The world demand for seafood is projected to increase by 30–40 million tonnes by 2050, with the bulk supplied from aquaculture. It is, therefore, not surprising that issues of intensification and sustainability are becoming increasingly pivotal. Moreover, much of this additional supply will have to come from the Asia-Pacific region. Very high degrees of intensification have been successfully accomplished in the case of several aquaculture species exemplified by striped catfish (Pangasianodon hypophthalmus) and penaeid shrimps, and all evidence indicates these are sustainable, barring fluctuations to be expected in any form of primary production. However, it is critical that future intensification is planned and implemented in compliance with globally accepted norms of sustainable development as originally envisioned by the 2000 Bruntland Report, “Our Common Future”.
Improved feed management represents a critical component in the sustainability equation, and the industry’s responses, particularly in respect to the use of fish meal and fish oil, will determine whether feeds are likely to become a limiting factor in attaining sustainability. The paper discusses plausible means of reducing dependence on these commodities as well as other avenues for intensification and sustainability.
Globally, around 25 percent of the marine fish catch, approximating 25 million tonnes, is utilized for fish meal and fish oil production, giving an approximate conversion of 5:1 and 110:1, respectively. Aquaculture uses nearly 63 percent and 85 percent of global fish meal and fish oil production, respectively. The leading producers are South America and Europe. Increasingly, in the Asia-Pacific region, fish meal and fish oil are produced using fish processing waste, thereby reducing the need for imports of fish meal by the animal husbandry and aquaculture sectors. Their use in aquaculture feeds has long been controversial since Wijkstrom and New coined the term ‘the fish meal trap” to highlight the dependence of aquaculture on marine wild stocks. A further objection was made on ethical grounds, arguing that reduction of a raw material (fish in this case) to produce fish meal and fish oil in order to produce a higher quality luxury animal foods is not ethical. The controversy has sparked a global dialogue and much research into reduction of the use of fish products in feeds. Of the 63 percent of global fish meal supply used in aquaculture, nearly 80 percent is used for salmonid, shrimp and marine fin fish culture- all high-value species, but collectively representing less than 15 percent of global aquaculture production.
Is availability of fish meal and fish oil likely to hinder intensification and sustainability of aquaculture in the Asia-Pacific region? Trends in aquaculture in the Asia-Pacific region suggest that its intensification and sustainability are unlikely to be constrained by fish meal and fish oil availability. For example, in the past decade the major growth in production is attributable to low trophic species such as striped catfish ( Viet Nam and elsewhere), Labeo rohita- rohu in Myanmar, and tilapia (in many countries in the region); all these require low protein feeds and hence minimal quantities of fish meal and often no fish oil in feed formulations. It is expected therefore that usage of fish meal and fish oil will become more rational as prices rise, and will tend to be used most for high-priced commodities such as the salmonids.
Secondly, the trend towards use of fish processing waste has reduced the demand for fish meal and fish oil. Thailand produces 500 000 tonnes per year of fish meal from trash fish and fish processing (mostly tuna) waste. In Viet Nam the stripped catfish sector generates 500 000–700 000 tonnes of processing waste from which oil is extracted for industrial purposes and the meal used for animal production, thereby releasing the availability of an equivalent quantity of fish meal for aquaculture development. Also, some of the developing countries in the Asia-Pacific region (e.g. India, Sri Lanka, Lao People’s Democratic Republic, Viet Nam etc.) apply non-fed practices in their culture-based fisheries; utilizing low trophic species relieves the use of fish meal usage in these systems.
It is, therefore, suggested that fish meal and fish oil availability are unlikely to act as a major constraint to intensification and sustainability of aquaculture in the Asia-Pacific region. Nevertheless, there is a continued need to reduce dependence on these commodities. A number of plausible alternative strategies should be considered. First, among all the researches undertaken on a variety of plant-based raw materials to identify substitutes to fish meal as a feed ingredient, only soy bean meal has achieved any degree of commercial success. Secondly, feed formulations should be revised in light of results demonstrating that at least for tilapia and carp species, the most cost-effective dietary protein level is significantly lower than previously claimed to result in the highest growth rate. According to these studies, using lower protein content feeds the stock grow slightly slower, but are compensated by improvements in focal conversion ratio (FCR) and Protein Efficiency Ratio (PER); the lower protein ration was most cost-effective.
The concept of “mixed feeding schedules” was developed by De Silva (1985), primarily based on the observations on the daily variation in apparent dry matter and protein digestibility of feed in the Asian chromid Etroplus suratensis (Bloch). The basic hypothesis was that when the fish were provided a high protein diet throughout the rearing period it might not be able to utilize the feed effectively to the same degree, day after day. This hypothesis has been tested on many tropical species by numerous authors in the laboratory. Based on this hypothesis, many mixed feeding strategies have been tested in a number of aquaculture environments. Data from trials using striped catfish farmers in the Mekong Delta, Viet Nam showed that although harvest time per cycle was 180 days as opposed 210 days for the mixed feeding schedules, saving on feed costs with the mixed feeding schedule ranging from US$20 000–24 000/ha/cycle, far outweighing the delayed in harvesting time. Moreover, nitrogen and phosphorus in the effluent is significantly reduced, making mixed feeding more environmentally friendly.
Culture-based fisheries (CBF) are a much-overlooked and environment-friendly means of facilitating intensification and sustainability in the Asia-Pacific region. According to FAO, the developing nations in Asia have approximately 66 710 052 ha of such water bodies suitable for aquaculture development.
As regional and global demand for food fish increases, it will be imperative that the sector in the region maintains its growth momentum. In order to continue to contribute to global food fish supply, the sector will have to intensify and do so within globally accepted norms for long-term sustainability.
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