# Advancing Zebrafish (Danio rerio) Welfare Using Immersion Analgesics

## TL;DR

This paper reviews immersion analgesics for zebrafish welfare, highlighting promising candidates and the need for further research to ensure effective and safe pain management.

## Contribution

The paper consolidates current knowledge on immersion analgesics for zebrafish and emphasizes the need for improved analgesic selection and water quality monitoring.

## Key findings

- Promising immersion analgesics include opioids, NSAIDs, local anesthetics, and natural monoterpenes.
- Analgesic effectiveness depends on stimulus duration and severity, requiring careful selection.
- Water quality monitoring and detailed parameter reporting are critical for fish welfare.

## Abstract

Evidence of pain perception in fish continuously raises concerns regarding their welfare. Despite this, the field of fish analgesia remains underdeveloped and lacks effective non-invasive solutions. The widespread use of zebrafish as a model organism exposes them to a variety of potentially painful procedures, placing them at the forefront of these concerns. This review summarizes the existing data on immersion analgesics by analyzing behavioral indicators of nociception. Although some promising candidates—opioids, NSAIDs, a local anesthetic, and natural monoterpenes—were identified, further research is needed to assess additional effects associated with their administration. These findings highlight the importance of selecting appropriate analgesics according to the duration and severity of the noxious stimulus, as well as the need for detailed water quality monitoring and parameter reporting to safeguard fish welfare. As research progresses, extending these insights beyond zebrafish is essential to improve welfare standards in a broader context.

Growing evidence of pain perception in fish has raised concerns about their welfare in different contexts, including research and aquaculture, where potentially painful procedures are standard. Despite ongoing efforts to advance fish analgesia, the field remains underdeveloped, particularly regarding less invasive methods that could improve welfare, such as immersion-based analgesia. As one of the most widely used models in research, zebrafish (Danio rerio) are often at the front of these concerns. This review aimed to consolidate the current knowledge on immersion analgesics by analyzing the behavioral responses of zebrafish exposed to noxious stimuli. Some promising immersion analgesics were identified; however, further research is needed to assess their effects on additional parameters and investigate potential adverse effects. These findings underscore the importance of selecting appropriate analgesics, as their effectiveness may vary depending on the duration and severity of the stimulus. Moreover, this review highlights the critical role of consistent water quality monitoring and detailed parameter reporting, as these factors may influence analgesic efficacy and compromise fish welfare. As research advances, applying these insights beyond zebrafish to other fish species will be crucial for promoting higher welfare standards.