In situ study of gastric emptying using X-radiography and macrocapsules

摘要

An in situ method for taking repeated radiographic images from unanaesthetized fish has been developed for gastric emptying studies. Fish are held in an aquarium with narrow compartments, and the fish can be fed in this aquarium. A standard feeding protocol was developed involving the use of gelatin macrocapsules to allow differentiation of the chemical and physical properties of meals. The capsules disintegrate in a predictable manner in the stomach of rainbow trout Oncorhynchus mykiss (Walbaum) (< 20 min at 5-20 deg C), and tests can be run by feeding the fish with capsules filled with known amounts of different ingredients. Rainbow trout accepted empty capsules and those filled with fish feed and barium sulphate. Measurement of gastric emptying often forms part of studies of feed intake regulation and fish nutrition as well as assessments of food consumption of fish in the wild. However, most methods used to measure gastric emptying are crude and accompanied by problems that may limit application of the results. The problems with the current techniques can be summarized as follows: Destructive methods do not allow repeated sampling of the same individual. Handling and anaesthetization may cause stress and reduce the feasibility of frequent sampling when gastric lavage is used. Individual-to-individual variation in gastric emptying cannot be assessed reliably because it is not possible to monitor the emptying of a specific meal by a given individual.