Unlocking the power of fatty acids as dietary tracers and metabolic signals in fishes and aquatic invertebrates

Abstract

Determining the transfer and transformation of organic matter in food webs is a fundamental challenge that has implications for sustainable management of ecosystems. Fatty acids (FA) offer a potential approach for resolving complex diet mixtures of organisms because they provide a suite of molecular tracers. Yet, uncertainties in the degree of their biochemical modification by consumers, due to selective retention or metabolism, have limited their application. Here, we consolidated 316 controlled feeding studies of aquatic ectotherms (fishes and invertebrates) involving 1404 species–diet combinations to assess the degree of trophic modification of FA in muscle tissue. We found a high degree of variability within and among taxa in the %FA in consumer muscle tissue versus %FA in diet regression equations. Most saturated FA had weak relationships with the diet ( r 2 < 0.30) and shallow slopes ( m < 0.30), suggesting a lack of retention in muscle when fed in increasing amounts. Contrarily, several essential FA, including linoleic (18:2n-6) and α-linolenic acid (18:3n-3), exhibited significant relationships with the diet ( m > 0.35, r 2 > 0.50), suggesting supply limitations and selective retention in muscle by consumers. For all FA, relationships strengthened with increasing taxonomic specificity. We also demonstrated the utility of new correction equations by calculating the potential contributions of approximately 20 prey items to the diet of selected species of generalist fishes using a FA mixing model. Our analyses further reveal how a broad range of fishes and invertebrates convert or store these compounds in muscle tissue to meet physiological needs and point to their power in resolving complex diets in aquatic food webs. This article is part of the theme issue ‘The next horizons for lipids as ‘trophic biomarkers’: evidence and significance of consumer modification of dietary fatty acids’.

Fatty acid accumulation in feeding types of a natural freshwater fish population

“…This pattern was particularly pronounced in DHA, where realized values of DHA in perch muscle tissue exceeded the theoretical values on average by a factor of five. Thus, our results are in-line with a recent meta-analysis of feeding studies in fish and aquatic invertebrates suggesting that DHA is retained even when supplied in high levels (Jardine et al 2020 ). Due to the important role of DHA in fish metabolism (e.g.…”

Essential Fatty Acid Requirements in Tropical and Cold-Water Marine Fish Larvae and Juveniles

“…During larval development, DHA is preferentially incorporated into nervous and retina tissue (Izquierdo et al, 2000;Villalta et al, 2008), and growth anomalies and high mortality are observed when DHA is insufficient (Tocher, 2010). Other dietary FA, including linoleic acid (LA; 18:2n-6) and α-linolenic acid (LNA; 18:3n-3), are stored in muscle tissue to meet physiological needs and are also related to fish growth and survival to some extent (Jardine et al, 2020). These FA are precursors of DHA, EPA, and ARA, but as already pointed out; the activities of the specific enzymes (desaturase and elongase) responsible for their biosynthesis are limited in most marine species.…”

Dietary fat concentrations influence fatty acid assimilation patterns in Atlantic pollock (Pollachius virens)

“…Thus, a key aspect of this approach is the adjustment of the predator's FA profile for these modifications. In QFASA applications, these modifications are taken into account using 'calibration coefficients' (CC) [13], defined as the ratio of the proportion of a FA in the predator's tissue relative to the proportion of the same FA in diet, after feeding the diet for a prolonged period [9]. While the basic biochemical processes that may occur are well known [12], the precise changes in FA concentration that arise from metabolism remain uncertain, making empirically derived CC essential.…”