growth-inhibiting hormone?

[ApacheDan]

I learn from the Discus people that the fish can produce a growth-inhibiting hormone by the Alpha males & females. For many years I was puzzled why I would start with a bunch of same-size discus and some would grow quick, while a few will stay smaller, given same tank, food, etc. The reason is that the bigger, dominant ones will have a breeding/eating advantage over the smaller ones if they manage to keep some of the competion from growing fast. The hormone travels in the water & that is one of the reasons discus keeper do constant water changes.

Now I got 18 small zebras...some 3/4" and some almost double in size. At this size, would it be advisable to split the group between bigger & smaller? Does anybody knows about similiar hormone problems with zebras? Thanks. Dan

[PlecoDamo]

Im not sure whether this is the case but it could make sense.

Maybe doing the same as the discus breeders would be the safest option

[rich1988oxford]

That is very interesting, people are always coming into the LFS i work in and telling me that they have had a group of angels,discus or even gouramies. And apparently one of the group that they purchased at the same size has not grown atall whilst the others are at least 4 or five times bigger. Thry say they the small one is eating just as much and has no visable deformities or ailments. That customer question has always baffled me!

Very interesting

[Pete]

I don't believe the hormone theory. In nature, in a huge river, such hormones wouldn't hang around long enough to affect any of the fish near the fish allegedly producing them.

I think the size thing is more simply: the bigger the fish the more chance it probably has at getting the food. Splitting up significantly differently sized fish would, all things being equal, probably be a good move.

[ApacheDan]

Just for the records, the hormone theory came from Wattley Discus. For those that don't know, Jack Wattley is considered the grandfather of discus, who has traveled worldwide Japan, Germany, etc doing research & author of several books. Wattley Discus is now run by Gabe Posada, who told me this personally. He also agrees that it does not affect fish in the wild, since they are in free-running water...but in tanks, it is a different matter.

[Pete]

I know who Jack Wattley is, but unless there is scientific proof, a theory is just a theory. If that proof exists, I'm always willing to learn.

Given that it doesn't affect fish in the wild, why would mother nature give the fish this ability? It would serve no purpose. Producing a hormone that slows the growth of other fish is hardly a great characteristic for survival of a species (as compared, say, to having a thin body which helps you hide) so natural selection wouldn't cause it. It just doesn't make any sense.

[ApacheDan]

Given that it doesn't affect fish in the wild, why would mother nature give the fish this ability? It would serve no purpose. Producing a hormone that slows the growth of other fish is hardly a great characteristic for survival of a species (as compared, say, to having a thin body which helps you hide) so natural selection wouldn't cause it. It just doesn't make any sense.

I agree with what you say, but I don't know if it applies to fish in the wild. Captive born discus have been around years and years before the L046 was even discovered. Strains such as Blue Diamonds, Marlboro Reds and more than 40 others do not exist in the wild either. My own theory is that the inhibiting hormone was actually man-made through so many F generations of captive breeding....and in a tank, it does make sense. I've visited Wattleys place many times & you will see all similar-sized discus in the same tank. When I asked why, Gabe informed me why. He also showed me a tank with same strain of medium to large sized discus and a few smaller ones. He said it was too late for the smaller ones....that's how they would stay & their growth was stunted pemanently. This makes sense to me...Dan

[ApacheDan]

This is a quote from the Gan Farm in Singapore, major breeder of discus worldwide:

"Ah Tiong gave the following pointers for discus keepers. He mentioned that changing water regularly helps accelerate growth in discus as Singapore water is one of the best for keeping discus. Adult discus also secrete some form of growth inhibiting hormone in the water which will slow down the growth of other discus in the same tank and changing water will help to remove this hormone for the other smaller fishes to grow faster. "

For more info just do a Google search under: "growth inhibiting hormone discus"

[ApacheDan]

I think I'm beginning to answer my own question. Bottom line, I will split my growing zebras & keep doing daily water changes...can't hurt, besides I'm used to it....

Here's another quote from famous Discus Authority Roy Khoo:

"Beta
I want to know your opinion on Wattleys GHH (growth hindering hormone) theory that discus excrete some substance which inhibit other discus from growing. Have you ever seen any signs to support it?

Roy
Not sure if my experience in keep fishes from juveniles to adults support the GHH theory but in a batch there are bound to be some fishes that will be slightly smaller than the rest in the group. The reason being there is always the weakest fish in the group which always gets bullied and will get to eat the food lesser and slower than the rest. This i think is due to the law of survival where the strongest fish will survive.
Regarding the GHH I would think it does exist but since we do about 90-100% water change everyday. I doubt the GHH will be in the water long enough and will deem negligible.



Any of you travelling to Singapore are welcome to visit his farm. Just call him before you go. Here are his contact details:
Discus Connexion
Plot L33 MK29 Pasir Ris Drive 12,
Lorong Harlus (inside Aquarium Iwarna)
Singapore
Phone: 006597659245
Mail: roykhoo@discusconnexion.com "

[ApacheDan]

If that proof exists, I'm always willing to learn.

.

Pete, you wanted scientific proof?....check this out...

": Comp Biochem Physiol C Pharmacol Toxicol Endocrinol. 1998 Jun;119(3):325-38. Links
Endocrine regulation of gonadotropin and growth hormone gene transcription in fish.Melamed P, Rosenfeld H, Elizur A, Yaron Z.
Department of Zoology, Tel Aviv University, Ramat Aviv, Israel.

The pituitary of a number of teleosts contains two gonadotropins (GtHs) which are produced in distinct populations of cells; the beta subunit of the GtH I being found in close proximity to the somatotrophs, while the II beta cells are more peripheral. In several species the GtH beta subunits are expressed at varying levels throughout the reproductive cycle, the I beta dominating in early maturing fish, after which the II beta becomes predominant. This suggests differential control of the beta subunit synthesis which may be regulated by both hypothalamic hormones and gonadal steroids. At ovulation and spawning, changes also occur in the somatotrophs, which become markedly more active, while plasma growth hormone (GH) levels increase. In a number of species, GnRH elevates either the I beta or the II beta mRNA levels, depending on the reproductive state of the fish. In tilapia, the GnRH effect on the II beta appears to be mediated through both cAMP-PKA and PKC pathways. GnRH also stimulates GH release in both goldfish and tilapia, but it increases the GH transcript levels only in goldfish; both GnRH and direct activation of PKC are ineffective in altering GH mRNA in tilapia pituitary cells. Dopamine (DA) does not alter II beta transcript levels in cultured tilapia pituitary cells, but increases GH mRNA levels in both rainbow trout and tilapia, in a PKA-dependent manner. This effect appears to be through interactions with Pit-1 and also by stabilizing the mRNA. Somatostatin (SRIF) does not alter GH transcript levels in either tilapia or rainbow trout, although it may alter GH synthesis by modulation of translation. Gonadal steroids appear to have differential effects on the transcription of the beta subunits. In tilapia, testosterone (T) elevates I beta mRNA levels in cells from immature or early maturing fish (in low doses), but depresses them in cells from late maturing fish and is ineffective in cells from regressed fish. Similar results were seen in early recrudescing male coho salmon injected with T or E2. T or E2 administered in vivo has dramatic stimulatory effects on the II beta transcript levels in immature fish of a number of species, while less powerful effects are seen in vitro. A response is also seen in cells from early maturing rainbow trout or tilapia, or regressed tilapia, but not in cells from late maturing or spawning fish. These results are substantiated by the finding that the promoter of the salmon II beta gene contains several estrogen responsive elements (EREs) which react and interact differently when exposed to varying levels of E2. In addition, activator protein-1 (AP-1) and steroidogenic factor-1 (SF-1) response elements are also found in the salmon II beta promoter; the AP-1 site is located close to a half ERE, while the SF-1 acts synergistically with the E2 receptor. The mRNA levels of both AP-1 and SP-1 are elevated, at least in mammals, by GnRH, suggesting possible sites for cross-talk between GnRH and steroid activated pathways. Reports of the effects of T or E2 on GH transcription differ. No effect is seen in vitro in pituitaries of tilapia, juvenile rainbow trout or common carp, but T does increase the transcript levels in pituitaries of both immature and mature goldfish. Reasons for these discrepancies are unclear, but other systemic hormones may be more instrumental than the gonadal steroids in regulating GH transcription. These include T3 which increases both GH mRNA levels and de novo synthesis (in tilapia and common carp) and insulin-like growth factor-I (IGF-I) which reduces GH transcript levels as well as inhibiting GH release.

PMID: 9827005 [PubMed - indexed for MEDLINE]"

[John]

I grew out 15 young ones in 1 tank of 60x60x60 cm. which holds about 180 liters with one weekly wc of 33%.
I did not notice any differences in growth in this batch of youngsters.
All fry grew well and allmost equal in size.
I know of this problem with discus as i have been keeping discus for several years, i can not confirm this problem with L46 or other species of the hypancistrus family.
So far my experience.

[Dave_C]

an importer was telling about this a few days ago apparently its the same thing as the discus he has had people buy zebras which they have had for 2 year and have only reached 1"-1"and a half he says they come from asia.apparently he can still get these zebras but he says i would be lucky for them to reach a inch and half.

[ApacheDan]

I grew out 15 young ones in 1 tank of 60x60x60 cm. which holds about 180 liters with one weekly wc of 33%.
I did not notice any differences in growth in this batch of youngsters.
All fry grew well and allmost equal in size.

John, my situation is a bit different. I got 18 youngsters, but from 4 different sources. Some are more than twice the size of the smaller ones...so that's what I got to start with....not youngsters of the same size. So if this holds true, it is possible that the older, bigger fish will inhibit smaller fish....if nothing else, competition for food & survival of the fitest. Last night I dig deeper into this research & found that it applies to Oscars, gouramies, even crabs...to name a few that I found. It might not apply to Zebras, but rather be safe than sorry.

[John]

It might not apply to Zebras, but rather be safe than sorry.

You're right

BTW i tought FL only got seminoles

[ApacheDan]

It might not apply to Zebras, but rather be safe than sorry.

BTW i tought FL only got seminoles

LOL, actually Florida also has the Miccosukee tribe. There is indian in my blood alright, but I'm neither that nor Apache. My great-grandfather was one of the original Headhunters (& head-shrinkers) from a latin tribe called Guaymis, which fought the Spaniards...