Influence of dissolved oxygen on growth of young eel.

Abstract

Experiments were carried out to examine the influence of nearly constant and of diurnal fluctuated dissolved oxygen level on growth, feeding and food conversion rates of Japanese eel Anguilla japonica. Eel at average weight of 2-5g were reared in 16l rearing tanks with continously supplied freshwater (23.4-25.0°C) of different DO levels. DO level was controlled by introducing N2 and O2 gas into the inflowing water. Growth, feeding and food conversion rates of eel decreased when they were exposed to con-start DO levels below 40% but were maintained almost at the same degree at the oxygen level from 60% to above air-saturation. Growth rate also decreased when DO level diurnally fluctuated (12:12h) from 90% or 60% to levels below 40%. Effects of diurnal fluctuations of DO on growth of eel were similar whether the DO level at recovery period was kept at 90% or 60%. But in the case of 60%, a longer exposure to alternate low DO levels brought more severe decrease in growth rate than 12h. Consequently, the desirable DO level for normal growth in both constant and fluctuated condition is expected to be more than 60%. No effects of DO level on protein digestibility and food requirement for maintenance of eel were observed. The reduction in food conversion rate at low DO level is presumed to be caused mainly by the decrease in food consumption of eel.