Sea Lice

A major critical threat to salmon farming

Sea lice (Lepeophtheirus salmonis) is a parasite that mostly lives off the skin mucus and blood of the fish. Infection with sea lice can result in large wounds on the skin and lead to anemia, secondary infections or even fatality. Based on legislation, there is a cap on the maximum number of lice that are allowed per farmed fish.

While there are different measures for preventing or controlling the infection, these methods either has a limited effect or cause high levels of stress on the animal. As a result, the direct and indirect costs of treatments can be significantly high. Total sea lice count on a group of fish is highly variable (Figure 1), and has shown to have a heritable component which we utilize in our breeding work.

LIce_distribution_2018-1
Figure 1: The figure shows the total lice count on each fish distributed on a large number of sea lice challenged fish from 2018.

Benchmark Genetics offers sea lice robust fish

Benchmark Genetics offers sea lice robust fish using GS, a program that started in 2015. Before the implementation of GS, the company has been selecting for sea lice resistance based on family levels since 2007. By moving from family-based breeding to GS, we were able to increase more than three times the genetic gain in our nucleus. Benchmark Genetics is currently working on novel approaches for identifying and selecting the most robust animals.

Together with Nofima, we investigated SalmoBreed families with high and low estimated breeding value (GEBV) for sea lice resistance. Families divergently selected for sea lice resistance shows significant phenotypic differences in sea lice attachment under test models, validating a realized response to selection.

The performance of SalmoBreed families were tested under two conditions.

  1. Mixed rearing of divergent high and low GEBV sea lice resistant families
  2. Separate rearing of GEBV sea lice resistant families.

Under mixed rearing low GEBV families showed a significantly reduced lice attachment and performed consistently well under separate rearing. When we reared the low GEBV families, that were predicted to get low lice attached during the challenge(alone in one tank), with the same amount of lice pressure as the mixed tanks, the lice numbers remained low

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