Transfer of cyanobacterial carbon to a higher trophic-level fish community in a eutrophic lake food web: fatty acid and stable isotope analyses

Abstract

The dietary utilization of cyanobacterial carbon by fish communities is poorly understood. We examined the transfer of cyanobacterial carbon to fish in a eutrophic lake using fatty acid biomarkers and measuring the stable carbon isotope ratios of fatty acid and bulk nitrogen. We collected five species of fish (Hypomesus nipponensis, Carassius sp., Cyprinus carpio, Tridentiger brevispinis, and Gymnogobius castaneus) as well as the seston from June to November 2016 from Lake Hachiro, Japan. Cyanobacterial blooms were observed from August to October. From June to August, cyanobacterial fatty acid biomarkers (18:2ω6 and 18:3ω3) accounted for only 1.4-4.3% of total fatty acids in these fish species, indicating a low contribution of cyanobacteria to fish diets during this period. However, the contribution of the cyanobacterial fatty acid biomarkers in these fish species increased sharply in September (10.5-17.1%), except in second-year H. nipponensis. In September, the stable carbon isotope ratios of 18:3ω3 in these fish species were almost equivalent to those in the seston, which was primarily composed of cyanobacteria. The trophic positions of the collected fish species ranged from 1.6 to 3.4, based on their stable nitrogen isotope values, indicating that some fish ingested cyanobacteria directly, while others acquired cyanobacteria indirectly, through the food chain. These findings indicate that cyanobacterial carbon is transferred up the food chain in eutrophic lake ecosystems with cyanobacterial blooms.

Origin of Carbon and Essential Fatty Acids in Higher Trophic Level Fish in Headwater Stream Food Webs

“…On the contrary, for 18:3ω3, the expected isotopic fractionation of epilithic biofilm to S. leucomaenis via aquatic insects was 1.6–8.0‰. Fujibayashi et al [29] found no significant difference of isotopic value of 18:3ω3 between freshwater fish and blooming cyanobacteria. However, the mechanism of this inconsistent and variable fractionation for 18:3ω3 was not explainable in this study.…”

“…; Supelco, Inc., Bellefonte, PA, USA). The operating conditions were as described by Fujibayashi et al [29]. Each essential fatty acid peak was identified as described above for the GC-FID analysis.…”

“…Correction for the effect of additional carbon from boron trifluoride methanol on δ 13 C was conducted according to Fujibayashi et al [29]. The stable carbon isotopes of fatty acids in S. leucomaenis , epilithic biofilms, and terrestrial litter samples were analyzed.…”

“…Moreover, an almost isotopically unchanged transfer of 18:2ω6 and 18:3ω3 between diet and zebrafish Danio rerio was observed in a 100-day feeding experiment with constant dietary sources [27]. Several aquatic food web studies have already assumed no fractionation of isotopic value of essential fatty acids [28,29]. On the contrary Gradyshev et al [30] found gradual depletion of stable carbon isotope ratios of essential fatty acids, including 18:2ω6 and 18:3ω3, through higher trophic levels in a stream food chain, suggesting that fractionation was negative.…”

Trophic transfer of lipids and fatty acids across habitats in tropical river food webs

“…Lipids and fatty acids (FA) are important biochemical components of aquatic food webs and access to food sources with specific FA profiles helps ensure high quality nutrition is available to support metabolic processes that can influence consumer fitness (Arts et al., 2001; Swanson et al., 2012). Research to date on the FA of river food webs has largely been focused on temperate regions (Fujibayashi et al., 2018; Twining et al., 2017). Few studies have reported on FA of freshwater food webs in the tropics with the majority of existing tropical freshwater FA studies coming from African lakes (Hecky et al., 2010; Kwetegyeka et al., 2008; Zenebe et al., 1998).…”