Fitness-related effects of growth investment in brown trout under field and hatchery conditions

The mortality of brown trout Salmo trutta over winter in a near‐natural stream was not significantly increased by growth hormone (GH) treatment, but lipid reserves were lower in GH‐treated fish. As GH‐treated trout grew faster than controls, GH appears to promote growth at the expense of investment in maintenance. However, the growth promoting effect of GH was much more pronounced in the hatchery than in the stream, suggesting that the pay‐off...