Why we can’t ignore fish disease in discussions about sustainable aquaculture

Many of the ongoing discussions about sustainability now involve water, our waterways, the health of our oceans and life underwater. It is impossible to look at any of these aspects in isolation without considering the many forms of life that thrive within it.

Aquaculture – or the rearing of aquatic organisms within controlled conditions in waterbodies – is today one of the fastest-growing food production systems in the world. It is currently responsible for the supply of over 50% of the total seafood globally and is expected to be the primary source of seafood. Demand is estimated to reach 232 million metric tons by then, which means aquaculture production will need to double. There is no better time than now for us to begin thinking about sustainable practices in aquaculture and all the ways to keep this practice going in a healthy and holistic way. Aquaculture practised in this manner can not only be a valuable source of food and nutrition but can also help provide livelihoods and fuel economies in developing parts of the world. According to a World Bank report for an aquaculture system to be truly sustainable, it requires a triumvirate of:

1. Environmental sustainability: Aquaculture should be practised responsibly, in a way that does not create any major disruption to the ecosystem, resulting in a detrimental loss of biodiversity, pollution or greater environmental impact.
2. Economic sustainability: For aquaculture to be a viable business with long-term economic benefits to communities engaging with it, it must be developed in an economically sustainable manner.
3. Social and community sustainability: Aquaculture must be socially responsible and contribute to community well-being.

Approximately 800 million people globally, depend on fisheries and aquaculture as a primary means of livelihoods. A bulk of the global aquaculture produce comes from developing countries, and from significantly low-income food-deficit areas. Additionally, aquaculture has the potential to be a sustainable, viable practice that can support and supplement fast-dying capture fisheries. This is a very good way to positively contribute to the pressing need to feed the world’s growing population as well as significantly contribute to employment for men and women alike. Which is why the aspect of sustainability and health of aquatic life begs to be looked into so that we can begin to:

1. depend on the naturally occurring biological cycles amongst aquatic organisms
2. research and develop various methods of disease control among fish
3. refrain from using synthetic fertilisers and other chemicals that could potentially harm fish and their environment

The World Fish Centre reports that fish disease poses a serious threat to the potential scope of growth within aquaculture, due to approximately “USD 6 billion lost annually due to the problem (World Bank 2014).” Particularly harmful when found amongst farmed-fish populations, dealing with fish disease has become an important topic when discussing sustainable aquaculture. Managing, curing and preventing further spread of fish disease is a crucial element to making aquaculture truly sustainable so that we may minimise production losses and significantly increase productivity.

What does “fish disease” look like?

Unlike other farmed animals like livestock, farmed fish pose a challenge in that the fish spend most of their lives underwater where it becomes difficult to observe changes as they occur. One of the most noticeable signs of disease in fish is a refusal to feed or come up to the surface for air. Sometimes there may be visible deformities like polyps or ulcers on the body, cloudy or colourless eyes, but these are not readily apparent until the disease has progressed significantly. Fish disease is, in fact, more prevalent in aquaculture than wild waters, and caused by pathogens existing within the environment. While pathogens are present in wild as well as farmed environments, they can spread faster and gain sufficient volume to produce epidemics amongst farmed fish due to the sheer concentration of numbers of fish that exist together.

Pathogens enter aquaculture enclosures due to several changes in the environment around them such as climate change that affects the composition and temperature of waters, excessive fishing that doesn’t stick to natural seasonal cycles, the effects of pollution emanating from the unchecked flow of untreated wastewater loaded with organic and chemical pathogens into our rivers and seas.

The major danger with disease in farmed fish is that large tracts of water contain a multitude of fish in close proximity, which increases the chances of pathogens spreading, crossing and multiplying.

There are seven major categories of disease amongst fish – bacterial, fungal, parasitic, protozoan, non-infectious maladies, viral and miscellaneous diseases. These include conditions like Red Pests, Mouth Fungus, Tuberculosis. Lymphocytis, Ergasilus, Anchor Worms, Brown Blood disease, to name just a few.

Are probiotics the answer to fighting fish disease?

As in humans, there is also a growing interest in the research and development of naturally occurring beneficial bacteria, or probiotics, as a key way to counter the effects of antimicrobials that are now being questioned in aquaculture. Probiotics are “good” bacteria that have a host of beneficial effects, by creating a natural balance in the microbial community within the organism’s body. Many of these bacteria are responsible for setting off and regulating essential biological functions within the system, such as feeding, and responding to fighting disease.

The use of probiotics and the need to work around establishing healthy gut systems is now being looked at as a viable route to improved animal health, especially in aquaculture.

A healthy gut that has a right balance of intestinal microflora working their magic has a positive impact on:
· the way the organism responds to, absorbs and assimilates the nutrition it receives
· prevention of pathogenic infections
· integrity and function of digestive organs and other major organ systems
· a robust immune system that can respond to and fight disease sooner

Soil and water probiotics are usually introduced into waters where fish are farmed, to restore the natural balance of microflora, and help maintain water quality and colour, as well as stabilise the dissolved oxygen concentration in the water in which fish are reared.

In commercial aquaculture, stocking densities are high, with space being limited. While such rearing conditions are often unavoidable, use of probiotics makes it far less detrimental to fish health and improves their immunity against diseases and environmental stress caused by such intensive breeding conditions.

They work to reduce levels of ammonia and toxic gases like Hydrogen Sulphide within the water. Also, fish can be fed probiotics along with their daily nutrition, to boost the presence of intestinal microflora within their systems, which helps better assimilation of nutrients as well as a stronger immune system.

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