7708

• UCREFRP Catalog Number: 7708
• Author: Madden, J. A. and A. H. Houston
• Title: Use of electroanaesthesia with freshwater teleosts
• USFW Year: 1976
• USFW - Doc Type: some physiological consequences in the rainbow trout,
• Copyright Material: YES

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PHYSIOLOGICAL CHANGES WITH ELECTROANAESTHESIA 461
nor magnesium levels appeared to be influenced by electroanaesthesia but both
cations increased in concentration to some extent following exposure to MS 222.
Neither method of anaesthesia was associated with significant changes in tissue
muscle magnesium levels, and both produced similar changes in muscle chloride and
potassium concentrations. The former decreased while the latter rose by some
15-20 mequiv/kg. Tissue sodium decreased in brook trout following chemical anaes-
thetization but was little influenced by electroanaesthesia. The reverse was true of
calcium. Similarly, the marked decline in extracellular phase volume encountered
in electroanaesthesia was not observed in trout exposed to MS 222.
Clearly, electroanaesthesia, like chemical anaesthesia, leads to some immediate
and marked alterations in the physiological status of trout. On the whole, however,
the immediate effects of the electroanaesthesia do not appear to be more extensive
or more pronounced than those encountered following exposure to the chemical agent.
Recovery from electroanaesthesia
Haematocrit and haemoglobin. Both haematocrit and haemoglobin fluctuated
irregularly during recovery but were similar to control values after 24 h. In this they
resembled the pattern of change previously reported for brook trout.
Plasma glucose. Plasma glucose rose sharply reaching a peak value of 124.5E
10.5 rl g/100 ml after 6 h. Values then declined steadily although remained well
above the control value during the 24 h period of observation. By contrast, glucose
levels in chemically anaesthetized trout plateaued at 110-120 mg/100 ml after 3 h
and remained at this level for at least 4 days.
Plasma electrolytes. Both major plasma electrolytes, sodium and chloride, exhibited
similar patterns of variation, rising by 8-10 mequiv/1 and falling to control values
after 24 h. This contrasts with the situation seen in brook trout. In that instance
sodium increased by some 15 mequiv/1 whereas chloride declined by about 10 mequiv/1.
As a consequence, and in contrast to the situation encountered in rainbow trout, the
chloride : sodium ratio exhibited a transient, but sharp decrease. If one assumes
that electroneutrality is maintained, and that increases in bicarbonate levels compen-
sate for chloride loss, there is some likelihood that chemical anaesthetization is
associated with compensated or uncompensated alkalosis. Of the remaining plasma
electrolytes, potassium exhibited a sustained decline in concentration, calcium a
transient increase of slight magnitude and magnesium little change. Comparable,
but on the whole more extensive variations were observed in chemically anaesthetized
brook trout.
Tissue electrolytes. Tissue sodium and chloride variations were the reverse of those
observed for plasma. A transient decrease was followed by return to near-control
values within 24 h. This pattern of change is consistent with the variations in extra-
cellular phase volume. As might be anticipated from foregoing observations such
was not the case in brook trout. Potassium levels, on the other hand, rose sharply.
This was also true of brook trout exposed to MS 222. Elevated tissue potassium levels
were, however, sustained for a longer period of time in the latter species. A distinction
may also be made in relation to tissue calcium. In this study calcium exhibited a
sharp initial increase, but declined rapidly. In brook trout, calcium concentrations
remained well below control values for at least 4 days. Finally, tissue magnesium
showed little variation following electroanaesthesia; a situation comparable to that
described in brook trout.