Stunted Growth -- causes. mechanism?

[Vitaly]

Okay so the concept of "stunted growth" for fish has come up in several discussions at Henry's meeting, on the board, etc. Obviously we all understand that putting a big fish, or one with the potential for getting big, in a small tank stunts growth. And I just want to quickly commend "RobynT" for being so diligent in finding a new home for the Tang.

Now, I am wondering what exactly causes stunted growth at the physiological level. For example, if you took and reproductively cloned Shaquille O'Neil and fed him a good diet (Wheaties), but kept him in a small room...he would still grow to be 7'1 (assuming the genetic program is identical). The human cells that grow in the lab I work in...will grow non-stop regardless of how large the container that they are stored in. They will stack on top of each other if they have too, just to continue to grow.

Thus, why does the growth potential of a fish become hampered by the size of its tank? Does anybody have an explanation or a reference to an article that does? I found some studes looking a whole communities and stunting that correlates with large population densities of fish and scarce resources.

*** Obviously I am NOT asking for a justification to house large fish in small tanks. Just curious if a mechanism for this phenomen is known.

Thanks gang...

[Benny Z]

i've kept freshwater oscars and was a member of an oscar forum for a long time. oscars are one of those fish that everyone buys when little, most starting them in a tank much smaller than they need. this was a big issue there.

the general concensus there was that it's not the size of the aquarium that stunts growth. think about it. if you keep a baby in a 6x3 room, is it going to grow to its full size? yes, provided it is healthy and you keep it fed and disease-free. will it be happy? no...but it will still grow up big and strong.

rather, it is the poor water conditions typically caused by a small water volume and stress that causes fish to get diseases that stunt growth.

so, it's not like the fish is all of a sudden going to stop growing just because it's in a small tank. if water conditions are good and the fish is healthy it should keep growing, but it's not going to be happy. eventually it will get too big for the tank. it won't just stop growing unless there is something else wrong with the fish.

[Vitaly]

See that is what I assumed the case to be; in that given good water conditions and the proper diet the fish would grow to its genetic potential.

I guess I interpreted some of the discussions that have occured amongst us the other RC threads (some on the Reef Fishes forum about triggers and tangs) as suggesting that the smaller tank in itself prevented the fish from growing. Such that the fish "sensed" the surroundings and would stop.

Thanks for the explanation "BennyZ."

[DKKA]

Originally posted by Benny Z

rather, it is the poor water conditions typically caused by a small water volume and stress that causes fish to get diseases that stunt growth.

I'm sure those are contributing factors. But I suspect there is more to the story. I've been on more than one freshwater lake that had a stunted population of bluegill, and/or crappie.
My Parent's have a cabin on a strip mine lake near Canton. You can throw a worm in about anywhere on that lake and catch a small bluegill, and crappie are only marginally harder to find.

Good luck catching one worth keeping though. It's been that way for 10 years. There must be plenty of food there for such a huge population of small ones to exist, but they never mature.
The lake is pretty decent size, plenty deep, and is spring fed. There is a decent population of bass, and they grow to a good size. Same with catfish, bullhead, and of carp. ie: I don't think it's a water quality issue.

Their association recently stocked some larger predators to bring down the population of panfish. They stocked with walleye, muskee, and flatheads.
It's only been two years, so probably too early to tell if this plan will make a difference. The bluegill and crappie I caught this year were marginally bigger, but that's probably wishful thinking.

Dan

[Vitaly]

Dan,

I was able to find some studies, though I do not remember what fish type, that did show strong correlation between population density and fish size.

So I think your observation is correct, that all the fish in that lake are small because their population is so high. The authors of the study suggest that the high population denisty results in less resources (food, shelter, etc) for the individual fish and this is the cause of decreased size.

[ecojoe]

Originally posted by DKKA
I've been on more than one freshwater lake that had a stunted population of bluegill, and/or crappie.

There must be plenty of food there for such a huge population of small ones to exist, but they never mature.
The lake is pretty decent size, plenty deep, and is spring fed. There is a decent population of bass, and they grow to a good size. Same with catfish, bullhead, and of carp. ie: I don't think it's a water quality issue.

Their association recently stocked some larger predators to bring down the population of panfish. They stocked with walleye, muskee, and flatheads.
It's only been two years, so probably too early to tell if this plan will make a difference. The bluegill and crappie I caught this year were marginally bigger, but that's probably wishful thinking.

Dan

You're right, stunting in bluegill can involve more than just limit food resources. My M.S. advisor did research on stunted bluegill and found large male bluegills release a chemical cue that juveniles sense and delay maturing until they reach a larger size. If all the large male bluegills are removed, it can cause the size of maturity to decrease resulting in small individuals. If you're interested in this research it was published in:
Aday, D.D., D.H. Wahl, and D.P. Philipp. 2003. A mechanism for social inhibition of sexual maturation in bluegill. Journal of Fish Biology 62:486-490.

You can see a copy of it here

Let me know if you have any other questions, I did my Masters research on energy allocation in bluegill and crappie.

Joe

[hcs3]

water quality has little if anything to do with it. consider illinois waters...lake shelbyville...all the farm chemicals run-off, top soil, etc, to the extent that humans have a maximum fish consumption rule because of chemical uptake in the fish's meat. yet the lake holds the state record for muskie (of which i missed by 1lbs in 2003!!)

stunted fish growth is not well understood. research is persistent and gaining knowledge, but still lacks the definitive answer. to this point scientists have concentrated on "resource limitation." this is rather brood, but incorporates such things as being over-crowded (dan's blueegill example), food availbility, etc.

what is known is fish growth is controlled by insulin growth factors (IGF) which is mostly produced in the liver but all other tissues produce IGF locally as well. a high concentration of IGF contributes to normal growth. a low IGF contributes to stunted growth. chemical cues within the brain determine how much IGF to produce.

with that said, all fish are considered to have plastic phenotypic responses to environmental change, aka it is not prediposed in the genetic make-up but rather can change as the environment changes. a stunted fish can begin normal growth if the stress factors are removed and th ebrain ups the production of IGF.

"... strong resource limitation is the single ultimate cause of stunting. Under conditions of low resource availability, individuals
will allocate resources mainly to maintain their biomass. Only small amounts of resources can then be invested into individual growth, resulting in a decrease of annual growth increments."

- Ylikarjula, Y., Heino, M., Dieckmann, U. 2000. Ecology and Adaptation of Stunted Growth in Fish. IIASA Interim Report IR-99-050 (1999). Evolutionary Ecology 13:433-453 (1999).

HTH

[pleaselaunchme]

Henry- If this is the case, does it necessarily mean a stunted fish is any less healthy or will have a shorter life term than a non-stunted fish?

Ben

[seldon]

From what I understood, "a stunted fish can begin normal growth if the stress factors are removed and th ebrain ups the production of IGF." Meaning that the fish being streesed is likely the cause of it being stunted. So, by being streessed it is not necessarily the healthiest of fish.

Seldon

[hcs3]

Originally posted by pleaselaunchme
Henry- If this is the case, does it necessarily mean a stunted fish is any less healthy or will have a shorter life term than a non-stunted fish?

Ben

don't think of "stunted growth" as only being the overall size of the fish. stunted growth involves the entire fish, including organs. lacking normal growth in the kidneys, liver, heart, brain, etc., will undoubtedly have an adverse effect on the lifespan of the fish.

it is an overall stress factor. humans can slam a 6pack of beer or pop a few pills to help alleviate stress. fish shut down normal body functions to concentrate the available energy at alleviating their stressor.

[hcs3]

Originally posted by Benny Z
so, it's not like the fish is all of a sudden going to stop growing just because it's in a small tank.

on the contrary, that is exactly what happens.

[pleaselaunchme]

Henry-
Thanks, my gut was telling me that, but confirmation is always nice.

Ben

[Vitaly]

Henry,

You da' man. Thanks for the clarification and the article reference.

Vitaly