Thought it was a dark koi fry but it is not, please help identifying what this is!
My koi have recently laid eggs and the fry are being raised in a stock tank. While cleaning a liter bottle moving bed filter I have set up with the fry I came across a dark brown colored fry looking critter with a goldish underside. It really stuck out because all of the fry in the tank are light colored. At first I thought it was just a dark colored fry but after closer observation I'm basically certain it's not but am not sure what it is and whether its safe to have around the other growing fry. Its the same size as the other fry at this point. It doesn't free swim and just hangs on the bottom but if I move something near it it'll wiggle/swim aggressively an inch or so away. I'm sure this guy is not a big concern, I just really am curious as to what it is now that it fooled me into thinking it was a dark colored fry initially. Any info would be great and very much appreciated. I'm attaching some photos taken of the top, side, and underside of the critter. Thanks!
Here is another photo from today where I sucked him up in a turkey baster to try and get a better look/photo now that he's a bit bigger, definitely has got 2 big eyes haha No idea how he would have gotten in the moving bed liter bottle filter, I have them covered with knee highs so the fry won't get sucked in. I also have the stock tank covered nightly with mosquito mesh but I guess it could have happened during the day or the moving bed filter bottle already had an egg in it coming from the previous setup. Who knows but I'm still keeping him around in a small bucket to see what he turns in to haha Thanks for the input and I'll definitely take a look at the amateur breeders forum you mentioned and share a bit about the spawn/fry/setup and ask some of my many questions I have too.