Pool colour, dye and making the water opaque

A camera doesn't see an animal; it sees a dark blob on a light background, or the other way round. So the colour of your pool and water has to be chosen around the colour of your animals. The original notes on rats put it in a nutshell: "HVS is like other systems, it tracks contrast." The full text is on the rats page.

In short, the original advice is a white pool with water made white (for example with skim milk powder) for hooded rats and dark mice, and a black pool with clear water for albino animals, taking care with reflections from the lights.

Questions people ask

Which pool colour or dye should I use for my animals' coat colour?

Pick the opposite of the coat: a dark pool (or dark, clear water) for white or albino animals, and white water or a white pool for black or dark animals. Use beige if you test both. Your local ethics committee, licence conditions and vet always take precedence.

More detail

Choose a pool or water colour that contrasts strongly with the coat, because the tracker separates the animal from the background by brightness. White tempera for black mice and a black pool with clear water for white mice [Bromley-Brits 2011]; pool interior opposite to the coat colour or beige [Vorhees & Williams 2024]. The tracker works on brightness contrast [HVS].

Going deeper

Under infrared lighting, some dark fur reflects more than you expect: test contrast with real animals under your test lighting.

Sources: Bromley-Brits et al. (2011). Morris Water Maze Test for Learning and Memory Deficits in Alzheimer's Disease Model Mice. Journal of Visualized Experiments (53). doi:10.3791/2920; doi:10.1016/j.crtox.2024.100151

Related: My black pool or dark water isn't tracking white animals. What should I change? · How big and what colour should cues be?

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