Interrenalectomy and Stress in Relation to Some Blood Components of an Elasmobranch (Raja radiata)

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Abstract
From the literature there was a doubt as to whether interrenalectomy would result in elevated plasma potassium levels in a elasmobranch; in this study, no elevation was observed by comparison with sham-operated thorny skate (Raja radiata) held in sea water for up to 44 days post-operative.Blood calcium levels were significantly elevated in the interrenalectomized animals between 13 and 23 days but the increase was only 10%.There was no change in osmolality, sodium chloride, magnesium, or urea which can be attributed to interrenalectomy. Noteworthy was the manner in which both sham and interrenalectomized animals were able to maintain plasma electrolyte levels during the long period of starvation after surgery. Whenever significant changes occurred during the course of the experiment, sham and interrenalectomized fish were similarly affected, apart from the exception noted for calcium.Plasma urea levels were significantly depressed after interrenalectomy when the skates were held in a 3:1 mixture of sea water: fresh water for 7–9 days. The same trend was observed for sham-operated animals but the decrease was not significant. Normal animals maintained plasma urea in 75% sea water but not in 60% sea water.