Graduate Thesis Or Dissertation
 

Modifications to Rearing Environments as a Method for Reducing Domestication Selection in Hatchery-reared Steelhead (Oncorhynchus mykiss)

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bz60d524k

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  • Since the decline of salmonid populations in the Pacific Northwest, supplementation programs have become frequently implemented by hatcheries as a way to protect and conserve wild stock. However, hatchery-reared fish have lower fitness than wild fish which is likely due to adaptation to the hatchery environment, i.e., domestication selection. Fish that excel in the hatchery do poorly in the wild meaning traits which are selected for in the hatchery are maladaptive in the wild. Size at release is correlated to survival at sea therefore, fish that are able to grow quickly in the hatchery are likely inadvertently experiencing selection in the hatchery for whatever traits make them perform well in that environment. Size is also highly correlated to family identification, so only certain families are represented in fish returning from the ocean to spawn. Larger fish tend to be more aggressive and bolder than smaller fish. Any change to advantage small or shy fish and reduce the variation in size among families would also decrease the opportunity for selection under hatchery conditions. Using families of steelhead (Oncorhynchus mykiss) I tested three different modifications to the hatchery environment that were hypothesized to reduce the variation in size among families: (1) the addition of structure to rearing tanks; (2) increased water flow; and (3) grading fish into separate tanks based on size. There was very little reduction in variation in body size among families between the tanks that received the structure treatment, tanks that had increased water flow, and control tanks that received no modification. There was an increase in growth overall in the tanks treated with increased water flow, but families that were the smallest in the control tanks remained the smallest in the treatment tanks. There is no evidence that the simple environmental modifications here reduce variation in size at release and would be effective methods for decreasing domestication in hatcheries. Despite the structure and flow studies being done at different facilities, there was high correlation among family means across the two treatments and their controls at both hatcheries, indicating the effect of family identity on size is very strong and not easily manipulated by simple changes to the hatchery environment. I then tested a more direct approach to manipulating growth under hatchery conditions by grading fish based on size into small body length, medium body length, and large body length groups to promote growth in the small fish with excess food and low densities, and slow growth in the large fish with restricted feeding and high densities. While the reduction to variation in size among families was statistically insignificant, the growth of the “large” group and “large” families was successfully reduced. Mean length in the “large” group was less than the means in the “medium” and “control” groups. This is likely due to the small fish which did not grow any faster in the graded tanks and it may be that a physiological or behavioral factor is restricting the small fish from growing any faster even under ideal conditions. The reduced variance in families due to the decreased growth of the large fish indicates that grading could be a tool used by hatcheries to lessen selection on salmonids. But first, further investigation is necessary into the factors limiting growth in smaller fish.
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  • Oregon Department of Fish and Wildlife
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  • Intellectual Property (patent, etc.)
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  • 2023-12-15 to 2024-03-28

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