Aquaculture Feed and Fertilizer Resources Information System

Rainbow trout - Growth

Rainbow trout is a freshwater species that also exhibits an anadromous form (the steelhead trout) that migrates from freshwater to the ocean at 1–3 years of age, followed by a marine residency of 18–30 months, after which maturing fish return to their natal stream or river to spawn. There is considerable plasticity among anadromous rainbow trout in life history as it relates to time spent in freshwater or the ocean. Growth of rainbow troutunder natural conditions is highly variable, depending on water temperature and food abundance. Trout in cold mountain streams may only weigh 20 g after one year, whereas fish in productive lakes may weigh 300–500 g. At maturity, anadromous rainbow trout weigh up to 19 kg and can be up to seven years of age, compared to 1–3 kg for freshwater fish and 3–10 years of age (Behnke, 1992). However, most anadromous rainbow trout mature at four years of age. Growth rates of rainbow trout in farms are much higher those that of wild fish, but growth rates in farms also vary with water temperature. In constant 15 °C freshwater, farmed rainbow trout reach 800–1 000 g in weight 12 months after eggs hatch (Figure 5).