CONQUERING THE DREADED HYDRA
by Delores Schehr
Reprinted from the Publication of the Michigan Cichlid Assn.
First, I begin by saying 50 years of experience keeping tropical fish does not give one the degree of "knowing it all". Working with and breeding these little gems is a daily learning experience. Well, the biggest learning experience I have ever had to this point came recently as a complete shock. Over the years I have had my share of losses of small baby fishes, such as the babies of Lamprologus, Julidochromis, Rainbowfish, Bettas, etc. When checking through the tanks of the adults, we collect the eggs, hatch them in small containers and when they no longer have their yolk sacs and start to swim and seek food such as live baby brine shrimp, they are transferred to another temporary home. This can be anything from a 2 1'2 to a 10-gallon aquarium. These tanks sometimes have gravel with an undergravel filter and other times they can be bare with a box or sponge filter.
Well, what is all this building up to? Always there are losses in baby fish, sometimes only a few, while at other times it can be the whole spawn that disappears. Next stage... what did we do wrong this time? Did we transfer the fish into water that was too fresh? If this was the problem, then we tried using the water from the parent's tank. It usually brought about the same results. We tried using water from tanks that housed very few fish and was very clean. This seemed to work for awhile, but then back to the baby fish mysteriously disappearing again. We asked ourselves if they might be getting pulled down into the gravel by the undergravel filter. Well, if this was the case we would put them in a bare tank. This trial and error went on for a couple years. Sometimes we thought we had the situation of dead or missing babies figured out, and then it would happen again. We would let young fry go into a tank and the next day the tank appeared empty. How about... shell dwellers spawn and you await the appearance of the new fry and it doesn't happen. Did they die? Did the parents eat them? Maybe you just thought they had spawned, but if you never see the babies you can't be sure, can you?
Then one night I got the answer to all my questions. I was spending one of my usual evenings water-changing and working with the fish, and as I was finishing up I realized there was one last job that needed done. A 2 1/2-gallon tank, holding approximately 350 Lamprologus tretocephalus fry 1/4" long needed to be transferred to a larger tank if they were to make it to morning. Amazingly there was a 10-gallon tank that had been emptied two days prior of it's inhabitants, so it seemed the logical place to move the "trets". Another thing in favor of this choice was the tank had been given a 75% water change the day before. So, I began by removing just enough water so I could pour the baby fish, water and all, out of the small tank and into the 10. As soon as the fry were poured into the tank they did what would be expected and all settled down on the bottom. What happened next left me stunned. The fry began to flail around as though they were trying to get free of something. Some of the trets were doing the same thing on the side glass. It was as though they were stuck there. What in the world could be causing this strange behavior? A close inspection, with the aid of a magnifying glass, soon told me what the mysterious goings on was all about. HYDRA!!! They were coming out of everywhere, grabbing the babies and killing them. I grabbed a siphon hose and tried to siphon out the fry I could, but it was no use as the ones I seemed to be rescuing had already been stung by the tentacles of the hydras, and soon died anyway. I felt defeated, and so stopped siphoning and left the tank about half way emptied.
The next morning when I went to the hatchery, I checked to see if I had any survivors - there were none. What I did find was a tank with the bottom totally covered with fat hydra. Although it was a tough lesson to learn, I realized then what had always been the cause of our fry disappearing, and I'm sure for many other hobbyists as well.
But that's not the end of the story... Hydra have always been present in my tanks and they seem to be where baby brine shrimp are fed. I have used different methods of decreasing their numbers, because sometimes hydra even form a carpet of green in some areas. There are several products that will eliminate some of them, but never completely. But now I knew what had been killing off our very small fry, something had to be available to get rid of their mortal enemy.
Before I get to the answer, let me tell you a little bit about hydra. I have checked the literature in most of the books, and there is little to no information on how they come to be in our tanks or what it takes to get rid of them. One thing I do know is that they seem to always appear where brine shrimp nauplii is being fed. The kost information I found was in the book "Encyclopedia of Live Foods" by Charles O. Masters. He says hydra is considered live food but is only eaten occasionally by some tropicals, such as the Blue Gourami. Not many aquarists try to culture hydra, but if you want to there are three basic essentials to consider: 1) clean water, 2) temperature of at least 70 degrees F. and 3) a reliable and continuous source of food. What are their foods? You guessed it - daphnia and brine shrimp Artemia. The numbers of hydra produced are directly proportional to the amount of artemia fed. This then sort of rules out the idea by quite a few aquarists that brine shrimp eggs bring in hydra, but instead it probably comes in through our water source.
The following information was taken from 1992 Grolier Electronic Publishing, Inc.
"Hydra are small coelenterates that commonly occur in fresh water. Mostly sedentary, their base is attached to a surface by adhesive mucous. They are simple, elongated polyps composed of a stalk and an oral region, containing a mouth surrounded by four to eight slender tentacles. The mouth opens into a gastrovascular cavity. Hydra are carnivorous. They kill their prey by injecting a poison released from stinging cells located on their tentacles, which place the prey into their mouths. Hydra reproduce asexually by a small bud appearing on the stalk which grows, develops a mouth and tentacles, and detaches itself, becoming a new and independent hydra. When a hydra is well fed, a new bud can form every two days."
Since this article was originally written I have become acquainted with another species of hydra that is even more dreaded. This species, which we call "Super Hydra", forms connected rows as it multiplies, and then will find something like a rock and cover it with much larger hydra. It will climb on the glass wall of the aquarium, and keep building as it goes. It also gives off a very pungent odor.
And now for the rest of the story...... Getting rid of hydra for most of us can become a real project, and every kind of method from salt to electrical impulses has been tried. Bit I found the way to get rid of them for quite a period of time, and it is so east it doesn't seem possible. The company "Aquarium Products" has a product called "Fluke Tabs" that I was using for another purpose, but found it totally eliminated hydra in the tank as well. All I do is dissolve the Fluke Tab in the aquarium where hydra is present and, in two to four hours, there is no sign of them left. It works well on super hydra too, but it takes as long as a day or two to rid the tank of them. The Fluke Tabs dissolve very readily in the aquarium, making them easier to use. The most wonderful part of the whole thing is that I have used Fluke Tabs on all species of baby fish and all sizes of fry, with great results without hurting the fish. They are used at a dosage rate of one tablet per 10 gallons of aquarium water. (Not to be used in a reef aquarium or with invertebrates.) I have cut back on the dosage when the tank was only slightly infested and had the same great results.
As I said in the beginning, every day is a learning experience, and now no more unexplained deaths or mysterious disappearance of baby fish.
Ed Note: I have used Delores' suggestion with good results. However, I found one species that both Fluke Tabs and Bausman' Tonic prove fatal to - Fundulosoma theirryi. I found this out the hard way by losing a full batch of fry with each treatment.