Diseases of aquaculture

The value of production of aquaculture in Australia is around $990 million¹ and consists of cultivation of over 40 species, most for food, but others such as pearl oysters and crocodiles are cultured for products for the fashion industry. A number of finfish are grown for food including salmon, barramundi, and silver perch, and other species include prawns, marron, abalone, oysters and mussels, whereas southern bluefin tuna are caught from the wild and farmed until they reach market size. A number of species are being investigated for aquaculture and these include octopus and sea cucumber¹.

Aquaculture is undertaken in all states of Australia plus the Northern Territory and the geographical location, environment including water source and temperature, and resources often dictates the type of aquatic animals cultured.

In New Zealand, aquaculture of oysters, mussels and salmon results in revenue of NZ$ 400 million with a range of other species being investigated for production that includes rock lobster, sea cucumbers, eels, and sea sponge².

Aquaculture farms may be land-based in tanks or ponds, or water-based in the ocean, river or estuary systems using cages, ponds or in the case of shellfish – cultured on racks or lines suspended in the water. By definition aquaculture is intensive farming and as such creates disease challenges related to stocking density similar to those seen in farming of terrestrial animals, or the effect of urbanisation on the epidemiology and transmission of diseases in people^3,4. Good farming practices are crucial for disease management. A disease outbreak in any type of aquaculture system can be devastating and there are instances where a single disease outbreak resulted in the failure of that business⁵.

As with all living things, the aquatic animal host is colonised by a range of microorganisms considered to be normal flora, but each host has a number of potential pathogens that includes bacteria, viruses, fungi, parasites etc.

Although not covered in this issue, a number of pathogens or saprophytes of aquatic animals or microorganisms in the aquatic environment and their biotoxins to which workers or fisherman may be exposed, are zoonotic or biohazards that can impact on human health and can cause infections or food poisoning⁶. Therefore, not only veterinary microbiology laboratories, but also medical laboratories may encounter these microorganisms.

Working in the area of aquatic animals, whether in a diagnostic laboratory or in research, presents interesting and exciting challenges, with in-depth knowledge required of a vast range of microorganisms.

Some of the challenges associated with detecting, identifying and controlling disease agents in aquaculture are presented in this issue of Microbiology Australia.