Patterns of gastric evacuation, digesta characteristics and pH changes along the gastrointestinal tract of gilthead sea bream (Sparus aurata L.) and European sea bass (Dicentrarchus labrax L.).

A comparative study of gastric evacuation rates (GERs) and digesta content, moisture and pH values along the gastrointestinal tract was performed between gilthead sea bream and European sea bass. In order to distinguish species-specific differences from diet-elicited effects, all parameters were determined under either a fishmeal diet or a carob seed germ meal diet that contained high levels of total and soluble non-starch polysaccharides. GERs were significantly different between species and they were not affected by diet. Similarly, species-specific patterns were revealed in the distribution of digesta and water content along the gastrointestinal tract. In sea bream, stomach digesta and water content decreased with time, whereas in sea bass stomach retained the highest digesta and water content throughout the sampling period. The anterior and distal intestine exhibited the lowest accommodating capacities of digesta and water in either species. Overall, sea bream performed stomach digestion at lower hydration levels and higher pH compared with sea bass. Diet affected stomach moisture in both species and pH of stomach digesta in sea bass and of all intestinal sections in sea bream. The results obtained indicated that water and inorganic ion exchanges through the gut may differentiate between the species and warrant further investigation.