Branchial arches of suspension–feeding Oreochromis esculentus: sieve or sticky filter?

Abstract

Only 4% of 600 particles slid on or adhered to buccopharyngeal surfaces of Oreochromis esculentus. Only a minute quantity of mucus was visible during feeding (0·6% of 68 224 video frames; 30 frames s–1), and very few particles were retained in this mucus. Filtration by mucus entrapment on the branchial arches is rejected as a mechanism of particle retention in this species. Since particles contacted the branchial arches infrequently, and the inter–raker spaces are too large to retain particles less than approximately 50 μm, sieving by gill rakers as a particle retention mechanism is rejected also. Unlike the suspension–feeding congener O. niloticus, O. esculentus does not use branchial arches to retain food particles by sieving or by mucus entrapment.