Effects of Hypoxia and Surface Access on Growth, Mortality, and Behavior of Juvenile Guppies, Poecilia reticulata

Abstract

Juvenile guppies (Poecilia reticulata) were fed ad libitum and maintained for 11 d at oxygen concentrations ranging from 0.5 to 8 mg/L (25–26 °C). With access to the surface, guppies showed high growth rates and low mortality at all concentrations. Without surface access, they exhibited a progressive reduction in growth rate below 2–3 mg/L and did not survive below 1 mg/L. Activity was influenced by oxygen concentration and surface access. Feeding rates declined sharply with oxygen concentration for fish without surface access and to a lesser extent for fish with access. Percent time in contact with the surface increased as oxygen decreased. Aquatic surface respiration is used even when this behavior is not necessary for survival. We suggest that aquatic surface respiration increases the energy available for growth under hypoxic conditions by augmenting oxygen supply, which permits greater ingestion rate, and possibly by decreasing the cost of ventilation.