Salmon Farming Challenges

Salmon and fish farming in general are not without critics, most of which centre around a question of sustainability.

As an example, the process of salmon farming involves the fish being grown in nets which are suspended in the sea or lochs for around 2 years until they are harvested for food. This has the potential to cause substantial environmental damage as feed, faeces and medicines sink to the sea or loch bed, altering the ecology below.

There are also issues surrounding the introduction of foreign chemicals, such as pesticides and antibiotics, into the environment which could potentially have devastating impacts.


Farmers are closely monitored by organisations like the Scottish Environment Protection Agency (SEPA) and must hold licences which limit the weight of fish and amount of medication allowed on a site at any one time; strict rules which are designed to protect the environment and welfare of the animals.

There have been instances recorded where licences have been breached for activities including overdosing the fish with medication which is intended to kill parasites harmful to their health, such as sea lice.

These findings have led to in-depth investigations by Marine Scotland, who assess the welfare of farmed fish. As well as the Local Fisheries Trust, who research wild fish populations and how they may be impacted by farming activities.

What can be done to combat aquaculture challenges?

Naturally, farming activities of all types have some impact on the environment. However, certain forward-thinking companies are looking into innovative methods to further protect the natural ecology of our waterways.

A modern approach already being taken involves treating fish for lice whilst submerged in water onboard the hull of a ship instead of directly dosing medicine into the sea or loch water. The fish are taken from their nets onboard the ship, treated, rinsed with fresh water and returned to the sea.

The contaminated water is contained within the hull and treated using a combination of treatment processes which remove the lice and medication before this water is returned to the environment.

This process prevents the ecology beneath the salmon farms from being damaged at all by the administration of medication.

In addition to this offshore application, in locations where the environment does not allow for external fish farming and fish are bred in tanks on land, water treatment is also of paramount importance for the welfare and the final quality of the fish.

Generally, the tank water is cleaned using a combination of steps including filtration to remove particles, biological treatment (ie. MBBR) and ozone dosing. This staged process is known as a recirculating aquaculture system (RAS) but comes with some limitations.

The recirculation of water can lead to by-product formation from the ozone process or build up of contaminants left untreated, such as geosmin and MIB. Therefore, some land-based fisheries are also seeking a new treatment option.