Sexually mature tilapia O. niloticus (35.3 ± 5.4g of mean body
weight) were randomly distributed through 12 tanks of 100 L. There
were 3 fish per tank and 3 tanks for each treatment in a total of n =
36. Fish from 3 tanks containing water without copper served as the
control group. Fish from the remaining tanks were exposed to water
copper concentrations of 0.5, 1.0 and 2.5mg L-1, supplied as
copper sulphate (CuSO4; MERCK, Lisbon, Portugal), during 21 days.
The copper concentrations were selected based on preliminary results,
shown to be sublethal after a 21 day period of exposure. The
experiments were carried out under constant temperature (25 ±
1ºC), controlled photoperiod (12D: 12L) and constant filtration. The
water had identical physical and chemical characteristics of the
acclimation tanks and the experiments described comply with the
Guidelines of the European Union Council (86/609/EU). Both control
and experimental tanks were submitted to a rate of water renovation
of 1/3 every two days. The water quality parameters mentioned
above were assessed in the experimental period, with no significant
changes being observed. During the experimental period fish were
once daily fed the referred diet to visual satiation and were fasted
for 24 h before sampling.
Sexually mature tilapia O. niloticus (35.3 ± 5.4g of mean bodyweight) were randomly distributed through 12 tanks of 100 L. Therewere 3 fish per tank and 3 tanks for each treatment in a total of n =36. Fish from 3 tanks containing water without copper served as thecontrol group. Fish from the remaining tanks were exposed to watercopper concentrations of 0.5, 1.0 and 2.5mg L-1, supplied ascopper sulphate (CuSO4; MERCK, Lisbon, Portugal), during 21 days.The copper concentrations were selected based on preliminary results,shown to be sublethal after a 21 day period of exposure. Theexperiments were carried out under constant temperature (25 ±1ºC), controlled photoperiod (12D: 12L) and constant filtration. Thewater had identical physical and chemical characteristics of theacclimation tanks and the experiments described comply with theGuidelines of the European Union Council (86/609/EU). Both controland experimental tanks were submitted to a rate of water renovationof 1/3 every two days. The water quality parameters mentionedabove were assessed in the experimental period, with no significantchanges being observed. During the experimental period fish wereonce daily fed the referred diet to visual satiation and were fastedfor 24 h before sampling.
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