Fish farm environmental impacts

Sea lice

What are Sea Lice?

'Sea lice' is a term used to describe many species of ectoparasitic copepods of the genera Lepeophtheirus and Caligus. The common name 'salmon lice' is frequently used to refer to L. salmonis, which has become an economically important parasite in salmon farming. Another important salmon louse in salmonid and marine fish farming is Caligus elongat us. In Scotland there are two other species of lice that may be a problem for cultured fish, Caligus curtis and Lepeophtheirus hippoglossi.

Where and When Might it Occur?

L. salmonis is very host-specific, preferring Atlantic Salmon (Salmo salar L.), and is commonly found in the Northern Hemisphere. C. elongatus, is important in salmonid and marine fish farming and has a wider range of host species. These two species are commonly found on wild salmonids. They are usually found in low numbers, although L. salmonis may cause damage to wild Atlantic salmon and sea trout (Salmo trutta L.) if present in large numbers. In Scotland, C. curtis has been reported from wild cod (Gadus morhua), and L. hippoglossi is associated with wild halibut, although it has been anecdotally reported from farmed halibut elsewhere.

Diagnosis

Salmon lice feed on host mucus, skin and blood and, when present in high numbers, cause serious damage to the skin, which can result in host death. The adult stages are highly visible on infested fish. Precise identification of sea lice can be achieved by examination of the parasites under a microscope.

Control

It is difficult to prevent infestation of farmed salmonids because sea lice are ubiquitous in the marine environment. However, control is possible through the use of licensed veterinary medicines and wrasse, such as the goldsinny (Ctenolabrus rupestris), that feed on sea lice. Other measures include the coordination of fallowing and stocking within agreed management areas. Vaccination has been proposed as a means of controlling salmon lice, although there seems little prospect of a licensed vaccine in the near future.

Ecological Effects of Sea Lice Treatment Agents

Background

A number of new medicines to treat sea lice infestations on salmonid fish are now being used across the world. Tests to ensure that these medicines comply with environmental regulatory standards are routinely performed on sentinel or indicator species which may not be necessarily typical of the relevant ecosystem.

The Post Authorisation Monitoring Project (PAMP) has been designed specifically to study ecosystem responses over several years which may be attributable to the use of these new medicines. The project ran from September 1999 to August 2004.

Objectives

• To determine effects attributable to the use of sea lice treatment agents on assemblages of macrofauna, zooplankton, meiofauna, phytoplankton, macroalgae and littoral communities
• To determine significant correlations between ecosystem response(s), time and treatment agent concentration
• To determine proportion of observed environmental variance attributable to treatment events against a background of responses due to other parameters such as waste organic materials and nutrients
• To model the dispersion and fate of farm wastes including each of several treatment agents in the environment post-treatment
• Final conclusions are now available in 4 sections (released April 2005)

Project sponsored by:

• Veterinary Medicines Directorate (VMD)
• The Department of the Environment, Fisheries and Rural Affairs (DEFRA)
• Scottish Natural Heritage (SNH)
• Scotland & Northern Ireland Forum for Environmental Research (SNIFFER)
• Scottish Quality Salmon (SQS)

Co-contractors:

• The Scottish Association for Marine Science (SAMS) at Dunstaffnage Marine Laboratory (DML)
• FRS Marine Laboratory (Aberdeen) - now Marine Scotland Science
• Plymouth Marine Laboratory (PML)
• Scottish Environmental Advisory Services (SEAS Ltd)