World Aquaculture Magazine - March 2021

WWW.WA S .ORG • WORLD AQUACULTURE • MARCH 2021 35 involves devising more precise methods for delivering feed in the required amounts and at the most appropriate times and locations within the culture system. Procedures that improve the feed conversion ratio, even marginally, often result in significant reductions in the use of feed-embodied resources such as water, land and energy. Examples of these include the use of demand feeders controlled by sound, sonar, heat sensing, image analysis and other high-tech solutions. These techniques contribute to maximize fish growth, avoid feed waste and minimize the overall use of resources. 5. Replace antibiotics and agrochemicals with soft technologies. The presence of antibiotic residues in the food supply is a serious human health concern as it can lead to the spread of antibiotic- resistant bacteria. Antibiotic use (and sometimes abuse) has been a serious challenge for the aquaculture industry, but luckily progress has been achieved at reducing or eliminating their use and that of other agrochemicals by alternative technologies such as biomimicry, prebiotics, probiotics, vaccination, alternative “green” therapies, development of disease-tolerant strains and biosecurity protocols. As aquaculture matures, increasing numbers of producers appreciate the value of preventing rather than treating diseases by reducing stress and boosting the immune system of farmed animals. Aquafarms should have an aquatic animal health plan and a contingency plan for responding to natural disasters and other emergencies. 6. Farm local species that convert feed into edible products efficiently. The selection of the species is another of the principal factors determining the sustainability of an aquaculture project. When non- native species are introduced for farming, they have the potential (indeed are likely) to escape to the wild and may cause deleterious effects on native populations or ecosystems, or introduce or exacerbate pathogens. Aquaculture should prioritize endemic or naturalized species to avoid these pitfalls. Although farming of exotic species has been common practice, it should only be considered when strong containment measures are implemented, particularly in completely closed systems that prevent release to the environment. Aquaculture organisms are “cold blooded” (poikilotherms), neutrally buoyant in the water, and dispose of nitrogenous wastes efficiently (ammonotelic). These metabolic advantages make them very efficient at converting feed into edible tissue by devoting energy to growth rather than to maintaining body temperature, supporting their own weight or processing metabolic wastes. Species low in the food chain such as seaweeds, oysters, mussels and clams require no artificial feeds, spend no energy in moving, improve water quality by assimilating excess nutrients, and fix significant amounts of carbon in their bodies and/ or shells. Aquaculture should concentrate efforts on species that are efficient converters of feed to edible meat (low feed conversion ratio, or FCR), grow fast and have attractive markets. 7. Use domesticated stocks. Domestication of farmed species is another technology that can lead to greater resource efficiency. In this regard, aquaculture lags in comparison to other plant and animal production agribusinesses, but research institutions and breeding companies are closing that gap by implementing selective breeding programs. These have focused on improving growth rates, tolerance to diseases and reproductive ability in aquaculture species. By helping to produce more seafood with less resources these technologies make farming more sustainable. It is reasonable to assume that genetic gains will continue and will accelerate by the adoption of advanced molecular tools such as marker-assisted selection, genomic selection, gene editing and others. Growth rate and tolerance to diseases and to climate change have a lot of room for improvement in aquatic species. Other commercially important traits such as feed conversion, performance on non-traditional protein sources, meat yield, and tolerance to high culture densities will increasingly enhance resource efficiency and sustainability. Selective breeding of stocks constitutes another reason to avoid the release of farmed animals to the environment to avoid interbreeding with wild conspecifics that has the potential to reduce the long-term fitness of wild populations. This issue is most relevant with farming of marine fish in cages. Mitigation strategies include improved containment through better management and design of net-pen systems and antipredator nets; shore-based rearing for part of the grow-out period; improved fish handling practices during stocking, rearing and harvesting; and use of sterile fish to eliminate reproduction (Rust et al . 2014). 8. Use technologies that reduce waste and turn trash into cash. Aquaculture companies should implement circular economy models to minimize waste of resources. This means reducing unnecessary inputs and using every by-product of the farm to generate added income. Farms can generate by-products with significant value; for example, shrimp farms can make use of shrimp shells (exoskeleton) by turning them into high-value chitin-associated products. Pond sludge can be turned into fertilizer. Fish trimmings and processing wastes can be used to produce protein concentrates. Fish feeds can make use of rendered by-products. There are also farming technologies that utilize resources more fully; for example, using waste heat from industrial processes for aquaculture. Integrated ( C O N T I N U E D O N P A G E 3 6 ) Pristine areas should be preserved.