Branchial release of free cortisol and melatonin by rainbow trout

Abstract

Individual rainbow trout Oncorhynchus mykiss were held in a specially constructed tank that enabled water to be collected separately from the anterior and posterior ends of the fish. Measurement by radioimmunoassay showed that >95% of the cortisol and melatonin released into the water originated from the anterior end (dominated by the gills). High performance liquid chromatography confirmed the identity of both hormones. # 2005 Crown copyrightA non-invasive stress assay for rainbow trout Oncorhynchus mykiss (Walbaum) has recently been developed (Scott et al., 2001;Ellis et al., 2004). This assay is based upon the extraction and measurement of cortisol that is released by the fish into the water. Both water cortisol concentration and cortisol release rate have been shown to be valid indicators of stress status, being related to plasma cortisol concentration and stress level . Although water cortisol concentration can be used as a relative indicator of stress status, over time or between replicate tanks, cortisol release rate is superior, providing an absolute measure. To calculate release rates, however, accurate information is required on fish stocking conditions (i.e. biomass and water flow rate). What is needed, in order to interpret water cortisol concentrations in the absence of such information (e.g. on fish farms), is an 'internal standard', a compound that is released into the water like cortisol, that is related to the biomass, but is unaffected by factors such as age, gender, feeding, reproduction and stress. Such a compound would also provide an intrinsic correction for environmental factors, such as temperature, that presumably affect the rate of release rate of cortisol.Defining such a compound is very difficult indeed. One potential candidate is melatonin, a hormone synthesized by the pineal gland and released in response

A comparison of two methods for the assessment of stress axis activity in wild fish in relation to wastewater effluent exposure

“…In fish, circulating steroids, including cortisol, are transferred from the bloodstream to the surrounding water across the gill epithelium (Ellis et al, 2005) and can be quantified after extraction and concentration of water samples from holding tanks or collection vessels. Steroids retained in water samples after transfer across the gill may be a more accurate surrogate of blood steroid levels than the multi-compartment total provided by WBIC: the rate of release of 6 cortisol to water has been shown to be proportional to the concentration of cortisol in the blood in a number of species (Félix et al, 2013;Gabor and Contreras, 2012;Scott and Ellis, 2007;Wong et al, 2008) including three-spined sticklebacks (Sebire et al, 2007).…”

Tilapia male urinary pheromone stimulates female reproductive axis

“…The fish gill is considered to be the main route for release of free steroids at a rate that reflects largely their plasma concentrations. Indeed, several studies suggest that free steroids are preferentially released via the gills and are found at much lower concentrations in the urine or faeces compared to conjugated metabolites (Ellis et al, 2005;Miguel-Queralt and Hammond, 2008;Scott et al, 2008;Siefkes et al, 2003;Vermeirssen and Scott, 1996). Therefore, changes of steroid concentration in water samples can parallel those in blood, taking into account the dilution effect, and estimation of sex steroids in the water is a reliable indicator of fish endocrine status (Scott and Sorensen, 1994;Scott et al, 2008;Sebire et al, 2009).…”

Non-invasive measurement of steroids in fish-holding water: important considerations when applying the procedure to behaviour studies

“…Although measurement of steroids has also been applied to fish urine (Oliveira et al, 2001) and faeces (Oliveira et al, 1999;Turner et al, 2003), a much simpler and more direct approach is available. This is based on the fact that, in fish, free steroids are able to diffuse from the bloodstream into the water through the gills (Cravedi et al, 1993;Vermeirssen & Scott, 1996;Sorensen et al, 2000;Ellis et al, 2005). Because this process appears to happen just as easily in reverse (Vermeirssen & Scott, 1996;Scott et al, 2005;Maunder et al, 2007), one hesitates to refer to it as an excretory process in the same way as urination or defecation.…”