Mystery shrimp like critters

[Crusis]

Hello, everyone!

I have a mystery visitor to my 75 gallon tank. It's a planted tank, I bet this is something that came in on a plant, but I'd like to know what it is and if I need to kill it or if I have nothing to worry about.

Some of you might remember my earlier post about this tank being the "Tank of Doom". The tank has settled down, I bought three Sunset Mollies and they ALL survived the introduction to the tank. One of the Sunsets even had babies, so now I have 9 fry in a breeding cell, and all the babies are doing well.

I have a new visitor, however, and it's NOT a fish. It's a crustacean. Or appears to be. Small critters, 1/3 centimeter in length, milky white, with a black area 2/3 of the way from the tail to the front on bottom. When you catch one, you can JUST make out the legs. I suspect these are some sort of crustacean, but what is it? The critters are all in one area of the tank at the base of a plant, and seem to be rather active. They frolic around the sand and stones in that area right next to the plant. A Cory cat swam right by them while I was watching and didn't give them a second look. They appear to be sighted, as the one I caught actively tried to avoid my small net.

Any ideas? If they are harmless, that's fine, but I don't want anything harming my fish after the recent parade of death that they have experienced.

 

[JohnPaul]

Could they be freshwater amphipods? They are sometimes sold as "feeder" crustaceans to some fish that like to dig around and find such snacks. There is a picture of them here, fourth item down on the list.

 

[Crusis]

That could be it.... very close in appearance, although the ones in my tank are a bit more gray and less cream colored. Could be species variation. As of yet they haven't assaulted any of my fish and sucked out their eyeballs, so I'll just keep observing. I bet this is what they are, though. Thanks, JohnPaul.

 

[JohnPaul]

If in fact I helped, glad I could help.

 

[frog girl]

Well I think they just eat detritus & tiny planktonic larvae & rotifers & stuff so unless they are doing damage enjoy their antics.

 

[Felf]

they're called gammarus or scuds but watch out because they're known to carry several fish diseases

http://www.bcadventure.com/adventure/angling/bugs/shrimp/shrimp.phtml

 

[Crusis]

I found another page that had some information on them, unfortunately the link to the picture of them is broken.

http://members.aol.com/larval1/critters.htm

Seems like a good page for figuring out the critter in your tank, though.

From what I can find out, other than the potential as disease carriers, these guys are harmless and will actually eat decaying plant material off the bottom of the tank. I think I'll let them stay as long as they don't get too numerous.