Peter U wrote:
My first questions would be from where does a fish obtain it's calcium for
bone development? How much can it absorb via water vs from it's dietry
intake? How quickly does the calcium get released from shell grit added
to a fry tank? <snip>
and..
I think the role of calcium supplements <snip>
All I'm asking for is some concrete evidence of this!
and..
The thing that I get tired of listening to is everyones theory on this or
that that they will swear is true but in reality they have never really
tested their theory properly. It's one thing to theorise (which can be
good, we do a lot of it on this list) but it's another to call it "Gods"
word. So many times we hear things put forward such as calcium and bow
fry that are "so" important. No one I have met in the US adds any
calcium to their fry (please correct me if I am wrong here Yankies :-) ),
which makes me ask is it that important?
gl - Prove It, show me controls - these are certainly two of commandments that
Peter and I (and several others on this list) live with as scientists, however
it doesn't always translate into our fishrooms. I am well aware that often
effects & outcomes are blamed on "causes" that have no valid reasoning and
eventually are discarded, albeit sometimes it takes a long time to destroy
these false folktales. I give as an example the thinking in the early 60's by
many of the aquarium books, to do very very small water changes, if at all.
Where would we be with rainbowfish if we follow that silly dictum today?
Calcium, my observations - I have been a "Bowmanite", ie a user of shell grit
for fry tanks for some time. In my article on P. tenellus (for RSG) I recalled
a group of fry that I had neglected (and grown w/o shellgrit) and found that
all of them ended up with deformities of their backbone. When the water was
checked for pH it was quite low (<5.0, bright yellow with bromthymol blue).
The ramshorn snails that were put in the tank to clean up any food left behind
also had very soft shells and could be crushed very easily. Unfortunately I
have unintentially run this experiment several times with other species, often
with the same results.
Is it the the low pH that causes the calcium in the water (or in their food)
not to be properly used or is it that the fish and the snails used up all of
the available calcium (in the water) which was essential for shell and backbone
growth? Does the addition of shell grit, (I think mainly calcium carbonate??
or at least that's what I can glean from my invertebrate Zoo. book) provide
mainly Calcium (part of the general hardness GH, along with Magnesium, Mg)
needed for bone formation or is it the carbonate (the KH) that helps buffer the
water and keep a higher pH, which in turn allows the available calcium (whether
in the food or the water) to be utilized by the fish and the snails? Or is it
something else like the organic wastes (that aren't removed w/o water changes)
that tie up available calcium? As aquarists how do we begin to run such an
experiment? Certainly we wouldn't use isotopes and even in the laboratory
environment this would probably be nixed as there are ways to determine the
difference between Ca and Mg besides our crude hardness kits.
In the design of such an experiment for the average aquarist we could put a
bunch of snails into a soft water environment (150 ppm or less GH), feed them
and then wait until their shells started getting much thiner - suggesting
Calcium depletion. (At least it is under this sort of condition that we start
seeing backbone deformities). This water could then be split into 3 parts. To
one part nothing would be done which would hopefully serve as a positive
control. To another part we would "add back" the proposed Calcium that was
lost from the system. From the healthfood stores in the US you can get
powdered dolomite which is roughly 2:1 ratio of Calcium carbonate to Magnesium
carbonate. If I remember correctly there are also some of the calcium health
products on the market now that are in the form of calcium citrate so you may
be able to add back calcium without adding back carbonate. Maybe something
like Kalkwasser (CaOH) could also be use but this would surely also raise the
pH. Another possibility might be something like Reef Calcium, a form of
chealated Ca for saltwater tanks but I have no idea how it would react with
freshwater. (Depending on which method of Calcium addition you chose you might
also increase the pH back to more "acceptable" growing conditions so you might
have to plan for another experiment where you add back calcium but also keep
the pH low.) In a third tank you would simply increase the pH, maybe with
something as simple as baking soda - sodium bicarbonate. I would then add to
the three (or 4) tanks equal #'s of 10-14 day old fry. I would use them
instead of merely hatching a given amount of eggs under each conditions as many
of us also believe that the addition of shell grit also aids in hatching.
{another experiment :-) }
Ideally you would like to start with DI or distilled water and then add back
components that we deem essential to the growing conditions. Whether the
average hobbyist would have at his/her disposal enough of the correct reagents
is uncertain. Many of the products in the US, such as RO right and pH stable
by Kent really don't list what chemicals they contain. Maybe you have some
ideas on what could easily be added back to mimic our natural waters, + and -
calcium. This could be an interesting experiment though and certainly one that
could generate a lot of cat or grunter food.
Again depending on what sort of GH and KH you have in your water you may or may
not have ever seen spinal deformities. Even with softer water if you've kept
up on your water changes it may be something you've never experienced.
Gary Lange
gwlang at ccmail.monsanto.com
RSG & ANGFA