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Photo#301526
Fly emerged from center of wound on subyearling (fall) Chinook salmonid smolt - Polypedilum - male

Fly emerged from center of wound on subyearling (fall) Chinook salmonid smolt - Polypedilum - Male
John Day Dam Smolt Monitoring Facility, Rufus, Sherman County, Oregon, USA
July 8, 2009
Size: approximately 5 mm
A random sample at the John Day Dam Smolt Monitoring facility yielded a small unclipped subyearling (fall) Chinook smolt (approx. 80 mm fork length) with a large circular wound on it's side. In the short time it takes to set up my photo station, three people observed a "black spot" slowly wiggle out of the center of the wound- which turned out to be some sort of fly (superficially midge-like).

I am not aware of any flies that purposefully parasitize fish, although I wouldn't be surprised if some do. I did not save the fish specimen to see if other flies emerged, but it was still alive. I am guessing that the gaping wound may not be associated with the fly at all- maybe it was recently eaten and just crawled through a previously existing hole? It seems like the fly was in too good of shape for that...

A few of the questions I have are can a fly pupate inside of a fish stomach? Could a midge larvae be eaten by a fish and take up residence inside the fish instead? How would it respire, etc?

I had seen only 2 other similar wounds on fish (out of several hundered thousand fish handled) over the years, and one of them had a "red worm" coiled up inside just under the surface of the skin.

Any help on possible identification or life history would be greatly appreciated. Also, extrememly wild or hardly imaginable ideas for what is going on here will also be taken into consideration :).

Images of this individual: tag all
Fly emerged from center of wound on subyearling (fall) Chinook salmonid smolt - Polypedilum - male Fly emerged from center of wound on subyearling (fall) Chinook salmonid smolt - Polypedilum Fly emerged from center of wound on subyearling (fall) Chinook salmonid smolt - Polypedilum - male

Moved
Moved from Orthocladiinae.

 
Images
Any value in keeping the 2 fish pictures if they had little to do with the larva other than it was found stuck to one of them (the one is a different fish)? I wonder if these are given a perceived value just because they are fish and not some inanimate object.

 
I think it depends...
If it turns out that this is some crazy species that's parasitic on fish, I could see some value in keeping them- If it's just a freak coincidence, maybe not so much. Really an interesting series of photos and a story either way though.

Polypedilum sp.
I sent the "putative parasitic" midge specimen to Dr. John Epler and he states that the specimen "...is somewhat intermediate between Polypedilum pedatum and P. sulaceps. There are no known Polypedilum species that are parasites, or that have any kind of life strategy anywhere near that. Larvae are filter feeders, leaf scrapers or leaf miners.".

Also, I should mention that Dr. Epler identified two other taxa found in our samples (free floating in the water, not on fish) to be from the genera Kiefferulus and Cricotopus.

Any how, I guess the details of how that Polypedilum pupae and salmon smolt became associated with each other may remain a mystery ...

Thanks to all for their contributions and I will try to post any follow-up information.

Moved
Moved from Midges (based on John Epler's tenative ID).

Thanks everyone for all the g
Thanks everyone for all the great information.

I located this on-line paper regarding parasitic midges in Brazil in case anyone is interested: http://www.biotaneotropica.org.br/v4n2/pt/fullpaper?bn03404022004+en

The paper has a table listing some potential hosts and nearly 20 are fishes so I, for one, have a bit more appreciation now of midge flies and their varied life histories.

 
pupa
Greg, did you by any chance save this pupa? If so, send it to me.

As I wrote earlier, I do not believe it is parasitic.

Parasitic chironomid larvae
This does look like a chironomid. The larvae of some species are parasitic on fish, and others are commensal. I’m not sure if a commensal species can become parasitic if given the opportunity, or whether parasitic species are only obligatory parasites. This image here looks like the head end of the chironomid pupa.

The larvae (some species match your “red worm” description) enter from the outside of the body, and not via the intestinal tract. Thanks for sharing the images and the excellent descriptions.

 
Fish parasites
Some midges, Icthyocladius in Orthocladiinae, are parasites of South American catfish. I have not yet found any information about parasites of salmon or North American fish.

 
Chironomid
I agree, it looks like Chironomidae, and probably a male based on what I presume to be the antenna. I will try to find out what kinds are parasitic on vertebrates. I know some are parasites of mayflies and molluscs.

 
Nice series
The pupa does suggest Chironomidae but I wasn't aware of any parasitic forms...a nice and bizarre find..moving to family page for now.

 
chironomid pupa
Yes, this is definitely a chironomid pupa. I can not be sure about what appears to be a thoracic horn, but if it is, then this specimen is most likely a member of the subfamily Orthocladiinae. A good shot of its dorsum, especially the abdomen, would enable better identification. It is a male and is in the process of eclosing (emerging from the pupal skin). Pupae of most subfamilies (except the Tanypodinae) are normally sessile but just before eclosion they will swim to the water's surface and emerge there, using the pupal skin as a raft. I would hypothesize that this pupa was on its way to the surface and got stuck on the wound of the fish.

The only parasitic midges in North America parasitize stoneflies, mayflies and megalopterans (for the most part); most midges occurring on "hosts" are not parasitic but are symphoretic.

 
Just for the record...
I had no idea what "symphoretic" meant. After about 40 minutes of searching I finally found a decent definition, which I will put here for the benefit of anyone else interested:

"Symphoresy is a commensal relationship which includes larvae of Chironomidae (Diptera) that live on the exoskeleton of larger hosts and are transported apparently without significant benefit or harm to their hosts, but with several possible benefits to the chironomid..."

So basically: larval midges stuck on the outside of other insects without much effect on the host.

Above "official" definition taken from:
First Report of a Symphoretic Association Between Nanocladius branchicolus Saether (Diptera: Chironomidae) and Argia moesta (Hagen) (Odonata: Coenagrionidae)
Lloyd M. Dosdall and Dale W. Parker
American Midland Naturalist, Vol. 139, No. 1 (Jan., 1998), pp. 181-185

I'm by
no means an expert, but I'm wondering if it could be a bot fly of some type.

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