Different utilization of plant sources by the omnivores jundia catfish (Rhamdia quelen) and Nile tilapia (Oreochromis niloticus)

Plant sources are receiving special attention as feedstuffs in aquafeeds because of fish meal and oil shortage. However, studies about the effects of dietary fibre in fish are scarce. The inclusion of plant ingredients containing different levels of dietary fibre broken rice (BR), ground corn (GC), wheat bran (WB), citrus pulp (CP) and soybean hulls (SH) were evaluated for the omnivores jundia catfish and Nile tilapia. Tilapia is a typical omnivore with long intestines, whereas jundia has short intestines and no pyloric ceca. Fibrous sources (CP, WB and SH) were less digestible for both species than the starchy ones (BR and GC). However, jundia presented less ability to utilize the starch and protein from plant sources than tilapia. Growth of tilapia followed plant sources digestibility but no significant differences were detected for jundia, probably because of its slower growth rate. Muscle layer was thicker in the distal intestine of jundia fed CP diet, which possibly indicates an adaptation to propel the large volume of viscous digesta along the intestine. Therefore, despite its lower ability to utilize starchy plant sources, jundia showed an adaptive capacity to utilize fibrous diets, which is in agreement with its omnivorous feeding habit.