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[APD] Re:Re: hydra

Semantics, RPH, semantics:

Robert H said, in part:

"I researched hydra and planaria last year and found numerous references
hydra feed on decaying organics and the parasites that are found in decaying

Then you researched the wrong places.  "Parasites" do not live on decaying
organics, the case is rather that parasites live on or in, and at the
expense of, living organisms.  Hydra are not parasites, but predators.
Their prey is any small free-living organism within a certain size range,
but this would only very rarely include parasites (some of which do have
free-swimming stages - such as the tomites of Ich, but I don't know if those
are nearly large enough to provide a living for hydra.  Ich tomites
certainly do not feed on decaying organics, they do not feed at all).  Hydra
will certainly feed upon infusorians which would include numerous types
which could well feed on decaying organics, but then fish fry would be
feeding upon the same infusorians.

Hydra definitely do not fit the same ecological profile as the nematode and
planarian outbreaks seen in tanks suffering from excess organics.  The do
fit all too well the profile of tanks fed with regular doses of small to
medium cultured infusorians, such as small fish fry needing such cultured

He also quoted the referenced article: ""Hydra can not live in water of poor
quality" but Robert H followed this by saying, in part: "I think he means
the opposite."

I tend to assume that an author intended to say exactly what he wrote.  That
a normal well maintained tank may or may not support a few hydra which are
unlikely to be noticed by the hobbyist.  But that if small live food
cultures are supplemented, as for food for small fry, or as filter feeder
food, then the hydra population can expand to easily noticed levels.  As
that concept aligns exactly with my experience, it struck me as quite

Could there be confusion between nematodes and hydra?  They are neither
similar nor related.  Nor have I seen similarities in my own tanks between
the appearance of noticeable nematodes or planaria versus the appearance of
noticeable hydra.  The former pair I certainly agree result from excessive
organics, the latter have only appeared in situations of added
infusoria-type foods.  To me that means that all were present previously,
but the noticed appearance of the particular beastie would be from
population expansion based on entirely different sources.

Robert Ricketts

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