The physical state of food passing through the gut varies with species and type of food. Fish, such as salmonids, which eat relatively large prey, reduce the prey in size layer by layer. Gastric digestion proceeds in a layer of mucus, acid, and enzyme wherever the stomach wall contacts the food. Food appears liquified only in the midgut and solidifies somewhat again during formation of faeces. Pellets of commercial feed seem to be treated similarly, i.e., pellets get smaller and smaller in size with time, although stomachs of some recently-fed salmonids have been found to contain moderate amounts of liquified pellets. Stomachs of juvenile Pacific salmon captured in the open sea contained a thick slurry of pieces of amphi-pods in various stages of solubilization. Fish whose food contains high levels of indigestible ballast, e.g., common carp feeding on a mixture of mud and plants, probably show minimal change in the appearance or volume of their food while it passes through the gut. Microphagous fish, such as the milkfish (Chanos) whose food starts out as a suspension of fine particles, probably also keep it in much the same form all the way through the gut. In general: there seems not to be the same degree of liquifaction of food in fish as is commonly described for mammals.