Fish scales as biosensors for catecholamines.

Certain fish scales contain specialized cells (chromatophores) with pigment granulas, which can be dispersed or aggregated in the cells. The degree of aggregation is determined by a transmitter substance, noradrenaline, released by the sympathetic nerve endings in the skin. Isolated scales from, for example, cuckoo wrasse (Labrus ossifagus) retain a large sensitivity to externally applied noradrenaline (or more generally catecholamines) for several weeks. The degree of aggregation in isolated scales can be measured objectively by simple photometric techniques. We demonstrate in this paper how fish scales can be used to monitor catecholamine levels in human blood plasma. A discussion of other potential biosensor applications of this intact biological receptor-effector system is also given.