High-energy diets for Atlantic salmon - Effect on growth, feed utilization, product quality and recipient loading / Høyenergi-fôr til atlantisk laks - effekt på vekst, fôrutnytting, produktkvalitet og utslipp
Growth, feed utilization, product quality and recipient loading were studied in Atlantic salmon (Salmo salar) in sea cages of medium and large size, with different ratios between the macronutrients in commercial feeds.
Atlantic salmon growing from 0.3 to 3.5 kg were fed iso-energetic and restricted, or to satiation with diets of different fish oil content resulting in different dietary fat content (22% or 30% fat). The high-energy diet (30% fat) was associated with the highest growth at feeding to satiation. The high-energy diet produced the lowest feed conversion ratio (FCR) and the highest nutrient retention (restricted feeding), and thereby the lowest outlets of nitrogen and phosphorus. Fish fed the high-energy diet had higher incidence of sexual maturation, slightly lower dress-out percentage and marginally higher fat concentration in carcass.
In another study diets with increasing fish oil content and decreasing dietary protein to fat ratio (P/F = 42/21, 39/26, 37/30 and 35/32, %) were fed iso-nitrogenously to Atlantic salmon growing from 0.1 to 0.6 kg. Growth increased with decreasing P/F. The best FCR and nutrient retention were achieved with diets of P/F from 37/30 to 39/26, and the highest dress-out percentage and lowest fat concentration in fillets were obtained with diets of P/F = 39/26 or higher.
In a third study Atlantic salmon growing from 1.0 to 4.3 kg were fed iso-energetic and restricted, or to satiation, with three diets containing 29% fat and protein to carbohydrate ratios (P/CH) of 34/21, 39/15 and 44/10 (%). The apparent digestibility (ADC) of starch and energy decreased with decreasing P/CH. Growth per g digestible protein increased, calculated nitrogen discharge decreased and calculated starch discharge increased with decreasing P/CH. There was a slight tendency for lower growth, higher FCR and lower dress-out percentage with the lowest P/CH, and no effects of diet on fat in fillet.
In the final study methods for adding external markers to commercial dry fish feed (by coating or inclusion in moist feed made from ground pellets) for determination of ADC were investigated. Moist feed had the lowest leaching of markers and was used in two digestibility experiments with Atlantic salmon, where faeces was collected by stripping. The ADC values obtained this way were compared to the ADC values obtained by an internal marker in an unaltered commercial dry feed. The ADCs measured in the ground and re-pelleted test feed were parallel but slightly lower than that of the unaltered dry feed.
