Most knowledge on the feeding ecology of fish has been based on the analyses of food remains from the alimentary tracks. This traditional method, however, only provides information about recently consumed food, and is burdened with a risk of incorrect assessment of the role of individual diet components due to the different rates of digestion. A method free from such limitations is the analysis of fatty acids. The objective of our study was to recognise the potential of fatty acid signatures in providing information on the diet and feeding habits of six fish species from the shallow brackish Vistula Lagoon, southern Baltic Sea (Anguilla anguilla, Abramis brama, Rutilus rutilus, Pelecus cultratus, Perca fluviatilis, Sander lucioperca). Multivariate statistical analyses of fatty acid signatures permitted relevant grouping of the fish according to species and their diet, as well as evidenced substantial ontogenetic changes in perch, roach, and bream. They might be caused by dietary changes but can also result from internal regulatory processes. The obtained results confirmed that fatty acids provide useful, time-integrated dietary information, contributing to expanding knowledge regarding the feeding ecology of fish in shallow coastal water ecosystems. They also pointed to the necessity of assessment of the invertebrates and fish's ability to perform endogenous synthesis of polyunsaturated fatty acids, particularly in research on benthic communities. To our best knowledge, this is the first attempt to investigate the feeding habits of fish and food-web relationships in the coastal waters of the Baltic Sea using fatty acids.
The exceptional preservation of the Las Hoyas coprolites allows the taphonomic study of inclusions on twelve morphotypes and twenty-three specimens. Non-destructive techniques were applied to study the digestion features (pitting, corrosion lines, shape of the fractures at the ends) and the arrangement, number, and size of inelusions. An analysis based on non-metric, multidimensional scaling ordination identified the similarities among the inclusion features and morphotypes. The morphotypes are clustered on the basis of the way of ingestion and the digestive process. The authors recognize three digestive strategies for the Las Hoyas coprolites: (1) ingestion of prey with limited processing in the mouth, scarce to less effective acid secretions, and/or defecation in a short period of time; (2) ingestion of the prey with mastication prior to deglutition, and defecation over a longer period of time; (3) mastication and long retention time of food in the digestive system with more effective acid secretions. This study is a first step in the understanding of the feeding ecology of the Las Hoyas Barremian lentic ecosystem, based on coprolites.
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