Modelling the role of highly unsaturated fatty acids in planktonic food web processes: Sensitivity analysis and examination of contemporary hypotheses

Handling and Storage Procedures Have Variable Effects on Fatty Acid Content in Fishes with Different Lipid Quantities

It is commonly assumed that the most accurate data on fatty acid (FA) contents are obtained when samples are analyzed immediately after collection. For logistical reasons, however, this is not always feasible and samples are often kept on ice or frozen at various temperatures and for diverse time periods. We quantified temporal changes of selected FA (μg FAME per mg tissue dry weight) from 6 fish species subjected to 2 handling and 3 storage methods and compared them to FA contents from muscle tissue samples that were processed immediately. The following species were investigated: Common Carp (Cyprinus carpio), Freshwater Drum (Aplodinotus grunniens), Channel Catfish (Ictalurus punctatus), Antarctic Eelpout (Pachycara brachycephalum), Rainbow Trout (Oncorhynchus mykiss) and Arctic Charr (Salvelinus alpinus). The impact of storage method and duration of storage on FA contents were species-specific, but not FA-specific. There was no advantage in using nitrogen gas for tissue samples held on ice for 1 week; however, holding tissue samples on ice for 1 week resulted in a loss of FA in Charr. In addition, most FA in Trout and Charr decreased in quantity after being stored between 3 and 6 hours on ice. Freezer storage temperature (-80 or -20°C) also had a significant effect on FA contents in some species. Generally, we recommend that species with high total lipid content (e.g. Charr and Trout) should be treated with extra caution to avoid changes in FA contents, with time on ice and time spent in a freezer emerging as significant factors that changed FA contents.

A case study of an enhanced eutrophication model with stoichiometric zooplankton growth sub-model calibrated by Bayesian method

Urban lakes in China have suffered from severe eutrophication over the past several years, particularly those with relatively small areas and closed watersheds. Many efforts have been made to improve the understanding of eutrophication physiology with advanced mathematical models. However, several eutrophication models ignore zooplankton behavior and treat zooplankton as particles, which lead to the systematic errors. In this study, an eutrophication model was enhanced with a stoichiometric zooplankton growth sub-model that simulated the zooplankton predation process and the interplay among nitrogen, phosphorus, and oxygen cycles. A case study in which the Bayesian method was used to calibrate the enhanced eutrophication model parameters and to calculate the model simulation results was carried out in an urban lake in Tianjin, China. Finally, a water quality assessment was also conducted for eutrophication management. Our result suggests that (1) integration of the Bayesian method and the enhanced eutrophication model with a zooplankton feeding behavior sub-model can effectively depict the change in water quality and (2) the nutrients resulting from rainwater runoff laid the foundation for phytoplankton bloom.

Egg boons: central components of marine fatty acid food webs

Food web relationships are traditionally defined in terms of the flow of key elements, such as carbon, nitrogen, and phosphorus, and their role in limiting production. There is growing recognition that availability of important biomolecules, such as fatty acids, may exert controls on secondary production that are not easily explained by traditional element-oriented models. Essential fatty acids (EFAs) are required by most organisms for proper physiological function but are manufactured almost entirely by primary producers. Therefore, the flow of EFAs, especially docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA), through aquatic food webs is critical for ecosystem functioning. A meta-analysis of data on the EFA content of marine organisms reveals that individual eggs of marine animals have exceptionally high concentrations of EFAs, and that superabundances of eggs released in temporally and spatially discrete patches create rich, but temporary, nutritional resources for egg predators, called "egg boons." Mortality rates of fish eggs are disproportionately higher than animals of similar size, and those eggs are consumed by predators, both larger and smaller than the adults that produce the eggs. Thus, egg boons are a major trophic pathway through which EFAs are repackaged and redistributed, and they are among the few pathways that run counter to the main direction of trophic flow. Egg boons can transport EFAs across ecosystems through advection of patches of eggs and spawning migrations of adults. Recognizing the significance of egg boons to aquatic food webs reveals linkages and feedbacks between organisms and environments that have important implications for understanding how food webs vary in time and space. Examples are given of top-down, bottom-up, and lateral control mechanisms that could significantly alter food webs through their effects on eggs. Our results suggest that trophodynamic food web models should include EFAs generally, and egg production and egg EFA content in particular.

Changes in the physiological parameters, fatty acid metabolism, and SCD activity and expression in juvenile GIFT tilapia (Oreochromis niloticus) reared at three different temperatures

We evaluated the effects of rearing temperature on the composition of fatty acids and stearoyl-CoA desaturase (SCD) activity and gene expression in GIFT (genetically improved farmed tilapia) tilapia. Three triplicate groups of fish were reared for 40 days at 22, 28, or 34 °C. At the end of the trial, the final body weight of juveniles reared at 28 °C was higher than that of fish reared at 22 or 34 °C. Feed intake, feed efficiency, and the protein efficiency ratio were also higher at 28 °C. The fatty acid composition of muscle tissue differed significantly (P < 0.05) among the treatment groups. The content of SFA decreased with decreasing temperature, whereas the UFA content increased. We observed high levels of PUFA, particularly n-3 PUFAs, in fish reared at the lower temperature. Rearing at low temperature significantly (P < 0.05) increased the expression and activity of the SCD gene. Increased SCD activity and gene expression can increase the biosynthesis of MUFAs in GIFT tilapia muscle. Additionally, cold acclimation can decrease the content of TC and TG in GIFT tilapia, which can help increase cold tolerance.