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

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 super(-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 mu m, 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.