Physiology and Reproductive Biology in Fish

A few fishes breed only once in their long life spawn eg. Pacific salmon . The fresh water eel breeds only once in 10-14 years . Most of the fishes breed in one season every year , they are called seasonal breeders , but some breed in all seasons, through out the year , and they are called year round spawners . • Seasonal breeders exhibit rhythmic changes in the structure and physiology of ovary and testes in different seasons. These changes are demarcated into five phases – 1. Resting phase (December - January) 2. Preparatory phase(February – April) 3. Maturing phase (may – June) 4. Spawning phase (July - September) 5. Post spawning phase(October - November) GONADOSOMATIC INDEX (GSI) • It is a ratio between body weight and the weight of gonad showing the status of ovary and testis in terms of maturity and denotes the phase of the reproductive cycle- GSI = Weight of the gonad × 100 Weight of fish-weight of the gonad • GSI of fish increases with the maturation of the fish i.e. lowest during post spawning phase and highest at the peak of maturity i.e. spawning phase.FEMALE REPRODUCTIVE ORGAN • Unlike mammals , the female reproductive system of teleosts.