Skin Mucus as a Relevant Low-Invasive Biological Matrix for the Measurement of an Acute Stress Response in Rainbow Trout (Oncorhynchus mykiss)

Abstract

Skin mucus is a non-lethal and low-invasive matrix appropriate to assess fish welfare as it contributes to their defence against external aggressions and reflects changes in fish health status. However, more information on the response of this matrix to specific stressors is needed. In this study, rainbow trout (Oncorhynchus mykiss) specimens were subjected to an acute stress by air exposure and sampled after 1, 6, and 24 h post-stress. Blood and skin mucus were collected, and a battery of biochemical biomarkers were measured in both matrices. Cortisol and glucose values showed the expected classical stress response in plasma, increasing after the acute stress. The same pattern was observed in skin mucus, corroborating previous data in fish, and allowing us to confirm that skin mucus can be a useful complementary matrix for stress assessment in fish. The results showed sensitivity to hypoxic stress in skin mucus for cortisol, glucose, alkaline phosphatase (ALP), aspartate transaminase (AST), alanine aminotransferase (ALT), creatinine kinase (CK), and calcium. From the 15 parameters evaluated, 12 did not show statistically significant changes between plasma and mucus; therefore, using skin mucus cannot replace the use of plasma. Finally, the principal component analysis in skin mucus revealed a complete separation between the two experimental groups, being ALP, AST, glucose, cortisol, and CK, the biomarkers that contributed the most to this separation.

Housing conditions affect adult zebrafish (Danio rerio) behavior but not their physiological status

“…Stress resilience was also shown when environmental enrichment (plants, shelters, and gravel) was introduced to adult zebrafish for several days (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28): chronic [4] and acute [53] stress did not elicit behavioral or physiological alterations in the enriched-housed animals compared with barren-housed animals. However, in another study [15], enrichment (gravel images and plants) did not induce a recovery after simulated predator presentation, air emersion, or fin clipping.…”

“…Cortisol is usually extracted from whole-body homogenates in zebrafish, which implies the animals' death and hampers the possibility of repeated measurements [17]. Skin mucus is a promising matrix to be studied because its composition has been described to be altered by the fishes health in a manner comparable to plasma; in addition is a non-terminal collection, minimally invasive, practical [18], and quick to collect. At the end, similar outcomes in both cortisol matrices should be expected, supporting skin mucus as a less intrusive matrix.…”

The gene expression profile of the glucocorticoid receptor 1 (gr1) but not gr2 is modulated in mucosal tissues of gilthead sea bream (Sparus aurata) exposed to acute air-exposure stress

“…Previous evidence demonstrated that air exposure stimulates both the HPI and HSC axes in gilthead sea bream, activating the transcriptomic response and the transitory enhancement of cortisol (Skrzynska et al, 2018). The analysis of cortisol in skin mucus appears as a very useful tool to less-invasively evaluate the activity of the HPI axis of fish (Carbajal et al, 2019;Franco-Martinez et al, 2022). The identification of cortisol in skin mucus is possible because of the lipophilic property that makes it feasible to diffuse it easily through cell membranes, thus reaching different biological matrices (i.e.…”

“…In this way, the measurement of cortisol in blood has been the traditional method for assessing the fish stress response performance. In the last years, new sample collection strategies have been used to measure cortisol including skin mucus (Khansari et al, 2018;Franco-Martinez et al, 2022). Importantly, it has been shown in rainbow trout that the measurement of cortisol levels in skin mucus accurately reflects plasma responses to stress at early times of exposure (Carbajal et al, 2019).…”

Preliminary Investigation into Developing the Use of Swabs for Skin Cortisol Analysis for the Ocean Sunfish (Mola mola)

“…In fish, DeMercado and colleagues [ 51 ] found that cortisol increased in the skin mucus of rainbow trout ( Oncorhynchus mykiss ) as early as 10 min upon capture. Most of these authors did not resample individuals under 30 to 60 min [ 38 , 50 , 52 , 53 ]. Our data suggest that it is important to sample quickly upon capture and handling to be able to accurately evaluate fish stress physiology.…”