers the promise of a sustainable, nutritionally complete prawn feed, but could also lead to more efficient utilisation of feeds, therefore boosting productivity and cutting costs.
Focussing on nutrition
Research on alternative prawn feeds and feeding practices has already shown some significant promise. The feed conversion efficiency of prawns—that is, the ability of prawns to convert feed into body mass—has improved despite an increasing trend in the replacement of fish meal with oilseed meal over the last decade. This trend is expected to continue, as shown in Figure 3. Feed conversion ratios of between 1 and 1.5 are readily being achieved for prawns which is very efficient compared to some other livestock production sectors.
The need for a reliable, inexpensive and nutritionally complete feed has become pivotal for further productivity and sustainability improvements. Formulated feeds are preferred to live/fresh foods as feed formulation allows control of nutritional content and quality and flexibility in accommodating fluctuating feed ingredient costs and availability.
Recent CSIRO research into the nutrition of alternative feed ingredients and feed additives has delivered the innovation required. NovacqTM, a novel bioactive from a natural food source produced by marine microbes developed over the last decade by CSIRO, is a major step change for the prawn industry. Results have shown that prawns can grow 20 to 40% faster in controlled tank environments when NovacqTM is added as a feed ingredient (at 10% inclusion), and a 20% higher weight gain has been achieved over eight weeks in commercial prawn ponds.
CSIRO’s studies have demonstrated that prawn feed without any fishmeal can deliver similar or better performance than classic fishmeal-based feed when the bioactive NovacqTM is added (Glencross et al., 2014). Prawns also perform better on low protein diets when NovacqTM is included, allowing more sustainable and efficient production (Glencross et al., 2015).
These results pave the way for the development of prawn feed with no wild caught marine ingredients.
Ridley Corporation Research Alliance Project
Ridley Corporation is the Australian and world licensee (excluding Vietnam and China) for NovacqTM. Commercialising this product in partnership with Ridley has opened up an opportunity for us to launch into an enriched program of science to assess the feed’s potential for use with other aquaculture species, and identify the molecular mechanisms underlying prawn growth, health and nutrition promoted by its bioactives.
Together with Ridley we will refine and optimise the production process to control product quality and yield. This collaborative research is multi-site and multi-disciplinary, spanning several science domains, such as zootechnology, nutrition, physiology, health, molecular biology, microbiology and biotechnology.
This research program is delivering the sort of innovation needed to produce bigger and healthier prawns to satisfy the global appetite for them, while working to alleviate entirely their pressure on the world’s precious marine stocks.
Dr Cedric J. Simon is a Senior Scientist in Aquaculture Nutrition, CSIRO Agriculture & Food, located at the Queensland Bioscience Precinct in Brisbane.
Dr Ha H. Truong is a Post-Doctorate Fellow in Aquaculture Nutrition, CSIRO Agriculture & Food, located at CSIRO’s Bribie Island Research Centre.
References
Alday-Sanz V. (Ed.). (2010). The shrimp book. Nottingham University Press.
Davis D.A. (Ed.). (2015). Feed and Feeding Practices in Aquaculture. Woodhead Publishing.
Deshimaru O. & Kuroki K. (1974). Studies on a purified diet for prawn. 1. Basal composition of diet. Bulletin of the Japanese Society of Scientific Fisheries, 40(4), 413-419.
Glencross B.D., Irvin S., Arnold S.J., Blyth D., Bourne N.B., Preston N.P. (2014). Effective use of microbial biomass products to facilitate the complete replacement of fishery resources in diets for the black tiger shrimp, Penaeus monodon. Aquaculture 431, 12-19.
Glencross B.D., Arnold S.J., Irvin S. (2015). Bioactive factors in microbial biomass have the capacity to offset reductions in the level of protein in the diet of black tiger shrimp, Penaeus monodon. Aquaculture 446, 74-79.
FAO. (2016). The state of world fisheries and aquaculture. Food and Agriculture Organization of the United Nations, Rome.
Williams, K.C., Smith, D.M., Barclay, M.C., Tabrett, S.J., Riding, G. (2005). Evidence of a growth factor in some crustacean-based feed ingredients in diets for the giant tiger shrimp Penaeus monodon. Aquaculture 250, 377-390.