Pet Store Goldfish Growth
Will goldfish from pet stores grow bigger, like 8 inches?
Before answering the question, let's clarify what measurement we will be discussing.
There are 3 ways to measure a fish:
1. Nose to the very end of the tail
2. Nose to the fork or V in the tail or
3. Nose to the end of the caudal peduncle where the tail joins the body.
Sellers of fish on sites such as eBay usually use the first method as it exaggerates the size of the fish.
Many fishing size limits use the second measurement.
Throughout this website I only use the third measurement which is body length.
The reason I do this is because of the vast range of possible tail fin lengths.
As an example if a fish has a 4 inch body length and a two inch tail, and another has a 3 inch body and tail, which is larger? It is the one with the 4 inch body as it will be twice as heavy.
I suspect you are also referring to body length as any comet Goldfish given enough room and food will easily attain a total
length including tail of 8 inches within two growing seasons.
To answer your question, yes pet store Goldfish can and will grow large.
For a Goldfish to get to this size, it will be a single tailed variety such as a Common, Comet or Shubunkin.
The Common Goldfish will grow the largest, getting to a maximum of around 1 foot (300mm). The Comet and Shubunkins would be considered large at 8 inches.
Most of the fancy varieties don't go much above 5 inches as they are growing body depth as well as length.
These sizes are usually seen in pond fish grown in ideal conditions. For aquarium grown fish, you can shorten the length by about 25-30%.