Does fish growth get stunted in an aquarium?

[fish farmer]

it might be helpful for this discussion for us to generate a list of possible reasons that some fish may be smaller in an aquarium than in the open ocean. Folks should add to this as they think warranted.

1. A chemical effect from something that accumulates (or is missing) in the water.

2. A nutritional effect of some sort. Could be missing nutrition, spacing of meals vs continuous picking, too much of some dietary ingredient, etc.

3. A physical exercise effect.

4. A biological effect driven by the psychology of being in a small space.

5. A biological effect of being forced into close proximity with other fish species.

What else?

This might fall under number 2 and 5. Competition with other tank mates. More aggressive fish may be more efficient at getting food than timid tank mates. The less aggressive fish may only get enough to maintain their body weight.

When I had a 120 fowlr which was lightly stocked with damsels, a wrasse and a regal tang, the regal was top of the hierarchy and grew well for several years. For the last ten years or so I was adding a foxface to the mix. The 2 foxfaces that I kept were more food motivated and would grow really fast topping out at 7 inches and usually living close to 6 years and be really fat. I struggled to get enough food in front of the regal with a foxface in the tank.

 

[TheOldSalt]

Well, I didn't read the previous 5 pages of replies, so I'm taking a risk here of repeating something that's already been said a few times, but the reason that fish don't grow to full size in aquaria is that in a tank there is a buildup of a hormone called Growth Inhibitor Hormone, GIH.

This hormone is released by fish to prevent overpopulation and starvation. The more of it there is in the water, the more fish there must be in that water, at least as far as the hormone receptor system knows. Growth is slown down to keep everyone from starving.

That said, while this is common in freshwater fish, I don't know if the same is true in saltwater fish. It would take a LOT of GIH to have any effect in the vast ocean.

Anyway, if you want your fish to grow to full size, do lots of water changes. That's what breeders and fish farmers do.

 

[Jacked Reefer]

Well, I didn't read the previous 5 pages of replies, so I'm taking a risk here of repeating something that's already been said a few times, but the reason that fish don't grow to full size in aquaria is that in a tank there is a buildup of a hormone called Growth Inhibitor Hormone, GIH.

This hormone is released by fish to prevent overpopulation and starvation. The more of it there is in the water, the more fish there must be in that water, at least as far as the hormone receptor system knows. Growth is slown down to keep everyone from starving.

That said, while this is common in freshwater fish, I don't know if the same is true in saltwater fish. It would take a LOT of GIH to have any effect in the vast ocean.

Anyway, if you want your fish to grow to full size, do lots of water changes. That's what breeders and fish farmers do.

Been said quite a few times! And as you speculated this is only true in some freshwater fish. As far as I know (still just a marine bio student) there have been no records of GIH utilized by any marine fish, as there is absolutely no reason to them to, as it would never affect any growth in the ocean.

I did speculate that in our tank environments more water chances will speed up growth by providing minerals and nutrients that may become depleted as fish grow, however there is no scientific founding in that idea. Just speculation.

 

[StoneNeo82]

Great question! I have really enjoyed reading everyone’s comments and about their experiences.

I currently have Lightning Maroon Clown in a 40 gal. It’s only grown about an inch in the last couple of years. Now about 3 inches. I have wondered if it will reach its full size. I never notice it’s size until I go to a lfs where they have a MC that’s full grown.

 

[AydenLincoln]

I was told the exact same thing by a veteran worker at a NLFS (I'm sorry, but a ten hour round trip is not "local"), and without evidence. I chalked it up as another apocryphal aquarium-trade story. Perhaps there's some truth to this in fish farms, where hundreds of specimens are kept in a single tank, but most of us keep only single specimens or a mated pair-- how could intraspecies competition become so intense in those conditions that it could lead to hormone saturation with a demonstrable physiological impact?

I think that wild fish are larger than aquarium specimens because most people can't keep their fish alive longer than a year or two, and the fact is that many fish can live for decades, and may not have terminal growth stages, and are therefore larger than what you'll likely find in home aquaria. It's going to be a long time before we (and I'm talking in generalities, and not @Paul B specifics) get to the stage where we can match life expectancies in the aquarium to what you'd find in a healthy ocean environment.

Laughing at the NLFS that’s a new one haha I love it!