Atlantic salmon (Salmo salar) is an important cultured carnivorous species that, in the past, has not tolerated high levels of most plant protein feed ingredients in their diet Gatlin et al. (2007). The inclusion of plant protein sources in aquafeeds is expanding due to the limited amount of fishmeal available for the production of animal feeds Glencross et al. (2005; Gatlin et al. 2007). Juvenile Senegalese sole (Solea senegalensis) fed diets that contain 5% fishmeal or less have been shown to have comparable growth to fish fed a 37% fishmeal diet when amino acids were supplemented Silva et al. (2009). For inclusion in the diets of rainbow trout (Oncorhynchus mykiss), many different plant protein sources have been examined, including plant protein meals and plant protein concentrates Lim and Webster (Lim et al. 2008). Canola protein concentrate (CPC), soybean meal and soy protein concentrates, pea protein concentrate, barley protein concentrate, rice protein concentrate, and wheat gluten meal have all been tested as fishmeal replacements with varying degrees of success Forster et al. (1999; Thiessen et al. 2003; Barrows et al. 2007; Lim et al. 2008; Gaylord and Barrows 2009). Many of these same protein sources have been tested in Atlantic salmon (Lim et al. 2008). Atlantic salmon was shown to have slightly reduced, but not significantly lower, performance when fed diets that were fishmeal-free and contained wheat gluten, corn gluten, fish soluble, and crystalline amino acids (Espe et al. 2006). Atlantic salmon fed a diet that contained 12% fishmeal had slightly decreased growth but produced 2 kg of fish for every 1 kg of fishmeal consumed (Torstensen et al. 2008). Stickwater, the water-soluble fraction that is produced in making fishmeal, has been shown to stimulate the growth of Atlantic salmon when fed low fishmeal diets (10% of the diet) and high plant protein diets (62% of the diet) (Kousoulaki et al. 2009). Amino acid supplementation is often needed to maintain the growth performance of fish fed plant protein-based feeds (Espe et al. 2007; Lim et al. 2008; Gaylord and Barrows 2009). A major challenge is to increase the amount of plant or other non-animal protein in the diet of carnivorous fishes while maintaining acceptable growth, feed conversion, and production costs compared to traditional diets.
Recently, multiple studies have been reported on the digestibility of various plant feed ingredients by Atlantic salmon () (Storebakken et al. Salmo salar
2000; Glencross et al. 2004a; Refstie et al. 2005; Aas et al. 2006; Aslaksen et al. 2007; Refstie et al. 2008). The protein digestibility was not significantly lower for the plant feed ingredients, except for extracted soybean meal, oat, canola, and sunflower. Canola meal contains a high level of carbohydrates and other antinutritional factors, such as phytic acid, tannins, sinapine, and goitrogenic compounds, lowering the nutrient availability of this feed ingredient to aquatic species (Kousoulaki et al. 2009). Further processing into a protein concentrate should remove more of the antinutritional factors and carbohydrates; however, significant amounts of phytic acid could remain (Burel and Kaushik 2008). In rainbow trout (O. mykiss), experimental diets that contained 20% fishmeal and 19.4% canola protein concentrate significantly lowered growth (Drew et al. 2007).
Both existing and new aquaculture operations are trying to increase the sustainability and reduce the environmental impacts by optimizing water use and reducing waste. Recirculating systems for cold water fish have undergone significant improvements within the last decade and can provide culture systems with reduced environmental impact. Such systems have greater control of the rearing environment, minimize water use, produce a concentrated and relatively small volume effluent, and can have improved biosecurity measures to control disease (Summerfelt et al. 2001).
The purpose of this study was to determine the effect of feeding multiple levels of canola protein concentrate in a commercial-type diet on the growth and nutrient efficiency of Atlantic salmon in a recirculating aquaculture system.