Pile Perch (Rhacochilus vacca) as a cleaner fish for sea lice on farmed salmon: Identification of pathogens of concern with respect to salmon and perch health

Description

The presence of sea lice is a significant economic and environmental burden to commercial salmon aquaculture. Since 2001, dietary emamectin benzoate (EMB) had been the treatment of choice for sea lice on farmed Atlantic salmon because of its high efficacy and ease of application. However, the development of EMB resistance among sea lice populations has reduced its usefulness as a treatment in Norway, Chile and eastern Canada. In British Columbia (BC), reports of variable EMB treatment efficacy suggests that resistance to EMB may be developing, stressing the need to find alternative tools for controlling sea lice.

In Norway cleaner fish (i.e., fish that can remove parasites off the surface of other fish) are commonly used to control sea lice infestations and reduce the reliance on chemical treatments. In BC, the potential for using native Pile Perch as a cleaner fish to control sea lice has been demonstrated in the laboratory. However, prior to commercial development and deployment of Pile Perch as a cleaner fish, it is necessary to understand the potential fish health risks, if any, posed by their use. It is also important to identify any infectious agents that may directly affect the Pile Perch. This project examined pathogens of concern to salmon and perch health, and sought to identify if Pile Perch could act as an alternative or reservoir host of salmon pathogens.

Findings

This project examined Pile Perch (Rhacochilus vacca) and other surf perch species, Shiner Perch (Cymatogaster aggregata) and Striped Sea Perch (Embiotoca lateralis). Perch were collected both near and far away from salmon farms and screened for pathogens of concern to salmon and perch health. Samples of multiple organs were screened for the following pathogens:

• Viral Hemorrhagic Septicemia virus
• Infectious Hematopoietic Necrosis virus
• Piscine Nodavirus
• Piscine orthoreovirus-1
• Renibacterium salmoninarum
• Moritella viscosa
• Aeromonas spp.
• Piscirickettsia salmonis

Of the 190 individuals tested, none were found to have any of these infectious agents.

Program name

Aquaculture Collaborative Research and Development Program (ACRDP)

Years

One year: 2018-2019

Principal investigator

Stewart Johnson, research scientist, Fisheries and Oceans Canada, Pacific Biological Station, Pacific Region
Email: stewart.johnson@dfo-mpo.gc.ca

Team members

Diane Morrison, Fish Health and Food Safety Director, Marine Harvest Canada
Ahmed Siah, research scientist, BC Centre for Aquatic Health Sciences

Collaborators

Joanne Liutkus, Regulatory Affairs and Research Manager, BC Salmon Farmers Association
Jim Powell, Chief Executive Officer, BC Centre for Aquatic Health Sciences