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Abstract.— Responses of rainbow trout, Oncorhynchus mykiss, to handling and confinement stress were used to validate the efficacy of portable instruments for measuring blood glucose and lactate, and plasma protein. Glucose and lactate increased with time and showed good linear correlation with time after disturbance. The Advantage blood glucose and Accusport™ lactate meters were similarly correlated, except that values were consistently lower than those obtained by established laboratory techniques. Refractometry gave higher plasma protein values than results from biuret reagent but with excellent correlation. These findings indicate a potential role for portable instruments in field and hatchery locations where relative rather than absolute values may be used to evaluate responses to stressors.

Muscle metabolites in resting, tank acclimated snapper, Pums aurafus, were monitored for 72 hr postmortem and compared with values from exercised or commercially caught fish. The physiological status of the live animal was quantified by plasma cortisol and blood chemistry. Cortisol levels were lowest in unstressed controls (6.8rt2.1 ng mL-r) while exercised laboratory fish had highest levels (67.7~ 11.2 ng mL-t). Control fish maintained a constant K-value for 72 hr in chilled storage; all other groups had significant increases. Onset of rigor development and muscle ATP depletion was delayed in unstressed fish and was more rapid in line-captured than exercised fish. Commercial users minimizing stress would maintain high flesh quality.

SUMMARYThe effect of altered oxygen transport potential on behavioural responses to environmental hypoxia was tested experimentally in snapper, Pagrus auratus, treated with a haemolytic agent (phenylhydrazine) or a sham protocol. Standard metabolic rate was not different between anaemic and normocythaemic snapper (Hct6.7 and 25.7gdl -1 , respectively), whereas maximum metabolic rate, and hence aerobic scope (AS), was consistently reduced in anaemic groups at all levels of water P O2 investigated (P<0.01). This reduction of AS conferred a higher critical oxygen limit (P crit ) to anaemic fish (8.6±0.6kPa) compared with normocythaemic fish (5.3±0.4kPa), thus demonstrating reduced hypoxic tolerance in anaemic groups. In behavioural choice experiments, the critical avoidance P O2 in anaemic fish was 6.6±2.5kPa compared with 2.9±0.5kPa for controls (P<0.01). Behavioural avoidance was not associated with modulation of swimming speed. Despite differences in physiological and behavioural parameters, both groups avoided low P O2 just below their P crit , indicating that avoidance was triggered consistently when AS limits were reached and anaerobic metabolism was unavoidable. This was confirmed by high levels of plasma lactate in both treatments at the point of avoidance. This is the first experimental demonstration of avoidance behaviour being modulated by internal physiological state. From an ecological perspective, fish with disturbed oxygen delivery potential arising from anaemia, pollution or stress are likely to avoid environmental hypoxia at a higher P O2 than normal fish.

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