Photoperiod manipulation of reproduction in salmonids

Abstract

The development of a farming industry for trout and salmon has increased the need to spread out production throughout the year. It is therefore necessary to use photoperiod manipulation in order to obtain reproduction all over the year in these species which normally spawn once a year. For example, the exposure of broodstock rainbow trout to long days for a period of 2 months following the normal spawning date and then to short days for 4 months, induces a new spawning period 6 months after the previous one. It is also possible to delay the onset of sexual maturation in females by subjecting them to continuous light when they first start to feed. This provides an alternative technique to triploïdization for the production of immature fish for marketing.