A comparison of changes in stable isotope ratios in the epidermal mucus and muscle tissue of slow‐growing adult catfish

Abstract

Although stable isotope analysis is a powerful tool for determining diet, migration patterns and the structure of food webs in aquatic systems, the slow response of isotopic ratios in the widely used muscle tissue often hampers this approach, particularly in slow-growing or adult fishes. We conducted a diet-switch experiment to compare the changes in the stable carbon isotope ratio (δ 13 C values) in the epidermal mucus and muscle tissue of five-year-old catfish (Silurus asotus). The isotope ratios in noninvasively sampled mucus changed more rapidly than those in the muscle tissue. As isotopic change in mucus was relatively rapid, this technique can be used over a finer timescale than traditional isotopic analyses using the muscle tissue. The isotopic change half-life in our experimental condition was 200 days, which would not be short enough for some research purposes. Examining mucus along with the muscle would enable food habits of slow-growing fishes to be determined over different timescales.However, the rate of isotopic change in the mucus was negatively affected by the size of fish and was slower than the previously reported rates in juvenile steelhead. These findings suggest that mucus turnover rates need to be determined prior to the field data interpretation. K E Y W O R D Sδ 13 C, fish slime, mucus, reaction progress variable, trophic discrimination factor, turnover rate

Estimating stable isotope turnover rates of epidermal mucus and dorsal muscle for an omnivorous fish using a diet-switch experiment

“…These generally lower turnover rates of mucus compared with muscle were consistent with findings from the small number of other studies that have compared the turnover rates of mucus versus muscle for other fish species (e.g. Maruyama et al, 2015Maruyama et al, , 2017Shigeta et al, 2017). In our experiment, the turnover rates of d 15 N were also always greater than the rates measured for d 13 C, irrespective of diet and tissue.…”

“…Tissues are considered at equilibrium with their diet after four to five half-lives (Hobson & Clark, 1992;Busst & Britton, 2018). As different tissues tend to have different turnover rates, they can potentially be used in combination to understand changes in consumer diet across different timescales (Phillips & Eldridge, 2006;Maruyama et al, 2017).…”

“…Studies on fishes including Silurus asotus (Linnaeus, 1758), Rhinogobius sp. and Pseudorasbora parva (Temminck & Schlegel, 1846) have also suggested mucus has a faster turnover rate than muscle (Maruyama et al, 2015(Maruyama et al, , 2017Shigeta et al, 2017). Nevertheless, there are considerable knowledge gaps relating to the SIA of mucus.…”

Non‐lethal sampling for stable isotope analysis of pike Esox lucius: how mucus, scale and fin tissue compare to muscle

“…It is explained by the relative abundance of 13 C‐depleted lipids in different tissues, with muscle generally containing more lipids than fin or scale (Pinnegar & Polunin, ). Mucus primarily consists of glycoproteins, therefore depleted 13 C is expected and, indeed, was evident here and elsewhere (Maruyama et al, ; Nolan & Britton, ; Shigeta et al, ). Across studies, δ 15 N isotopic relationships between muscle and surrogate tissues are more varied (Hanisch et al, ).…”

Diet of invasive pikeperchSander lucioperca: developing non-destructive tissue sampling for stable isotope analysis with comparisons to stomach contents analysis

“…The epidermal mucus was collected by scraping the dorsal surface of each fish with a cover slip, with the sample then cleaned with forceps as per Maruyama et al (2015) and transferred to a sample tube. This method was used in preference to the filtration method of Church et al (2009), as it was demonstrated to result in reduced error (Maruyama et al, 2017). Scales were collected from the body area between the dorsal fin and the lateral line.…”