If fingerlings are selected for breeding, retain additional fingerlings from random samples. This ensures that an adequate number of females is selected, because the larger fingerlings are males. Mix the randomly sampled fish with larger fish and when mature, sex them when selecting to ensure the desired sex ratio. Determining Sex Secondary sex characteristics are often used in sex determination. These characteristics include body shape and coloration.
Males are usually larger and have broader heads than females.
As spawning season approaches, males become lean, develop large muscular heads, and turn a dark bluish to black color. Females' heads are narrower than their bodies when viewed from the top. As spawning season approaches, they develop soft, swollen bellies. Their color remains gray to olive. Genital Examination Turn the fish belly up.