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    Hydra - Some Facts

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    HYDRA Some facts!!!

    Hydra are a fresh water animal that belongs to the same group as jellyfish, corals and anemones, The name Hydra stems from Greek mythology. It was the name given to a many headed sea serpent. The hydra that we know resembles this mythological monster by its many tentacles.

    Hydra are found in nearly all clean fresh water systems in Australia and around the world . They have a range of colours from brown, green white, and many other variations .

    Many people have Hydra in their aquariums, but are unaware of their presence. They are very small approx. 2 - 3 mm in length ( but can extend to around 1cm when hunting) when hanging from the underneath of leaves of water plants are hard to distinguish


    A Hydra infestation does not just mysteriously appear in your aquarium and is not caused by poor tank maintenance or anything like that. The animal has to be introduced from some external source.

    It is usually introduced to aquariums from plants ,wood, rocks etc collected from wild creeks, rivers lakes and billabongs.

    Hydra have a sack shaped body that consists of a mouth /anus combination on the top surrounded by a crown of tentacles that carry an array of stinging cells.

    on the bottom of the tube body there is a "foot" ( basal Disk)a device the animal uses to anchor itself to plants ,rocks aquarium walls and the like.

    Hydra live attached to vegetation, rocks and walls by this "foot" with all its tentacles suspended into the water waiting for it's pray to blunder into them. Small animals that happen to blunder into the tentacles are stung and paralysed.

    within a short time all of the tentacles are wrapped around the victim conflicting many more stings. the victim is then drawn to the mouth and swallowed. Digestion is done over a period of several hours .Any un digested material remaining after this period is then expelled back through the mouth.

    The hydra is then ready to hunt again .

    It takes several hours for their weapons to recharge which it does while digesting it's food. Small aquatic animals like Rotifers, insect larvae, and ( especially) small crustaceans such as daphnia, seed shrimp and water flee, are their main pray.


    Hydra do not always stay in the one spot in the aquarium. they are able to move about in a couple of ways. They are able to secrete a sticky mass under the basal disk and they use this fluid to kind of slide themselves along to a new position. Another way is they detach the basal disk, bend over placing their tentacles on the substrate and then somersaulting re attaching the "foot" further along, they will continue to do this action until they reach their preferred position.

    The third manoeuvre noted is that they are able to produce an air bubble in the basal disk this raises them to the top of the water where they hang suspended waiting for pray.


    Hydra do most of their reproduction in the summer months. Most reproduction is "A" Sexual and involves a process called "Budding" in which a new Hydra develops as a bud on the parent central column . When conditions are right the bud breaks loose and continues life as an individual. These offspring are genetically identical to the parent ( true clones) .

    Under very good conditions hydra may possess several buds at various stages of development. Sexual reproduction is usually confined to the cooler months. Ovaries develop as an oval swelling near the column base. testis form as conical protrusions further up the column the sperm is free floating and can fertilize itself and other hydra. the young develop directly without a larval stage. HYDRA are beautiful but a bit annoying creatures.

    Given their reproductive abilities, their capability for moving around when they choose and the ability to eat pray several times their size. it's clear why hydra are not welcome in freshwater aquariums .

    They are believed to be able to cause harm or kill newly hatched shrimp, and in laboratory conditions they have been proven to eat baby brine shrimp. Adult shrimp are not effected by hydra stings except possibly as an annoyance. The larger Hydra have also been shown to eat small fish fry as large as newly borne guppies . Once hydra are introduced into an aquarium they can be difficult to get rid of them. ( but it's not impossible) If you are lucky to only have a small infestation you should be able to physically remove them, I removed the infestation that I had by wiping the tank sides down with a clean cloth, removed all rocks ,wood, from the tank and scrubbed them, plants I soaked in a light bleach solution for around 10 minutes before rinsing in fresh water and replacing. Another non intrusive way is to add some fish to eat them Gouramis or mollies will do the trick. ( not a good idea if you keep shrimp).

    Heat is another method. ( you have to remove all your livestock to do this) heat your aquarium water to around 40C for about 2 hours. this should kill them, Perform a minimum 50% water change and make sure that the water temp is back to normal before returning your live stock .

    Chemicals that can be used are potassium permanganate, or many of the fish anti fluke medications especially if they contain formalin. WARNING THESE CHEMICALS MAY BE HARMFUL TO SHRIMP, SNAILS, PLANTS and sometimes FISH. USE AT YOUR OWN RISK!!!! Some preventative measures are to inspect all live plants carefully( look for small jelly like substances) soak all plants in an approved solution before adding them to your aquarium. Avoid live foods from local rivers creeks etc. Boil all substrate wood rocks collected from the wild before adding to your tank .

    References used :- Bugguide Version Jan 2009 Information sources Wikipedia. org/wiki/imdra Williams 1980 Pennak 1989 Gooderham & Syrlin 2002 Offwell Woodland & wildlife Trust UK Researcher Wayne Summerhayes Febuary 2013.

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