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

Abstract

A procedure previously used for sex steroids was adapted to extract free cortisol and cortisone from water samples taken from rainbow trout Oncorhynchus mykiss tanks. Both corticosteroids could be readily detected by radioimmunoassay (RIA), with cortisol being predominant. All stages of the sampling, 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 corticosteroids were 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 cortisol release rates increased in response to handling stress, and that both were correlated with plasma cortisol concentrations. The potential for using water cortisol concentration and release rates to assess the primary stress response of fishes as a non-invasive alternative to blood sampling is discussed.# 2004 Crown copyright

The relationship between social status, behaviour, growth and steroids in male helpers and breeders of a cooperatively breeding cichlid

“…In reef fishes (Chromis dimidiatus and Pseudanthias squamipinnis), it was observed that the F levels measured in water correlated with the social situations of these fish, with higher excretion levels in more stressed fish (Oliveira et al, 1999). In rainbow trout, there was a positive correlation between stress situation, F release in water and F levels in plasma (Ellis et al, 2004).…”

“…Fish release several fractions of steroid hormones into the water; the free fraction is mainly released through the gills, the conjugated fractions through urine (sulphated fraction) and faeces (glucuronidated fraction) (Scott and Sorensen, 1994;Vermeirssen and Scott, 1996;Ellis et al, 2004). The hormone measurements were carried out following the procedures to measure steroids from fish holding water described by Scott and Sorensen (1994) and from fish urine described by Oliveira et al (1996).…”

“…In the present study, we compared only similar sized fish (see also Scott and Sorensen, 1994;Vermeirssen and Scott, 1996;Ellis et al, 2004). Our results can therefore not be confounded by hormone level differences due to body size.…”

Retinal light input is required to sustain plasma melatonin rhythms in Nile tilapia Oreochromis niloticus niloticus

“…Aliquots of pooled rainbow trout plasma were used as quality controls (QCs) and the intra-and inter-specific assay coefficients of variation were 2.1-3.7 % and 5.5 %, respectively. Cortisol was assayed by radioimmunoassay previously described by Ellis et al (2004) and modified by North et al (2006). Aliquots of pooled rainbow trout plasma were used as quality controls (QCs) and the intraspecific assay coefficients of variation was 4.2 %.…”

Safeguarding the many guises of farmed fish welfare

“…For example, indwelling catheters might provide very accurate data on the stress response experienced by an individual fish but this does not provide information that is valuable at the level of the population. Assays based on water cortisol levels have considerable potential to produce valuable population level data but these are not yet practicable (Ellis et al 2004). Therefore, we are restricted to point-source samples of cortisol and it is arguable whether such samples provide any valuable insight into the welfare state of the fish.…”