Lionfish Invasion: Density-Dependent Population Dynamics

Parasites on fish farms

Two large netted enclosures sitting on a large body of water
A closeup of red lesions and pale yellow patches on the skin of a fish.

Many fish eaten as seafood are bred and raised in fish farms. The fish on a farm can be infected by parasites called sea lice: small crustaceans that feed on a fish’s blood and skin, which may injure or even kill the fish.

Jansen and colleagues (2012) analyzed sea lice infections on trout and salmon farms. They used data reported by many fish farms on the numbers of sea lice found on their fish. The scientists compared the number of sea lice with the “local farmed fish biomass density,” which is a measure of population density that accounts for both the number and biomass (or size) of fish on a farm.

The effect of local farmed fish biomass density on the counts (numbers) of sea lice per fish

Each point represents the mean fish density and sea lice count for a group of farms in a specific year.


A scatter plot graph with the x axis labeled Local farmed fish biomass density in metric tons with values ranging from 0 to 400 in increments of 100. The y axis is labeled Sea lice counts ranges from 0 to 3 in increments of 1. A sloped line begins around 50 metric tons and just under 1 sea lice count and rises to around 2 when biomass is at 400 metric tons. An equal number of points lie above and below this line.

Use what you've learned above to answer the following questions:

Case Studies