Differential effects of low pH and aluminium on the caudal neurosecretory system of the brook trout, Salvelinus fontinalis

Abstract

Brook trout were subjected to soft water at pH 6.5, 5.5 or 5.0 without aluminium added, or to water at pH 5.5 with 200,300 or 500 pg Al I-' added. The response of the caudal neurosecretory system to low pH or aluminium was evaluated after one week by measuring the urotensin I and urotensin I1 concentrations in the urophysis by radioimmunoassay, and by morphometric analysis of the caudal neurosecretory cells. A positive correlation was found between urotensin I concentrations and acidity, and a negative correlation was found between urotensin I1 concentrations and total aluminium in the water. Morphometric indices (cell size and proportion of lobed nuclei in the caudal neurosecretory cells) suggested increased synthetic activity in the caudal neurosecretory cells of fish at pH 5.5 compared to pH 6.5.