Animal welfare, encompassing the physical and psychological well-being of animals, is crucial for aquatic species. Emphasizing welfare enhances ethical standards, productivity, and sustainability in aquaculture. The “Five Freedoms” principle ensures basic needs and minimizes negative experiences. Welfare definitions vary: nature-based emphasizes natural behaviour, function-based focuses on health and growth, and feelings-based considers emotional well-being. Despite rapid growth in aquaculture, fish often endure poor conditions, causing stress and high mortality. Ethical frameworks guide improvements in practices, habitat preservation, and education. Recognizing the sentience of aquatic animals and addressing ethical concerns are vital for sustainable aquaculture. Aquatic animals exhibit species-specific needs and behaviours driven by evolutionary adaptations and ecological niches, including shoaling, territoriality, migration, complex social structures, and cognitive enrichment. Optimal welfare requires maintaining appropriate water quality, habitat structures, sufficient space, proper social dynamics, species-specific diets, and environmental enrichment. Ethical considerations in research ensure humane treatment through the three Rs: replacement, reduction, and refinement. Balancing scientific necessity with animal welfare is essential, with ethical review processes and regulatory frameworks ensuring compliance, promoting transparency, and public trust. Non-invasive research methods, such as underwater observation, behavioural studies, remote sensing, biochemical techniques, computer modelling, surrogate species, and in vitro studies, aim to reduce harm while obtaining valuable data.