Abstract
Simple SummarySkin mucus biomarkers have become relevant indicators for studying fish physiological status and welfare. Here, we evaluated them in terms of the acute osmotic response of the sea bass. Change of mucus volume exuded and main stress-related metabolites explain the putative energy loss implied in a hyper/hypo-osmotic response. We demonstrated that skin mucus is a valuable tool, comparable to classical blood markers, for evaluating sea bass response to acute salinity challenges as well as some other potentially stressful situations. This technique will allow ecologists, physiologists, and aquafarmers to monitor fish welfare and to analyse endangered migrating species without affecting their vulnerable populations.European sea bass is a marine teleost which can inhabit a broad range of environmental salinities. So far, no research has studied the physiological response of this fish to salinity challenges using modifications in skin mucus as a potential biological matrix. Here, we used a skin mucus sampling technique to evaluate the response of sea bass to several acute osmotic challenges (for 3 h) from seawater (35‰) to two hypoosmotic environments, diluted brackish water (3‰) and estuarine waters (12‰), and to one hyperosmotic condition (50‰). For this, we recorded the volume of mucus exuded and compared the main stress-related biomarkers and osmosis-related parameters in skin mucus and plasma. Sea bass exuded the greatest volume of skin mucus with the highest total contents of cortisol, glucose, and protein under hypersalinity. This indicates an exacerbated acute stress response with possible energy losses if the condition is sustained over time. Under hyposalinity, the response depended on the magnitude of the osmotic change: shifting to 3‰ was an extreme salinity change, which affected fish aerobic metabolism by acutely modifying lactate exudation. All these data enhance the current scarce knowledge of skin mucus as a target through which to study environmental changes and fish status.
Highlights
European sea bass (Dicentrarchus labrax) is an euryhaline diadromous marine teleost species of considerable economic interest for aquaculture
Total volume of skin mucus exuded as well as mucus exuded per unit of collection area and per unit of body weight are shown in Table 1, together with the stress-related biomarkers, such as glucose, lactate, and cortisol
With regard to mucus levels, to our knowledge, the only study supplying data on skin mucus glucose for similar-sized European sea bass, reported glucose values of around 10–30 μg·mL−1 [28], which are in agreement with the data we present in this study
Summary
European sea bass (Dicentrarchus labrax) is an euryhaline diadromous marine teleost species of considerable economic interest for aquaculture. Fresh water (FW), and sometimes inhabit areas with fluctuating salinities such as estuaries, lagoons or coastal areas that are used as nurseries [1,2,3]. This species is found in upper-river FW reaches [4,5]. Movements from SW to FW and vice versa are usually reported for migratory diadromous species [6], while euryhaline teleost species undergo a crisis-and-regulation pattern when subjected to salinity challenges.
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