Shiner Perch have weird parasites!
Haemobaphes diceraus
Yes, it looks really nasty! And it can be very bad news for a small fish like this young Shiner Perch.
Haemobaphes diceraus may look like a red worm, but it is actually a penellid copepod—a group of tiny crustaceans that are relatives of crabs and shrimp.
Most of the copepods in the ocean are calanoid copepods, tiny shrimp-like swimmers that mainly graze on minuscule green algae and other phytoplankton year–round and form a large part of the diet of smelt, herring and other “forage fish” that feed larger fish such as salmon and rockfish.
But some copepods have evolved into parasites on the fish that used to eat them, and the penellid copepods are the most bizarre. They begin life as free swimming crustaceans but when the female is mature, she wraps herself around the gill tissue of a fish, and then re-absorbs all of her body parts and exoskeleton except for her gut and her gonads. She sucks blood and makes eggs (they are the two light-colored coils in the photo) until her eggs hatch. The effect on the fish is loss of blood, lassitude, low blood oxygen levels, and reduced resilience to stress.
