A survey of water chemistry used in zebrafish facilities and their effects on early zebrafish development

There are a variety of published standard methods and water chemistry recommendations for zebrafish ( Danio rerio) husbandry, but empirical evidence for their justification is often lacking, as is information on some variables that have important biological effects on fish. Importantly, these different recommendations could contribute to variability in results and fish welfare between or within institutions.

Here we document the current range of water chemistry used by various research institutions around the world and report initial findings on their effects on the development and growth of zebrafish. Over 40 institutes responded to a survey that revealed a large variation in water chemistry used for zebrafish husbandry including differences in the set-points and acceptable ranges for temperature, pH and conductivity. In subsequent experiments, zebrafish ( D. rerio, WIK) embryos/larvae exposed to a large range of salt concentrations (50μM to 10mM Na ⁺ or 30 - 2500 μS/cm) and CO ₂ levels (400 - 8,000 μatm).

Larvae exposed to the lowest salt concentration (5 μM Na ⁺ or < 30μS/cm) had a slower response to touch and their swim bladders were not inflated. Larvae exposed to 5-100 μM Na ⁺ were 5 % shorter in total body length than those exposed to higher salt concentrations (>100 μM Na ⁺). Zebrafish embryo/larvae exposed to intermediate pCO ₂ values (~2000 μatm) were 1 to 3.5% longer than those exposed to either ambient (400 μatm) or higher (4000 μatm) pCO ₂, but pCO ₂ did not affect developmental endpoints up to 4 dpf.

Overall, we highlight the magnitude of variation in water chemistry used within zebrafish research and provide some empirical evidence to show that not all of these water conditions might be optimal for developing zebrafish and reproducibility of research, although further research is necessary to determine longer-term effects of water chemistry on older larvae, juveniles and adults.