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PaulRobertsJuly 16th, 2016, 8:15 pm

Posts: 1776
Filmed in a freshwater pond in Colorado. It is likely a larval...something...and appears to be around a bit under an inch (20mm) in length. It appears to be nearly transparent, long thread-like tails, and a smooth gliding swimming behavior. I took a wild stab at a Gastrotrich, but an expert in Italy, Antonoio Todara, didn't think so. "Too big", he thought.

It's not a very clear video so its best viewed small -like NOT full screen. Best guesses?
MillcreekJuly 17th, 2016, 3:17 pm
Healdsburg, CA

Posts: 356

Maybe a water scavenger beetle? Something like these.

The bottom link you'll have to scroll down to get to the water scavenger beetles.
PaulRobertsJuly 19th, 2016, 3:26 pm

Posts: 1776
Thanks, Mark. But... I don't think so. The transparency and slow gliding movement through open water is unique. I'm at a loss.
KonchuJuly 23rd, 2016, 10:11 pm
Site Editor

Posts: 505
Any chance it could have been a fairy shrimp, or some other kind of crustacean? It had that kind of movement.
PaulRobertsJuly 25th, 2016, 7:13 pm

Posts: 1776
Hi Luke! That's the best guess so far. Long, lean, gliding, and transparent would describe both critters.

The cons are: Supposedly they don't do well with fish predators around and there are plenty of bluegills and bass in this pond. And, fairy shrimp are pretty fast swimmers, I think. The guy I recorded was cruising pretty slow.

Thanks for piping in.
CrepuscularJuly 26th, 2016, 7:13 am
Boiling Springs, PA

Posts: 923
how about a leech? i've seen some pretty light colored ones from time to time.
PaulRobertsJuly 26th, 2016, 10:18 pm

Posts: 1776
I don't think so -they undulate. I'm stumped. Not even sure what else to consider. Best guess so far is fairy shrimp.
Jmd123July 27th, 2016, 12:13 am
Oscoda, MI

Posts: 2611
A transparent larval fish of some sort, perhaps a baby lamprey, or other eel-like species? Or a baby bowfin?? I mean we're talking just out of the egg here if that's what it is...??? I see a very slight degree of undulation, but not much, like the swimming leeches I saw today. I go for larval fish of some sort.

No matter how big the one you just caught is, there's always a bigger one out there somewhere...
PaulRobertsJuly 27th, 2016, 9:47 pm

Posts: 1776
I'd considered that Jonathon. I looked at larval gizzard shad and carp (this is a warmwater pond), but I didn't see a fit. Some saltwater fish have leptocephalus larvae that free drift before undergoing metamorphosis. Shad have fairly "underdeveloped" larvae, but they didn't fit.

Unfortunate that the image is so poor.
MartinlfJuly 29th, 2016, 7:46 am
Palmyra PA

Posts: 3233
Another mystery. It amazes me that for all we humans know, we still run into things that we can't explain. Oh, I assume somebody would know what this creature is, but it doesn't seem to be very easy to identify for some pretty knowledgeable folks. Love it. Thanks, Paul.
"He spread them a yard and a half. 'And every one that got away is this big.'"

--Fred Chappell
PaulRobertsJuly 29th, 2016, 10:14 am

Posts: 1776
Thanks, Louis. A bit off-topic for a trout focused site, but I was stumped. My best stab was a Gastrotrich, so I contacted a world authority. He didn't know what it was, only to say it wasn't a Gastrotrich. I have no more guesses so I thought I'd shoot it out here where reside people who are interested and willing to delve into cool things, even those tiny and complex. Thanks for trying all. It will remain labelled "strange critter".
EntomanJuly 29th, 2016, 1:08 pm
Northern CA & ID

Posts: 2604
Hi Paul,

Were there a a lot of tails or just a few? Were mandibles noticeable or not? Were there any noticeable legs or other appendages? If it weren't for the size I would have thought phantom midge larvae, but it still may be dipteran of some kind...
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
PaulRobertsJuly 30th, 2016, 7:18 pm

Posts: 1776
Hi Kurt,

I have no anatomical details to offer, only the video posted. I know it's not much to go on.

Phantom midge is a good guess: transparent, elongate, open water. But the vids I watched of them show them with a twisting swimming motion, like mosquito larvae.
PaulRobertsAugust 11th, 2016, 11:50 pm

Posts: 1776

I'm still guessing.

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