Anaesthesia plays a critical role in the ethical treatment of animals in both laboratory and field settings. While established protocols exist for laboratory species, fieldwork often presents unique logistical challenges that require practical yet effective methods for anaesthesia and euthanasia. This study investigated the dose efficacy of two anaesthetics: AQUI-S, a widely used aquatic anaesthetic, and 2-Phenoxyethanol, a cost-effective alternative that is less volatile, can be used at more workable volumes, and reportedly does not alter water composition. We conducted a controlled experiment using the smallmouth hardyhead (Atherinosoma microstoma), a common estuarine species in Australia, to compare sedation and euthanasia responses across a range of doses for both solutions. Key metrics included time to sedation and recovery, and thresholds for ethical euthanasia. We also assessed whether increasing anaesthetic concentrations led to changes in water pH, as shifts can agitate fish. Additionally, we synthesised data from 26 diverse fish species in the literature to evaluate sedation and recovery times of both anaesthetics, while also unpacking the influence of body size and temperature. These findings provide practical dosing guidelines, and highlight species- and context-specific considerations, supporting the ethical use of two distinctive anaesthetics in an Australian field context.