Salmonid fish raised in hatcheries often have lower fitness (number of returning adult offspring) than wild fish when both spawn in the wild. Body size at release from hatcheries is positively correlated with survival at sea. So one explanation for reduced fitness is that hatcheries inadvertently select for trait values that enhance growth rate under the unnatural environment of a hatchery, but that are maladaptive in the wild environment. A simple prediction of this hypothesis is that juveniles of hatchery origin should grow more quickly than fish of wild origin under hatchery conditions, but should have lower survival under wild conditions. We tested that hypothesis using multiple full sibling families of steelhead (Oncorhynchus mykiss) that were spawned using either two wild parents (WxW) or two first-generation hatchery (HxH) parents. Offspring from all the families were grown together under hatchery conditions and under semi-natural conditions in artificial streams. HxH families grew significantly faster in the hatchery, but had significantly lower survival in the streams. That we see this tradeoff after only a single generation of selection suggests that the traits involved are under very strong selection. We also considered one possible alteration to the hatchery environment that might reduce the intensity of selection among families in size at release. Here we tested whether reducing the fat content of hatchery feed would reduce the variance among families in body size. Although fish raised under a low-fat diet were slightly smaller, the variation among families in final size was unchanged. Thus, there is no evidence that reducing the fat content of hatchery feed would reduce the opportunity for selection among families on size at release.

Full sibling families of fry were pooled together and raised in 400 L tanks, or in artificial streams at a research hatchery.  These datasets provide family average growth to compare with family survival, and the individual growth data.

File 'Family_survival___family_Avg_size' contains average sizes of families of steelhead raised under hatchery conditions at Oregon State University's Aquatic Animal Health lab in 2017.  Tanks were fed either a high-fat diet or a low-fat diet.  The families were pooled together in each tank, and then were sorted out at the end of the experiment via DNA genotyping. The same families were also pooled and released into artificial streams at the Oregon Hatchery Research Center. The file also contains counts of survivors from each family out of 120 fish per family put into the artificial streams. 

Column names are:

DIET = high fat or low fat diet

FISH-TYPE = offspring of a cross between two wild fish (WxW) or two 1^st-generation hatchery fish (HxH)

FAMILY = the family identity

AVGFAMSIZE = the average fork length of each family

SURVIVAL(COUNT) = number of survivors per family out of 120

File 'Sizes_of_indiv_fish_in_tanks' contains the individual sizes (fork length) of each fish from each tank in the hatchery.

Column names are:

TREATMENT = high or low fat food for each tank

TANK = tank identification number. 

SUB-TANK = each tank was divided into two tanks half way through the growth period.  Sub-tank is the name of the tanks after they were split.

INDIV = individual ID for each fish

LENGTH = fork length

FAMILY = family

ORIGIN = same as fish-type above (offspring of a cross between two wild fish (WxW) or two 1^st-generation hatchery fish (HxH))