Incidence of Black Spot Disease on Minnow Populations of the Swannanoa
Abstract. The fish of the Swannanoa river are infected
with a parasite known as black spot disease, also called black grub disease.
This parasite is a digenic trematode or fluke, and it is located just under
the scales or between the fin rays of the fish. It is identifiable by the
black spots that are formed 2-3 weeks after the parasite infects its host.
There are several species of this parasite but is hard to know which one
is present in a population of fishes unless the adult form is known. This
parasite has a complex life cycle involving three hosts; snails, fish,
and finally Herons and Kingfishers.
There were several questions that I set out to answer. Using minnow traps baited with different baits I caught minnows out of the Swannanoa. I wanted to know which species of minnows are being infected by this parasite and at what levels of infestation. Also within a species what size groups have the highest level of infection, in larger fish the parasite has little damaging effect, but in smaller fish it causes weight loss, and even mortality in large numbers. Finally I wanted to know if this parasite causes any behavioral changes in its host that might make them more susceptive to predation by the final host. This research is focused on getting an overall picture of what is going on with this parasite in the minnows of the Swannanoa.