Fish Lice: Branchiura

Physical characteristics: The abdominal lobes of fish lice are broadly rounded. The notch between the lobes is not very deep and less than half the length of the lobes. The first three pairs of thoracic limbs are dark at their bases. Adult females measure 0.39 inches (10 millimeters) in length, while the males are 0.35 inches (9 millimeters).

Geographic range: They are found in Europe, east to central Asia and Siberia.

Habitat: Fish lice are external parasites on many kinds of freshwater fishes.

Diet: Fish lice eat fish skin and blood.

Behavior and reproduction: After hatching, the larvae swim in open water for two or three days before attaching themselves to a host.

Up to four hundred eggs are laid at a time in two to six rows. The eggs hatch after twenty-five days at temperatures of 59°F Fish lice are external parasites on many kinds of freshwater fishes. (Illustration by Bruce Worden. Reproduced by permission.) (15°C). Depending on temperature, the first larval stage lasts about six days, and the animal molts every four to six days until reaching adulthood.

Fish lice and people: They sometimes infest fish hatcheries and aquariums. Their feeding activities spread disease and weaken or kill fish.

Conservation status: Fish lice are not considered threatened or endangered. ∎