The Attack Of The Planarians

by: Donna Dohrn, JAS member

Imagine waking up morning - only to discover that you have been invaded by what seems like hundreds of little white worms. Sounds like something out of a science fiction movie, doesn't it? Well, this was for real and it was happening to us. Our 20 gallon aquarium had creatures crawling all over the glass

It was instant chaos; what did we do wrong, where did they come from and better yet - how were we going to get rid of them? To make matters worse, our Angelfish "Morph & Mindy" had recently spawned again and we had fry as well as eggs in the tank.

Bill and I were afraid to do to much to the tank for fear of harming the fry, so we simply cleaned the glass and added Methylblu. We did this for several more days, then realized that we would probably lose the fry if we didn't do something more. We left the fry in the tank, but put them in a baby holder, then did a small water change. We continued this for 3 or 4 days - but still the worms came! Not only were they on the glass, but now we could see them swimming in the tank. Time to call in the Big Guns!

I have a friend working at the State Fish Pathology Lab, so we called and asked if we could bring in a water sample for analysis. After an interesting look under the microscope. the pathologists were able to identify our aliens and we could breath a sigh of relief. They were nothing more than Turbellaria - commonly called flatworms. We had 2 different kinds, the microscopic Stenostomun and the common laboratory planarian, Dugesia. Both are called free -living, which means that they are non-parasitic, and completely harmless to the fish. In fact, you might say that our fish had their own fast food restaurant right in the tank. No wonder they never seemed to be hungry!

We learned that the Turbellaria live in lakes, ponds, streams and springs where they occupy bottom habitats. They are usually introduced into freshwater tanks by live food, but can also be brought in on live plants.

When we got back to the house, I decided to learn a little more about our uninvited guests. I got out the dictionary and some of our books on fish. I wasn't able to find much on the subject.,but here are some interesting facts:WEBSTERS NEW WORLD DICTIONARY - THIRD EDITION, defines Turbellarian as; any class of flatworms, mostly aquatic and nonparasitic, characterized by a leaf-shaped body covered with many cilia. It also defines Planarian as; any of an order of small, soft-bodied, free-living, turbellarian flatworms moving by means of cilia.THE NEW AQUARIUM HANDBOOK by: Ines Scherumann, states that Planarian are sometimes brought into the tank with live foods. They are acceptable in Tropical aquariums, but must be removed from breeding tanks.

AQUARIUM ATLAS by: Dr. Rudiger Riehl and Hans A. Baensch, states that Planarians or diskworms are usually introduced with live foods, and if conditions are right, they will quickly multiply. They are predators and compete with fish for food. They are partial to fish eggs, greatly reducing the likelihood of successful breeding. Planarians have also been found on young fish.

Turbellaria are difficult to control. Baiting is generally the better approach. Fill a small gauze or fabric bag with meat and at night, hang it near the bottom of the tank. The worms scent the meat and will gather in quantities. If the bag is removed before morning, the worms come with it. They can then be destroyed in boiling water. Planarians are also eaten by Macropods.

We are not sure how the flatworms got into our tank in the first place, but think it must be from live plants since we don't feed our fish live food. We also noticed that the worms did not attack or harm the eggs in any way. They developed and the fry didn't look any different from other spawns.

When we cut down on the amount of food we were feeding our fish (I have a tendency to overfeed) and continued with our frequent water changes, we were able to control and eliminate the problem. So, if you wake up one morning and find that you have uninvited guests living in your aquarium, maybe this article will help you to understand them a little better.

© Copyright by Donna Dohrn, All Rights Reserved, May 1997.