Farmed Salmon Diet Research

Two years ago NZ King Salmon Ltd initiated a $5.2 million, four-year research project into the specific dietary requirements of King salmon, also called Chinook salmon, farmed predominantly in New Zealand. That trial work had never been done before specifically for King Salmon. The project partners are NZ King Salmon, Seafood Innovations Ltd (SIL), Cawthron Institute, the Nelson Marlborough Institute of Technology and the Danish aquaculture feed company BioMar. Funding comes half from commercial partners and half from SIL, a research partnership supported by the Ministry for Business, Innovation, and Employment. The trial work is being done at the Cawthron Aquaculture Park, in Nelson. 

NZ King Salmon is the largest producer of King salmon or Chinook salmon, in the world, with around 55% of NZ salmon production and 40% of world production. It is a high quality salmon, with high levels of healthy Omega-3s and superior culinary attributes. NZKS revenue is around $150m annually, from whole fish sale prices between $17-24/kg, and sales 50% whole salmon and 50% value-added. Target harvest weight is between 4kg and 4.2kg, bled and gutted, when the fish will have spent 6 to 12 months in freshwater hatcheries, followed by 16 months in sea cages. One third of revenue is spent on feed and labour costs (called “cost of fish harvested”) and the imported feed is the biggest single expense in salmon aquaculture. 

King salmon may share the same name with Atlantic salmon (which accounts for a majority of world farmed salmon) but it is closer genetically to Rainbow trout. King is the largest species of the Pacific salmon family (including Sockeye, Coho and Pink) and has the best taste, texture and nutritional quality. 

All the trial work is done with King salmon at the Cawthron Aquaculture Park research facility at Glenduan, Nelson. There, in a series of outdoor tanks, fish are grown from approximately 1.5kg to 3kg-plus over 60-120 days periods, and then weighed, measured and sampled for the results. The team takes fish of known parentage and various sizes and intends to improve the digestibility of the food they are given, thereby to improve the feed conversion ratio. 

Kevin Heasman is an aquaculture scientist, and lead researcher at the Cawthron Institute. He explains the system can control; temperature, water quality, oxygen content, etc., which enables researchers to do away with as many variables as possible. The aim is to leave the only variables as food ingredients and intake, in terms of weight, frequency of feeding and the time of the day. The composition of feed is very important, containing different minerals and vitamins, and the 10 essential proteins needed by the fish. “The number of variables makes it a complex trial to undertake, but it is also exciting to attempt,” Heasman says. 

Fish of known parentage reduces the amount of genetic variation in the trial fish. Transition from fresh to sea water changes the physiology of the fish, and as they grow their energy to protein requirements change. Fish are among the best food conversion ratios (FCR) of the main domesticated animals for meat/fish production – 1.7kg of feed to 1kg of fish, comparable with chicken at around 2, and 3-4 for pigs, 5-6 for lambs and 6-plus for beef cattle. 

Fish are efficient converters of feed to flesh because they are cold blooded and live in a weightless environment. 

King salmon in aquaculture have a mainly vegetable-based feed, containing energy and proteins, which are the building blocks of muscle, especially the right balance of the 10 proteins that fish cannot make for itself. Not enough energy in the feed means protein breakdown from muscle and too much energy goes into fat, which is a wasted product. 

International nutritionists participate in the trial and different feeds from different manufacturers are available, including bespoke feed, if needed. 

Essentially the Cawthron salmon sustainability trial is looking at the optimum growth rates for the lowest feed intakes. An improved FCR will also reduce the feed wastage, for a better environmental performance for the hatcheries and sea farms. 

The project team weighs samples of the feed pellets, total feed given to the known number of fish, by tank, deducts uneaten pellets, and then weighs the fish and takes measurements, and then slaughters a sample for various protein and fatty acid composition figures, to work out daily growth rates and food conversion ratios. 

Heasman said the trials needed to be long enough for the fish to double in weight, say from 1.5 to 3-plus kilograms, which is a sample size, and that would take between 60 and 110 days.

That length of time and weight gain was considered meaningful in terms of food conversion efficiency, he said. Trials start at different ages of fish because their dietary requirements change with age. 

Salmon farming is a relatively new industry and R&D has been a priority. Cawthron got a 2016 MBIE grant to look at the relationships between fish genetics and feeding requirements, among other things. It is a $13m, 5-year project called Improving Chinook Salmon Feed Efficiency for Industry Growth. It is additional to the $5m King salmon sustainability trial. 

Currently global suppliers produce feed based on environmental and economic considerations for the Atlantic salmon species. NZ King Salmon chief operating officer Rubén Álvarez said the company was committed to best practice and the highest quality product and that drove the need to fully understand the species’ dietary requirements. 

“I came to New Zealand with a background in farming other salmon and trout species around the world and was prepared to apply that knowledge to growing salmon here. I immediately realised we were lacking detailed dietary information on King salmon. Although the unique qualities of the King salmon are an advantage for us in our sales and marketing activity, it also means that information based on the nutritional needs of the more common species is not always applicable and R&D for King salmon is not a broader industry priority. It was obvious that if we didn’t drive this research, it would not happen.” 

For NZKS the aim of the world-first study is to develop a high-quality, species-specific feed that improves vastly on the generic products currently available. This is a fine-tuning exercise to further improve on the diet, NZKS fish health manager Mark Preece says. Fish had been bred for weight gain and eating characteristics and they now needed a diet that optimised the breeding programme. 

Over the past 18 generations of approximately 100 breeding families, NZKS has made considerable progress. Potentially, another 10% gain in food conversion efficiency would be worth big money to the company. Preece says there was a wave of growth in aquaculture around the world, because of the food conversion efficiency, and NZKS operated at the top end, based on the quality and prices paid for King salmon. 

As project partners learn more, extensions of the project are possible. Currently it will run to the end of 2020.