Abstract

Monitoring programmes have demonstrated seasonal and short term variation of inlet water quality in Chilean salmon hatcheries. Potentially toxic levels of copper (Cu) and aluminium (Al) in many cases may explain observed increased mortalities during the early life-stages of Atlantic salmon. Therefore, there is a need for efficient water treatments methods. Two alternative water treatment methods were tested to reduce the toxicity of Cu and Al in fresh water production systems (egg to first feeding): crushed marble filtration treatment (MF) and sodium silicate addition (SA) treatment. To mimic the observed natural conditions an experiment was set up with short term (2-3 days) pulses of elevated Cu (20 and 30 mu g L-1) and Al (80 and 130 mu g L-1) concentrations. The effect of the two treatments was tested during 3 distinct developmental periods of the salmon, from 401 to 424, 551 to 567, and 729 to 736 accumulated thermal units (Am). Treatments were compared with a positive control group with metal addition (PC), and a negative control group (NC) exposed to untreated water with no metal addition. Compared to the groups that received metal pulses with no treatment (PC), mortalities were significantly reduced by both silicate addition and marble filtration. Both at 896 and 1013 ATU marble filtration (MF) group showed the lowest mortality. The present study suggests that crushed marble filtration and sodium silicate addition is well suited to treat Al and Cu pulses in the relevant concentration range tested. This constitutes a low cost and robust alternative for freshwater aquaculture facilities that need to improve the quality of their inlet water, and may consequently decrease mortality and improve fish welfare for Atlantic salmon. (C) 2014 Elsevier B.V. All rights reserved.