PMC

Oxygen consumption rate (VO₂) of northern snakeheads switched from water respiration to aerial respiration. n=14 for each group. Data are presented as the mean±s.e.m. The values with symbols (*, control group; †, suprabranchial organ group) were different from the resting VO₂ in water by a paired samples t-test (P<0.05). Filled circles with solid line, control group; open circles with dashed line, suprabranchial organ group.

(A,B) General anatomy of the gill and suprabranchial cavities of Anabantoidei (A) and Clariidae (B). (C) In the Anabantoidei species, the suprabranchial cavity was lined with a special type of epithelium, with multiple cavities (red arrows). The labyrinth plate was supported by bone and thick connective tissue, with collagen fibers strongly stained with aniline blue. (D) The dendritic organ of the Clariidae was supported by fibrous cartilage and a thinner connective tissue layer (compared to the Anabantoidei specimens). LO—labyrinth organ; DO—dendritic organ; SBC—suprabranchial cavity; GC—gill cavity; Roman numerals label the gill arches; modified AB/PAS, scale 1000 µm.

(A) Gill filaments (f) of Alcolapia grahami showing secondary lamellae (s) emanating from both sides of gill filaments. Scale bar, 0.4 mm. (B) Gills arches (*) and gill filaments (i) of a crab, Potamon niloticus. Scale bar, 0.3 mm. (C) Respiratory organs of the catfish, Clarias mossambicus, showing gill arches (a), labyrinthine organs (y) and suprabranchial chamber membranes (t). Scale bar, 10 mm. (D) Transverse capillaries (v) lining the suprabranchial chamber membranes of Clarias mossambicus and tracts occupied by mucous secretory cells (n). Scale bar, 10 μm. (E) Internal subdivision of the lung of the savanna monitor lizard, Varanus exanthematicus, showing primary septa (e) that line the central air space and peripheral septa (p). Scale bar, 0.1 mm.

Immunohistochemical demonstration of mast cell nerve interaction in the epithelium of the suprabranchial chamber of Clarias gariepinus. Section stained for Pis 1 (in red) and 5HT (in green) showing the close anatomical association of Pis-positive nerves (arrowheads) with Pis-positive mast cells (arrows). Eosinophils (E) showing 5HT immunoreactivity. Scale bar = 20 µm.