Estimation of oxygen‐diffusing capacity in the gills of different sizes of a tilapia, Oreochromis niloticus

Measurements on gills of features that affect gas exchange have been studied in relation to body weight in specimens (0.0112–812.3 g) of a tilapia, Oreochromis niloticus. The data were analysed with respect to body weight by means of logarithmic transformations (log Y= log a+b log W). The slopes (b) of the log/log regression lines for the gill area, harmonic mean diffusion distance and oxygen diffusing capacity were 0.777, 0.077 and 0.700, respectively. The gill respiratory area of O. niloticus (Trewavas) increases as the fish develops because the number and bilateral area of secondary lamellae increase. The scaling value for oxygen‐diffusing capacity is less than the value for gill area because of the slight increase in harmonic mean diffusion distance with development.