Will fish grow at same rate in a small or bigger tank?

  • We are currently upgrading MFK. thanks! -neo
I don't believe that anyone is arguing the fact that both water quality & diet are key in the growth of a fish, but there is a point where too much food can actually have a negative effect on both the health & growth of juvenile fish. This has been well established in commercial aquaculture for several decades.

Juvenile fish can only assimilate so much nutrients in any given period of time, the excess gets excreted which results in excess nitrogen and phosphorus. (requiring more water changes) Also any excess amino acids (protein) must be deaminated by the liver before they can be excreted, which also requires energy, energy that could have been used for growth. There have been a number of studies that have shown the effects of excess protein & the growth of juvenile fish, where when higher than normal protein levels were used the fish were actually smaller, compared to their siblings raised at lower protein levels.

The following comments were posted a number of years ago on a local forum by a fellow hobbyist who has a BSc in aquaculture & a MSc in aquaculture engineering.

When I was doing my fish studies at UBC (BSc-Aquaculture & MSc-Aquacultural Engineering), we did several feed trials using salmon and trout. One of the little things we observed was that when we were feeding at higher levels, the fish poop would actually look like pellets. To test this, we used a tarp-net at the bottom of the net with a underwater camera system. The feces we examined from overfed fish were almost undigested pellets. In other words, we found that if the fish at too much, too fast, it was pooping out the pellets before they could be fully digested inside the stomach. When we fed at a slower rate, the feces were normal.

BTW, my prof's & I came up with the highly scientific term for this phenomenon:

"Fecal-pellets"

I know, very original.

When we tested it at the lab in UBC, it still contained about 80-90% of the original nutrition. This is one of the main reasons why I try to never overfeed with pellet foods.


At West Coast Fishculture, I was in charge of feeding 3.5 million smolts & in the four years I was there, the feed conversions (how many KG feed to produce 1 KG of fish mass) went from about 3:1 down to 1.17 to 1. On my own site, we actually achieved a 1 to 1 feed conversion ratio (FCR). Feeding less, but using underwater cameras to minimize feed wastage, we were able to grow the fish just as fast or faster but with only a third the amount of food. That translated to a $370,000 feed bill savings in my last year there.

When I had my Fowlr tank going, I would feed 1/2 to full sheets of Nori (sushi paper) to the fish. My elongated tang would always be the most ferocious when it came to eating more than his fair share & he would eat so fast & so much that at the end of his binge, nori flakes would shoot out his butt & the other fish would happily follow him around gobbling it up. Just thought I'd put that image into everybody's head just around dinner time. Bon appetite.

I observed that when fed less & he didn't get to pig out like that, then his poops would be long & stringy (normal). The other fish though (angels & tangs) would still try to eat it. Ewwwww.

What my prof & I theorized is that if fish eat too much, too fast, the new food they consume may actually push out the earlier food. To test this theory, we lowered the feeding rates at the different farms & the West Van DFO research station & found that the poops became normal again.
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peathenster;4942354; said:
It has happened to me several times that when I moved fish to a bigger tank, they'd almost immediately have a growth spurt. Same feeding routine. So I'd think bigger tanks probably do promote growth.

GIS is an interesting idea. Keep in mind, however, that fish haven't been in a glass box for long. It's hard for me to imagine that they would secret hormone growth inhibitors - what happens to themselves, and how could this possibly work in the vast body of water in the wild....Stress is probably a much more important factor...
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I have experienced this same thing many times, just last week even. Every time i move a fish into a bigger tank it seems to explode with growth. So much that i have thought about having a fish rotation to get fish to grow faster lol
 
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