tiny jellyfish looking propeling things

Question
Hi Susan, I just noticed many of these tiny jellyfish looking things in my freshwater aquarium. I don't see tentacles, but the way they propel themselves make them look jellyfish like. They are clearish, about a mm large.

In my tank are two adult angels and 12 pinky fingernail size babies. I feed the babies frozen brine and the adults flakes and sometimes bloodworms.

Any ideas?

Answer
Hi Gail,
There are many different types of little creatures that can show up in our aquariums. It can be difficult to identify them and give an exact name to the species but the most common critters are "Copepods" or "Ostracods". The good news is they are harmless crustaceans that will not bother your adult angels or their babies. The somewhat bad news is their presence usually means the tank's nutrient level may be a bit high.

I know this is quite possible since you are raising young baby angels in the tank and they require very frequent feedings in order to grow well and be healthy. I've raised angelfish fry myself several times before and all you really need to do is vacuum the bottom of the tank everyday. The young little fish will also have a growth spurt if they are getting daily water changes (like around 30% depending on the size of the tank). Obviously this will lower the nutrient level in the tank and the jellyfish-like creatures won't be able to survive or sustain their population.

If the population is well established this may take awhile, but patience and persistence will pay off.

Best of luck with your Angelfish and Angelfish children :-)
I hope this helps!
Susan~