Education

Where there is Krill, there is a way

  • By Lena Burri and Geronimo Leonardi
    In Print: May,2021 issue

  • A lifeline with this powerful feed supplement which improves nutritional composition and attractability of plant- based or reduced fish meal feeds, and therefore growth and health of white shrimp.

The production of farmed shrimp is projected to grow by 5.4% between 2018 and 2021 - more than twice the recorded growth from 2012 to 2017 (Anderson et al., 2019). Despite this positive prediction, surveys identify that disease outbreaks and feed costs remain top concerns to further growth. Renewed outbreaks of Decapod Iridescent Virus 1 (DIV1) continue to threaten shrimp farming in China, according to seafoodsource.com and fish meal supply continues to decline whilst prices increase with demand (FAO, 2020; Sherrard, 2019). This directs new attention at plant-based aquafeeds as more sustainable alternatives (Tacon et al., 2010). To be a viable option, however, these alternative feeds need to measure up to traditional fish- based feeds in terms of zootechnical performance and environmental footprint of feed production and farming activity. Purely plant-based feeds suppress feeding stimulus because of antinutritional factors, a lack of chemoattractants and a poorer match between the amino acid profile of the feeds and the nutritional requirements of shrimp (Figure 1). Such feeds can severely impair shrimp growth and therefore curb production. Fortunately, the supplementation of plant-based shrimp feeds with krill meal has shown promising results by circumventing the nutritional deficiencies of a plant-based diet, whilst increasing shrimp growth and survival (Nunes et al.,2019; Suresh et al., 2011).

Figure 1. Essential amino acid profile (as g/100g-diet) of plant- based diets that do not contain fish meal or other animal-based protein sources (green line) with 3% fish meal (blue line), or with no fish meal and krill meal supplementation (orange line; krill meal inclusion at 110g/kg). Krill meal supplementation in no fish meal diets results in an equally high feed nutritional profile. Source: Moreno-Arias et al. (2018) for plant-based diet profile, and Nunes et al. (2011) for the fish meal and krill meal diet profiles.

Antarctic Krill fisheries

Krill meal is produced from Antarctic Krill (Euphausia superba) found in the Southern Ocean around the frozen continent. Krill survive their first winter living in the water column on the underside of sea ice where they feed on the available microscopic algae. Adult krill are shrimp-like in appearance, but, in contrast to their bottom-dwelling crustacean relatives, krill inhabit the open ocean. Here, krill aggregate in swarms of up to 20km in length where they feed on microscopic algae during the day and migrate to greater depths during the night to evade predators. Krill appear transparent with some red and green colouration. The red colour is caused by the carotenoid pigment astaxanthin embedded in chromatophores. The crustacean can change the size and intensity of the red spots to balance the need of UV protection closer to the ocean surface with higher transparency for camouflage (Auerswald et al., 2008). The green colour is observed in their digestive system and underscores their reliance on an algal diet. In fact, krill can consume up to 20% of their own body weight per day but can also survive for up to 200 days without food. During the Antarctic summers, when photosynthetic algae bloom, the sheer abundance of krill makes it one of the largest protein sources on Earth - a source eagerly sought by fish, whales, and humans alike.

Antarctic krill is exclusively caught in area 48 off the Antarctic peninsula and limited to 1% of the total estimated biomass in that area. Over the last 3-4 years, the total catch ranged between 230,000 to 390,000 tonnes annually; this represents only approximately 0.3% of the unexploited biomass. While annual variability in sea ice cover causes variation in recruitment, the estimated biomass of krill has increased from 60.3 million tonnes, as measured in 2000 to 62.6 million tonnes in 2018-2019, according to findings from the Commission for Conservation of Antarctic Marine Living Resources (CCAMLR). The conservative catch quota and trends in biomass ensure that krill stocks are amongst the best managed and underutilised marine resources to date.

Krill Meal is the superfood among Aquafeeds

Supplementation with krill meal has been known to improve aquafeed quality since well over a decade (Yoshitomi et al., 2007). Yet, the stagnating and even declining fish meal production from capture fisheries reinforces once again the need for a more sustainable protein source for the shrimp farming industry. Besides, a better understanding of nutrient requirements of shrimp has renewed the interest to look for alternative feeds and supplements that boost shrimp production and quality (Auerswald et al., 2008). Krill meal is uniquely suitable to meet these challenges. After processing, the brownish – orange Krill meal powder contains roughly 60 % protein with nutritionally well – balanced amino acid profile (Figure 1) and a long list of feed effectors, including chitin, astaxanthin, nucleotides and phospholipids (Sabry – Neto et al., 2017; Derby et al., 2016). Such feeding effectors increase feed attractability and palatability, lower feeding latency time thereby reducing nutrient leaching and feed wastage, and consequently reduce overloading ponds with excess nutrients.

“ On top of that, the main phospholipid contained in Krill meal - phosphatidylcholine not only supplies omega – 3 fatty acids, but also choline. This is a rare but vital vitamin like that supports neurotransmission and osmoregulation. ”

Additionally, the dietary properties of several of these feeding effectors enrich krill meal to allow shrimp to cope with stressful situations (e.g. high plant-based diet, salinity, or temperature changes). For instance, chitin may play a dual role as a feeding attractant and immunological stimulant to resist infections (Wang and Chen, 2008). Similarly, the antioxidant astaxanthin pigment has anti-inflammatory properties.

In contrast to fish meal, where omega-3 fatty acids are bound to triglycerides, these fatty acids in krill meal are neatly packaged with phospholipids. This in turn means omega-3 fatty acids from krill meal are effectively incorporated in tissue (Rossmeisl et al., 2012). On top of that, the main phospholipid contained in krill meal - phosphatidylcholine - not only supplies omega-3 fatty acids, but also choline. This is a rare but vital vitamin-like nutrient that supports neurotransmission and osmoregulation. This combination of chitin, astaxanthin, dietary phospholipids, omega-3 fatty acids, and other attractants allow shrimp to resist stressful farming conditions, while improving health and growth (Figure 2).

Figure 2. Benefits of incorporating krill meal into aquafeeds.

A case for Krill

The importance of this potent combination of nutrients in krill meal as a dietary supplement for the shrimp farming industry has been made clear in several, recent scientific studies. Initially, the protein, lipid and nutritional values of fish meal, fish oil, soybean lecithin and cholesterol were proven to be replaceable by including krill meal with no costs to performance of white shrimp, Litopenaeus vannamei (Nunes et al., 2011). First, Suresh et al. (2011) showed that blue shrimp Litopenaeus stylirostris fed a diet containing a high level of poultry by-product meal with a mere addition of 3% krill meal reached a comparable final body weight to those fed a purely fish meal-based diet. Later, Nunes et al. (2019) devised a study to compare growth performance of L. vannamei reared on a high plant-based diet with a stark reduction of fish meal content to only 3%. The diets were then supplemented with either 3% krill meal or six different marine chemoattractants. After 74 days, the final body weight was highest in shrimp fed the krill meal-supplemented diet (Figure 3). Feed conversion ratio was also lowest for shrimp fed with krill meal (1.31±0.05).

Figure 3. Final body weight of Litopenaeus vannamei juveniles fed with a soybean-based plant diet (negative control) supplemented with either 3% fish meal (positive control), krill meal or five other chemoattractants (except for sardine hydrolysate which was included at 5%) over 74 days. Different letters denote statistically significant differences between experimental diets (P<0.05). Source: Nunes et al. (2019).

In both studies the authors also assessed feed preferences. In the pairwise comparison, Nunes and colleagues fed shrimp with an excess of different feeds simultaneously twice a day over a total of 10 consecutive days. Leftover feeds were dried and compared. White shrimp clearly preferred krill meal and shrimp head meal supplemented diets over the other dietary supplements. Interestingly, in direct comparisons between shrimp head meal and krill meal, L. vannamei preferred the shrimp head meal-based diet. However, final body weight, growth, yield gained, and survival of the group fed with shrimp head meal were lower than that of shrimp fed a krill meal diet. A possible explanation could be the high presence of the biogenic amines cadaverine, putrescine, and tyramine in shrimp head meal, all known feeding attractants. Yet, these findings indicate that feed attractability alone does not necessarily make up for the poorer nutritional quality of the feed. Importantly however, these results emphasise the advantage of krill meal supplementation over other dietary supplements in a reduced-to-minimal fish meal-based diet.

A study by Sabry-Neto et al. (2017) went one step further removing fish meal altogether. The researchers reared L. vannamei on either a plant-based diet with no krill added or four additional diets with gradually increasing levels of kill meal supplementation (0.5, 1, 2, and 3 %). Amongst these feeds the main dietary protein came from soybean meal- an all in all more sustainable source of protein than traditional fish meal diets. The addition of krill meal was predicted to overcome the anti-nutritional factors and nutritional deficiencies of such a pure plant-based diet. The results showed increased feed intake at 1% krill meal inclusion and significantly improved shrimp growth, with improvement in gained yield, feed intake and feed conversion ratio with 2% or higher krill meal inclusion.

Figure 4. Effect of krill meal inclusion (1, 2 or 3%) on Litopenaeus vannamei growth, gained yield and feed intake. Results are shown as percentage increase compared to the control plant- based diet without alternative ingredients or feed additives. Source: Sabry-Neto et al. (2017).

Figure 5. Differences between R- and B-cells in the hepatopancreas of shrimp fed non-krill meal supplemented diets and 2-6% krill meal-supplemented diets. The cell enlargement suggests improved digestive enzyme production, nutrient absorption, and lipid/glycogen storage functions.

Shrimp growth and yield increased by an additional 16.3% and 20.1%, respectively, with a maximum survival of 99% at a 2% krill meal inclusion, when compared to the 1% krill meal inclusion (Figure 4). The study concluded that a minimum of 2% of krill meal in a plant-based diet enhanced all the major shrimp performance parameters with no costs to survival and health.

Figure 6. Impact of Krill meal inclusion in feed cost in India, one of the world’s key shrimp production areas (dietary treatment with 12 % fish meal and different Krill meal inclusion rates). Different letters denote statistically significant difference between experimental diets (P<0.05). Source: Aker Biomarine Antarctic AS.

Burri et al. (2020) supports these findings further. The authors compared a high fish meal diet (20% tuna meal) with a highly reduced fish meal diet (7.5%; negative control) and, additionally, three levels of krill meal supplementation (2, 4 and 6%). Aside from the recurring trends of higher yields, increased weight gain and growth, when shrimp were fed krill meal, the histopathology of the hepatopancreas showed improved development of healthy star-like tubules with enlarged epithelial cells in shrimp fed with krill meal only (Figure 5). The different epithelial cells of hepatopancreas play important roles in nutrient absorption and storage as well as protein synthesis and, by extension, immunity. The superior performance of shrimp fed with krill meal enhanced diets may therefore stem from improved physiological development. Crucially, the authors highlighted that improved shrimp health and performance through krill meal supplementation can be achieved at no additional economic cost (Figure 6) and substantially reduced fish meal inclusion.

Conclusion

Krill is naturally abundant and nutritionally rich. Unsurprisingly, therefore, krill meal acts as a powerful feed supplement improving nutritional composition and attractability, and hence enhancing growth and health in shrimp. Krill meal supplementation throws a lifeline to an industry challenged by reduced fish meal availability at increased costs and nutritionally inferior plant-based feed alternatives. Moreover, increased yields at comparable feed costs result in a net profit in production and revenue (Figure 6). This was highlighted in a recent study by Leonardi and colleagues (submitted) that compared shrimp performance and economic viability of a control diet relying heavily on fish meal-derived protein and an experimental diet, that instead, used less fish meal and included high- protein krill meal. Both feeds were comparable in terms of feed price, but because the krill meal supplemented diet produced a much higher yield, the cost of the 3% krill meal supplemented feed (USD 1.08 / kg shrimp) ended up being lower than the cost of the feed with higher fish meal content (USD1.19/kg shrimp). Since Antarctic krill is protected from overfishing by CCAMLR and Aker BioMarine Antarctic AS has obtained the Marine Stewardship Certification to prove sustainable fishing. QRILLTM Aqua is an attractive shrimp feed ingredient that maximises feed performance in a sustainable manner and increases profitability of shrimp farming overall.

ABOUT AUTHORS:

Dr. Lena Buri is Director R&D, Animal Nutrition and Health at Aker Biomarine AS.

Mr. Geronimo Leonardi is Sales Director – Latin America, based at Aker Biomarine AS.

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