英语翻译

英语翻译
The water levels were maintained constant by regulating the water flow of the outlet
and inlet from the reservoir and fish tanks.The fish tank was always filled completely
with water so that no air was trapped inside the cover.Thus the fish could only obtain
air from the tube open to the air where it was forced to disturb a table tennis ball
whose movements were registered by means of a lever and a kymograph drum.Time
intervals between air breaths were measured from these recordings.Opercular fre-
quencies were counted at £ h intervals and the depth of breathing was assessed by
visual observation alone.
The fish was introduced into the tank 1 or 2 days before the start of an experiment.
On the completion of an experiment the water was changed to normal tap water and
the fish was kept in the tank until the start of another experiment on the following day.
The fish was fed at intervals of 3 or 4 days.Most observations were made at a tempera-
ture of 25 °C ± 1 °C.Total period of observation in a given experiment ranged from
5 to 11 h.Gas exchange