Stress-Related Effects of Hatchery Rearing Density on Coho Salmon

Abstract Juvenile coho salmon Oncorhynchus kisutch were reared for 12 months at four densities in rectangular concrete ponds. Increasing fish density was associated with significant decreases in weight, length, condition factor, and food conversion efficiency; elevated body water content; reduced fat and protein contents; and increased mortality (which did not exceed 3%). Skewness in length distribution changed from positive to negative with increasing fish density. At the time fish were released into the ocean, interrenal cell nuclear diameters in small fish held at the highest density were significantly greater than in large fish or in fish of either size held at the lowest density. This suggests that crowding stress particularly affects small fish.