- The performance of an organism or organismic subsystem is
the result of the interaction between the performance capacity of
the system and Its environment. Environmental conditions can
stress an organism and thus affect it's performance. In this
study, three whole organism performances were examined: critical
swimming speed, fatigue time and response time to a sudden
bright light. In addition, subsystem performances were examined
by measuring changes in hematocrit and plasma levels of cortisol,
glucose, lactic acid, osmolarity, sodium and potassium.
Performance tests were made on juvenile chinook salmon stressed
0, 1, 2 or 3 times, with 1 or 3 h between stresses, and on fish
allowed to recover 1, 3, 6, 12 and 24 h after each level of stress.
A stress consisted of holding the fish in a dip net in the air for 30
sec. The physiological responses and the swimming tests were
conducted on salt water adapted fish while the behavioral
response was measured with fish in fresh water.
Plasma levels of cortisol, lactic acid, osmolarity and sodium
increased cumulatively following several acute handling stresses
spaced I h apart, though each parameter returned to control levels
in 6-12 h. Plasma glucose rose significantly by 1 h after the first
stress and remained higher than control levels at all levels of
stress and through 24 h after stress. Plasma potassium increased
initially following one and two stresses, dropped below control
levels within 1-6 h after the last stress, and then increased above
control levels for the remainder of the 24 h. Following three
stresses potassium was lower than controls initially and then was
similar to the levels for one and two stresses throughout the rest
of the 24 h recovery period. There was a decrease in hematocrit
3-6 h after each level of stress followed by a return to control
levels within 12 h of the last stress.
Critical swimming speed was measured by increasing the
water velocity in a flow-through swim tube and noting the
velocity at which each fish stopped swimming. Critical swimming
speeds after handling were highly variable and no differences were
found between stressed fish and unstressed fish at any level of
stress or any recovery time.
Fatigue time was measured as the time a fish can maintain
position in a swim tube at a given constant water velocity (60
cm/sec). Following each fatigue test, fish were killed and blood
samples were obtained. Unlike unstressed fish, which all fatigued
within13 min, the times to fatigue of stressed fish varied with
some fish fatiguing within a few minutes and some fish swimming
the 60 min period. There was a depression in fatigue times
immediately following one and three handling stresses spaced 1 h
apart. Immediately after two stresses and with all groups given
time to recover from stress, fatigue times were similar to or
higher than for unstressed fish.
Plasma levels of cortisol, glucose, osmolarity and sodium
were higher in swimming fish than in non-swimming controls.
Plasma concentrations of cortisol, glucose and lactic acid were all
highly variable in fish following fatigue and no differences were
found betweeen fish handled in a dip net and unhandled fish at any
level of stress or any time after stress. Plasma osmolarity and
sodium levels in fatigued fish immediately after one stress were
higher than levels in unstressed fatigued fish. Plasma potassium was higher in fatigued fish than in unstressed fatigued controls at
several time periods after one and three stresses.
The behavior test consisted of exposing groups of salmon in
fresh water to a sudden bright light and measuring the time it took
each fish to reach cover. Unstressed fish reached cover within 15
sec. Stressed fish took longer to reach cover, with the greatest
delay immediately after stress and a gradual decrease in response
time with recovery from stress. Exposure to two and three
consecutive stress with 3 h between stresses increased the
response times and the recovery times indicating that the effects
of stress were cumulative.