Lack of a Depth Effect on the Growth of the Air-Breathing Catfish, Clarias macrocephalus

Abstract

In juvenile Clarias macrocephalus, distance travelled to breathe air increased strongly with depth, but growth rate was not significantly affected. Forty-seven fish (4.60 ± 0.12 g, 8.4 ± 0.07 cm, mean ± SE) were initially raised for 28 d in individual cages (30, 60, 90, and 118 cm deep) at 27 °C and 0.72 mg O2∙L−1, with a daily ration of 6% body weight. Distance travelled increased from 15.5 m∙h−1 at 30 cm to 51.2 m∙h−1 at 118 cm. When fish were subsequently maintained without food for a further 14 d, at 0.15 mg O2∙L−1, distance travelled averaged 6.6 and 22.7 m∙h−1 at 30 and 118 cm, respectively. Despite the increase in activity, depth had no significant effect on specific growth rate of either fed (3.62 ± 0.08%∙d−1) or fasting (−0.70 ± 0.03%∙d−1) fish. Strong effects of depth on the growth of air-breathing fishes may not be as general as previously suggested.