Smell of Infection: a novel, non-invasive method for detection of fish excretory- secretory proteins

Chemical signals are produced by aquatic organisms following predatory attacks or perturbations such as parasitic infection. Ectoparasites feeding on fish hosts are likely to cause release of similar alarm cues into the environment due to the stress, wounding and immune response stimulated upon infection. Alarm cues are often released in the form of proteins and peptides and provide important insights into bodily function and infection status. Here we outline a non-invasive method to identify potential chemical cues associated with infection in fish by extracting, purifying and characterizing proteins from water samples from cultured fish. Gel free proteomic methods were deemed the most suitable for protein detection in saline water samples. It was confirmed that teleost proteins can be characterised from water samples and that variation in protein profiles could be detected between infected and uninfected individuals and fish and parasite only water samples. Our novel assay provides a non-invasive method for assessing the health condition of both wild and farmed aquatic organisms. Similar to environmental DNA monitoring methods, these proteomic techniques could provide an important tool in applied ecology and aquaculture biology.