Glowing fish can finger chemical culprits.

Raldua, D and PJ Babin. 2009. Simple, rapid zebrafish larva bioassay for assessing the potential of chemical pollutants and drugs to disrupt thyroid gland function. Environmental Science and Technology doi: 10.1021/es9012454.

Flourescing fish may offer a quick and easy way to test if specific chemicals – or  complex mixtures found in the environment – will affect the thyroid gland and its normal hormonal functions. Researchers describe the technique in an online article published in the journal Environmental Science and Technology.

With so many chemical contaminants in the environment, rapid screening tools that target specific physiological processes or tissues are increasingly valuable to regulators and researchers. This assay appears useful to assess potential threats to the thyroid system from complex chemical mixtures.

The thyroid gland controls many biological processes including metabolism, nervous system development, calcium regulation and responses to other hormones.

In the study, researchers altered zebrafish larvae so they would glow brightly when the thyroid gland functions normally. Because the zebrafish thyroid is quite similar to human thyroid, this screening assay can be used to quickly monitor for the presence of thyroid-disrupting compounds.

The authors tested the fish with a variety of chemicals, drugs and environmental contaminants known to change thyroid function. They used immunofluorescence staining to monitor thyroxine (T4) activity.

Normally functioning thyroid exhibits bright fluorescence, whereas impaired thyroid exhibits less – or in extreme cases – no fluorescence. Contaminants such as 2,4-D, DDT, fenoxycarb, 4-nonylphenol and methyl mercury all decreased fluorescence, as did drugs used to target T4 activity.