Title sums it up.

In which species ?

Question sums it all.

bass

saw this on another site

Biologists will tell you that you need to have training and tests on most bass. males seldom reach over 5 pounds, males will normally have elongated body, but when they are young, a lab is needed to determine the sex.

The only way at the naked eye you can differentiate a female from a male is by size except during the spawn, males northern subspecies seldomly reach 4 pounds, bigger than that it 's a female, males florida subspecies seldomly reach 6 pounds, more than that it 's female. Fish below 4 pounds are indistinguishable.

There 's another way, you add a drop of methilene blue solution to the anus, wait a couple of seconds and rinse, males have 2 openings in the genital papilae, females have 3. Easier said than done because it takes practice and being taught by someone who knows.

most of the time especially around spawn the males eyes turn kinda wicked red looking.I dont know how correct I am in the statement though.

To tell during the spawn most males will travel in a certain perimeter while the female will stay still. The male chases other species away from the eggs while the female ensures nothing will get near

The female will be wearing lipstick.  

The one in my avatar is a male. The only way I know that is he was trying to spawn with a huge female.

Muddy is turning three shades of purple holding back what he really wants to post here.  ;D

Ill say it, shake the bass if it rattles its a male ;D

Avid must not have read this one yet...

Simple...I kiss them...the males hit a lot harder, but only once...the females don't slap quite as hard, but they smack me over and over again!