As a dietary supplement in aquaculture feed, Antarctic krill is a superior source of phospholipids, an essential part of the fish diet during the early stages of development.
As the saying goes, 'you are what you eat'- which is especially true if you are a marine fish. Fish feed impacts factors such as growth, survival and the overall health of the fish. Fish farmers today seek feeds with the right combination of nutrients that are also cost-efficient and sustainable.
The hunt for the 'super ingredient' shines the spotlight on Antarctic krill (krill meal) as a sustainable and nutrient-packed alternative to fishmeal.
The right nutritional balance is especially essential during the larval and early juvenile stages of fish development. Due to its high values of phospholipids, among other essential nutrients, krill meal (as part of the fish diet) can contribute to a growing and healthy fry. With krill in the diet, the larvae digestive systems show improved functioning, along with greater utilisation of lipids, which reduces the occurrence of intestinal absorptive cell injuries and reduces the fat accumulation in liver.
It's also important at this stage to increase stress resistance and survival rates of the larvae, which krill phospholipids do through the improved transport of fatty acids and lipids.
The phospholipid effect on larval and early juvenile marine fish
It was decades ago that scientists came to the consensus that phospholipids are indeed essential to fish development in the early stages of life. Phospholipids is a general term that includes all lipids containing phosphorus. They are structural components of cell surface membranes and the membranes within the cells, helping to maintain the strength, flexibility, and integrity of the membranes. In addition, phospholipids have the responsibility to carry long chain omega-3s eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) into the cell membranes. These ingredients provide flexibility to the cell and travel around your body bringing its benefits to various tissues and organs.
By adding a phospholipid source to the marine fish diet, scientific research reports better growth, increased survival rates and decreased occurrence of malformation in larvae, as well as increased stress resistance among developing fish. By adding krill phospholipids to the larvae and juvenile diets, the fish will exhibit enhanced lipid mobilisation in their livers and overall improved dietary lipid utilisation.
It is also apparent that the intestines of fish larvae and juveniles are better protected with the aid of krill phospholipids, which contributes to the overall health of the fish. Generally, the level of phospholipids required in the fish diet is around two to four percent for juvenile fish, with higher levels recommended for larval fish.
Over the years this beneficial 'phospholipid effect' has been tried and tested on various fish species, the general consensus from the scientific community being that phospholipids are a dietary requirement for developing fish. However, not all sources of phospholipids are created equal.
'Moreover, krill meal is a very interesting ingredient for developing feeds for new species with fast growth rates, such as Atlantic Bluefin tuna or meagre' explains Dr Mónica Betancor from the University of Stirling, who has long been developing feeds for new aquaculture species, adding that 'due to its favourable content of phospholipid, krill meal is a highly palatable and has a balanced amino acid source'.
Krill as a superior source of phospholipids in marine fish diets
Phospholipids sourced from marine species, such as Antarctic krill, have proven to be more effective than those sourced from plants. Generally, research shows marine-sourced phospholipids yield a higher nutritional value for the early development of marine fish larvae, in comparison with plant or soybean lecithin phospholipids.
During the early stages of development, when cell membranes, tissues and organs are rapidly growing, krill-sourced phospholipids play a key role and serve as energy sources for the developing fish.
When put to the test (against other plant-based energy sources), a krill-supplemented fish diet reveals improved growth, boosted skeletal mineralisation and reduced chance of malformation. In addition, studies have shown that krill in the diet stimulates better digestion, greater resistance to stress and, in juveniles, increased feed intake – hence, better growth rates. One of the reasons for the increased feed intake is due to the krill flavor, which marine fish find highly attractive, resulting in greater feed ingestion.
Ensuring absorption of essential nutrients
Krill is also a powerful source of omega-3 fatty acids, which are widely agreed to be essential in the fish diet. However, not all means of delivery of these essential nutrients are equally effective.
When comparing phospholipids versus triglycerides in terms of transporting omega-3s into the body, the phospholipid form of omega-3 shows better absorption by the body. This means that more omega-3s get into the cell membrane, which results in better functioning cell membranes and overall healthier fish. When krill is the source of omega-3 in the fish diet, the omega-3s are carried by phospholipids in the body, ensuring effective utilisation and absorption of this important nutrient.
Krill is also rich in astaxanthin, a natural antioxidant that protects tissues and cells. Astaxanthin plays an important role in the immune system development of larvae and early juvenile marine fish, as well as supporting the successful production of eggs and larvae. It's also the key to securing the reddish-pink colour that consumers find highly attractive in fish, such as sea bream.
Enhanced production of high quality and healthy fry is, of course, a key driver for the successful expansion of the aquaculture industry. Developing a better understanding of the mechanisms that control early development and growth is therefore critical, as it enables the key periods during development that introduce growth variation to be identified. Armed with such knowledge, growth can be maximised and the incidence of developmental disorders that have a negative impact on product quality can be greatly reduced.
Sustainably sourced super ingredient
The world's growing population continues to seek more sustainable sources of food.
According to the World Resource Institute, aquaculture is expected to increase its production by two million tons by 2050 to meet this future demand. This means that the production of the aquaculture food supply requires sustainable ingredients that do not sacrifice nutrition for cost reduction. One of the key sustainability recommendations is to make use of marine ingredients from the lower trophic levels in today's fish feeds.
Widely considered to be an attractive marine resource with a large and healthy biomass, Antarctic krill is that is currently under used, with catch-levels well below the limits. Through extensive research Antarctic krill has shown that it can contribute to the complete or near-complete replacement of fishmeal and fish oil in feed for marine fish.
To this point, the International Union for Conservation of Nature has recommended the inclusion of certified krill in order to reduce the use of fishmeal and fish oil, in order to produce more sustainable aquafeeds. It has even received an 'A' rating from the Sustainable Fisheries Partnership, and krill products from Norway-based Aker BioMarine were the first to receive MSC Certification in 2010, which was later renewed in 2015.
With its sound harvesting practices and strict governance, Antarctic krill has proven its value for more sustainable fish feed. It also contributes to healthier and overall higher quality fish products, as it not only delivers the powerful phospholipid effect, but it also secures essential and effective nutrients at critical stages of fish development. While the fish farmers' supply of fishmeal dwindles and becomes increasingly costly, they need to look no further than Antarctic krill to secure a more sustainable aquafeed and an overall healthier population of marine fish.
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