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Table 3.

Nutritional performance of rainbow trout after 8 weeks on low-, normal-or high-iron diets

Dietary Fe
VariableLowNormalHigh
Initial mean mass (g)  79.1±5.0  
Final mean mass (g) 124.2±7.8 133.5±12.1 130.7±12.1 
Index    
   SGR (% day) 0.92±0.13 1.04±0.19 0.92±0.22 
   FCR 1.95±0.5 2.03±0.71 1.97±0.49 
   Condition factor 1.18±0.05 1.20±0.05 1.20±0.05 
   Hepatosomatic index (%) 1.14±0.09 1.11±0.13 1.15±0.08 
Fe retention    
   Faecal [Fe] (μmol g—1 d.m.) 3.4±1.1a 12.3±3.5b 45.1±2.9c 
   Final whole body Fe content (μmol fish—128.4±2.5a 27.6±2.2a 95.1±6.7b 
   Apparent net Fe retention (%) 23.2 4.1 2.7 
Proximate composition    
   Moisture (%) 72.4±0.8 72.8±0.3 73.0±0.5 
   Protein (%) 56.0±0.5 54.7±2.0 55.0±1.5 
   Lipid (%) 18.4±0.9 17.5±0.9 19.4±0.1 
   Ash (%) 12.0±0.1 12.1±0.3 12.0±0.2 
Dietary Fe
VariableLowNormalHigh
Initial mean mass (g)  79.1±5.0  
Final mean mass (g) 124.2±7.8 133.5±12.1 130.7±12.1 
Index    
   SGR (% day) 0.92±0.13 1.04±0.19 0.92±0.22 
   FCR 1.95±0.5 2.03±0.71 1.97±0.49 
   Condition factor 1.18±0.05 1.20±0.05 1.20±0.05 
   Hepatosomatic index (%) 1.14±0.09 1.11±0.13 1.15±0.08 
Fe retention    
   Faecal [Fe] (μmol g—1 d.m.) 3.4±1.1a 12.3±3.5b 45.1±2.9c 
   Final whole body Fe content (μmol fish—128.4±2.5a 27.6±2.2a 95.1±6.7b 
   Apparent net Fe retention (%) 23.2 4.1 2.7 
Proximate composition    
   Moisture (%) 72.4±0.8 72.8±0.3 73.0±0.5 
   Protein (%) 56.0±0.5 54.7±2.0 55.0±1.5 
   Lipid (%) 18.4±0.9 17.5±0.9 19.4±0.1 
   Ash (%) 12.0±0.1 12.1±0.3 12.0±0.2 

Values are mean ± s.e.m. At the end of the experiment,week 8, N=21 fish per treatment, except faecal Fe N=6, and whole body Fe content, N=9. Specific growth rate (SGR) and mean fed conversion ratio (FCR) were calculated from the mean mass gain/treatment between weeks 2 and 8. Whole body Fe contents are calculated from mean fish mass/treatment over the duration of the experiment and whole carcass Fe concentrations in Table 1. Whole body Fe content of initial fish was 17.7±0.9 μmol fish—1. Apparent net Fe retention = (final carcass metal content — initial carcass metal content/metal consumed)×100%. Proximate composition is expressed as a percentage of dry matter (mean± s.e.m., N=9 fish per treatment for moisture and N=3 tanks per treatment for pooled analysis of protein, lipid and ash. Initial fish moisture, protein, lipid and ash, respectively, were (% dry matter, mean ± s.e.m., N=6 fish per treatment for moisture and N=3 tanks per treatment for other parameters):72.1±1.90, 57. 6±0.4, 18.1±0.4, 12.0±0.2%. No differences were observed in SGR, FCR, condition factor, HSI or proximate composition between initial and final fish (Student's t-test, P>0.05). Different letters indicate significant differences within rows (t-test, P<0.05).

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