Large-scale practical cardiovascular classes with <i>Danio rerio</i> : overcoming ethical, financial, and logistical challenges associated with mammalian models

Traditional laboratory practicals exploring cardiovascular physiology and pharmacology rely on mammalian models, presenting ethical, financial, and logistical challenges. <i>Danio rerio</i> (zebrafish) larvae offer a compelling alternative that aligns with the partial replacement principle of replacement, reduction, and refinement (the 3Rs), while providing an opportunity for students to develop desirable in vivo skills to improve their employability. Here, we introduce an engaging set of in vivo laboratory practicals suitable for large undergraduate cohorts that utilizes larval zebrafish to investigate cardiac ion channels and receptors. The practical involves two 3-hour sessions where students measure heart rate in 72- and 96-hour postfertilization larvae in response to various treatments. The first session introduces students to handling larval zebrafish before exploring the effects of a reduced ambient temperature and application of the commonly used zebrafish anesthetic tricaine (MS-222) on both heart rate and the zebrafish startle reflex. Finally, students apply the well-known adrenergic agonist adrenaline. The second session empowers students to develop their own testable hypothesis regarding which ion channels or receptors are likely to influence zebrafish heart rate, providing them with the autonomy to select two pharmacologically active drugs from a carefully curated list [e.g. isoproterenol (β-adrenergic receptor agonist), propranolol (β-adrenergic receptor antagonist), and nifedipine (L-type calcium channel blocker)] that will enable them to address their hypothesis. Students' subsequent data for analysis allows them to develop an understanding of the conserved and divergent aspects of cardiac physiology between zebrafish and mammalian systems, and an appreciation of the importance of appropriate model selection in physiological and pharmacological research.<b>NEW & NOTEWORTHY</b> The document outlines how large-scale undergraduate practical classes involving <i>Danio rerio</i> (zebrafish) can be used to teach cardiovascular physiology. It emphasizes the educational value of using live zebrafish to explore heart rate, drug effects, and homeostasis. The process supports active, inquiry-based learning, fostering engagement, critical thinking, and collaborative skills. It also addresses ethical and logistical considerations. Overall, the approach effectively combines hands-on experimental experience with core physiological concepts in an impactful educational format.