Chickakoo Rainbows

[Wulfespirit]

Went out to Chickakoo this evening with the wife and managed to bring home a few rainbows. Filetted them and found dark/black little spots/cysts (maybe 2mm diameter at most) on all of them just under the skin - some worse than others.

Many of them stayed attached to the filet when stripped of the skin. Doesn't really tempt the appetite.

I'm assuming these are some kind of parasite or larvae... any ideas?

These were NOT present in rainbows from this pond a month ago.

[walker197]

i've seen these on the rainbows from sauer as well, usually later on in the year

[TippyCanoe]

The common name is "black spot". They are a parasite, although it is not a harmful parasite to the fish or to people. They typically show up later in the year when the water warms and are transported and introduced to waterbodies through bird feces. Once the water turns cold in the late fall the parasite will die off and you will no longer see them in the fish tissue. That's why you don't see them during ice fishing season.

A lot of species will carry this parasite through the warm water season.

Ok to eat but I ussually don't as they don't appeal to me.

[Paul C]

What is the name of that parasite ??

[tonyflyfish]

The lifecycle of the "black spot" parasite is complex. The adult parasite is found in a fish ... chris63 davemitr DrDerby hungry for trout hunternitz ...copied from the net-i didn't know this

[TippyCanoe]

Black spots

"Black spot disease is commonly observed in rock bass and other sunfish, bass, pike, perch, minnows, and other fish species. It can be identified by the presence of small black spots, usually about the size of a pin head, in the skin, the fins, the musculature, and the mouth of the fish. The black spots are caused by pigment that the fish deposits around the larval stage of a parasitic digenetic trematode, usually a Neascus spp.

The lifecycle of the "black spot" parasite is complex. The adult parasite is found in a fish eating bird, the kingfisher. The larval parasite is transferred from the infected fish to the bird during the feeding process. In the kingfisher, the larval stage develops into an adult parasite. The adult parasite in the intestine of the bird produces eggs that are eventually deposited in the water. There the eggs mature, hatch, and develop into the miracidium stage of the parasite. The miracidium infects a snail. In the snail, the miracidium develops into the cercaria life stage. The cercaria leaves the snail and actively penetrates a host fish. In the fish, the parasite becomes encysted. In about 22 days, black spots form around the cyst. This entire lifecycle takes at least 112 days to complete.

In general, the presence of the "black spot" parasite does not affect the growth or the longevity of the infected fish; however massive infections in young fish may cause fish mortality. The parasite is incapable of infecting humans and, as is the case with all fish parasites, it is destroyed by thorough cooking. When fish are heavily infected, some anglers prefer to remove the skin to improve the appearance of the cooked fish.

For further information please reference:

Parasites of North American Freshwater Fishes
by G. L. Hoffman (This book may be available from your local University Library)
Click here for a University of Michigan web page on flat worms.
Numerous state Fisheries' agencies and other web sites describe parasites --- try typing "Neascus" or "Clinostomum" in search engines to learn more.

Like many biological phenomenon, prevalence of worms and parasites may be greater in some years and during some seasons for a variety of reasons, including an abundance of intermediate host mollusks and birds. Bluegills are a colonial spawner and congregations in early summer provide opportunity for infested fish to be in close proximity to one another."

[Paul C]

Thx ! for a complete answer.