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±7.8133.5±12.1130.7±12.1
Index
   SGR (% day)0.92±0.131.04±0.190.92±0.22
   FCR1.95±0.52.03±0.711.97±0.49
   Condition factor1.18±0.051.20±0.051.20±0.05
   Hepatosomatic index (%)1.14±0.091.11±0.131.15±0.08
Fe retention
   Faecal [Fe] (μmol g—1 d.m.)3.4±1.1a12.3±3.5b45.1±2.9c
   Final whole body Fe content (μmol fish—1)28.4±2.5a27.6±2.2a95.1±6.7b
   Apparent net Fe retention (%)23.24.12.7
Proximate composition
   Moisture (%)72.4±0.872.8±0.373.0±0.5
   Protein (%)56.0±0.554.7±2.055.0±1.5
   Lipid (%)18.4±0.917.5±0.919.4±0.1
   Ash (%)12.0±0.112.1±0.312.0±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).