gender determination in fish?

How do you tell the gender of fish? some are obvious (like male vs female rainbow darter having obvious color differences) but others are not?

How do you tell male from female in brownish darters (tesselates, swampys, etc.), sunfish, and shiners/dace?

I have two longnose dace of similar size, one is greyish, the other is brown with reddish find and chin. Are these color differences gender based?

How do you tell the gender of fish? some are obvious (like male vs female rainbow darter having obvious color differences) but others are not?

How do you tell male from female in brownish darters (tesselates, swampys, etc.), sunfish, and shiners/dace?

I have two longnose dace of similar size, one is greyish, the other is brown with reddish find and chin. Are these color differences gender based?

Loaded question. More focus next time.

Most reliable method is to manually express gametes as it works on virtually all species during their respective beeding seasons. Coloration can be gender based with most North American species having males that are more brightly colored. With sunfishes, males are generally more intensely colored and having more flowing / pointed vertical and pelvic fins. Also look into thread entitled "Vent Sexing" which uses green sunfish as an example.

Other characters to consider are tubercles, size and behavior. I have had trouble sexing really young adult sunfishes. By isolating an unknown for a few days and then introducing a known female I could get many males to produce male-only behavior.

Loaded question. More focus next time.

Most reliable method is to manually express gametes as it works on virtually all species during their respective beeding seasons. Coloration can be gender based with most North American species having males that are more brightly colored. With sunfishes, males are generally more intensely colored and having more flowing / pointed vertical and pelvic fins. Also look into thread entitled "Vent Sexing" which uses green sunfish as an example.

Other characters to consider are tubercles, size and behavior. I have had trouble sexing really young adult sunfishes. By isolating an unknown for a few days and then introducing a known female I could get many males to produce male-only behavior.

As usual centrarchid is spot on. And I would like to emphasis a point: As someone who is now producing his own fish in ponds and attempting to have a large monosex pond of feed trained male only bluegills and female only perch, where there is no reproduction (I prefer to have reproduction in smaller more manageable ponds where I have a more control), it's imperative I get it right 100 percent of the time. I will tell you from past mistakes it's crucial to sex fish when they are in peak spawning colors and fecundity, and they will exude gametes via gentle hand pressure or a catheter tube. Sexing by appearance only can be flawed in some cases as we all know sunfish can mimic the other sex etc. If you're really serious and want to be 100 percent correct I would only trust the appearance of gametes. Sure 99.9 percent of the time a male bluegill in spawning colors is hard to miss but slightly off spawning season the two sexes may not be so obvious.

I have a photo of a gravid female bluegill from a stained pond and if it were not for the bulging abdomen of eggs she looks for all purposes a male. She has a bright orange breast and is dark just like a male in spawning colors. I also have a picture of a female that has the black anterior dorsal scale tipping of a male something I've never seen before in a female.

At Pond Boss we've noticed male bluegills tend to have longer opercular tabs than width (varies with strain), distinct black scale tips anteriorly and dorsally -- especially during spawning season, and a bright or deep orange breast area that may or may not radiate back to the rest of the fish. And the males tend to get darker in color during spawning season.

Edited by az9, 15 July 2009 - 01:24 PM.