Non-invasive monitoring of hormones in fish

Ellis T., Scott, A.

Cefas Weymouth Laboratory, Barrack Road, The Nothe, Weymouth, Dorset, DT4 8UB, UK

e-mail: tim.ellis@cefas.co.uk

Fish excrete hormones and their metabolites via the gills, urine and faeces. The methods, advantages, problems and future potential of non-invasive monitoring of hormones in fish via these routes will be discussed. Although steroids can be measured in fish faeces, most workers have measured steroids in the water. Fish release free (non-conjugated) steroids into the water across the gills, which are readily concentrated from fresh- and sea-water samples by solid phase extraction. Water-based measurement can remove sampling effects, enables collection of time series data, and assessment of hormone status of fish that are too small to blood sample. Water can be sampled either directly from holding tanks (non-intrusive and non-invasive) or after confinement in a small volume of clean water for a short (≤ 30 min) period (non-invasive). Steroid release rates generally correlate with blood steroid concentrations, and the method has proved suitable for studies of stress (by measuring cortisol) and changes in steroids (androgens, oestrogens and progestins) through reproductive cycles. A disadvantage of the water method in comparison to blood sampling is that water hormone concentrations need to be converted to hormone release rates using data on fish biomass, water volume, exposure time and dilution. The direct method is unsuited to situations where the quantities of steroid released are small relative to dilution, or accurate information on fish biomass and dilution is unavailable (e.g. fish farms). Our attempts to find a solution to this obstacle to field application have so far been unsuccessful, i.e. investigation of other metabolites to normalise water hormone concentrations for fish biomass and dilution. Fish do release creatinine and melatonin into the water, but both are affected by feeding rate (and fish feed is a significant source of water creatinine). Nevertheless, non-invasive monitoring of water hormones is proving a powerful procedure in carefully planned experiments.

All experimental studies at Cefas Weymouth were conducted under licenses regulated by the UK’s Animals Scientific Procedures Act 1986, and underwent additional peer-review approval by the Local Ethical Review Process.