Cephalic circulation in the air-breathing snakehead fish, Channa punctata, C. gachua, and C. marulius (Ophiocephalidae, Ophiocephaliformes).

Abstract

The macrocirculation in the head of three air-breathing species of Channa was examined with the aid of vascular corrosion replicas and a scanning electron microscopic study was conducted on the pseudobranch, choroid gland and lentiform body. Two facultative air-breathing murrels, C. punctata and C. gachua, and one obligate air-breather, C. marulius were examined. In all three, the air-breathing organs (ABO) and systemic circulations were in-parallel, and both were in-series with the branchial circulation. Efferent branchial arteries from the first and second gill arches formed the arterial supply to the ABO, whereas the third and fourth arch efferents perfused systemic tissues. Postbranchial blood from the second gill arch also entered the systemic circulation directly via a shunt from the efferent branchial artery to the lateral aorta and via hypobranchial arteries. Vascular specialization to prevent mixing of oxygenated ABO venous and deoxygenated systemic venous blood was evident in arterial, but not venous circuits. Pseudobranchs of C. gachua and C. punctata are tri-lobed, in C. marulius they have numerous lobules. Pseudobranch lamellae are wider and shorter along the axis of blood flow than gill lamellae and folded perpendicular to this axis. Pseudobranch lamellae appear to be modified to minimize their epithelial surface while retaining an extensive vascular endothelial-pillar cell surface area, counter-current amplification is also possible. The choroid gland is an extensive planar counter-current capillary rete. The lentiform body of the eye is a globular capillary rete but there is no evidence of a counter-current circulation. The choroid and lentiform rete may have distinct physiological functions.