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

Abstract

A key aspect in the use of fatty acids (FA) to estimate predator diets using quantitative FA signature analysis (QFASA) is the ability to account for FA assimilation through the use of calibration coefficients (CC). Here, we tested the assumption that CC are independent of dietary fat concentrations by feeding Atlantic pollock ( Pollachius virens ) three formulated diets with very similar FA proportions but different fat concentrations (5–9% of diet) for 20 weeks. CC calculated using FA profiles of diet and triacylglycerols in pollock liver were significantly different for the three diets. To test the robustness of diet estimates to these differences, we used the CC set derived from feeding the diet with the lowest fat concentration, published prey FA profiles and realistic diet estimates of pollock to construct ‘pseudo-predators'. Application of QFASA to each pseudo-predator using the three sets of CC and the same prey FA profiles resulted in diet estimate biases of twofold for major prey items and approximately fivefold for minor prey items. This work illustrates the importance of incorporating diets with fat concentrations that are similar to natural prey when conducting feeding experiments to calculate CC. This article is part of the theme ‘The next horizons for lipids as ‘trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.

Improving the application of quantitative fatty acid signature analysis in soil food webs: The effects of diet fat content

“…Future experiments featuring supplemented yeast spiked with lower levels of marker fatty acids (e.g., 0.05%, 0.1%, and 0.5%) should fit this data gap. Similar effects were observed in marine QFASA research (Budge et al., 2020 ), where the diets in many feeding experiments already exceeded the fat levels representative for natural food. Further, as dietary resources in soil are typically low in fat, the rate of de novo fatty acid synthesis is high (Fernando‐Warnakulasuriya et al., 1988 ; Stanley‐Samuelson et al., 1988 ), leading to soil consumer metabolism with very variable CCs.…”

“…As the QFASA algorithm bases its calculation on the proportion of dietary fatty acids incorporated into the consumers’ lipid signature, factors with impact on this proportion are a prime target to advance the model. While ideally the CCs of a fatty acid should be close to static, several studies have shown CCs vary strongly within the same consumer, when fed on different resources (Magnone et al., 2015 ; Rosen & Tollit, 2012 ) as well as with the fat content of the diet (Budge et al., 2020 ). Similarly, the study focusing on QFASA in soil ecosystems observed variation in CCs between diets (Kühn et al., 2020 ), suggesting the fat content to be particularly important due to the generally low quality of soil food web resources.…”

Fatty acid isotopic composition in Atlantic pollock is not influenced by environmentally relevant dietary fat concentrations

“…Adult wild Atlantic pollock were caught using a commercial long line and transferred to the Aquatron Facility at Dalhousie University. Detailed descriptions of animal care, feeds and experimental design can be found in Budge et al (2020). Briefly, 11 fish were immediately euthanized to serve as initial samples and the remainder were tagged with a passive integrated transponder tag near the dorsal fin.…”

“…They were then separated into 9 tanks with 12 fish in each tank. Diets were formulated as moist pellets with lipid contents of ~5, 7 and 9% (wwb; referred to as Diets L, M and H, respectively) as described in Budge et al (2020). After pooling all batches of a diet, six samples of each were taken for determination of lipid concentration and FA profile.…”

“…Liver TAG FA FA proportional data for liver TAG FA of these fish were reported in Budge et al (2020) and are summarized here for only the FA that were also analyzed for  13 C (Supplementary Data Table 1). Except for 16:1n-7 and 18:1n-7 in the fish fed Diet L, all FA portions were substantially different than the initial fish.…”