A lot of "maybe's" in your post to still stand by the "hormone" theory. I don't believe in this theory. To state that it's either Nitrate, or hormones at play when it comes to Discus fish not growing to their full potential is rediculous. Do you know how many things are at play when people talk about "good quality" vs "bad quality" water? I'm sure you know that young Discus cannot be grown in "pure" water also, right?
By your theory, the Alpha male would be secreting this "hormone" to inhibit the growth of young Discus, possibly his own offspring. This does make sense, but what about when you're growing out young Discus that hasn't reached maturity? Are they also secreting such "hormone" to inhit their own growth? Surely you're not implying that young Discus also secret this unidentified "hormone"? What's the purpose for young Discus to do such a thing?
There's a much better theory out there than "hormones". One that deals directly with water quality, something that can be measured, and not guestimated.
Shawn
Sure there are a lot of maybes, but there always a lot of maybes. I don't think it's ridiculous at all to say that it's either nitrates or something being secreted by the fish. Why? Because stunting happens in tanks with low TDS, high TDS, low KH, high KH, low pH, high pH, low temperature, high temperature, etc. The same can be said about many other parameters and thus they can be eliminated as the culprits of stunting.
Now look at the water in instances where fish AREN'T stunted and you'll find that nitrates are low or nonexistant. This is the result of many water changes or live plants removing the nitrate from the water for their own growth. Many hobbyists have reported that live plants seem to make their discus grow faster than without them. I keep a barebottom tank with sub adults (now) and potted live plants and my discus have grown well on a not so regular water change schedule. So maybe nitrates inhibit discus growth.
Also, you are assuming that discus fry are receptive to this hormone and I never suggested that at all. Quite possibly discus become receptive and also secrete this hormone when they are juvies. This would make sense if you consider what follows.
Discus are a schooling fish and there is an alpha male and an alpha female. They have to be the healthiest of the group to ensure the survival of the group. They eat first, they determine the pecking order, and quite possibly they secrete a hormone to prevent the others from growing as large. Why would they do this? Because that allows them to grow larger and stronger and when confronted by a predator, the school's alpha leaders will be the targets, since they stick out as they are the largest. They are also very healthy and strong and just maybe they draw the predator away from the rest of the school to ensure the survival of the rest of the group. If the alpha is eaten, a new alpha quickly arises and puts on much size as has been evidenced in many hobbyist's tanks (when the alpha was removed). They alpha may have sacrificed itself, but the group as a whole survives.
This would make sense for they fry situation as well, IF you believe that the fry are affected by the hormone. I do not believe this as it would be detrimental to the growth of the fry more than it would ensure their protection and that's why I think they don't become receptive to the hormone until they become juvies. At this point they may be starting to look for mates and to prove to a potential mate that they are strong and healthy. What better way to do this than to sabotage the competition? It makes sense though that the parent would want to have a predator see the parent as a target rather than their offspring. Both parents take care of the fry and are capable of feeding them so if one of the parents gets killed the fry can still survive with the other parent. But if this were the case, the parents would be brightly colored when spawning and the opposite is true. Parents darken to attract fry, it's the same reason albinos are far more difficult to get the fry to attach to than something like a blue diamond pair. Some theorize that the albino fry don't have the pigments in their eyes to see the parents well, but the same thing happens in snow white/white diamond pairs where the fry have a difficult time finding the parents. Must be the color of the parents more than the lack of pigments in the frys' eyes.
You say that there is a MUCH BETTER theory out there that explains the stunting that deals directly with water quality. I've supported the theoy I belive in based on what I've heard, read, and seen. You say that there is much support out there for the water quality theory and I stated that stunting happens in tanks with low and high levels of many parameters, except nitrate. Water changes would remove nitrates and the hormones as well, so something like KNO3 would have to be added back into the water to ensure a high level to rule out nitrates as the stunting variable.
By the way, you do know that these hormones would be considered a water quality issue, right? And once identified, their levels in the tank could be calculated and monitored, provided that someone owns the right equipment. It may not be cost efficient, but proving that they are there, and finding the level at which stunting occurs are the first steps that need to be taken.
