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Growth, heat increment of feeding and gut blood flow in rainbow trout Eliason, Erika Jennifer

Abstract

Juvenile rainbow trout were fed to satiation three different isocaloric diets of high (H), medium (M), or low (L) protein (P) and lipid (L) concentrations [protein: lipid ratios were: 55%:10% (HP:LL); 45%:15% (MP:ML) and 35%:20% (LP:HL) ] during an 8-week growth trial. Fish fed the HP:LL diet were composed of significantly more protein (18.2%) and significantly less lipid (9.1%) compared to those fed the other two diets. However, growth performance parameters (specific growth rate, feed efficiency and dry feed intake) did not vary significantly among diets. Even so, the LP:HL diet resulted in a greater percent protein deposition (37.6 ± 2.2%) over the 8-week trial and a greater protein efficiency ratio (2.3 ± 0.1) compared to HP:LL diet (29.4 ± 1.0% and 1.6 ± 0.0, respectively), suggesting a protein sparing effect. These same fish were maintained on the diet treatments and postprandial gut blood flow (GBF) and oxygen consumption (MO₂) were assessed following a single meal (by gavage) of 2% of their body mass. There were no significant differences among diet treatments for MO₂, GBF or heart rate. When the three diet treatments were pooled, standard metabolic rate (SMR), baseline GBF and baseline heart rate were 52.6 ± 2.5 mg O₂ kg⁻¹ h⁻¹, 4.0 ± 0.2 ml min⁻¹ kg⁻¹ and 34.2 ± 1.8 beat min⁻¹, respectively. Compared with these values and after accounting for the effect of handling for gavage, minimum MO₂, GBF and heart rate had increased significantly by 4-h postprandial, and peak increases were 119%, 153% and 75-115%, respectively. In fish equipped with a Transonic flow probe fed a second time, all three variables had returned to baseline levels between 24-h and 48-h postprandial, as was the case in un-probed fish. In contrast, fish with a GBF probe fed 48 h after surgery displayed elevated postprandial MO₂ and GBF for the entire duration of the 80-h study. This extended elevation was likely due to prolonged digestion associated with surgery. The metabolic cost of the diets (as a % of digestible energy) was low (4.0-9.7%) and did not differ among these diet formulations.

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