|dc.description.abstract||Four groups of rainbow trout, Salmo gairdneri, were acclimated to 2°,
10°, and 18°e, and to a diurnal temperature cycle (100 ± 4°C). To evaluate
the influence of cycling temperatures in terms of an immediate as opposed
to acclimatory response various ventilatory-cardiovascular rate functions
were observed for trout, either acclimated to cycling temperatures or
acclimated to constant temperatures and exposed to a diurnal temperature
cycle for the first time (10° ± 4°C for trout acclimated to 10°C; 18°+ 4°C
for trout acclimated to l8°e). Gill resistance and the cardiac to ventilatory
rate ratio were then calculated. Following a post preparatory recovery
period of 36 hr, measurements were made over a 48 hour period with the first
24 hours being at constant temperature in the case of statically-acclimated
fish followed by 24 hours under cyclic temperature conditions.
Trout exhibited marked changes in oxygen consumption (Vo ) with temp-
erature both between acclimation groups, and in response to the diurnal
temperature cycle. This increase in oxygen uptake appears to have been
achieved by adjustment of ventilatory and, to some extent, cardiovascular
activity. Trout exhibited significant changes in ventilatory rate (VR),
stroke volume (Vsv), and flow (VG) in response to temperature. Marked
changes in cardiac rate were also observed. These findings are discussed
in relation to their importance in convective oxygen transport via water
and blood at the gills and tissues.
Trout also exhibited marked changes in pressure waveforms associated
with the action of the resp; ratory pumps with temperature. Mean differenti a 1
pressure increased with temperature as did gill resistance and utilization.
This data is discussed in relation to its importance in diffusive oxygen
transport and the conditions for gas exchange at the gills.
With one exception, rainbow trout were able to respond to changes in
oxygen demand and availability associated with changes in temperature by
means of adjustments in ventilation, and possibly pafusion, and the conditions
for gas exchange at the gills. Trout acclimated to 18°C, however, and
exposed to high cyclic temperatures, showed signs of the ventilatory and
cardiovascular distress problems commonly associated with low circulating
levels of oxygen in the blood. It appears these trout were unable to fully
meet the oxygen requirements associated with c~ling temperatures above 18°C.
These findings were discussed in relation to possible limitations in the
cardiovascular-ventilatory response at high temperatures.
The response of trout acclimated to cycling temperatures was generally
similar to that for trout acclimated to constant temperatures and exposed
to cycling temperatures for the first time. This result suggested that
both groups of fish may have been acclimated to a similar thermal range,
regardless of the acclimation regime employed. Such a phenomenon would allow
trout of either acclimation group to respond equally well to the imposed
Rainbow trout showed no evidence of significant diurnal rhythm in any
parameters observed at constant temperatures (2°, 10°, and 18° C), and under
a 12/12 light-dark photoperiod regime. This was not taken to indicate an
absence of circadian rhythms in these trout, but rather a deficiency in the
recording methods used in the study.||en_US