Publication Abstract

A non-invasive stress assay based upon measurement of free cortisol released into the water by rainbow trout

T. Ellis, J.D. James, C. Stewart and A.P. Scott

It has been established previously that fish release free (i.e. unconjugated) sex steroids into the water via the gills and that, for some of these steroids, the amounts released reflect the blood plasma concentrations of the steroid. This led us to hypothesise that measurement of free corticosteroids in the water might provide a ‘non-invasive’ means of monitoring the primary stress response of fish. The procedure used for sex steroids was adapted to extract free cortisol and cortisone from water samples from rainbow trout. Both steroids could be readily detected by radioimmunoassay (RIA) with cortisol being predominant. All stages of the extraction and RIA procedure were validated for cortisol. An intermittent problem with poor replication was traced to the use of diethyl-ether during the extraction procedure, and was overcome by the use of ethyl-acetate. Other modifications were also introduced to speed up the procedure. The concentration and time course of release of both steroids was shown to be related to the degree of stress that the fish had been subjected to. It was confirmed that cortisol concentrations in water (and estimated release rate) increased in response to handling stress of trout - and also correlated with plasma cortisol concentrations. The application of, and potential for, applying water concentration / release rate for assessing the primary stress response of fish as a non-invasive alternative to blood sampling are discussed.

Reference:

T. Ellis, J.D. James, C. Stewart and A.P. Scott (2004) A non-invasive stress assay based upon measurement of free cortisol released into the water by rainbow trout. Journal of Fish Biology, 65: 1233-1252