Diet and Fatty Acid Signatures
Influence of diet variation on fatty acid signatures of the Atlantic stingray, Dasyatis sabina.
Accurate characterization of trophic relationships among species is needed for proper management of fish populations. The traditional method for delineating food habits and trophic interactions is to examine a predator's gut to identify and quantify recently eaten prey or indigestible parts of prey. This method, while providing some data on prey selection, is subject to bias and limitations. For example, the method of capturing a predator might be biased such that only "hungry" fish are caught. Recently eaten prey also provide only short-term data on food habits, giving no indication of the long-term dietary history of a predator. In addition, prey items that do not have hard, indigestible parts and/or have low retention time in the gut could be underrepresented in diet reconstruction. Finally, excluding the few exceptional cases where gut extrusion or lavage is feasible, the predator must be killed to extract the gut contents.A modern approach to diet analysis has focused on evaluating fatty acid compositions of predator tissues. The biochemical properties of many dietary fatty acids (particularly essential fatty acids) result in their incorporation into organisms with little or no modification. Analysis of the types, number, and proportions of fatty acids in an organism results in a characteristic "fatty acid signature." A prey item has a fatty acid signature that reflects its recent dietary habits and physiological requirements. After a predator consumes a specific prey item, over time, storage tissues of the predators will incorporate some fatty acids of the prey not immediately used for biological processes. Comparisons of fatty acid signatures in predators and potential prey items can provide data for diet reconstruction without direct examination of stomach contents. Furthermore, fatty acid analysis is not subject to the biases associated with traditional gut content analysis and can be performed on tissue biopsies, often eliminating the need to sacrifice the animal. Many studies have shown fatty acid composition to be useful in determining trophic relationships at both the bottom and top of food webs. However, to date, no study has examined the influence diet may have on elasmobranch fatty acid profiles. Furthermore, although the technique has been widely used in studies of feeding ecology of marine organisms, it has rarely been validated experimentally with known diets.
The goal of this study was to evaluate potential influences variation in diet can have on stingray fatty acid signatures in a controlled laboratory settings. To this end, a feeding experiment using the Atlantic stingray, Dasyatis sabina (Lesueur), as a test species was conducted. Two biochemically distinct diets were fed to captive rays to evaluate changes in muscle and liver fatty acid composition from a wild (control) diet to the experimental uniform diets. Preliminary results indicate little ability to distinguish diets from the predator tissues, suggesting this technique may not be suitable for stingray diet reconstruction.