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How to Tell the Gender of a Rock Bass Fish

Rock bass fish, also known as goggle-eye perch, rock sunfish and black perch, belong to the sunfish family. Rock bass have large mouths, but are not typically large fish, usually measuring between 9 and 12 inches in length and about a pound in weight. Sexing a monomorphic species by its external features is no easy task; rock bass all look alike, even for an experienced person. While an autopsy is the most definitive manner of sexing a fish, the live rock bass does provide a few subtle anatomical clues to its gender.

Things You'll Need

Gloves
Towel or large sponge
Capillary tubes

Instructions

- 1
  
  Have someone help hold the fish so the underbelly of the fish can be seen.
  
  Turn the fish so the underbelly can be seen. Wear gloves to help keep a good hold on the fish. Place the fish on a towel or sponge for stability.
- 2
  Locate the anal opening, found near the anal fins. Fish genitalia, called papillae, are dark and pointed in the male. Female papillae are rounded, red at the ends and may be swollen. In the spring, females have bloated abdomens.
- 3
  Look at the area between the anus and the papillae; this area will have few to no scales. This patch of skin is more circular in the male, while in the female, it is elongated. The fine edges of the anal and pelvic fins are black in males, but whitish-yellow in females.
- 4
  
  Fish eggs may be released with a gentle push on a female fish's belly.
  
  Press very gently on the fish's belly. If the fish is female, a few eggs may be released from the papillae. If the fish is male, a few drops milt, a liquid resembling milk, may be expressed.
- 5
  Insert a capillary tube, using care not to hurt the fish, into the papillae of the fish to extract eggs or milt to determine the gender without a doubt.

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