Comparative study of gill dimensions of three erythrinid species in relation to their respiratory function

Abstract

Gill dimensions were analysed in relation to body mass in three erythrinid fish, an air-breathing species, Hoplerythrinus unitaeniatus, and two ecologically distinct water-breathing species, Hoplias malabaricus and Hoplias lacerdae. Evidence was obtained of remarkable differences in patterns of increase in filament length, number of secondary lamellae, bilateral area of the secondary lamellae, total area of the secondary lamellae, and mass-specific area of the secondary lamellae among these three species. The analysis showed a large increase in respiratory surface area relative to body mass in H. malabaricus (b = 1.14) compared with Hoplias lacerdae (b = 0.81) and H. unitaeniatus (b = 0.66). This difference is mainly attributed to an increase surface area of individual secondary lamellae together with an increase in filament length and total number of secondary lamellae. The results indicate that the increased respiratory surface area of the H. malabaricus gill facilitates oxygen uptake in hypoxic environments as the fish grows and this suggests that gill dimensions may reflect ecological factors and not only respiratory requirements.