Krill: Biology, Ecology and Fisheries
`Edited by lni go Everson
`Copyright © 2000 by Blackwell Publishing Ltd
`
`Chapter 10
`Products Derived from Krill
`
`Stephen Nicol, Ian Forster and John Spence
`
`10.1
`
`Introduction
`
`Small—scale krill fisheries, which have provided sources of fishing bait and feed for
`
`fish culture, have developed in a number of regions (Fisher et al. , 1953; Mauchline &
`
`Fisher, 1969). In some areas these fisheries have grown into larger-scale operations
`
`(Nicol & Endo, 1997, 1999). Lately, a fishery for Antarctic krill (Eiiphausia superba)
`
`has been carried out on a large scale (Miller, 1991). The Antarctic krill fishery
`
`developed primarily because of the large size of the krill population and its apparent
`
`ease of harvesting, but development has slowed recently because of the high cost of
`
`fishing, and the lack of a suitable product, or products, with a reliable and effective
`
`economic return (Bykowski, 1986). Because most of the northern hemisphere krill
`
`fisheries were developed to supply localised markets for bait and for aquaculture
`
`feed, there has been limited development of new products from northern fisheries,
`
`until recently. In contrast, there has been a considerable effort devoted to producing
`
`a range of products from the fishery for Antarctic krill, and in developing a market
`
`for its products. The products of the Antarctic krill fishery have been reviewed a
`
`number of times (Eddie, 1977; Everson, 1977; Grantham, 1977; Suzuki, 1981;
`
`Budzinski et al., 1985; Suzuki & Shibata, 1990). We will concentrate primarily on
`
`recent developments in fisheries products and their uses.
`
`10.2 Constraints to using krill
`
`Introduction
`
`Krill are generally smaller in size than most other organisms that have been com-
`
`mercially harvested. Antarctic krill, with a maximum wet weight of approximately 2
`
`g, is the largest euphausiid that has been harvested, while the smallest harvested krill
`
`are of the order of 0.01-0.02 g (Nicol & Endo, 1997 Although other small species
`
`of crustaceans have been commercially harvested, and there are large fisheries for
`
`species such as sergestid shrimps (Parsons, 1972; Omori, 1978; Neal & Maris, 1985),
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`the small size of krill, and some of their biological characteristics, have made their
`
`harvesting and processing particularly problematic.
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`Rapid spoiling
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`The digestive gland in the cephalothorax of krill contains powerful hydrolytic
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`enzymes, including proteases, carbohydrases, nucleases and phospholipases, which
`
`begin to break down the body tissues immediately following death, particularly if
`
`crushing has occurred (Bykowski, 1986). Because these enzymes cohabit, they are
`
`mutually protected against
`
`their degrading effects, a property rare in nature
`
`(Anheller et al., 1989). These enzymes are controlled by an inhibitor system which is
`
`disabled on death, facilitating the rapid process of autolysis (Sjodahl et al. 1998).
`
`The characterisation of these enzymes has been most complete for Antarctic krill
`(Sjodahl et al., 1998), but there has been some research into the enzymes of
`Meganyctiphanes norvegica (Peters et al., 1998) as well. Because of the different
`
`trophic niches of species of krill, it is likely that they will possess different suites of
`
`enzymes, but it appears that most species, certainly those that are currently har-
`
`vested, all suffer from rapid spoiling as a result of autolytic processes (Bykowski,
`
`1986). Although this property of krill has its drawbacks for commercialisation, it
`
`also has been utilised in the development of commercial products (see later sec-
`
`tions).
`
`The level of digestive enzymes in krill is highest in those individuals that have
`
`been actively feeding. These animals have a distinct greenness in the digestive gland,
`
`which is associated with a ‘grassy’ flavour in krill products manufactured for human
`
`consumption (Bykowski, 1986). Actively feeding krill also contain more acids and
`
`some ketones, alcohols and sulphur compounds than non—feeding krill, and the
`
`presence of volatile compounds affects the odour of krill (Gajowiecki, 1995). For
`
`these reasons, green krill are avoided by the Antarctic fishery and the catch is
`
`graded on its quality by reference to its greenness (Ichii, Chapter 9). Charts for this
`
`purpose have been produced (CCAMLR 1993; Plate 2, facing p. 182).
`
`Krill proteins have a relatively high level of solubility, when compared to fish
`
`proteins, and this solubility increases with the degree of autoproteolysis (Kolo—
`kowski, 1989). This can present challenges in temporary storage prior to processing
`
`(Bykowski, 1986), when loss of soluble fractions can occur. The high solubility of
`
`krill proteins also has some advantages for producing certain types of end product,
`
`however (see hydrolysates in section on aquaculture feed additives).
`
`The lipids of E. Superba are subject
`
`to change during refrigerated storage
`
`(Kolakowska, 1988), with the critical factors being the time between capture and
`
`freezing and the temperature of freezing. Free fatty acids increase markedly fol-
`
`lowing death, and rapid deep freezing is necessary to maintain product quality.
`
`Bacteria
`
`The bacterial flora of Antarctic krill have been described, and their activity in the
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`gut may contribute significantly to spoilage (Donachie & Zdanowski, 1998), but
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`their abundance and role as krill symbionts is uncertain (Fevolden, 1981; Virtue er
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`al., 1997). They do seem, however, to play a smaller role in the post—capture
`
`breakdown of krill
`
`than do auto digestive processes (Rakusa—Suszczewski &
`
`Zadanowski, 1980). Bacteria have also been shown to have a digestive function in
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`M. norvegica, but the spoilage effect of bacteria on species of krill harvested at
`
`higher temperatures is unknown (Donachie er al. , 1995).
`
`Parasites
`
`Krill may be intermediate hosts of parasites, which can be passed on to other
`
`organisms that ingest them; this may be of particular importance when uncooked or
`
`unprocessed krill are used in aquaculture feeds. The issue of biosecurity has been
`
`viewed as the greatest threat to shrimp aquaculture, and there is particular sensi-
`
`tivity concerning the introduction of viruses in feed produced from other crusta-
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`ceans (Lotz, 1997). Nothing is known about the viral infections of krill.
`
`There is evidence that M. norvegica and Thyscmoessa raschii are important
`intermediate hosts of the helminth Anisakis Simplex (Hays er al., 1998). North
`
`Pacific euphausiids have a low level of occurrence of larval digeneans, cestodes,
`nematodes and acanthocephalans (Kagei, 1985), and such parasites were looked for
`
`but not found in Antarctic krill (Kagei er al. , 1978). Other symbionts of krill with less
`
`harmful potential have also been reported (Nemoto, 1970; Kulka & Corey, 1984;
`
`Nicol, 1984; Rakusa—Suszczewski & Filcek, 1988), but reports on studies examining
`
`parasitism in krill are rare.
`
`Fluoride
`
`The high fluoride content of the exoskeleton of krill was first indicated by research
`
`into E. superba (Soevik & Breakkan, 1979), but all other species of krill so far
`
`examined have been found to have similarly high levels (Sands er al. , 1998). It seems
`
`likely that high exoskeleton fluoride concentration is a general
`
`feature of
`
`euphausiids and that fisheries on krill will have to take this feature into account
`
`when assessing potential products.
`
`The fluoride in krill is localised in the exoskeleton, where it can reach con-
`centrations of 3500 ug F g”1 dry weight (Virtue et al. , 1995), but concentrations in the
`muscle and other internal tissues appear to be less than 100 ug F g’1 dry weight
`(Sands er al., 1998). Once krill die, however, there is very rapid leaching of the
`
`fluoride from the exoskeleton into the tissue (Adelung et al., 1987), even if frozen to
`
`—20°C (Christians & Leinemann, 1983). Freezing to temperatures lower than
`
`—3OOC is necessary to prevent migration of fluoride from the shell into the muscle
`
`tissue. Rapid peeling appears to be the most efficient way of separating the fluoride-
`
`rich shell from the flesh, although boiling also fixes fluoride in the shell (Bykowski,
`
`1986). The chemical form of fluoride in the shell is unknown but there are tech-
`niques which can produce a low fluoride (5-21 ug F g’1 dry weight) krill paste or krill
`protein concentrate by washing with organic acid or water (Tenuta-Filho, 1993).
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`Vertebrates that are fed on krill tend to accumulate fluoride to deleterious levels
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`in their bones and tissues (Krasowska, 1989) and the levels of this element in krill
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`meal are as much as four times the allowable levels in feed for the European
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`Community (Bykowski, 1986). Those animals with a natural diet that contains krill,
`
`however, appear to be able to maintain low tissue fluoride levels and tolerate high
`
`bone fluoride levels (Schneppenheim, 1980; Oehlenschlager & Manthey, 1982).
`
`Many fish species naturally eat krill and do not appear to accumulate fluoride in
`
`their tissues or bones, consequently, whole krill can be used as an aquaculture feed
`
`for many species without long—term accumulation of tissue fluoride (Grave, 1981).
`
`Despite many feeding trials on the use of krill meal for a variety of domestic
`
`animals, it seems that the high fluoride level of most krill meal, and its high cost,
`
`have prevented further developments in this area (Kotarbinska & Grosyzk, 1977;
`
`Oehlenschlager, 1979; Bykowski, 1986).
`
`10.3 Current uses of krill
`
`Introduction
`
`There has been considerable effort expended in developing Antarctic krill products
`
`for human consumption, but, most of the krill catch has been used for domestic
`
`animal feed, and, particularly in recent years, for aquaculture feed. The Japanese
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`Antarctic krill fishery, which takes most of the current catch, produces four types of
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`product: fresh frozen (46% of the catch), boiled—frozen (10% of the catch), peeled
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`krill meat (10% of the catch) and meal (34% of the catch). These products are used
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`for aquaculture and aquarium feed (43 % of the catch), for sport fishing bait (~ 45%
`
`of the catch) and for human consumption (~12% of the catch) (1999 figures, T. Ichii,
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`Japan National Research Institute of Far Seas Fisheries, pers. comm.).
`
`E. pacifica caught off Japan is used for sport fishing (~ 50% of the catch), feed for
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`fish culture (particularly as a reddening agent), and a small amount is used for
`
`human consumption (Kuroda, 1994). Most of the E. pacifica from the Canadian
`
`fishery is frozen for export to the US, Where it is used in the production of fish feed
`
`or pet food (Haig—Brown, 1994).
`
`The proposed fisheries for M. rtorvegica, T. inermis and T. raschii off the East
`
`coast of Canada are aimed at producing frozen krill. In addition, it is intended to
`
`produce freeze—dried krill for ornamental fish and for public aquaria and freeze-
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`dried krill as an ingredient in salmon feed and as a flavourant for food for human
`
`consumption (Nicol & Endo, 1997). E. mma caught off the Uwajima Bay, South
`
`East Japan, are used as feed for red sea bream (Y. Endo, pers. comm.).
`
`Yields in the manufacture of products from Antarctic krill vary from nearly 100%
`for krill hydrolysates, to 80-90% for fresh—frozen and boiled—frozen (Plate 6, facing
`
`p. 182), to 8—17% for peeled krill and 10-15% for meal. There has been research
`
`into ways of improving the efficiency of recovery in the Antarctic krill fishery and
`
`reducing Waste. Press waters and liquid by-products can contain significant amounts
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`of protein and lipid, which can be removed by filtration, enzymatic or biotechno-
`
`logical methods (Dolganova, 1994).
`
`Krill for human consumption
`
`Individual krill products
`
`Much of the available information on krill products for human consumption has
`
`been summarised in earlier reviews (Budzinski et al., 1985; Suzuki & Shibata, 1990;
`
`Plate 7, facing p. 182). Currently, 43% of the Japanese Antarctic krill catch is
`
`processed for human consumption as boiled then frozen krill or peeled krill tail
`
`meat frozen in blocks on board. Canned tail meat is no longer produced from the
`
`Japanese catch. Information on products for human consumption from the Ant-
`
`arctic krill fisheries from nations other than Japan is not generally available. In the
`
`past, Antarctic krill has also been used for the production of fermented protein
`products, for spun protein products (i.e. surimi) (Suzuki & Shibata, 1990). A small
`
`amount of E. pacifica caught off Japan is also being used for human consumption
`(Kuroda, 1994).
`
`Efforts have been made to produce low shell (hence fluoride) products. Krill
`
`paste produced by traditional methods (Budzinski er al. , 1985; Plate 8, facing p. 182)
`
`and alkaline and acid processed krill protein concentrates have been produced in a
`
`low fluoride form, by either organic acid washings or by simple water washings
`
`(Tenuta—Filho, 1993). Using either treatment, fluoride concentrations of less than
`21 ug g’1 (dry matter) were obtained, whereas untreated protein concentrates may
`have values of ~25O ug g’1 (dry matter) (Oehlenschlager, 1981). These processes
`yield high protein recovery and a product with low enough fluoride concentrations
`
`for human consumption.
`
`Considerable research has been carried out in Poland into producing krill pre-
`
`cipitates using autoproteolysis, making use of krill’s high level of proteolytic
`
`enzymes to produce a high yield (80% protein recovery) concentrate (Kolakowski
`
`& Gajowiecki, 1992). In this process, whole krill is mixed with water and heated.
`
`The hydrolysate is centrifuged to remove the shells and the precipitate is coagu-
`lated. The final product has low fluoride content (< 29 mg F kg’1), a protein content
`of 18-22%, fat less than 7% and a high level of carotenoid pigments, giving the
`
`precipitate a pink-red colouration. This product is used mainly as a colorant and a
`
`flavourant additive to fish feeds and other products for human consumption.
`
`Krill as 61 food additive
`
`Freeze-dried krill concentrate prepared from peeled tail meat is currently being
`
`marketed as a food additive and as a health food supplement by a Spanish com-
`pany.1 This ‘Antarctic Krill Concentrate’ is advertised as having a number of useful
`properties such as: high n-3 fatty acid content, moderate caloric content, high
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`nutritional value and ease of digestion, and is advertised as having a major revita-
`
`lising function on the body. Suggested uses of this product as a dietary supplement
`
`include during: pregnancy, lactation, pre— and post—menopausal stages, growth, post-
`
`operative procedures, cancer prevention, radiotherapy, chemotherapy, syndromes
`
`of immunodeficiency and treatment of various nutritional disorders. Antarctic Krill
`
`Concentrate is advertised by the manufacturer as containing important oligo—
`
`elements, including antioxidants and minerals required to prevent dental cavities
`and osteoporosis. The recommended dosage is approximately 5 g day’l. Antarctic
`Krill Concentrate is promoted as being 100% natural and free of any side effects,
`
`even when taken at higher dosages. The n—3 fatty acids in dehydrated krill products
`
`are reported to remain unaltered even if stored for longer periods, retaining all their
`
`beneficial properties.
`
`Antarctic Krill Concentrate is produced as flakes, or as a loose powder, with
`
`different degrees of granulation, and these have a light salmon—pink colour and an
`
`excellent shrimp—like taste. It is promoted as an excellent natural colouring and
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`flavouring agent, which is effective even in small quantities when used in a variety of
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`foods. It is claimed to be suitable for the production of special dietary meals and
`
`growth food products and requires no special storage conditions. Such specialty
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`products are likely to be of high value, but will utilise only small volumes of krill.
`
`Aquaculture feed
`
`Products
`
`The development of krill products for human consumption has been a focus of the
`
`Antarctic krill fishery in the past, but products for aquaculture are likely to domi-
`
`nate in the near future. Global aquaculture production more than doubled between
`
`1986 and 1996 and currently accounts for over one-quarter of all fish consumed
`
`(Naylor et al., 1998). Consequently, demand for quality aquaculture feed and feed
`
`ingredients is growing rapidly and supplies are uncertain (Rumsey, 1993).
`
`The existing or proposed coastal krill fisheries in the northern hemisphere have
`
`been developed to provide local sources of feed for aquaculture and there have been
`
`similar proposals in other areas, e.g. Nyctiphanes aL£StI’dliS in South Eastern Aus-
`
`tralian waters (Virtue et al., 1995, 1996). It seems likely that stocks of other species
`
`of krill will also be investigated once krill has become a more established aqua-
`
`culture feed. Currently, most of the krill caught in all the commercial fisheries is
`
`used for aquaculture feed. For Antarctic krill, 34% of the Japanese catch is fresh
`
`frozen and 20% of this is used for aquaculture and 32% is used to produce meal
`
`which is used in fish culture. Fifty per cent of the Japanese E. pacifica catch and
`
`much of the Canadian catch of this species is used as an ingredient in feed for fish
`culture.
`
`One company, Specialty Marine Products, based in West Vancouver, Canada, is
`
`planning a major project to harvest Antarctic krill for the burgeoning aquaculture
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`industry. The company currently markets limited quantities of krill hydrolysates
`
`(liquid and spray—dried) to the global livestock and aquaculture industries. The
`
`company expects to begin its sustained harvest programme during 2000. The krill
`
`will be processed on board the harvest vessels to ensure that the high standards for
`
`product quality demanded by the global aquafeed industry will be met.
`
`The use of euphausiids in aquafeeds has steadily increased in recent years (Nicol
`
`& Endo, 1997; Storebakken, 1988). Aquafeed manufacturers have been including
`
`krill products in feeds primarily to enhance the palatability of the feed, but krill is
`
`also a good source of astaxanthin, a carotenoid pigment which is used to give a
`
`characteristic red colour to some species.
`
`Krill is available commercially in a variety of forms for use in aquafeeds: as a
`
`meal, as frozen blocks of whole krill, and more recently as hydrolysates. Krill meal is
`
`produced by much the same methods used in the manufacture of fish—meal
`
`(Bykowski, 1986), Whereas krill hydrolysates are prepared by the partial enzymatic
`
`digestion of Whole krill under controlled conditions. Freeze—dried krill and krill
`
`hydrolysate have been used in fish feeds on an experimental basis, but their gen-
`
`erally high costs have precluded large—scale use.
`
`As with any ingredient, the freshness of the raw material and the type of pro-
`
`cessing influences the suitability of the final product for inclusion in feeds. This is
`
`particularly the case for krill, since many of the components that contribute to the
`
`flavour, as well as the pigments, are easily oxidised if exposed to excessive tem-
`
`perature during processing and drying. Typically, antioxidants are added prior to
`
`processing to reduce this loss and to preserve the lipid quality (D. Saxby, pers.
`
`comm.).
`
`Krill species have a number of features that make them attractive ingredients for
`
`aquaculture feeds (Anderson et al., 1997). These include: palatability enhancement
`
`of feeds; a source of carotenoid pigments; a source of essential fatty acids; a well-
`
`balanced amino acid profile; and an improvement of larval fish survival. To date, the
`
`suitability of adding krill to feeds has been tested with a wide variety of fish species,
`
`including: Atlantic and Pacific salmon (Salmo salar and Onchorynchas spp.); red sea
`
`bream (Pagms major); largemouth bass (Micropteras salmoides), eels (Anguilla
`
`spp.); yellowtail (Seriola qainqaeradiata); yellow perch (Perca flavescens); Walleye
`
`(Stizostedion vitream); Whitefish (Coregom/is Clapeaformis); sea bass (Dicentrarchas
`
`labrax); sea bream (Spams aarata) and Australian seabass (Lates calcarifer).
`
`Adding krill hydrolysates to aquafeeds, even at levels of only a few per cent by
`
`weight, make them more palatable (Forster, 1998), increasing feed consumption,
`
`resulting in higher survival and Weight gain. Using krill hydrolysate to improve
`
`palatability enables the production of feeds that include higher levels of inexpensive
`
`nutrient sources (e.g. plant and other protein sources) without affecting fish pro-
`
`duction (Oikawa & March, 1997
`There is considerable literature on the nutritional value of krill in cultured fish
`
`diets (Storebakken, 1988). All species of krill that have been examined are highly
`
`nutritious and can be used successfully as a source of protein, energy and flesh
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`pigmenting carotenoids for aquaculture species. Krill also contain a good balance of
`amino acids and are effective feed stimulants as well. Krill—fed salmon were also
`
`found to have a superior taste, but did not significantly accumulate fluoride from the
`
`krill exoskeletons in their flesh. This paper (Storebakken, 1988), should be con-
`sulted for a review of the earlier literature.
`
`Aquaculture feed additives
`
`In recent years, several studies have been conducted to examine the value of krill
`
`products in aquafeeds. The primary focus of this research has been to demonstrate
`
`the effectiveness of krill as a feeding stimulant. Krill is known to have a positive
`
`effect on the feeding behaviour of some fish. Shimizu et al. (1990) showed that diets
`
`supplemented with krill meal stimulated feeding behaviour in sea bream (Pagrus
`
`major) and that this effect was probably due to the presence of proline, glycine and
`
`glucosamine. Not only does krill stimulate feeding, it promotes growth in some
`species of fish (Allahpichay & Shimizu, 1985). The growth promoting factors seem
`
`to be steroids located in the cephalothorax region, and thus are available in non-
`muscle meal.
`
`The use of krill
`
`pacifica) as a food source for hatchery—reared salmon smolts
`
`has contributed to increased disease resistance (Haig—Brown, 1994). This is attri-
`
`buted to the early development of the immune system when using krill as a food
`
`source. The nutritive value of Nyctiphanes australis has recently been assessed with
`
`regard to its possible use as an aquaculture feed by Virtue er al. (1995). These
`
`researchers found that N. australis contained, on average, 52% protein and up to
`
`9.5% lipid on a dry weight basis. The lipid content of N. australis was marked by the
`
`presence of high quantities of unsaturated fatty acids with n—3 fatty acids accounting
`
`for 49% of the total fatty acid content. Carotenoids were present at levels of up to
`320 ug g’1 and were mainly (79.5%) in the form of astaxanthin. Fluoride levels were
`as high as those reported in other species of krill (up to 3507 pg F g’1).
`Krill hydrolysates are effective feeding stimulants in rainbow trout diets (Oikawa
`
`& March, 1997 A control diet containing a mixture of fish-meal (20% of diet), and
`
`plant protein sources (wheat (20%), soybean protein concentrate (10%), corn
`
`gluten meal (10%), and canola meal (22%)) was compared to the same mixture
`
`supplemented with 2% krill hydrolysate in replacement of fish-meal; and a third
`
`diet, which also contained 2% krill hydrolysate, but this was blended into the oil and
`
`coated on to the pellets. Krill hydrolysate significantly increased consumption of
`
`diets in this trial and reduced feed wastage. Fish fed the second diet, with 2% krill
`
`hydrolysate added, consumed 34% more feed and wasted less than half as much as
`
`those fed the control feed containing no krill hydrolysate, as a proportion of total
`
`feed input. This difference was even greater for fish fed the diet in which krill
`
`hydrolysate was coated on to the pellets. In this case, the fish consumed 69% more
`
`feed and again wasted less than half as much of the test feed, relative to those fed
`
`control feed. This study further indicated that, because fish fed diets containing the
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`krill hydrolysates consumed the feed more rapidly, they required less time to reach
`
`satiation than those that were fed the control diet. The growth rates of the animals
`
`followed the pattern of feed intake.
`
`Krill products have been shown to be very effective in stimulating feeding in fish
`
`that are in transition between life cycle stages. For example, weaning largemouth
`
`bass (Micropterus salmoides) from live feeds to commercial dry pellets is facilitated
`
`by feeding freeze—dried krill as a starter diet for four days (Kubitza & Lovshin,
`
`1997). Following transfer to seawater, feed consumption by salmon smolts is often
`
`inhibited, and it can take several weeks for full feeding to resume. Atlantic salmon
`
`smolts fed a krill hydrolysate coated feed have higher feed intake, better feed
`
`conversion efficiency (0.74 vs 0.87), faster growth, and lower percentage of ‘failed
`
`smolt’ than those fed a regular smolt feed (Santosh Lall of the Department of
`
`Fisheries and Oceans Canada, pers. com.). The results of these trials were used in
`
`the development of commercial smolt transfer diets.
`
`Protein and lipid content
`
`The protein content of krill is generally 60-65%, on a dry weight basis. The amino
`
`acid profile of this protein is very well balanced with respect to fish—meal and the
`
`requirements of cultured fish and crustacea (Table 10.1).
`
`The digestibility of the protein of krill products is variable. The controlled
`
`hydrolysis of many protein sources improves amino acid availability. A portion of
`
`the amino acids in krill hydrolysates is present either in free form, or as short—chain
`
`polypeptides, which tend to be more available than is intact protein. A comparison
`
`of in vitro protein digestibility of krill hydrolysate and two krill meals, one from a
`
`Japanese source and one from Russia, indicated considerable differences (I. Forster,
`
`unpublished results). The Modified Torry Pepsin Digestibility coefficients of the
`
`Japanese and Russian krill meals were 45 and 42%, respectively, while the diges-
`
`tibility coefficient of krill hydrolysate was 86%.
`
`Lipid levels in krill products range from 10-20% on a dry weight basis. Krill oil is
`
`rich in highly unsaturated fatty acids, most notably of the n-3 fatty acids (Table
`
`10.2). These fatty acids are especially prone to degradation by oxidation and care
`
`must be taken to ensure the freshness of the raw material and that appropriate
`
`conditions are maintained during processing, including the addition of suitable
`
`levels of antioxidants (Kolakowska, 1989, 1991b).
`
`Pigments
`
`Carotenoids levels in krill are around 30 ug g’1 and these appear to deteriorate
`rapidly during storage if not refrigerated below 0°C (Czerpak er al., 1980; Kola-
`
`kowska, 1988). E. pacifica contains large amounts of carotenoid pigments, especially
`
`astaxanthin. For this reason, up to 50% of the Japanese E. pacifica catch is used as
`
`an ingredient in fish feeds to add a reddish colour to the skin and meat of fish species
`
`Page 9
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`Page 9
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`

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`Products Derived from Krill
`
`271
`
`
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`
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`Page 10
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`272
`
`Krill: Biology, Ecology and Fisheries
`
`Table 10.2 Fatty acid profile of krill hydrolysate (E.
`superba)6.
`
`Fatty acid
`
`Liquid
`
`Spray-dried
`
`6Bi0zyme Systems, Inc. internal data
`
`such as red sea bream, coho salmon, rainbow trout, yellowtail, and others (Kuroda,
`
`1994). Extracts from Antarctic krill have also been successfully used as pigmenting
`
`agents for yellowtail and coho salmon (Fujita et al., 1983a; Arai et al., 1987). As
`
`Odate (1991) pointed out, red is traditionally viewed by the Japanese as an indi-
`
`cation of good luck and red sea bream and lobsters are often used as offerings in
`
`celebrations. Moreover, a reddish colour in fish meat is thought to stimulate the
`
`appetite.
`
`The principal pigment in krill is astaxanthin, although other carotenoid pigments
`
`are also found (Czerpak er al., 1980; Czeczuga, 1981; Yamaguchi er al., 1983;
`
`Kolakowska, 1988; Funk & Hobson, 1991). The level of astaxanthin can vary con-
`
`siderably among different krill products and species, but generally is between 150-
`
`200 ppm (dry basis) for E. superba, while E. pacifica can contain considerably more.
`
`Astaxanthin is present in free form, or esterified to either one or two fatty acids
`
`(mono- and di-ester, respectively). By contrast, synthetic astaxanthin, which is
`
`widely used in aquafeeds, is exclusively in the non-esterified form. The esterified
`
`forms of astaxanthin must be converted to the free form prior to being absorbed
`
`from the gut. Krill has been shown to be effective in pigmenting a variety of fish
`
`(Fujita et al., 1983a, b; Arai er al., 1987), although this has not always been found to
`
`be the case in salmonids (Foss er al., 1987; Whyte et al., 1998). Recent work with
`
`Atlantic salmon compared the bioavailability of astaxanthin from spray-dried krill
`
`Page 11
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`Page 11
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`

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`Products Derived from Krill
`
`273
`
`hydrolysate, krill meal and synthetic astaxanthin at levels in the experimental diets
`
`up to 50 ppm. The astaxanthin from krill hydrolysate was 91% available as the
`
`synthetic source (I. Forster, unpublished data), whereas the bioavailability of krill
`
`meal was much less. Astaxanthin is very susceptible to degradation from high heat,
`
`such as occurs during the manufacture of aquafeeds. In general, under these con-
`
`ditions the destruction is expected to be about 10-15%, and is about the same for
`free and esterified forms.
`
`Minerals
`
`Krill products are a good source of minerals for aquatic animals (Table 10.3).
`
`Recent work has shown that rainbow trout fed feeds containing krill as the principal
`
`protein source had significantly less dorsal fin erosion than did those fed the fish-
`
`meal based control feed (Lellis & Barrows, 1997). Fin erosion is a common problem
`
`among cultured salmonids, and may negatively affect survival, disease resistance,
`
`desirability among sportfish anglers and the commercial value of the fish. This
`
`beneficial effect of krill is thought to be derived from the balance and availability of
`micro minerals (Rick Barrows, US Dept. of Fish and Wildlife, Bozeman, Montana,
`
`pers. comm.).
`
`Table 10.3 The mineral content of krill hydrolysate
`(E. superba).
`
`Sodium
`Calcium
`
`Copper
`
`Phosphorus
`Potassium
`Sulfur
`
`Magnesium
`Zinc
`Iron
`
`7Bi0zyme Systems, Inc. internal data. Values are on a dry
`weight basis.
`
`Krill as shrimp feed
`
`Little work has been done to date, to investigate the potential of krill products in
`
`feeds for shrimp. Krill products also provide many of the nutrients known to be
`
`important for shrimp; e.g. amino acid, fatty acid and minerals. In addition, they are a
`
`good source of astaxanthin, and it is believed that they possess excellent olfactory
`
`attractant characteristics, which is of particular relevance to companies involved in
`
`the development of penaeid shrimp feeds. Much work remains to be done in this
`area.
`
`Page 12
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`Page 12
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`

`
`274
`
`Krill: Biology, Ecology and Fisheries
`
`Uses of krill in aquafeecls
`
`Krill products are added to feeds for aquatic animals in a variety of company and
`
`product specific ways. Some feed manufacturers add whole krill to the feed mixture
`
`prior to extrusion, in partial replacement of water. Other companies add dried krill
`
`by spraying a blend of the powder and fish oil on to the pelleted feed. Krill products
`
`(freeze-dried krill and krill hydrolysate) have been added directly to culture water
`
`to stimulate feeding of larval fish.
`
`A new product which uses the enzymes of krill to hydrolyse and liquefy krill,
`
`before pelletising and drying is being developed in British Columbia for salmon
`
`farming and may be applicable to krill fisheries elsewhere (Haig—Brown, 1994). A
`
`Canadian firm, Biozyme Systems, Inc., is producing these high value krill hyd