One fish, two fish, little fish, littler fish.

[PlatyLady]

The arrival of my little monster fry this morning got me thinking about past fry and how fast they grew.

Do platies and guppies grow to the size of their tank? Do they grow for a certain length of time? When are they fully grown?

I have a 7 month old male platy, and his sister is 3 months old and is significantly bigger than he is. Neither of them are anywhere near the size of their parents though. Has he just stopped growing? He doesn't look any bigger than he did a month ago. He was born in a smaller tank than she was, but they both live in my 28 gal now. Any ideas?

[Allivymar]

Fish won't grow to the size of the tank. They will grow according to their gene instructions with the right amount of available food and good water quality. I'm not sure about platies n guppies, but some species of fish apparently give out growth inhibiting hormones which keep the others from getting as big (I think goldfish do this). As long as they are getting enough food, and I'm sure your water quality is good, i think they will both likely wind up close to the same size, with him just a little smaller.

[platylover]

Allivymar is right on target. Platy males are usually about a half inch smaller than the females of this species. Platies will still grow to about 2.5 inches for the females, even in a one gallon tank, but the growth rate is severely reduced. I don't know if this has anything to do with growth inhibiting hormones or not, but that does sound like a probable cause. I have the same thing happening with a set of fry that were born on the same day. One female is easily twice the size of her brothers and sisters. I let all of them grow in my main tank together, which is actually getting pretty crowded when you add up all the fry swimming around the tank. I do agree totally with the last sentence in Allivymar's post, your male will catch up with your female after a while.

[PlatyLady]

Thanks guys! I'll keep watching and waiting for the little guy to grow and catch up with his "little" sister. He is definitely more colourful though!