Current techniques for heart rate determination in adult zebrafish require specialist expertise and are often invasive, technically challenging and not readily transferable to other laboratories for routine assessment. Here, we present a simple, noninvasive and inexpensive light-cardiogram technique to assess heart rate and frequency in adult zebrafish. Brightfield microscope paired with a high-resolution camera and ImageJ (an open source software) were employed as core recording and processing platforms respectively. The heart was visualised ventrally and located by juxtaposing an isosceles triangle between the opercula as reference to analyse pixel intensity fluctuations generated by each cardiac cycle to derive heart rate and frequency. Compared to transparent embryos, the cardiograms generated reverse light signal oscillations, with contraction and relaxation of the heart (ventricle) corresponding to reduced and increased pixel intensities respectively. The heart rates (♂ 122.58 ± 2.15 and ♀ 121.37 ± 2.63 beat/min) and mean dominant frequency (♂ 2.04 ± 0.035 and ♀ 2.05 ± 0.048 Hz) between the sexes were not significantly (P > .05) different at 28 °C. However, the FD amplitudes between males (0.26 ± 0.03) and females (0.45 ± 0.05) were significantly different (P < .05) suggesting sex specific diastolic cardiac outputs. Collectively, the technique can be used to measure heartbeats as well as readily adaptable to record relative cardiac outputs and compare differences between physiological states (e.g. sexes). Moreover, the approach could be amenable to automation and applicable to other fish species, enabling researchers the flexibility to measure these and other critical heart health endpoint with relative ease.

中文翻译：

---

心电图，一种确定成年斑马鱼Danio rerio心率的简单技术。

当前用于确定成年斑马鱼心率的技术需要专业知识，并且通常具有侵入性，在技术上具有挑战性，并且不易转移到其他实验室进行常规评估。在这里，我们提出了一种简单，无创且便宜的心电图技术来评估成年斑马鱼的心率和频率。明场显微镜与高分辨率相机和ImageJ（开源软件）配对，分别用作核心记录和处理平台。心脏通过腹侧可视化，并通过在reference骨之间并置等腰三角形作为参考来定位，以分析每个心动周期产生的像素强度波动，以得出心率和频率。与透明胚胎相比，心电图产生反向的光信号振荡，心脏（心室）的收缩和放松分别对应于像素强度的减小和增加。两性之间的心率（♂122.58±2.15和♀121.37±2.63节/分钟）和平均显性频率（♂2.04±0.035和♀2.05±0.048 Hz）在28°C时无显着差异（P> .05） 。然而，男性（0.26±0.03）和女性（0.45±0.05）之间的FD振幅显着不同（P <.05），表明性别特异性舒张期心输出量。总的来说，该技术可用于测量心跳，也可轻松用于记录相对心输出量并比较生理状态（例如性别）之间的差异。此外，该方法可能适用于自动化，并适用于其他鱼类，