Aquaculture is often perceived as being the sustainable solution to the severe overfishing and exploitation of our oceans (Greenpeace, 2008), but is that really the case? Asia accounts for the vast majority (about 88%) of global aquaculture production (FAO, 2014). The worldwide expansion of this sector from about 3 million tonnes in the 1970s to over 66 million tonnes in 2012 has allowed the region to supplement its ever-growing appetite for fish (FAO, 2014). It also greatly contributes to the economic development of the region via export (SEAFDEC, 2012).
Unfortunately there are numerous drawbacks to aquaculture, particularly if it is unregulated and unmanaged. Coastal habitat degradation is a major negative effect of the aquaculture industry. The prime place to build an aqua farm is along the coast and as a result Southeast Asia has lost more than 26% of its mangroves between 1980 and 2005 through both aquaculture and coastal development, and some countries, like Vietnam, have lost up to 80% (FAO, 2014). Mangroves are an incredibly important habitat providing a sheltered area for fish and invertebrate feeding, spawning and nursery grounds. The loss of these therefore seriously impacts marine fisheries productivity.
Once the farm has been built, fish larvae are imported. These are usually sourced from wild capture marine fisheries, thus adding more pressure on wild fish stocks. These ‘foreign’ fish can often introduce pathogens to the aquaculture operation leading to the spread of infectious diseases not only among the population in the farm, but also to wild species in the vicinity, if there are any. This can sometimes severely reduce production capacity and lead to food security and environmental concerns. This was the case in Taiwan with disease outbreaks and negative environmental impacts causing a decline in overall production in the 1990s (Chen & Qiu, 2014). Effluents, such as faecal matter and excess feed, can seriously impact the surrounding marine environments by degrading the water quality and causing eutrophication and disease, among others (Witter et al., 2015).
A significant proportion of the species raised in aquaculture are carnivorous. With an increasingly growing industry, the demand for aquafeeds is on the rise. These are often mostly comprised of fishmeal which is made of ‘trash’ fish (Witter et al., 2015). Trash fish is the term commonly used for low-value catches that are often actually juveniles of commercially important species. However this term is increasingly inaccurate as the demand for fishmeal is sufficiently high enough that instead of the untargeted species being discarded, they are retained. This has led to indiscriminate fisheries no longer targeting any particular species. ‘Trash’ fish simply becomes ‘fish’ due to their value in the aquaculture sector.
The use of trash fish for aquafeed is also incredibly wasteful due to inefficient feed conversion rates, which diverts fish proteins away from human consumption. For reef fish (LRFF in graph below) commonly eaten in Hong Kong this can be as high as 10:1 (15:1 for grouper), versus 2:1 for poultry. This is means that for every kilogram of fish produced from an aqua farm, 10-15 kilograms of fish is inputted. That is an enormous amount of wasted protein.
Some of these impacts can be somewhat mitigated through proper management and the enforcement of certain restrictions. Over-feeding should be avoided and facilities should be located in areas with high flushing and deep water to avoid a built up of bacteria from effluents (FAO, 2014). Faecal matter can also be treated before it is discharged and the use of various chemicals and antibiotics can be banned (SEAFDEC, 2012). The proportion of fishmeal in aquafeeds can also be reduced through partially substituting with plant proteins, such as soybean, but a complete substitution has not yet been achieved. Fish offal can also be used to provide much better feed conversion efficiency than trash fish. However, there are very few fish farmers in the SCS that follow any of these guidelines so there is still a long way to go before even this level is achieved (SEAFDEC, 2012).
Aquaculture is certainly part of the solution to dwindling fish stocks, but until it is properly managed it can create more pressure on marine fisheries and coastal habitats. When eating farmed fish, please make sure you are choosing environmentally responsible and sustainable options so we can continue to enjoy fish long into the future.