"Gill Passman" wrote in message
.. .
Dick wrote:
On Sat, 31 Dec 2005 00:29:23 -0500, "NetMax"
wrote:


"Gill Passman" wrote in message
k...

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.

The growth rates of different species, and in varying environments would
make a great book. All I can tell you is that there seems to be a moment
of diversification which varies according to several factors, and water
quality (unless to an extreme) is not a big factor. For example, when a
medium sized substrate spawning cichlid (ie: Jack Dempsey, Rainbows,
Firemouths, Texans etc) has a batch of fry, it's remarkable how close in
size the fry are and for how long. While the fry are under parental
control, there is minimal size differences (there is always a few fry
which follow a slightly different growth rate). If the parents are
removed, the differences between the smallest and the largest suddenly
seems to increase. Add a different species of fish (ie: some corys), and
the differences increase again. Add a more food-competitive fish (fry
from a slightly older generation), and again the difference between
smallest and largest increases, to the point it looks like you have more
than 2 generations of fry. Mess with the water temperature, or their
diet and again you see this divergence occuring.

At the other extreme, look at fish which have relatively few fry (cichlid
mouthbrooders), and the fry will just be starting size divergence before
they are even released from the parent. After 3-4 months, the fry will
appear to have come from 2 broods instead of one. Livebearers are the
same. Fry are all born at relatively the same size, but quickly diverge
in size.

I think the mechanisms at work in the first few months of fry growth are
more related to species, genetics, temperature, competition and food
supply (quantity, quality and interval), than water parameters as factors
to cause runts. jmo

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?

It would suggest that there is relatively little difference in water
quality, due to your water change routine, but there are so many
factors...

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....

Just last night I was talking with someone, arranging a new tank for
their Tiger Oscar and Silver dollars. He was leaning towards a 70g
Oceanic, and I was leaning more towards a 90g (or larger Perfecto for the
same cost). We talked about the factors which make them grow, grow
faster, not grow, grow slowly etc. The owner (who is a very diligent and
conciencious hobbyist) went away from the conversation with ideas which
would keep the Oscar growing slower and not get quite as big as possible,
but in a responsible & humane way. Deliberate stunted is not neccesarily
negative, or bad for the fish, but it's a fine line to manage, so it's
far easier (imo) to provide optimal conditions and let the genetics be
the constraint.

Gill

Sorry about your Platy Gill. I wonder what took him out so quickly? In
aquariums, fish persist which would in nature, quickly become part of the
food-chain, but occasionally' nature's crowd control methods sneak into
our tanks, leaving us a little perplexed.
--
www.NetMax.tk