Aquaculture  - Biotechnology topics

Feed accounts for 35-60% of the cost of farmed salmon production, half of which is from the protein component. Future feed costs are expected to increase significantly unless the cost of that protein component can be reduced. Fish meal makes up roughly 30-50% of the protein component of fish feed, thus, finding cheaper, but equally palatable and digestible alternatives to fish meal would significantly reduce one of the major costs of salmon aquaculture production.

Premium quality fish meal is derived from small, bony, pelagic fish that are not generally used for human consumption. These are cooked, pressed and the presscake (usually supplemented with condensed fish solubles) is low-temperature dried, finely ground and stabilized with antioxidant.

Alternative protein sources, such as canola meal, have been proposed as partial substitutes for fish meal. Canola meal is a by-product of oil extraction from canola seed and has an excellent essential amino acid profile. It is used as a protein supplement in poultry, swine, cattle and fish feeds and is less than half the cost of fishmeal on a per kilogram of protein basis.

The problem with canola meal is that it contains substances which fish are unable to digest. One of these substances is phytic acid, a form of phosphorus that inhibits digestive absorption of some minerals and amino acids. Salmon can’t digest phytic acid because they lack the enzyme ‘phytase’, which means that most of the phytic acid phosphorus ends up being excreted into the water. In freshwater hatcheries, where cultured salmon spend a portion of their lives, excess phosphorus can promote the proliferation of algae and phytoplankton that consume oxygen, leading to oxygen-starving of fish and other aquatic organisms in the system.

Two general approaches are being pursued to try and address these problems:

• use of low-phytate canola; and
• use of phytase supplements to salmon diets.

Researchers at Fisheries and Oceans Canada (DFO), along with their industry partners, are undertaking a three-year investigation of both approaches to determine their potential for reducing salmon feed production costs.

DFO and its partners will first assess how well salmon digest ordinary and low-phytate canola. Low-phytate canola can be produced in three ways:

• Canola plants can be genetically modified to produce low-phytate canola seeds. These varieties are now under development.
• Traditional, high-phytate canola can be processed using high temperatures to reduce the level of phytic acid present.
• Novel strategies can be developed that treat canola with phytase (in a process called dephytinization).

The researchers will examine several different types of canola protein products: ordinary high-phytate canola, low-phytate genetically modified canola, both of the preceding types of canola processed using high temperatures to reduce their phytic acid content, and dephytinized canola meal. They will assess digestibility and conduct long-term nutrition trials, to determine which types of canola promote optimum salmon performance (growth, feed intake, feed and protein utilization, health and survival) and minimum phosphorus excretion.

The researchers will also determine which diet composition maximizes the activity of phytase supplements. Moreover, they will assess how salmon perform on a high-phytate canola-based diet that has been supplemented with various levels of phytase, and that has also been altered in other ways that may improve oral phytase activity.

There are a range of potential benefits from this research, including:

• lower-cost feeds that give Canadian producers and suppliers a competitive edge that should translate into savings for consumers;
• a cleaner aquatic environment due to less phosphorus waste; and
• reduced reliance on wild fish sources of protein for salmon feed.