Photoperiod can be used to enhance growth and improve feeding efficiency in farmed rainbow trout, Oncorhynchus mykiss

The current studies examined whether photoperiod techniques could be successfully transferred to commercial freshwater rainbow trout farming practices, with the key aim being to enhance winter grow-out and production in “open/uncovered systems”. Four experiments were undertaken to assess the effects of photoperiod in relation to: growth and feeding regime in tank reared fry; light intensity and growth in tank reared fry; growth and feeding efficiency in cages; and the use of different lighting technologies (bulb colour temperature) in cages. Commercial field trials conducted over a 3-year period showed that exposure of different developmental stages of rainbow trout to periods of constant light from autumn to spring appeared to enhance growth rates and could improve feed conversion. Furthermore, exposure to higher light intensities appeared to promote greater growth and feeding efficiency in all stages of production. The importance of even light distribution in the culture system rather than a critical light intensity was also evident. The outcome of artificial light regimes has been the ability to increase growth rates by up to 25%, alter stock out times, and reduce production time by as much as 2 months.