Digestibility, growth and nutrient utilisation of Atlantic salmon parr (Salmo salar L.) in relation to temperature, feed fat content and oil source

Summary

An experiment was conducted to investigate the effects of temperature, feed fat content and dietary oil source on growth and nutrient utilisation of Atlantic salmon parr (∼19 g). The fish were reared in freshwater at 2 or 8 °C for 6 months at light/dark cycles of 12 h:12 h. Each of four feeds was provided to triplicate groups of fish at each temperature. The feeds were formulated with marine fish oil or a blend of rapeseed and linseed oil at low or high inclusion levels to give feeds with 340 g kg−1 fat and 400 g kg−1 protein or 210 g kg−1 fat and 500 g kg−1 protein. Fish weights doubled over the 6 months at the lower temperature, whereas a fivefold increase was seen over the same period at the higher temperature. At the lower temperature, growth was similar for fish in all four dietary groups (SGR; 0.40±0.01% day−1), whereas significantly better growth was found for fish fed the low fat feeds at the higher temperature (SGR; 0.99±0.01% vs. 0.93±0.01% day−1). Feed efficiencies were higher for fish at the lower temperature. Apparent fat and protein digestibilities were high at both temperatures, but fat digestibility was significantly lower at the lower temperature (ADCfat; 96.3±0.5% vs. 98.2±0.4%). Fat digestibility was higher for the high fat feeds, but significant differences between the groups were found only at the lower temperature. Protein digestibility was also lower at the lower temperature (ADCprotein; 90.8±0.4% vs. 91.2±0.4%), and was significantly improved when vegetable oils were used in the feed. Protein retention efficiency (PRE: [g protein gain g protein ingested−1]×100) was significantly higher at 8 °C than at 2 °C (PRE; 52±1 vs. 49±2), and high feed fat content improved protein retention. Energy retention (ERE: [kJ gain kJ ingested−1]×100) tended to be higher for fish at the lower temperature (ERE; 55±2 vs. 50±1). Energy retention was also significantly higher for fish fed the high fat feeds. There was no evidence that vegetable oils were inferior to marine fish oils at either temperature, and at low temperature vegetable oil enhanced protein digestibility.