Dick wrote:
On Sat, 31 Dec 2005 00:29:23 -0500, "NetMax"
wrote:


"Gill Passman" wrote in message
...

NetMax wrote:

'Stunted' tends to have a negative connotation, and if it's due to bad
conditions, then it's deserved. It's interesting to note that stunted
fish (I call them runts) are also naturally occurring. I think this
is part of their evolutionary strategy of constant diversification
through mutation. Non-natural runts (stunted by environment rather
than genetics) can occur from a variety of reasons. The most
predominant would appear to be diet (ie: feeding only a flake food),
but it was explained to me that water parameter dilution also plays a
major part, especially with certain species.

The explanation was as follows: A growing fish will release hormones
which it can then detect back from the water.

If the hormones are not detectable or very low, then the body of water
is large and/or there is no or little competition from similar
species, so the proper action would be to expend more energy on growth
(until some other constraint develops, such as genetics, food supply
etc).

If the hormones detected back are high, then the body of water is
small (or shrinking), or there is significant competition from similar
species (both indicating a reduced food supply), so a proper action
might be to not expand energy on growth, and stay small (surviving on
less food).

If this analysis is correct (and I suspect that there is significant
truth behind it), then it would go a long way to explaining why total
sizes for fish are so different from an aquarium (where these hormones
are in high concentration) and from nature.

Loaches in particular are mostly from the Mekong river system fed from
mountain ranges (refreshed from heavy rainfall and snowmelt), so their
reaction (stunting) to accumulated elements in an aquarium (nitrates,
hormones etc) might be much more acute than lake fish, such as African
mbuna, which do approach and even exceed their natural size in nature.


Hmmm....interesting

I have a "stunted" Platy. He's around 1 year old and has never grown
above 1cm. Platy fry from the same parents but in the "parent" tank
grow rapidly to "adult" size.

The "stunted" Platy has always lived in a 5gall tank (was born in it).
His last contact with Platys was at around 2 months old when I netted
out the fry and took them to the LFS - he remained only because he
jumped out of the bag and so I decided that he may as well stay. His
only fishy companions have been single bettas. Diet has always been
varied - flake and frozen and the odd bits of pea that have been fed to
the betta yet he has always remained small.

My guess is that he is a "natural runt" but as he had never had any
competition from other platys I've also wondered if this has been
another reason for the lack of growth. Maybe sharing the tank with a
betta might also have meant that staying small has been to his
advantage in keeping out of trouble.

I actually spotted some dinky platys (I'm guessing very young) at the
LFS and bought him 3 small companions today - his days as a betta
companion are over. If they get too big they will move on to a larger
tank. It will be interesting to see if he grows at all now he is mixing
with his "own kind"

Gill

Two things came to mind reading your post. The first was a vague
recollection of a correlation between growth and competition, such that a
competitive environment causes them to grow faster.

The 2nd was that the longer a fish is exposed to the environmental
conditions which cause them to stop or reduce their growth, the less
likely it becomes that they will resume their normal growth rate or reach
their normal size after the conditions have been corrected. This is only

from personal observation.


A Black Molly had 50 fry in a 10 gallon tank. There sizes varied
widley as they grew. If the chemical explaination were the answer, I
would think they all would be stunted, whereas most were normal or
even larger than normal. Of course as they grew large enough they
were moved to other tanks. The last ones in the breeding tank were
smaller than normal. A few died, but most lived.

Anyway, I am happy my Clowns have remained a good size for my tanks.
I wonder how the chemical influence explains the 2 that have lived in
my 10 gallon tank versus the 6 in the 75 all being similar in size?

dick

My experience has been varying sizes from each batch of fry. If left in
the Community tank it is only the strongest that survive. The stunted
Platy survived, I believe, because he was not given this type of
competition...in nature or even in the artificial confines of a
community aquarium he would not have lived as long as he did - sadly I
made a big mistake by putting in some Platy friends for him - I found
him dead this morning :-(

I think that nature/genetics does play a big part in the size fish grow
to - but yes I also agree that a fish will not thrive if the conditions
are wrong. I probably wouldn't put Clown Loaches in a small tank unless
it was for QT purposes. However Dick's experience in fish keeping and
stocking levels have allowed him to do this successfully - I wouldn't
trust myself to be diligent enough to make it work.


The 2nd was that the longer a fish is exposed to the environmental
conditions which cause them to stop or reduce their growth, the less
likely it becomes that they will resume their normal growth rate or
reach
their normal size after the conditions have been corrected.


This observation made me wonder if this is where the idea that fish
"will only grow to the size of the tank" comes from. Sadly, I still hear
this comment as an excuse for keeping large fish in unsuitable
"over-stocked" tanks as a justification for doing so - everytime I hear
it I try to explain that just because they survive short-term it is not
in the best interests of the fish....

Gill