Fatty‐acid biomarkers and tissue‐specific turnover: validation from a controlled feeding study in juvenile Atlantic croaker Micropogonias undulatus

Abstract

Fatty-acid (FA) profiles of liver and muscle tissue from juvenile Atlantic croaker Micropogonias undulatus were examined over a 15 week diet-switch experiment to establish calibration coefficients (CC) and improve understanding of consumer-diet relationships for field applications. Essential FAs [docosahexaenoic acid (DHA), 22:6n-3 and eicosapentaenoic acid (EPA) , 20:5n-3] decreased and 18:2n-6 increased in tissues of M. undulatus fed diets with increasing proportions of terrestrial v. marine lipid sources. Non-linear models used to estimate the incorporation rate and days to saturation of per cent 18:2n-6 in tissues showed that livers incorporated 18:2n-6 faster than muscle, but the proportions of 18:2n-6 in muscle were higher. CCs were established to determine proportions of FA deposition in tissues relative to diet. Many CCs were consistent amongst diet treatments, despite growth and dietary differences. The CCs can be used to discern FA modification and retention within tissues and as tools for future quantitative estimates of diet histories. Incorporation rates and CCs of 18:2n-6 were applied to a sub-set of field samples of wild M. undulatus to understand habitat use and feeding ecology. Altogether, these results suggest that FAs provide a time-integrated measure of diet in aquatic food webs and are affected by tissue type, growth rate and the influence of mixed diets.

Terrestrial fatty acids as tracers of finfish aquaculture waste in the marine environment

“…For example, when examining uptake rates of terrestrial (C 18 ) FA, Copeman et al (2013) found an uptake rate of ALA of 0.6-0.13% per day in the liver and 0.021% per day in the muscle of juvenile gadids Pacific cod (Gadus microcephalus) and Walleye Pollock (Theragra chalcogramma). This is similar to the uptake rates of LA reported by Mohan et al (2016) in juvenile Atlantic croaker (Micropogonias undulates). However, variation between diets was found with Atlantic croaker fed a mixed diet showing higher uptake rates (0.09% per day for liver, 0.02% per day for muscle) compared to fish fed on a terrestrial diet (0.02% per day for liver and 0.01% per day for muscle).…”

“…This is similar to the uptake rates of LA reported by Mohan et al . () in juvenile Atlantic croaker ( Micropogonias undulates ). However, variation between diets was found with Atlantic croaker fed a mixed diet showing higher uptake rates (0.09% per day for liver, 0.02% per day for muscle) compared to fish fed on a terrestrial diet (0.02% per day for liver and 0.01% per day for muscle).…”

“…Storage of TAG within tissues has been found to more closely reflect the FA composition of dietary lipids than structural PL (Budge et al 2012). In addition, liver tissue has a quicker incorporation rate, reflecting recent dietary consumption, compared to muscle tissue which provides a comparatively longer term indication of dietary trends (Mohan et al 2016). Thus, we could assume that differences between muscle and liver FA composition could suggest a recent move closer to, or further away from terrestrial source components in diet.…”

Simultaneous estimation of diet composition and calibration coefficients with fatty acid signature data

“…The method produces quantitative estimates of diet composition, with associated measures of precision, and the estimates are pertinent to a longer period of time than estimates obtained using many other methods (Budge, Iverson, & Koopman, 2006). Sampling can be nonlethal and requires only the collection of a relatively small portion of fat tissue, although lipid stratification and the region of the body sampled can be important with some species (e.g., Guerrero et al, 2016;Lambert, Meynier, Donaldson, Roe, & Morel, 2013;Mohan, Mohan, Connelly, Walther, & McClelland, 2016). Diet estimation usually involves a relatively large number of fatty acids, which allows the contribution of a corresponding number of prey types to be estimated and greatly reduces the problem of underdetermined systems common with stable isotope models (Brett, 2014;Phillips & Gregg, 2003).…”

“…In feeding trials, calibration coefficient estimates have been found to vary by the species of the consumer and various aspects of feeding trial design (e.g., Budge, Penny, & Lall, 2011;Rosen & Tollit, 2012;Thiemann, Iverson, & Stirling, 2008;Wang et al, 2010). Further, fatty acids may be deposited or turnover at different rates in different tissues (Mohan et al, 2016;Nordstrom et al, 2008), and diet composition, physiological state, and the age of an animal can affect fatty acid metabolism (Williams & Buck, 2010). Designing a feeding trial to develop calibration coefficients that are robust to so many factors is complex and perhaps not even feasible.…”