Understanding the biology and ecology of sea lice

Submitted by Webmaster on Wed, 01/10/2018 - 14:55

a woman using a scoop net
Netting fish into sentinel cages for 7-day deployment.
Catherine Frederick is a Ph.D. candidate in marine biological resources in the School of Marine Sciences at the University of Maine, studying the ecology of sea lice and how they are distributed and transmitted in Cobscook Bay, Maine.

Sea lice are a group of marine parasitic copepods with “direct” life cycles, meaning the parasite requires only one host for successful reproduction. The specific host varies by species, but none infect or are harmful to humans. So, what is their relevance and why do we care about their ecology?

a sentinel cage on the water
Sentinel cages were placed at a total of four sites in Cobscook Bay.

Aquaculture is the breeding, rearing, and/or harvesting of aquatic organisms, such as seaweeds, shellfish, and ornamental and food fish. In the state of Maine, Atlantic salmon are reared as food fish, first in freshwater tanks and then in marine net pens. As in any agricultural setting, a greater density of organisms introduces risk of infection and re-infection. Think of how easily a cold or flu can spread across a college campus and the effort of administrators to reduce risk and exposure. Fish farms must do the same and a major concern happens to be sea lice. Sea lice infection is not unique to Maine, as it occurs worldwide in all countries with active salmon farms. There is even a biennial conference dedicated solely to the research of sea lice and how to reduce infection and improve animal welfare with new methodologies and technologies.

We must understand the biology and ecology of sea lice, including transmission dynamics. Three species of sea lice are the most impactful and account for disease observed on farms and in wild populations near them. They are Caligus elongatus, C. rogercressyi (Chile), and Lepeophtheirus salmonis, the latter is commonly known as the salmon louse and is the main subject of my dissertation.

gloved hands performing a fish dissection under a light
Examining Atlantic Salmon for sea lice using dissecting scopes.

With funding from Maine Sea Grant, I was able to conduct a two-year survey of where and when sea lice infect fish in Cobscook Bay, where Atlantic salmon are raised and harvested. It may sound simple, but this study has yet to be done for this region and was crucial for establishing a baseline of infection. We surveyed four sites based on council from marine extension specialist Chris Bartlett and Cooke Aquaculture. Sentinel cages were placed in the outer and central sub-bays of Cobscook and fish were deployed monthly for seven-day exposure periods. This experimental setup allowed fish to become naturally infected by copepodids (the infective stage) so that lice counts and disease metrics could be calculated. Data loggers were also deployed in the seven-day period to collect information on salinity, temperature, and surface current velocity. This information provided spatial and temporal patterns of infection for the region. We will also use mathematical models to examine how key abiotic factors influence lice counts.

We are still analyzing the data, but plan to present the results this spring.

Email Catherine Frederick with any questions.