Integrated pest management

Ectoparasites can be one of the major infectious pathogens an aquaculture operation has to manage and treat. Not least of these parasites are sea lice, which continue to present significant challenges for salmon farmers around the world.

The cornerstone of managing ectoparasites, particularly sea lice, is the practice of Integrated Pest Management (IPM), a strategy employed by various industries, from agriculture to forest management, and of course aquaculture. IPM is a multifactorial approach to managing pests; this includes applying the knowledge of a given pest’s biology and lifecycle to the development of effective management strategies, including the utilization of a broad range of control measures and treatments. Regular monitoring of the host and pest of interest is also a key component of IPM.

Through the effective use of IPM, we can keep pests which pose a threat to our livestock at bay, while preserving the use of the treatments we have available to us.

Having a thorough knowledge of a parasite’s biology is critical to effectively managing it, including information such as its stages and length of development, and how these might differ depending on certain environmental parameters (e.g. temperature), which stages of development are not susceptible to treatment, and how and when the parasites reproduce. Understanding when a parasite is vulnerable to various treatments and /or control measures is also crucial information. This knowledge can then be used by your veterinarian to design a management strategy, including the timing of treatment options.

In the case of sea lice, several species and subspecies of lice are of fish health concern in salmon aquaculture (e.g. Lepeophtheirus salmonis, Caligus spp.); these vary depending on where in the world you are farming fish. Each of these species has their own unique traits and characteristics which influences how we manage them. Furthermore, the regulatory requirements for sea lice management can vary significantly between different jurisdictions. Regulatory requirements are hopefully based on various biological factors (e.g. species of sea lice present, wild fish populations, environmental conditions, etc.), though sometimes regulations can be a bit arbitrary and/or made in response to political pressure. Understanding biological factors such as how quickly an attached immature louse (chalimus stage of development) becomes sexually mature, as well as knowing which stages of development are vulnerable to specific treatments will influence the treatment schedule.

Chemotherapeutants, particularly those delivered in-feed, have played a huge role in the treatment of sea lice, and continue to be an important component of sea lice management.  The importance of IPM in the context of sea lice came to the forefront when sea lice in certain regions stopped responding to in-feed treatments. Antimicrobial resistance (AMR), wherein pests and pathogens become decreasingly responsive to certain treatments, is a significant threat to aquaculture and fish health management. Particularly when there are so few treatments and products available, it is even more important to protect the tools we have, to ensure their continued efficacy.

In certain places of the world, some sea lice treatments are now largely ineffective or only effective against immature attached stages of sea lice. In other parts of the world, resistance to certain treatments started to develop, largely because no other treatment options were licensed and/or available to fish farmers. With the approval and introduction of additional treatments, and improved ability to utilize IPM strategies, the increasing tolerance of sea lice to certain treatments was curbed, and reversed to the point where treatments with previously decreasing efficacy could be successfully used again with confidence.

In addition to in-feed chemotherapeutants such as SLICE (emamectin benzoate), there are several other medicinal and non-medicinal sea lice treatment modalities available to farmers. One of these modalities includes in-water or “bath” treatments, which can include the use of chemicals or pesticides, for example hydrogen peroxide, or can be performed with freshwater to successfully treat sea lice. Bath treatments of salmon generally involve significant infrastructure, whether using a wellboat or large tarps to perform the treatment.

Other treatment modalities include mechanical removal with equipment such as a Hydrolicer, or in some cases, by hand picking (e.g. if dealing with a small valuable population such as broodstock) and thermal removal with equipment such as a Thermolicer or an Optilicer. Sea lice treatment modalities continue to evolve and develop, and newer technology is always on the horizon.

Through using multiple treatment modalities as part of IPM, we can help ensure the continued efficacy of our sea lice treatment options. Much like with bath treatments, many of these technologies represent a significant expense to the fish farmer. Unfortunately, the cost of these treatments makes it especially difficult for smaller producers to have access to their use; this emphasizes the importance of having a regulatory framework which enables new treatments and control measures to enter the commercial market more efficiently, particularly when such treatments are already being used safely and successfully in other parts of the world.

As previously mentioned, a key component of IPM is regular monitoring, including quantifying and qualifying infections. Without knowing if there is an active parasitic infection, how serious the infection is and at which stages of development those parasites are in at the time of monitoring, it becomes much more difficult to time appropriate treatment and management strategies. Establishing a regular and consistent monitoring program with trained staff is something that should be implemented by any operation looking to effectively manage parasitic infections in its livestock.

As with sea lice management, IPM can also play an important role in managing other parasites, whether in saltwater and freshwater, such as various amoeba species, parasitic copepods (Salmincola spp.), or Ichthyophthirius multifiliis, to name a few. With increasing threats to the stability of our food supply and food production systems, effective management of our livestock’s health and productivity is critical to continued sustainable food production. Your veterinarian would be more than happy to help you further develop and implement IPM at your operation. 

Dr Mykolas Kamaitis is a private practice aquaculture veterinarian and owner of Belwood Lake Veterinary Services in Ontario, Canada. He previously worked in the salmon industry in British Columbia as a vet and Fish Health Manager with Mowi Canada West. During his time at Mowi, Mykolas developed a strong background in production medicine and continues to take a preventative and production-focused approach to fish health management. He was named president of the Association of Aquaculture Veterinarians of British Columbia (AAVBC) in 2018 and continues in the role to this day.