Economic success through healthy fish

As in almost all aquaculture systems, there is also a latent threat of disease outbreaks in trout farms, which brings with it considerable risks for fish populations and thus threaten the economic success of the company. To prevent such problems, welfare-oriented animal husbandry and proactive health management play a vital role. Good professional practice and compliance with legal duty of monitoring are essential.

AWorld Bank-commissioned study in 2014 put the annual economic losses in global aquaculture due to disease outbreaks at around USD6 billion. An extremely cautious and certainly far too low estimate, especially since the “farm gate value” of world aquaculture has increased since 2014 from USD160 billion to USD282 billion (2020) according to FAO. is gure overlooks the nancial losses and reductions in growth from parasites like sea lice, something that salmon and salmon trout farms have to spend hundreds of millions of dollars every year to control. Disease outbreaks reduce animal welfare, and the necessary treatments bring about enormous costs. ey represent a constant challenge for aquaculture operations, for which there is no easy solution in most cases. For sh farmers, farm managers, and sh veterinarians, preventing disease outbreaks is crucial for the success and sustainability of their operations. It is important to develop e ective management strategies and implement tools that can help mitigate the risks of diseases and limit their consequences. Disease prevention and management are critical for the success of all types of aquaculture, including trout farming.

Almost all living beings are naturally susceptible to parasite infestation, pathogenic germs, and fungal infections. In aquaculture, this is particularly true for sh that are reared in intensive farming environments. Under such conditions, the high stocking densities can increase stress and exacerbate the spread of diseases. at is why proactive health management is particularly important in intensive breeding. e water quality and the health status of the sh must be constantly monitored. Quarantine for newly arriving stocking sh would be an e ective measure to prevent the introduction of diseases into aquaculture farms, however, it may not always be possible due to space limitations.

Tighter regulation becomes increasingly restrictive in aquaculture

In Europe at least, the aquaculture sector is strictly regulated by law, and many management decisions do not solely lie in the hands of sh farmers. ere are detailed regulations for environmental, water and consumer protection, and animal health is monitored by regular veterinary checks. e abundance of rules and regulations in aquaculture can help to ensure high production standards. However, for sh farmers who are less legally savvy, it can be di cult to keep track of the regulations. To make matters worse, some data are collected multiple times and by di erent administrative levels. Aquaculture operations are subject to approval and require a permit under water law. ey are also subject to accounting obligations resulting from various laws and regulations. ese include food, animal health and pharmaceutical legislation. Compliance with all of these obligations is monitored as part of o cial operational controls.

An important focus of the inspections is the health and welfare of the sh. Trout can be a ected by a number of bacterial and viral pathogens and parasites, creating particular vulnerabilities in both freshwater and marine environments where salmon trout, like salmon, are reared in net pens. Sea lice, for example, have become a major problem for marine salmonid cultures. ese parasitic copepods eat the skin and blood of salmon and trout, causing lesions that can lead to secondary infections. e producing countries have now switched to far-reaching health management measures, since direct control measures are expensive, time-consuming and rarely lead to lasting success. Both national and regional biosecurity plans aim to reduce the sea lice problem. ese measures include, for example, the spatial and temporal separation of the sh stock in individual areas, more e ective controls of transporting the equipment and personnel within and between the farms, the thorough disinfection of the equipment used and the observance of rest periods between restocking of the net enclosures. In combination with drug-based sea lice control campaigns, which are subject to strict regulations and are usually carried out by veterinarians, the problem should be limited and, if possible, suppressed. However, biosecurity plans also prevent the spread of many other diseases.

Fish are exposed to many hazards in open systems

e risk of disease outbreaks is particularly high in open waters because the sh are constantly exposed to potential external pressure from pathogens. It is di cult to control sudden changes in water quality that a ect the resistance of the sh to disease. e cause of a disease outbreak is often not a virus, a bacterium, a parasite or a fungus alone, but is usually a co-infection in combination with environmental stressors. Infectious diseases often break out when the sh are under constant stress due to inadequate environmental conditions, suboptimal husbandry practices and poor hygiene. is weakens their immune system and makes them susceptible to pathogenic germs. e combination of virulent pathogens, a vulnerable host animal, and adverse environmental conditions creates ideal conditions for diseases to spread rapidly if they are not caught early and treated. Unlike in open waters, the water quality can be in uenced to a limited extent in many trout farms and thus diseases can