Thermally selected male rainbow trout selectively bred at high temperatures were crossed with females of the Nikko strain with normal thermal tolerance. The F2 pedigrees, comprising 1641 individuals, were divided into 26 batches. The fish were acclimated to 17 °C, then their thermal tolerance determined by measuring the effective time (ET) required for them to lose equilibrium at an approximate upper lethal temperature (28 °C). The fish were categorized into 0- to < 20-, 20- to < 40-, 40- to < 60-, and ≤ 60-min ET groups. The individuals that survived the first treatment were subjected to a second experiment to determine the ET again for their respective groups. High reproducibility, i.e., 100%, for the 0- to < 20-min ET group was observed in the third experiment for individuals grouped into this ET category in the second experiment; 85.5% of individuals classified into the ≤ 60-min ET in the first experiment were recovered in the second experiment. Thus, our findings demonstrate that ET is a useful indicator for discriminating phenotypes according to their thermal tolerance.

中文翻译：

---

基于有效时间的虹鳟鱼耐热性测定及其对大量鱼类的重现性

在高温下选择性繁殖的热选雄性虹鳟鱼与具有正常耐热性的 Nikko 品系的雌性虹鳟鱼杂交。F2 系谱包含 1641 个个体，分为 26 个批次。这些鱼适应了 17 °C，然后通过测量它们在近似上限致死温度 (28 °C) 下失去平衡所需的有效时间 (ET) 来确定它们的耐热性。将鱼分为 0 至 < 20-、20- 至 < 40-、40- 至 < 60- 和 ≤ 60 分钟 ET 组。在第一次治疗中幸存下来的个体进行第二次实验，以再次确定各自组的 ET。对于在第二个实验中归入该 ET 类别的个体，在第三个实验中观察到 0 到 < 20 分钟 ET 组的高重现性，即 100%；在第一个实验中归类为≤ 60 分钟 ET 的个体中有 85.5% 在第二个实验中恢复。因此，我们的研究结果表明，ET 是根据其耐热性区分表型的有用指标。