baby guppies in my reef rock? ID, please.

[Sk8r]

In a thumb-sized hole in my rather holey reef rock, we've noticed some back and forth swimming motes that (because they're in a hole) we can only see in silhouette against the back glass. They're very active, and fairly numerous. They resemble baby guppies in their flitting behavior and in size and shape.

The tank is 6 months old, with really ancient live rock from somebody else's tank. Everything else lived, but I think eggs from that far back would be odd.

This leaves us with the current population: hermits (scarlets and blueleg); fish, all singles, no 2 of same species; snails of various sort; a solo emerald crab; and a LOT of crawling life. We thought maybe amphipods, but they're a straight line with a stomach, and flit.

Ideas?

[venwu225]

might be mysis shrimps, unless you are really sure that the animals are fish? and how about some pictures? :D

[Sk8r]

I am by no means sure they're fish. I wondered about hermits (I know of one spawn I assume went down the outflow) but I'd think swimmerlets would have become crabs by now. I wish I had a good enough macro to get in there, but it's way back and dark. I can only see them where they cross the light and you never know when they'll flit. Mysis, eh? Highly possible. I get a lot of amphipod molts and the tank sand just crawls at night. I feed phyto for the clam and pods and have gotten a huge bloom of sponge and very healthy featherdusters, so mysis could be having a convention inside that rock, which has chambers there's no seeing into.

[acan_guy]

more than likely these are mysid shrimp. Do they cruise around in a circle motion more or less?

[H@rry]

Mysis can usually be seen at night with a flashlight. Look in the nooks and crannys for fast moving critters with a yellow eye that swim in circles.