How can you tell a male and female common goldfish apart?

Answer 1

The only reliable way to tell is when the male is in breeding condition (and the fish have to be 1 1/2 -2 years old). Males get breeding tubercles along the gill covers an along the front edges of their side fins. There's also a difference in the shape of the vent openings. See this link for photos of these: http://www.bristol-aquarists.org.uk/goldfish/info/sexing-fs.htm

Answer 2

A male betta is the "quite" one, with the long flowing fins. a female would not have the attractive fins...they seem kinda stubby. A female and male purely like 2 male bettas can't be in a similar tank jointly. the two male's will attack one yet another, and the female will attack the male. The can stay with goldfish.

Answer 3

Males have bigger tails. And sometimes females will have bigger tails but check if they have nipples. I'm not exactly sure.