Sexual Characters in Fishes

Monomorphism No external characters to distinguish the sexes e.g. sardine, seer fish, carangids, etc. Sexual dimorphism It is possible to determine the sex from their external body features. Permanent dimorphism Distinguished after the onset of sexual maturity. e.g.: fighter fish (Betta splendeus). Temporary dimorphism Distinguished only during the spawning season. e.g. common carp (Cyprinus carpio)

Sexual Polymorphism Sexes distinguished by more than one character. e.g: Salmon. Primary characters Males – testis and ducts Female – ovaries and ducts - found out by dissecting the fish. Secondary characters It have no relation with reproductive process but serve as additional structures for spawning. e.g: Claspers, Gonopodium, Papillae etc.

Body shape Females heavier and larger - because of the ovaries. Genital papillae Small tube in cloacal aperture - distinguishes male from females. e.g. darters, lampreys etc. Pearl organ (Nuptial tubercles) Horny short structures seen on the snout, cheek (head region) only in males. e.g. common carp, minnows. Fins Fins are larger in males than the female and In males, fins are rough and grainy in nature e.g. Indian major carps.

Coloration Most male fishes are brightly coloured. e.g. Parrot fishes Accessory sexual characters Modification of anal fin to an organ called gonopodium in males. e.g. Guppies Pelvic fins The pelvic fins are modified into claspers in males. e.g. Sharks Female accessory sexual characteristic is seen in the form of egg laying tube or ovipositor. e.g. Asiatic lump sucker

Head characters Males develop knob like hook and is called leype, seen at the tip of both the jaws. e.g. Salmons Size Deep sea male angler fish parasitic on the body of female. Sexual dimorphism is least pronounced in case of fishes which don’t exhibit parental care