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Re: Aquatic 'worms'

On Wed, 10 Nov 1999, Kevin Buckley wrote:

> Is there a tropical freshwater equivalent of the terrestrial worm (grub,
> snail, fish etc); i.e. something small & benign that spends a lot of time
> digging around in the gravel at the bottom of the tank & keeping it loose &
> aerated?

Malaysian trumpet snails.

> Also, does anyone know what fish poo is actually made of (not how it's made
> - - I know that already)?  Also, in an aerobic environment what happens to it
> over time (apart from the fact that you seem to get more of it!)?

This is highly variable, depending on the fish in question and the food
they eat.  I read recently of a food consumption "model" based on the
caloric content of food compared to the caloric requirement for fish
growth (in the case of that study, the fish were salmonids).  I think the
authors assumed that anything in the food present in amounts out of
balance with the calorie content and general composition of the fish would
be produced in wastes.  They also accounted for a few other details, like
digestability of the foods and so on.

There's also an excellent aquacultural book by Halvorson (if I remember
the name right) titled "Fish Nutrition".  It's been a few years, but I
think that in very general round numbers fish will use only about 60% of
what they eat, and the rest is passed.  This varies a lot.  I.e.
Single-gutted fish can't digest most plant material so pass almost all of
it, but long-gutted fish can digest more.  Certain fats and oils are
completely undigestible to fish and they will pass all of it, while other
fats will be mostly digested. And of course, if you have driftwood and
plecos, then the pleco poop may contain a lot of wood fiber. And on and
on.  There are many variations.

What happens to it over time is an interesting question, and one that I
wish I could answer in more detail.  First it disaggregates fairly quickly
then it appears that given sufficient time most of the wastes would be
converted biologically to CO2 and mineral nutrients (plant food).  How
much and how quickly the conversion actually happens depends on your
hardware and maintenance schedule among other things.  Getting rid of fish
wastes and fish feeding wastes (which for regulatory purposes are
generally similar to feed lot wastes) is one of the biggest problems for
aquacultural facilities that reuse water.

> Final question - Apart from plants, what do aquatic snails eat & what waste
> products (solid & liquid) do they produce?

Only a few of the snails commonly kept in the hobby will normally eat
plants.  Generally they eat algae, detritus (like fish poop and plant
debris) and the bacteria and other critters living on surfaces and in the
substrate.  They eliminate waste carbon as CO2, nitrogenous wastes as
ammonia, and solids through the usual route.

Roger Miller