Sexing Rainbow Fish using dorsal fins?

MichelleParry

Member
Hi everyone,
I’m new here and hoping to get some help sexing my boesemani rainbows. I was told by the guy at the fish store that the males have a longer front dorsal fin that will overlap the second one. Based on this he selected a M/F pair for me. Now that I have them home I think they might both be male. In the dorsal fin parameter reliable?
 

Demeter

Member
This is not likely to be a reliable way of sexing them especially if they are young fish. A young male can easily be mistaken for a female. You have to wait till the fish are of breeding age to be able to sex them properly. Males will certainly be the first to color up but those slow to develop males are the ones to look out for.

If you are wanting mixed genders then buy a group of several fish. Rainbows are schoolers anyways so they should be kept in groups, the more the merrier. A small group can sometimes end with the dominant fish being a real jerk to the others or the least dominant fish being bullied by all the others so a large group is ideal. 8+ provided you have a large tank.
 
  • Thread Starter

MichelleParry

Member
Demeter said:
This is not likely to be a reliable way of sexing them especially if they are young fish. A young male can easily be mistaken for a female. You have to wait till the fish are of breeding age to be able to sex them properly. Males will certainly be the first to color up but those slow to develop males are the ones to look out for.

If you are wanting mixed genders then buy a group of several fish. Rainbows are schoolers anyways so they should be kept in groups, the more the merrier. A small group can sometimes end with the dominant fish being a real jerk to the others or the least dominant fish being bullied by all the others so a large group is ideal. 8+ provided you have a large tank.
Thanks! I have 2 Bosemanis, 2 Goyder Rivers and 8 Praecox. I’m trying not to have all the same gender so if these 2 Bosemanis are male I’ll gets a couple of females. I think I’ll wait for them to grow up some more to be sure of what I have.
 

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