The colour of farmed salmon has attracted so much attention within the aquaculture industry as it can be appreciated that the typical pink-reddish colour of salmon is symbolic of quality and value, with retailers demanding stringent criteria for farmed fish such as Atlantic salmon and trout to meet consumer expectations.

1. March | April 2012
Feature title: The Quest To Keep Salmon In The Pink Naturally
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2. FEATURE FEATURE
modulate various selected muscle quality achieve acceptable results. A minimum size Some evidence suggests reduced pigmen-
parameters, including the degree of pigmenta- threshold exists to initiate pigmentation in tation efficiency may result in fish fed diets
tion in salmon was noted by Nordgarden salmon and trout and maintain deposition with elevated plant oils over extended peri-
et al. (2003). These investigators concluded during the initial freshwater stages of growth ods during growth.
that rapid period of growth achieved under in fish of above 80-100 grams mean body However, consumer tests seem to indicate
The quest to keep continuous lighting compared to natural
photoperiod resulted in elevated growth of
weight. This extends with subsequent transfer
as smolts to sea water with salmon typically
that there are no significant differences in pub-
lic perception regarding the overall appear-
Salmon in the pink
salmon and increased oxidative stress with fed 65mg/kg total carotenoids either as astax- ance of salmon colour when fed diet regimes
marked reductions in fillet vitamin E levels anthin or in combination with canthaxanthin that include appreciable levels of vegetable
naturally
(a-tocopherol) and astaxanthin. with the latter not exceeding 25mg/kg in the oil sources to replace fish oils (Rosenlund et
mixture (EU directives). Maximum permitted al. 2003).
Environmental factors levels for astaxanthin in the USA is 80mg/kg This is of importance given the trend
Other environmental factors that may of feed (FDA, 2010). of using higher amounts of plant oil blends
affect the efficiency of pigmentation would However, revision of such levels is the for a major part of the production and the
by Simon J Davies, School of Biosciences, Plymouth University likely include water quality and flow rates that basis of much scientific activity to optimise strategy of using ‘fish oil’ enhanced ‘wash out’
England, UK would interact to modulate growth and nutri- their use and minimise wastage and cost. diets in the final stage to harvest to achieve
ent retention. Stocking density and exercise Over the last decade, feed manufactur- high omega 3 fatty acid concentrations in
T
are known to affect fish performance and ers have been able to significantly lower the the flesh of salmon prior to market. Quinton
he colour of farmed salmon has derivatives in the skin such as red sea bream viewed as conditionally essential nutrients for optimum fish stocking densities will produce inclusion of pigment in feed. Instead, it is rec- et al (2005) conducted trials with salmon to
attracted so much attention within and red tilapia (Gouveia et al, 2002). This is salmonid fish species. superior growth and feed conversion leading ommended by some, that a three-phase pig- ascertain the influence that genetics can play
the aquaculture industry as it can also a characteristic of high value and accept- Davies (2005) previously reviewed sev- to improved fish quality. mentation strategy with post-smolts being fed in affecting the absorption of dietary carote-
be appreciated that the typical ability to consumers who perceive this to be eral aspects of biochemical and physiological Similarly, adequate flow rates, water pigment at a relatively high level of 60-75mg/ noids, metabolism and the efficiency of flesh
pink-reddish colour of salmon is symbolic of superior compared to un-pigmented fish. parameters affecting salmonid pigmentation exchange rates will promote firmer fleshed kg with a transition to an intermediate level deposition.
quality and value, with retailers demanding The efficacy of flesh colouration by dif- with particular emphasis on post-prandial fish and may enhance pigmentation in of 40-50mg/kg from a body weight of 2-3kg These workers in Canada evaluated the
stringent criteria for farmed fish such as ferent carotenoids is a function of complex absorption kinetics and retention efficiency fish under intensive production systems as before a final regime maintained on a finishing genetic parameters in different year classes of
Atlantic salmon and trout to meet consumer physiological processes followed by a series of and explained that considerable amounts of described previously in relation to muscle diet prior to harvest of 25-35mg/kg of dietary Atlantic salmon reaching harvest.
expectations. biochemical events that involve metabolism astaxanthin and canthaxanthin is excreted by quality. Colouration and its relationship to carotenoids concentration (Sinnot, 2006). They determined sexual maturation char-
primarily in the liver as well as the intestinal fish and therefore efficiency of utilisation is flesh quality in farmed trout and salmon There are some scientific rationales for acteristics and associations to colour score,
Indeed this has often proved controver- tract (Page et al 2005, Page and Davies, 2006). quite low (~20 percent) compared to other was extensively reviewed by Davies (2008) supporting higher diet pigment levels in the astaxanthin, canthaxanthin, oil, and moisture
sial in the media when the farming of fish Evidence from the research investigations nutrients such as proteins, amino acids, vita- which addressed carotenoid function in fish later stages of growth for the feeding of large contents of flesh. Positive genetic correlations
has been criticised on many grounds with of White et al (2003a) suggests that a major mins and minerals. as well as the physiological, biochemical adult fish. This is based on the view that larger were found between body weight and with
negative statements alluding to the use of syn- fraction of absorbed astaxanthin is trans- There are many production related factors aspects and aesthetic attributes leading salmon can pigment more efficiently than pigment retention levels.
thetic agents and even dyes suggested as the formed into vitamin A in the intestinal tissue that can influence the degree of pigmentation towards optimal pigmentation of salmonid smaller fish. Since pigmentation develops quite Obviously, there is the scope to exploit
source of artificial colours being prominently of rainbow trout and most likely salmon as of farmed salmonids. These include species, fish. rapidly from post- seawater transfer, pigmen- more efficient stocks for their pigmentation
expressed by the misinformed. well. race or stock type, intra-population variation, Our knowledge of fish nutrition has tation rate generally slows down when fish get capacity using selective breeding programs.
Carotenoids comprise a complex group of In addition there is increasing evidence age of fish, type and quantity of carotenoids expanded considerably in recent times and bigger although the absorptive efficiency may Such findings could result in more even and
xanthophylls and carotenes, which are diverse that carotenoids are involved in gene regula- ingested over specific period, seasonal effects, there have been numerous investigations that actually increase. consistent flesh colour for salmon and trout
in their chemical structure to provide the host tion and signal transduction thereby affecting maturation, health and state of physiological have addressed the effects of dietary levels It is still therefore wise to promote a strat- and tailored to different production systems.
of yellow to orange red, and pink colours the entire metabolism of fish (Azzi, 2007; stress, dietary formulation, regulated feed dep- of both astaxanthin, canthaxanthin separately egy based on using higher levels in early phase
found extensively in nature as also or in combination on the flesh colouration of feeding with a reduction to a maintenance Less intensive conditions
seen in the plumage of birds such trout and salmon. level in fish approaching harvest. for farmed fish
as flamingos. The type of feed, level of feeding and Traditional use of commercially synthetic
The main carotenoids of matrix effects on carotenoid uptake will affect The impact of plant oils sources of astaxanthin in compounded feeds
importance to salmon and the degree of pigmentation in and can signifi- on pigmentation adds greatly to their costs and the value of the
trout are astaxanthin and can- cantly alter the colour characteristics resulting Choubert et al (2006) have reported that resulting products.
thaxanthin, which are specific in possible tainting with background colour. the pigmenting efficacy of astaxanthin fed to The annual sales of synthetic astaxanthin
in their mode of activity and An optimum dietary level of about 65-mg/ rainbow trout was affected by the composi- for aquaculture alone were estimated at more
in their manner of metabolism. kg astaxanthin is preferable in general to tion of dietary oil present. than US$200 million at 2010.
Astaxanthin is recognised to be
the predominant red carotenoid
found in salmonids in nature
with canthaxanthin also used
commercially to a more limited extent. Lordan et al 2008). They are also potent rivation periods maintenance feeding, slaughter Extruder OEE for the Production of Fish Feed
anti-oxidants that can interact with vitamin conditions, visualisation of colour, processing
A dietary requirement E (α-tocopherol) and can prevent fatty acid conditions: storage, smoking, cooking etc.
Salmon and trout do not possess the oxidation due to free radical generation within The high growth rates achieved in modern
inherent metabolic ability to synthesise these tissues. salmon production can result in a reduction of
pigments but instead require them within There are also positive benefits on the pigmentation and uneven distribution within
the diet as preformed molecules that are post mortem quality of fish under frozen stor- the flesh. It is well known that considerable
absorbed and subsequently deposited in tis- age conditions when fed high levels of caro- variations can occur in the ability of fish to
sues (Bjerkeng, 2000). tenoids thus prolonging shelf life of products retain carotenoids within the muscle and this
It should also be noted that pigmentation (Jacobsen et al (2011). In this way astaxanthin can sometimes manifest as very low pigmen-
AMANDUS KAHL GmbH & Co. KG, Dieselstrasse 5-9, D-21465 Reinbek / Hamburg, Phone: +49 40 727 71 0, Fax: +49 40 727 71 100
leading to the reddish-pink and orange colour and canthaxanthin have pro-vitamin and met- tation or indeed excessive levels in different info@amandus-kahl-group.de, www.akahl.de
of integument is also favoured for certain fish abolic functions well beyond their standard regions of muscle.
that can deposit carotenoids or metabolic role for pigmentation and could therefore be Indeed the fact that seasonal changes can
16 | InternatIonal AquAFeed | March-april 2012 March-april 2012 | InternatIonal AquAFeed | 17

3. FEATURE
Recently, however, there has been a grow- mentation
ing demand in the production of farmed fish to fish that
under less intensive conditions, and with deposit
more emphasis on natural additives and sup- these in
plements in the diet. As such, a number of muscle and
investigations have reported the feasibility of skin.
various single cell products such as the red The red
yeast Phaffia rhodozyma and Haematococcus carotenoid-
pluvialis algae with respect to their pigmenta- rich bacte-
tion ability compared to the synthetic form rium Paracoccus
currently available to the industry (Lagocki, carotinifaciens is
2001). permitted as a sensitive addi-
Investigations have confirmed that Phaffia tive for use in salmon and trout with a
can effectively pigment salmonid fish but only maximum content of 100mg, expressed fleshed
few products are currently available for this as the sum of astaxanthin, adonirubin and salmon in
purpose. Choubert et al (2006) found differ- canthaxanthin per kg complete feed. The the same manner as a wild salmon accumu-
ences with respect to the colour of rainbow current carotenoid composition of the lates pigment is a widely accepted principle
trout fed Haematococcus pluvialis compared product is specified as 3–5g canthaxanthin, advocated by a number of market surveys
to synthetic astaxanthin with higher reported 10–15g adonirubin and 20–23g astaxan- in which the pink flesh colour of salmon
colour and flesh retention. thin/kg. The applicant proposes to modify scores consistently higher as a desirable fac-
The prevailing consensus has been that the ranges of canthaxanthin to 1–5g, and tor second only to fish freshness (Baker, and
the synthetic commercial astaxanthin is read- that of adonirubin to 7–15g/kg product, Günther, 2004)
ily available for assimilation by fish, and is a while maintaining the astaxanthin range. In terms of feed costs it is well known
more stable and consistent product. The European Food Safety Authority (EFSA) that the added costs of including astaxanthin
It should also be noted that the astax- of the European Commission has expertly in feeds amounts to an extra 10-15 percent,
anthin present in H pluvialis is found as reviewed the terms of authorisation of the which manifests as an additional 4-6 pence
complex esters which confer different assimi- product for fish and verified its efficacy and per kilogram produced, that is a cost of
lation properties compared to other sources safety. UK£40,000-UK£60,000 per 1000 tonnes of
adding to variable results under practical Indeed a number of trials in Scotland production.
conditions (Bowen et al, 2002; White et al, by leading feed manufacturer’s and salmon In Europe, it is common practice to pig-
2003b), there is current interest in sea weeds producers have proved most encouraging ment rainbow trout to a defined level at por-
and extracts from macro-algae which can with favourable results obtained in produc- tion size although this is not so usual in the
contain appreciable levels of carotenoids as tion cages. United States where un-pigmented (white)
well as waste products from krill and shrimp Flesh pigment deposition and stability fleshed rainbow trout is more favoured by
processing. comparable to that of synthetic pigmentation the consumer. Several feed companies have
However, these materials are inconsist- regimes proved acceptable and quite compa- evaluated the costs of pigmenting rainbow
ent in availability and carotenoid levels may rable with orthodox products. The feedback trout towards harvest with strategies for
vary with seasonality. However, speciality received so far on fish pigmented with more economic approaches advocated by
seaweeds may have a promising future as Panaferd -AX® has been consistently good several feed companies and fish farming
feed additives combining functionality as from the retailer and consumer standpoint. operations.
prebiotics and contributing to natural caro- "To have all the colour in our salmon
tenoid intake. derived from naturally occurring organisms is Colouration is an emotive issue
the culmination of years of hard work," said The question of fish colouration in farmed
Algal and yeast sources managing director Nick Joy of Loch Duart aquatic species will always be an emotive
Despite the potential of both algal and salmon in Scotland who have been pioneer- issue since it is easily visualised and can be
yeast sources of carotenoids being able to ing the product in their bespoken feeds. measured by suitable techniques ranging
effectively pigment salmon and trout, these "As a farmer, I am proud that we rear form direct chemical analysis in feeds and
have been prohibitive in terms of their well-nourished salmon that look and taste flesh or by a selection of optical methods
considerable costs and variable qualities great," he has stated. based on colour scale assessments and
compared to synthetic products with consist- advanced image analysis.
ent characteristics. Consequently, an exciting Consumers and retailers The aquafeed industry and fish nutritionist
development is the product Panaferd-AX® are driving the agenda must be responsive and embrace the oppor-
produced by a leading Japanese company It seems that Panaferd® will benefit tunities for innovative products including
Nippon Oil Corporation. Panaferd-AX® salmon producers globally by offering oppor- natural pigmenting agents. With the need
contains the dessicated cells of Paracoccus tunities for diversification in the marketplace. to consider ‘organic’ certification for farmed
carotinifaciens, a soil-inhabiting bacterium Since the product has full FDA and EU fish and the quest for sustainable ingredients,
which naturally contains carotenoids. approval for use and is available for applica- research is needed to evaluate the efficacy
The bacteria are cultured by fermentation tion in the industry it’s likely to be used of carotenoids from a wide spectrum of
and have been selected to yield high caro- increasingly in main- stream production. potential sources.
tenoid concentrations without the need for It is the requirements of the consumer This will be a continuous challenge as
genetic modification. Although astaxanthin is and retailers that are driving the agenda and feed formulations become refined and as
the major pigment within Panaferd-AX®, it generating the need for more information in new candidate species become available for
can also express appreciable levels of natural this area with media attention to colouration aquaculture. ■
adonirubin and canthaxanthin. Both of these of farmed fish and crustacean species.
carotenoids can also support additional pig- The question of producing a ‘pink/ red’ References available on request
18 | InternatIonal AquAFeed | March-april 2012

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