Early phases
Nofima carries out a lot of work with feed for marine larvae such as cod and halibut. Marine fish larvae are particular about what they eat and prefer feed that moves. Living crustaceans such as the rotifer Brachionus sp and Artemia (brine shrimp) are used as feed in the earliest stages but, owing to low nutritional value, they can often be enriched with extra nutrients. Nofima has a host of projects concerning enrichment with minerals, protein and fat.
It is desirable to supply food to the fish in dry form as early as possible. Nofima is involved in the development of transitional feed and grow out feed for salmon, cod and halibut.
As well as the fish getting sufficient energy to grow, it is particularly important to secure sufficient access to minerals so that the biomass develops in line with the muscle mass. Securing that all the essential nutrients are in sufficient supply for the fish is a demanding process. Nofima has found that there is a clear effect on development of deformities in fish which have received marginally too little phosphorous in periods of rapid growth.
Grow out phase
Salmon has a six-moth growth phase in freshwater before it is ready for transfer to seawater. It then weighs around 100 g and is referred to as smolt. After around two years in sea cages, the salmon has reached a weight of approximately 4-6 kg and is ready for slaughter.
The raw material situation today is such that there is an enormous need to find new and effective feedstuffs so that the use of fishmeal and fish oil can be reduced. There has also been steadily more focus on sustainability and resource utilisation, and a major effort is being made to develop more effective feed. The majority of feed used in aquaculture is used to feed large fish. As such, it is feed for large fish where the greatest opportunity to increase resource utilisation exists.
Pre-slaughter pigmentation
A goal for fish farmers is to produce Atlantic salmon containing a minimum 7 mg astaxanthin per kilo of fillet where this is regarded as sufficient to achieve an acceptable colour. However, this has shown to pose problems at certain times of the year.
The utilisation of the carotinoids in the feed is seasonally dependent. In Norway, temperature, feed intake and growth are the factors subject to seasonal variations.
Reduced pigmentation of muscle is often noticed in periods of the production cycle with very rapid growth. Fish that grow rapidly also have a high feed intake, which leads to the feed going quicker through the intestine, and there is consequently less time for absorption through the intestine wall of compounds such as astaxanthin. A low digestibility combined with rapid growth can lead to a dramatic reduction of carotinoid in the fish muscle.
When the feed intake increases, the relationship between the amounts of astaxanthin that is absorbed from the intestine and the growth rate decreases. Therefore, there is less available astaxanthin that can be deposited in the muscle per kilo of mass increase, which can explain the problems with achieving satisfactory pigmentation of muscle in periods of high growth. It is important to be aware of this and take it into consideration when you are planning the carotinoid levels in the feed for different stages of the life cycle, particularly in the period before slaughter. If you know when the periods of rapid growth take place, it would pay to ensure sufficient levels of pigmentation before these periods take effect as this may provide sufficient pigmentation by maintaining these levels through the growth spurt period.
There is a need for more research about the mechanisms that form the basis for the observed effects and what consequences these have in the end for the utilisation of astaxanthin. It is also important to establish how the combination of change in temperature and feed intake influences the digestibility and retention.
Seasonal variations
The seasons have a major influence on feed intake, fat accumulation and growth in the sea phase. Nofima is working on developing dynamic feed that is adapted for these seasonal fluctuations in a way that predictability and profitability in production increases.
When young salmon smolt is transferred from freshwater to saltwater, it enters a period of several weeks with reduced growth, and during this period the smolt is more susceptible to illness. The virus infectious pancreatic necrosis (IPN) is one of the major health challenges in the aquaculture industry, and it particularly strikes salmon smolt in the first weeks after transfer to seawater. Scientists at Nofima have found that one method to ensure the smolt has enough energy to fight off the disease is to add bioactive fatty acids to the feed. In trials with the bioactive fatty acid TTA (Tetradecylthioacetic acid), the fish that received the TTA had a mortality rate of 2.3 percent, compared to 7.8 percent for the group that received normal feed.
Further description
