Behavioural and metabolic effects of chronic exposure to sublethal aluminum in acidic soft water in juvenile rainbow trout (Oncorhynchus mykiss)

Triplicate groups of 15 softwater-acclimated juvenile rainbow trout (Oncorh ynchus mykiss) were randomly allocated to one of three treatments: pH 6.5 w ith no aluminum, pH 5.2 with no aluminum, and pH 5.2 with 30 mu g labile al uminum.L-1. The aluminum dose was sublethal and continued for 34 days. Trea tment effects on swimming behaviour, metabolism, feeding, food conversion e fficiency, and blood parameters were determined. Fish exposed to aluminum d isplayed hypoactivity that was statistically distinct from both control gro ups from day 1 onwards. Exposure to acid alone elicited no behavioural effe cts. There were no significant differences in metabolic rates between the t reatment groups. Feeding rates of the fish exposed to aluminum became depre ssed, reaching a minimum on day 15, and gradually recovered thereafter, but never to the preexposure levels. Swimming behaviour was a more sensitive i ndex of exposure to aluminum than feeding. Fish exposed to aluminum had sig nificantly fewer red blood cells and lower haematocrit than the controls, i ndicating haemodilution. Aluminum is known to act as a respiratory toxicant , restricting aerobic scope. In addition, these data suggest that fish resp ond to aluminum exposure by reducing metabolically costly activities such a s routine swimming behaviour to allow for the increased maintenance costs a ssociated with acclimation and damage repair.