Feeding and Digestion in Elasmobranchs: Tying Diet and Physiology Together

1. Introduction2. Feeding Habits of Elasmobranchs 2.1. Techniques for Studying Elasmobranch Diets2.2. Elasmobranch Diet Composition and Dietary Shifts2.3. Food Consumption Rates and Gastric Evacuation3. Elasmobranch Gastrointestinal Tract Anatomy 3.1. The Buccal Cavity, Pharynx, and Associated Structures3.2. The Esophagus3.3. The Stomach3.4. The Intestine and Associated Structures3.5. The Colon, Rectum, and Rectal Gland3.6. Ontogeny of the Gastrointestinal Tract4. Digestive Enzymes and Secretions 4.1. Stomach Enzymes and Secretions4.2. Intestinal Enzymes and Secretions5. Effects of Digestion on Homeostasis6. Future PerspectivesExamining the diet of elasmobranchs provides important ecological and physiological information. There are several techniques available for determining the diet of elasmobranchs including stomach content analysis, stable isotope analysis, and fatty acid analysis. Each technique has its own advantages and drawbacks and the aim of the study will determine the choice of technique, along with other technical considerations. Furthermore, diet preference appears to be dependent on both intrinsic and extrinsic factors that can provide insight into elasmobranch physiology. In addition, the diet may ultimately determine the physiology of the gastrointestinal tract itself, from overall activity level to enzyme expression. Anatomically, the elasmobranch gastrointestinal tract consists of several discrete structures and associated organs. Each organ has distinctive functions in digestion and elasmobranchs possess several unique organs not found in other species. The digestion of consumed food proceeds through an assortment of digestive enzymes and secretions. The secretion of the enzymes is most likely dependent on the diet consumed, while activity levels appear enhanced in elasmobranchs compared to other aquatic ectotherms. Overall, elasmobranchs occupy a number of ecological niches and their species-specific physiology is suited to this spectrum of demands. Future work is needed to expand our knowledge of how the consumption of a variety of diets affects the gastrointestinal tract and elasmobranch physiology.