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Hydra is a polyp from the Genus Hydrozoa, which attaches itself to plants(also under duckweed!), stones or the side of an aquarium. They are often pale brown or green.When fed well Hydra multiply so rapidly, that they can become a plague. They can multiply in three different ways, by budding, by spores and by division. Budding is when a smaller hydra grows off the body of the adult, separates, and attaches itself to a new location. Spores are only formed in autumn, when living conditions become less favorable. The tentacles have stinging cells which they use to capture prey like small water fleas.

Phylum Coelenterata or Cnidaria. The cnidarians are the most primitive animal where the cells are organised into different layers.

Hydra are usually introduced with live food caught from pools.A few hydra are easily overlooked when introduced in an aquarium In the normal community tank they pose no threat, but in a breeding tank they can rapidly deplete all newly hatched fish.

Prevention: If you catch your own live food, you should always place it in a bucket for 15 minutes. The present Hydra will attach themselves to the side and the bottom of the bucket.

Treatments:

1) Raising the temperature to 45 degrees((110F). Prior to this remove the fish and the snails from the tank. The plants can be left in the tank since they can stand this temperature. The temperature only needs to be kept this high for a short period, 5 minutes will suffice.

2) Treat the aquarium with Dactycid(Colombo).

References: microscopy Uk, Innes,sterba et al

Picture references: All pictures and drawing: E. Naus

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