In the Indian subcontinent, majority of the freshwater fishes breeds during the monsoon following their pre-monsoon maturity during summer. The time of breeding of each species is so precisely adjusted that spawns and fries are produced in an environment when their chance of survival is maximum. It appears that natural selection possibly favors genomes of individuals that produce their young ones at a time when their chance of survival is maximum. Due to paucity of information, the integrated concept of environmental impact on maturation and spawning of fishes is not yet known. It is assumed that fishes sense, through extero receptor, the environmental cues with the approach of breeding season and such cues initiates endogenous rhythm to be in right phase for breeding. A variety of sensory receptors such as eyes, pineal gland (sensitive to light), olfactory organs, taste buds and thermo receptors help in detecting these cues. Among all the environmental factors photoperiod, temperature and seasonal rainfall are the main factors in regulating reproductive cycles in teleost fishes. The approach of wet season following a long dry one brought out sudden and marked seasonal changes in water quality and food availability which help trigger maturation and spawning. The major group of teleostean fishes and their response to photo-thermal cycles towards attaining maturity and spawning as observed during experiments are as below
