The Effects of Environmental Enrichment on the Behavior of Laboratory Zebrafish (Danio rerio).

Adult Danio rerio raised with plastic plants, toys, or gravel show significantly reduced aggression in a mirror test versus standard-housed controls.

• Why it matters: Laboratory zebrafish are increasingly common but are often kept without enrichment, leaving welfare-relevant behavioral effects insufficiently tested in this species.
• What they did: Adult fish were raised under three enrichment regimes (plastic plants, toys, or photos of gravel) or standard housing, then aggression, reproduction, and growth were measured at sexual maturity.
• The result: Enrichment reduced aggression in all treatments; reproduction was largely unchanged, with decreased egg production after gravel and increased egg survival after plant treatment, while growth showed no significant effects.

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