Data from: An evaluation of rearing densities to improve growth and survival of hatchery spring Chinook salmon

We evaluated growth and survival of spring Chinook salmon (Oncorhynchus tshawytscha) reared at varying densities at Warm Springs National Fish Hatchery, Oregon. For three consecutive brood years, density treatments consisted of low, medium, and high groups in 57.8 m3 raceways with approximatly16,000, 24,000, and 32,000 fish/raceway, respectively. Fish were volitionally released in both the fall and spring to mimic the downstream migration timing of the endemic wild spring Chinook salmon stock. Just prior to the fall release, the rearing density estimate was 4.24 kg/m3 for the low density group, 6.27 kg/m3 for the medium density group, and 8.42 kg/m3 for the high density group. Weight gain did not differ among density treatments (P = 0.72). A significant difference was found in median fork length (P &lt;0.001) for fish reared at different densities in the one year length was measured in the fall. Fish reared at high density exhibited the highest on-hatchery mortality rate during two brood years; however, differences in mortality rate among densities were not significant (P = 0.20). In one brood year, adult recovery rates appeared to support the hypothesis that lower initial densities improved post-release survival (P &lt; 0.001). All rearing densities utilized in this evaluation were relatively low and may partially explain why more differences were not readily apparent among density groups. In addition, the volitional release was a confounding factor in our study because we were unable to quantify the number of fish released in the fall. Even though the effects of initial rearing density on survival and growth were not clearly evident, high water temperatures observed each summer (22.8oC max) are a concern. Given current climate change predictions, hatcheries dependent on a surface water supply should regularly monitor water temperature and optimum rearing density may need adjustment.本研究于俄勒冈州沃姆斯普林斯国家鱼类孵化场（Warm Springs National Fish Hatchery），评估了不同养殖密度下饲养的春型奇努克鲑（spring Chinook salmon，Oncorhynchus tshawytscha）的生长与存活情况。连续三个繁殖年度，实验设置低、中、高三组密度处理，养殖于57.8立方米的流水养殖槽中，每组对应的养殖量分别约为16000尾、24000尾、32000尾/槽。试验鱼于秋季和春季进行主动放流，以模拟当地野生春型奇努克鲑种群的下游洄游时序。秋季放流前的估算养殖密度为：低密度组4.24 kg/m³，中密度组6.27 kg/m³，高密度组8.42 kg/m³。不同密度组的体增重无显著差异（P = 0.72）。秋季测量体长时发现，不同养殖密度组的试验鱼平均叉长存在极显著差异（P < 0.001）。高密度组养殖的试验鱼在两个繁殖年度内的孵化场养殖死亡率最高，但各密度组间的死亡率差异未达显著水平（P = 0.20）。在其中一个繁殖年度，成鱼回收率结果支持“初始养殖密度越低，放流后存活率越高”的假说（P < 0.001）。本试验所用的所有养殖密度均相对偏低，这或许可以部分解释为何各密度组间未显现出更多显著差异。此外，主动放流操作是本研究的一个混杂因素，因为我们无法量化秋季放流的试验鱼数量。尽管初始养殖密度对试验鱼存活与生长的影响未显现出明确规律，但每年夏季观测到的最高水温达22.8℃，这一情况值得关注。结合当前气候变化预测，依赖地表水供水的鱼类孵化场应定期监测水温，且可能需要调整最佳养殖密度。