Re: Fwd: factors relating to growth

["Darren J. Hanson" <djhanson@calweb.com>]

At 11:04 PM 9/29/97 PDT, Ed Pon wrote:

>I have noted the slowdown in growth when fry get to a certain size and I 
>wonder if it is attributable to the anti-growth hormone theory.  There 
>is a theory that some cichlids emit anti-growth hormone that cause fish 
>of the same species to slow down in growth and even get sick.  The 
>theory is that this is survival-enhancement for drought periods when the 
>pools of water may be smaller and food is less abundant.  I wonder if 
>increased water changes at this stage or lessening the amount of fish in 
>the tank may help.  In raising bearded dragons, a type of lizard, the 
>intimidation from some of the faster growing lizards seems to stunt the 
>growth of their cohabitants whereas if the lizards were raised 
>individually, they all have roughly the same growth rate.  Perhaps 
>intimidation from certain individuals in the growth are slowing down the 
>growth of others because of stress and the inability to eat more because 
>of bullying.

I don't think there is so much a hormonal/chemical process involved as one 
of the strongest/most aggressive specimens getting the most food while the 
weakest/least aggressive specimens get less food or even starve. This has
been noted among tank breed angelfish. After several generation specimens
exhibit behavior totally different than their wild counterparts including 
a tendancy to eat their own eggs and fry. In the wild this type of uncontrolled
agression would be bred out of the line by such fish being incapable of 
successful breeding while in a commercial hatchery the eggs are routinely 
hatched and raised artifically and so even the worst specimen in terms of
parental care can and does successfully spawn time after time.

Most examples of chemical attack between aquatic organisms that I have seen 
documented are of the form of eliminating competing species, not supressing
lesser members of ones own species.

The solution I have attempted, with uncertain results, to counteract this
disparity in feeding behaviors is to feed several small feedings in a short 
period of time. Instead of adding as much food as the fish will eat in 2
minutes,
I add as much food as the fish will eat in 30 seconds over and over again until
some is finally falling to the bottom of the tank. This often results in more
food being eaten than would be in a single feeding. Also, with young fry their 
intestinal tracks are so short that it is imperative to feed them at least
several 
times a day, and the more meals/day you can arrange the better.

But don't take my word for it, Kaycy's the REAL expert in the family....

- -- dj