Changes in the duration of sunlight, or photoperiod, can stimulate some species of bony fishes to begin reproduction. Temperature change may trigger the maturity of bony fishes in temperate and subpolar areas. Other factors that may affect reproduction are presence of the opposite sex, currents, tides, moon stages, and presence of spawning areas. Reproduction is generally cyclic in bony fishes. The duration of cycles may be as short as four weeks or as long as many years.
Some species spawn continuously throughout the spring and summer.
Some bony fishes may spawn many times a year. Many bony fishes reproduce once a year until they die. Other bony fishes may reproduce only once during their lifetime. Diadromous fishes must have access to both marine and freshwater systems to complete their life cycle. D. Embryonic development.