A simple primer on sea lice management.

Very simple primer on sea lice for a non-farming audience.

This article aims to provide a straightforward overview of the challenges related to sea lice and their management impacts. Though I am not a veterinarian, my firsthand experiences with this parasite inform my perspective. My goal is to help non-farmers understand the issues sea lice present in net pen farming.

Sea lice are naturally occurring marine parasites that mainly affect Atlantic salmon and trout. The two primary types are Lepeophtheirus (Leps) and Caligus. Leps are larger and problematic in the North Atlantic (Norway, Scotland, Ireland, Iceland, the Faroes, and eastern Canada), while Caligus are smaller and more problematic in the eastern Pacific Ocean (Chile and the west coast of Canada). Both species have a multi-stage life cycle involving free-swimming and attached stages. During the attached stages, sea lice feed on the mucous and skin layers of infected fish, causing considerable damage.

Farmers must treat sea lice for two main reasons:

1. **Fish Health and Welfare**: Sea lice can reproduce rapidly, especially during summer months. Uncontrolled lice populations can cause significant damage and mortality in farmed stocks.

2. **Regulatory Requirements**: Regulations vary by region, but generally, salmon farmers must conduct regular sea lice counts, report to regulators, and treat if levels exceed a certain threshold.

Integrated Pest Management

I've often been asked to rank control methods or identify the best one. A key thing that non-farmers need to understand, however, is that no single method remains effective if used exclusively. Farmers need an integrated pest management system targeting lice in various ways to prevent resistant strains from developing. During summer, sea lice populations can go through several generations, adapting to many challenges.

Types of Control Strategies

Control strategies fall into five major categories:

1. **In-Feed Treatments**: These target the shell-forming stages of the lice life cycle. Most are chitin inhibitors to interfere with the louse’s ability to form a shell during certain phases. They were introduced early in salmon farming, but resistance has developed. Effective in-feed treatments are ideal because they are gentle on fish, allow continued growth, and require no special equipment. Promising new in-feed treatments are on the horizon.

2. **Bath Treatments**: Fish are either pumped onto a holding vessel or enclosed in a pen with a tarp. A parasiticide is added to the water, causing lice to detach from the salmon. In vessel treatments, lice are filtered out of the water; in tarp treatments, they are released into the environment. Tarp treatments are gentler on fish but harder to manage. Resistance can be a problem in some regions.

3. **Mechanical Treatments**: These include thermal treatments and flushing systems. Thermal treatments immerse fish in warm water, shocking lice into detaching. Flushing systems spray or brush against salmon to dislodge lice. Both methods can be hard on fish, disrupting their primary immune defenses and causing injuries.

4. **Hybrid Systems**: These combine bath and mechanical treatments. Fish are pumped onto a vessel, held, and then pass through a mechanical system as they are discharged back into the pen.

5. **Prevention Strategies**: These include lumpfish, lice tarps, deep feeders, and laser systems. They are useful for prevention but may not be effective for dealing with acute sea lice pressure.

Sea Lice Management Strategy

A comprehensive management strategy might include:

1. **Early Season Bath Treatments**: Clean up lice levels when water temperatures are cooler, and lice reproduce slowly. The goal is to reduce lice levels as much as possible before temperatures rise.

2. **Mid-Summer Treatments**: Ideally, effective in-feed treatments allow uninterrupted feeding and growth. Without such treatments, a combination of bath, thermal, and mechanical treatments offer the best results, avoiding lice adaptation to a single control type.

3. **Late Summer Treatments**: In regions where lice are dormant in winter, the goal is to control lice populations until temperatures drop. If conditions are under control, switch to targeted treatments of individual pens in late winter and early spring. In regions where lice do not become dormant, aim for the lowest possible lice counts while avoiding handling fish during sensitive times.

Thank you for reading. Feedback is welcome.