Larger fish..bred smaller?

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AC Members
Nov 28, 2002
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Of course it can be done. Dwarfing species has been done with everything from birds to ponies to dogs to... well, whatever. Size is a trait that can be bred for selectively like any other. I'm sure it's already being done to fish by someone, somewhere.

I don't think there is profit in it. People just take their fish back to the store when they get large, or continue keeping them in a tank that's too small. Or the fish's growth is stunted by tank conditions, or dies before reaching maturity. Look how big bala sharks and tinfoils and oscars get, look how few people have an appropriately sized tank, and yet look how many are sold in every LFS on the planet. I don't see how dwarfing them would increase sales by much.


AC Members
Mar 26, 2002
Syracuse, NY
As Keely said, It can be done. Size is one trait just like color, fin shape, body shape, etc. All critters (including people) have a genotype based on genetics and a phenotype which is the physical expression of the genetics (i.e., how we look and act).

Although I am not a breeder, developing variations within a species is more complicated than taking two small parent fish. The technique usually used is called line breeding. This is where parents are bred with selected offspring, selected siblings are bred to each other, etc. This process is repeated over and over again. Every now-and-again, an "outside" fish may be introduced because it has a trait (small size, fin shape, etc.) and the breeder wants to introduce its genetics to his line. I understand that this has to be done carefully.

Anyway, line breeding has the effect of decreasing genetic variability so that the breeder can get more consistent results (e.g., smaller fish) than by randomly breeding parent fish who are small.

Gene splicing is a different animal altogether and is not to my knowledge used in the breeding of fish. My sister is a molecular microbiologist and routinely takes dna from one critter and puts it into a new critter....usually to see if she can get the new critter to do something productive like make (or breakdown) specific chemical compounds. Could it be used to "speed up" the line breeding process? I don't know.