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Effects of feeding diets containing various dietary protein and lipid ratios on the growth-performance and the sensory attributes of post-juvenile Coho salmon (Oncorhynchus kisutch) reared in seawater Chan, Judy Chuk Kwan

Abstract

Six extruded dry diets formulated to contain one of two levels of digestible protein (37% or 44%) and one of three levels of digestible lipid (16%, 23%, or 30%) on a dry weight basis as well as a seventh commercial diet were used to feed triplicate groups of post-juvenile coho salmon (Oncorhynchus kisutch) in sea water. Fish were fed to satiation twice daily for 168 days beginning October, 1997. The performance of the fish was assessed by measuring changes in mean body weight (BW, g), mean specific growth rate (SGR, %, (In (final mean weight) - In (initial mean weight)) ∙100 ∙ number of experimental days⁻¹), mean feed intake (g ∙ fish⁻¹), mean feed efficiency ratio (FE, weight gained (g). dry feed intake (g)⁻¹), and mean protein efficiency ratio (PER, wet weight gained (g). protein consumption (g)"1) of each replicate group every 28 days. In addition, mean protein deposition (%PD, %, protein gained in fish (g). 100 . protein consumed (g)⁻¹) and mean gross energy utilization (GEL), %, gross energy gained in fish • 100 ∙ gross energy consumed (MJ)⁻¹) of each replicate group were determined at the end of the experiment. On the final day, Day 168, of the growth experiment, samples were taken from each replicate group per diet treatment for determinations of whole body and muscle proximate compositions. Fatty acid compositions and astaxanthin concentrations in both the experimental diets and fish flesh were also assessed by gas chromatography (GC) and high performance liquid chromatography (HPLC), respectively. In addition, skinned fillets from pan-sized coho salmon were sampled for the determination of effects of dietary treatments on various sensory attributes. The degree of pigmentation of raw fillets was analyzed using the Roche Color Card (RCC) for Salmonids, SalmoFan (SF), and a Hunter Lab Labscan. The texture of cooked fillets was assessed via a Texture Analyzer using the Texture Profile Analysis (TPA). Intensities of salmon aroma, salmon flavor, off-flavor, texture, and the overall acceptability of cooked fillet samples were evaluated using quantitative descriptive analysis by a group of 11 trained panelists. Although not significantly different (p > 0.05), results from the growth study showed that as a general trend, the coho salmon fed the diets contained the higher levels of lipid (23 - 30 %) exhibited improved feed efficiency, protein efficiently ratio, percent protein deposition, and percent gross energy utilization. Also, as a general trend (p > 0.05), the diets containing higher protein content supported better growth than those that had lower protein content. However, fish fed the lower protein level (37%) diets generally (p > 0.05) demonstrated higher protein efficiency ratio, % protein deposition, and gross energy utilization. Colorimeter studies showed that fish fed the diets with the high levels of lipid (23% or 30%) generally had higher values for Hunter a, Hunter b, chroma, and astaxanthin content in raw flesh. Color intensities also increased (p < 0.05) with increasing fish size. Texture profile analysis failed to show any significant difference among cooked fillets from salmon given the different dietary treatments; however, the analysis indicated that salmon generally (p > 0.05) become softer with increasing size. Sensory assessments by sensory panel revealed that fillet from fish fed the diet with high protein and high lipid content had significantly (p < 0.05) greater salmon flavor and softer texture than the fillets from those fed the control diet. The intensities of salmon aroma, off-flavor, and overall acceptability of fillets were not affected (p> 0.05) by dietary treatment as were detected by the sensory panel.

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