NORWAY - Phosphorus is a vital mineral that must be added to salmon feed to ensure that the fish grow normally and develop a healthy skeleton. Global reserves of phosphorus, however, are limited, and industries that depend on this mineral must increase their use of current sources. An unexploited gold mine of phosphorus for the aquaculture industry is available in filleting waste.
Filleting waste contains high levels of phosphorus, but a large fraction is bound in poorly soluble mineral complexes in fish bones. Salmon have a limited ability to digest phosphorus from fish bones, and most of this phosphorus in the feed is therefore excreted in an undigested state into the environment.
The food research institute Nofima has long been working to develop biotechnology solutions that can make the nutrients in fish bones more readily available for salmon.
Senior researcher Sissel Albrektsen and her colleagues at Nofima have worked on a project financed by the Norwegian Seafood Research Fund (FHF). They have managed to garner a large fraction of the phosphorus present in herring filleting waste.
“It’s difficult to obtain the phosphorus present in herring filleting waste, which has a lower content of bone than other raw materials that we have experience of using. But we managed it after careful adaptation of a method we use for other marine raw materials to process and acid treat filleting waste. Our results show that herring filleting waste may be a significant source of phosphorus with this technology,” said Ms Albrektsen.
As much as 90 per cent of the phosphorus in the herring bones can be obtained using this method. This is compatible with previous experience from other fish species, and salmon fry and smolt can use this source of phosphorus very efficiently.
An excellent source for salmon smolt
“We have shown that salmon fry during start-up feeding and salmon smolt after release to the sea can both take up and use the phosphorus extremely well,” said Ms Albrektsen. “The results suggest, however, that salmon fry are slightly more sensitive than salmon smolt with respect to the neutralising agent that is used as buffer during the production. We need to examine this more closely, and it will be important in whether commercial production can be successful.
The phosphorus in fish bone hydrolysate can be absorbed from the intestines just as other readily soluble phosphorus salts used in salmon feed. The results for rate of growth, phosphorus digestibility and the amount of phosphorus from the feed that is stored in the fish all show that this is the case. Our experiments have also shown that the skeleton develops normally when the fish obtain sufficient phosphorus from the diet, and this is very important to avoid deformities in farmed salmon.”
Environmental and financial benefits
Phosphorus is a limited resource and Ms Albrektsen pointed out that we will have to find more efficient ways of using the resources we have.
“We have shown that upgrading bone raw material, which has sometimes been seen as hazardous waste from the production of fishmeal, has a large potential and may be enormously beneficial as an ingredient in feed. There are indications that fish bone hydrolysate has further positive properties, such as an ability to improve the digestibility of several other nutrients and to give improved growth. We plan to continue to work on this in order to understand fully the potential of the new ingredients.”
The method is not yet ready for industrial use, but Nofima is involved in the Forny project, with the goal of commercialising the new technology.
“We do know that the production process for acid hydrolysis requires relatively small and simple changes in a company, and the requirements for increased expertise to handle the new processes and product lines are also relatively small. The investment required is also reasonable, particularly if the new production lines are located at existing fish landing or fishmeal production facilities. The greatest investment is needed during the initial phase,” concluded Ms Albrektsen.
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