Score sheets for zebrafish

The scoring list can be an important tool for determining humane endpoints. A scoring list is an (electronic) form on which the clinical status of each individual experimental animal is recorded at regular, predetermined intervals.

A scoring list will provide an overview of the health status of an animal over time. In the Dutch Code of Practice Welzijn Proefdieren, this report is known as a wellness diary (or “welzijnsdagboek”; see video). 

There is no standardized list of terms for zebrafish. There is, however, a growing interest in health and welfare problems in zebrafish, including genetically engineered mutants. 

For every scientific procedure a separate scoring list can be designed on which to record the most pertinent clinical findings in the course of the experiment. With new procedures, potential clinical findings may be unknown, requiring that assessment of the animal cover a wide range of clinical aspects. For familiar procedures, assessment can be limited to the relevant clinical parameters and any unusual findings. The scoring list must be logical and consistent, it must be easy to use and specific, and at the same time sufficiently discriminating to visualize subtle changes in animal welfare.

Analysis of the scoring list will show the pattern of recovery or deterioration of each animal’s condition over time, and offers insight into the effect of the procedure on the animal’s health. A scoring list is an essential instrument in determining humane endpoints. 

Example score sheet (source: BfR)

Researchers in Germany have designed an evaluation sheet for the assessment of the health and welfare risks of genetically altered (mutant) zebrafish and Japanese rice fish (medaka). The sheet can be downloaded on the right (document 1). The criteria upon which decisions must be based, are set forth clearly in the related article (document 2). Both documents are written by the Bundesinstitut für Risikobewertung (BfR).

Assessment takes place during the larval stage (at the time when EU regulation starts to apply, which is >120 hours (hpf) or >5 days post fertilization) and when the fish are sexually mature (can be seen here: between days 90-120 post fertilization); the latter uses clinical impairment, as indicated above.
An important metric to report is the number of fish with clinical impairment (see the final page of the document “Severity assessment of genetically altered fish”). It goes without saying that genetic alterations that lead to serious health problems must be closely monitored and intervention must be considered. 

The sample score sheet on the right van be used for the assessment of the degree of suffering as a result of genetic alteration in zebrafish. Adult fish are observed for the presence of a variety of clinical signs (both in appearance and behaviour) and the number of animals affected is an important metric to be scored. The larva and adult fish risk profile is the basis for final assessment of the severity of suffering resulting from of a particular genetic alteration.


Example score sheet (source: UQ)

By scoring clinical signs and their severity in a list, a health record is created over time. The score sheet can contain the number of animals affected as well as the severity of the observed changes. These data can be the basis for decisions on euthanasia. The score sheet of the University of Queensland in Australia serves as an example; it is used to reach a decision on when to perform euthanasia (see document 3) Zebrafish_Score_Sheet-2.doc. In this score sheet, several aspects are scored: swimming behaviour, weight, muscle tone abdomen, distended abdomen (dropsy, swelling), preferred tank location, and gulping air at the water surface. All are scored as normal or abnormal (mild, moderate or severe) and the scores are totalled. Depending on its value, the score may or may not require an intervention, and possibly euthanasia.