Like the fish hook flea, Bythotrephes cederstroemi was introduced into
the Great Lakes in the 1980's, and rapidly spread throughout the lakes. Most
likely transported from Europe in ballast water or mud. The distinguishing feature
that separates it from other swimming invertebrates is its tail spine, which
comprises about 70 percent of its total length. When the animal molts (sheds
its exoskeleton in order to grow) it does not shed the tail spine. The spine
contains from one to four pairs of thorn-like barbs. Juveniles have just one
pair, so these barbs can be used to determine the age of the animal. The animals
propel themselves through the water with antenna located just behind the head.
Bythotrephes have a very rapid reproduction rate. Most of the time they reproduce
asexually, producing one to ten eggs that develop into new females without mating
or fertilization. In warm weather, these clones may be produced in less than
two weeks. When food becomes scarce, or the weather turns cold, the females produce
male offspring. These males mate with the surviving females, producing resting
eggs. The resting eggs are first carried as orange-brown spheres in the brood
pouch on the females back, and are later released to fall to the lake bottom.
These resting eggs can remain dormant form long periods of time.
compete directly with young fish for food, monopolizing the food supply to
the determent of the fish. Although larger fish may eat them, small fish
have difficulty swallowing them.