Laboratory Fish Alternatives and the 3Rs in Aquatic Research

Fish are the most numerous vertebrates used in laboratory research globally, and applying the 3Rs framework to aquatic research is gaining scientific and regulatory momentum.

Key Facts

Approximately 20 million fish are used in research annually in the European Union alone
Zebrafish are the most widely used model organism after mice, valued for their transparent larvae and rapid development
The 3Rs framework — Replace, Reduce, Refine — applies to fish research but has historically been less rigorously applied than to mammals
Alternatives to live fish include organoids, cell lines, zebrafish larvae with reduced sentience concerns, and computational models
Larval zebrafish under five days post-fertilisation are not regulated in some jurisdictions despite growing evidence of pain sensitivity
Scientific consensus on fish sentience has strengthened substantially since 2020, prompting regulatory reviews

Welfare Considerations

Fish welfare in research has long been underprioritised relative to mammalian research subjects. Growing evidence that fish experience pain, stress, and fear is changing regulatory expectations. The 3Rs require active implementation: replacing fish with validated alternatives where possible, reducing numbers through better experimental design, and refining procedures to minimise pain, distress, and lasting harm. Anaesthesia protocols, humane endpoints, and environmental enrichment in holding systems are essential refinements.

What You Can Do

Support research funding bodies that require 3Rs justification for all fish research proposals
Advocate for regulatory updates that extend full protection to larval fish across all research jurisdictions
Ask institutions to publish their fish use statistics and 3Rs implementation strategies
Follow the work of organisations like NC3Rs that develop and validate fish research alternatives