Water quality dependant recovery from aluminum stress in atlantic smolt

Summary

In Norway, a variable pH target (pH 6.2-6.4 during most of the year, but 6.4 during the smoltification period) is used to reduce the cost of liming salmon rivers. Here we test the adequacy of this liming strategy. Atlantic salmon smolts exposed to sublethal acidic water (pH 5.9, <25µg Ali l-1) for more than 3 months showed impaired seawater tolerance, elevated gill-Al concentrations, severe gill tissue changes, elevated blood plasma glucose concentrations, but having no effect on blood plasma chloride. It is usually assumed that smolt will recover from prior aluminum (Al) exposure if water quality is restored. Recovery rate is here used as an indirect measure of water quality improvements achieved after treating acid water (pH 5.8, 85 µg Ali l-1) water with lime to reach pH-target levels of 6.0 - 6.3. Fish were exposed in a channel-tank set-up, exposed for >210 h in water aged from 1 minute up to 2 hours after treatment (in a flow through system). More Al was eliminated from the gills when the fish were exposed to pH 6.3 than at pH 5.8 or 6.0, and when water was aged after pH increase. Recovery, defined as return of normal gill morphology, blood homeostasis and establishment of seawater tolerance was achieved within 210 h in channels treated with lime to pH 6.3, while a similar recovery was not obvious at lower pH values. Liming to pH 6.3 detoxified Al better than pH 6.1.