Know your enemy – understanding the movements of a devastating parasite to outsmart it

Sun Tzu’s ‘The Art of War’ tells us we must know our enemy if we hope to defeat it. In modern aquaculture, the greatest enemies are parasites that plague production and are a key part of many environmental effects. One of the worst parasites in salmon farming is a pesky amoeba that causes severe gill damage. As parasite outbreaks are extremely costly, the search is on for methods to reduce infection rates. One strategy is to reduce contact between salmon and the parasites in fish farms. But to do this, we must first know where these tiny parasites are and what drive their movements.

In a new study published in Aquaculture Environment Interactions this month, Dr Daniel Wright and colleagues from the University of Melbourne hunted for this marine parasite in Tasmanian salmon farms over 2 years. After taking over 300 separate water samples at farms and in their surrounds, there was no clear pattern between where the parasite was, depth in the ocean or the swimming depth of the fish.

Now we know our enemy, we have a better idea of which control methods will work and which won’t. For other parasites, control methods we developed that permanently change the swimming depth of fish swim are very successful. But they won’t work for this amoeba. We must now look for other possibilities to disconnect amoeba from salmon. These could include spreading fish densities more evenly at night with underwater lights and moving fish into brackish water that makes the amoeba leave the gills.