Juvenile Leuciscus cephalus L. were forced to swim against a current of 25 cms−1 (3–5 body lengths s−1) intermittently for more than 2 months. Their metabolic responses to acute handling stress and recovery were compared to those of untrained L. cephalus.

The concentrations of glycolytic intermediates, malate and phosphocreatine were determined in whole-body homogenates of different fish before and immediately after mechanical stimulation leading to exhaustion, as well as after 5, 15, 30, 60 and 120 min of recovery.

The time course of recovery was described by fitting a bi-exponential equation. In untrained fish glycolytic metabolites, except pyruvate, showed maximum concentrations immediately after termination of the stress period, whereas in trained fish these maxima were delayed.

In trained L. cephalus the concentrations of all metabolites investigated returned to pre-exercise levels much faster than in untrained fish. Most characteristically, lactate was removed about four times faster from the tissues of trained than from those of untrained L. cephalus.

It is argued that anaerobic recovery, a well-known characteristic of exercise physiology in man and other vertebrates, is the driving force of accelerated recovery of trained L. cephalus.

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