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The e¡ects of handling on haematocrit, haemoglobin, plasma glucose, lactate and total amino acids, liver glycogen and hepatic activity of fructose 1,6-bisphosphatase (FBPase) and alanine aminotransferase (AAT) were investigated in common dentex (Dentex dentex Linnaeus,1758). A total of 42 ¢sh (50-g weight) were subjected to handling (netting and shaking in the air for 45 s). Six ¢sh were sampled at 0, 0.5, 1, 2, 4, 8 and 12 h after handling. Six unstressed ¢sh were also sacri¢ced at each time and used as controls. Handling resulted in a rise in plasma glucose and lactate levels, as well as in enhanced hepatic FBPase and AAT activities. In most cases values returned to control levels 8 h after handling. There were no signi¢cant changes in haematocrit, haemoglobin, plasma total amino acids and liver glycogen levels as a consequence of handling. The results suggest that dentex is rather tolerant to handling; apparently, sensitivity to handling is not the main factor responsible for the low survival exhibited by this species in aquaculture.

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The influence of long‐term administration of high‐carbohydrate/low‐protein and high‐fat/non‐carbohydrate diets were studied in relation to kinetic behaviour of glucose 6‐phosphate dehydrogenase in liver and kidney of rainbow trout. In all cases studied, the saturation curves of these enzyme showed typical hyperbolic kinetics without evidence of sigmoidicity. After 30 days of feeding with a high‐fat diet (170 g kg−1), there was a significant decrease in Vmax and specific activity (45%) as well as catalytic efficiency (39%) without changes in Km or activity ratio of hepatic glucose 6‐phosphate dehydrogenase. These changes agree more with a clearly decreased cell concentration than with an inhibition of the pre‐existing enzyme. The administration of a high‐carbohydrate diet (60 g kg−1), contrary to what was previously thought, decreased Vmax by 21% and specific activity and catalytic efficiency by 30%, without significant changes in the other kinetic parameters of the hepatic enzyme. The kinetic behaviour under these nutritional conditons was due to the rejection of this diet by the fish and thus could be considered a low‐feeding situation. On the other hand, no variations in the kinetics of renal glucose 6‐phosphate dehydrogenase were found, clearly demonstrating that in this organ, the pentosephosphate pathway showed no adaptive response related to fattyacid and other lipid synthesis. The activity of the renal enzyme was consistently half that of the hepatic enzyme.