Colour Enhancement of Ornamental Fishes through Application of Dietary Carotenoids
Colour is an important component in determining the market value of ornamental fish. The sale of fading ornamental fish fails to pique the curiosity of potential consumers. The value of the ornamental fish trade is predicated on the ability to produce healthy, appealing animals in a short amount of time. In this regard, as has been demonstrated for the cultivation of food fish species, special attention should be paid to feed formulation and nutritional aspects of ornamental fish in order to reduce feed conversion ratios, increase growth performance and survival rates, and also produce attractive colourful fish, all of which will ultimately affect the economic aspects. As a result, several research studies involving nutritional needs have been done, investigating the feasibility of using herbal and microbial additions; herbal additives, in particular, are important in feed formulation. Carotenoids are the most common major source of coloration in fish skin. This is a category of lipophilic chemicals that includes over 600 colours and is made up of C-40 based isoprenoid pigments. Carotenoids are split into two primary classes based on their chemical structure: carotenes and xanthophyll. Carotenes are hydrocarbon molecules that lack oxygen, whereas xanthophylls are oxygenated carotenoids that include at least one oxygen atom (Olson and Krinsky, 1995). The prominent members of the carotene group are βCarotene, α-carotene, and lycopene. The essential xanthophylls, including structural components of hydroxy and keto groups, include zeaxanthin, lutein, -and-cryptoxanthin, canthaxanthin, and astaxanthin (Stahl and Sies, 2005). Plants, phytoplankton (microalgae), zooplankton, and crustaceans can manufacture carotenoids; however, other creatures cannot synthesis them and must get them from the food or alter dietary carotenoid precursors through metabolic processes (Maoka, 2011). Carotenoid pigments can be deposited directly in fish chromatophore cells or transformed by cellular metabolism and applied to the skin and other tissues in an array of colours (Chapman and Miles, 2018). Carotenoid is an important nutrient (Craik, 1985; Grung et al., 1993) that is necessary for animal development, reproduction, and disease resistance (de Carvalho and Caramujo, 2017), and should be provided in all aquatic diets. Dietary carotenoid pigments and other competing physiological traits may be passed on from mother to offspring in carotenoid-adorned animals. Increased yolk carotene accumulation boosts offspring growth and survival, improves offspring immunity, and lowers offspring oxidative stress (Blount et al., 2002; McGraw and Ardia, 2003; BazyarLakeh et al., 2010). A lesser concentration of carotenoids will remain in maternal fish ornaments if a large quantity of carotenoids is contributed by maternal fish to offspring growth and survival (Sefc et al., 2014).
Aquarium keeping in home is considered as the most popular hobbies in the world and it is said to be 2nd largest hobby in the world. Indian waters posses over 250 indigenous varieties of ornamental fishes. Ornamental fishes have very attractive colour and peaceful nature and they are also known as ‘living jewel’. Colourations in fishes are highly correlated to their behaviour and habitat. Many fishes are exploited from natural environment or raised in confined environment only because of their colouration. This lead to the development of one of the most important industry called ornamental fisheries. Ornamental fish trade is a multibillion-dollar industry in which approximately more than 125 countries involved the trade. Singapore has been the ornamental fish capital of the world with an export value is US$42.97 million, contributing to 12.7% of the total exports in 2016. Till today it remains the main trading hub in Asia, with more than 30% of the fish exported having been sourced from other countries. The second position was occupied by the Spain with exports worth US$39.56 million in 2016. Among the top 10 importing countries in 2016, USA was the single largest importer of ornamental fish with an import value of US$56.57 million, contributing to 19.7% of the total imports in 2016. The UK occupies the second position with imports worth US$23.02 million. Export value for the Indian ornamental fish industry in 2016 was US$ 1.06 million and it contributed 0.3% of the total export. Import value for the Indian ornamental fish industry in 2016 was 192,511 US$ and it contributed to 0.1% of the total imports. India holds 66th position in the world among the importing countries. Each pattern and each colour could provide basic behavioural data about that fish species and give an idea about its mode of communication. The peculiar colour patterns in some fishes will help in performing mimicry and camouflage for their life and survival. The functions may vary like imparting ornamental value, helping for camouflage /mimicry (cryptic), giving warning coloration (aposematic) etc.
SOURCES OF COLOUR:
Colouration of fishes is due to the presence of two types of special cells called the chromatophores and iridocytes. The chromatophores are branched connective tissue cells situated in the dermis either above or below the scales. These cells contains varies kinds of pigment granules which may be carotenoids, melanin, flavines, purines, pterins, porphyrins and bile pigments. Depending upon the colour of the pigments the chromatophores are designated as erythrophores (red or orange), xanthophores (yellow) and melanophore (black). The carotenoids are obtained by the fish through its food, while melanin is the break down product of some amino-acids. Other shades like blue, green and brown seen in fishes are the result of suitable mixing of the above three kinds of chromatophores. The iridocyes contain a crystalline substance guanine which is opaque, whitish or silvery. It is a waste product and is deposited in the form of granules or rounded, polygonal bodies, or in the form of plates. These are opaque and posses great reflection power, so that the iridocytes may also be called the mirror cells. They give white or silvery appearance to the fish.
Sources of carotenoids: Natural sources carotenoids can be divided into two- plant sources and animal sources. Plant based carotenoid are mainly derived from micro algal pigments and other aqua feed formulation are Yellow corn, corn gluten, alfa alfa, and marigold. Algae such as Chlorella vulgaris, Dunaliella salina, Arthospira maxima and Haematococcus pluvialis are used in aquaculture as carotenoid source. Marigold contain astaxanthin which gives red or orange yellow colour; yeast contain canthaxanthin which gives orange colour; alfa alfa contain lutein, zeaxanthine which gives yellow orange colour; algae contain β – carotene, α- carotene which gives greenish yellow colour. Seaweeds are also considered as a good source of plant based carotenoid which contains beta carotene and fucoxanthin which yield greenish yellow colour. Carotenoids containing foods are often red, yellow or orange, but not always. Carrots, yams, potatoes, papaya, watermelon, cantaloupe, mangos, spinach, tomatoes, bell peppers and oranges are among the fruits and vegetable in which carotenoids can be found. Dose of carotene @ 125 ppm from plant source furnish admirable coloration. In rainbow trout higher doses ranging from 125 to 300 ppm further enriching coloration.
Shell fishes such as shrimp, krill, crabs, lobsters, etc. are used as potential animal based carotenoid sources. They also rich in mineral salts (15-35%), proteins (25-50%) and chitin (25-35%). Among the microorganisms, yeast (Phaffia rhodozyma) and fermentation product of Xanthophyllomyces dendrorhous are the widely used plant sources of carotenoid are the main astaxanthin source. These are the rich source of carotenoid astaxanthin which are added as an ingradiant in aqua feed formulation to enhance colouration in fish. Animal based natural carotenoids are limited in supply as there is declining trend in catches of crustaceans like shrimp, crabs, crayfishes, etc. Animal sources of carotenoids are very expensive and thus aquaculture feed production becomes costlier. Animal cannot manufacture carotenoids themselves, they have to get it in their diets. Carotenoids need to be consumed with a fat in order for the body to absorb them.
LOCATION OF CAROTENOIDS: In nature, more than 600 types of carotenoid have been determined. Carotenoids are localized in subcellular organelles (plastids), i.e. chloroplasts and chromoplasts. In chloroplasts, the carotenoids are chiefly associated with proteins and serve as accessory pigments in photosynthesis, whereas in chromoplasts they are deposited in crystalline form or as oily droplets. Some of the carotenoids such as the xanthophylls are involved in photosynthesis by participating in energy transfer in the presence of chlorophyll in plants.
Carotenes and their isomers:
Carotenes and their isomers: There are two broad classifications of carotenoids: carotenes and xanthophylls. The difference between the two groups is chemical: xanthophylls contain oxygen, while carotenes are hydrocarbons and do not contain oxygen. Also, the two absorb different wavelengths of light during a plant’s photosynthesis process, so xanthophylls are more yellow while carotenes are orange. Though fishes cannot synthesize carotenoids, certain fishes have the capacity to convert one form of carotenoid into another form.
Based on this capacity, fishes are classified into three types: 1. Red carp type: in this group litein is converted into asthxanthin. 2. Sea bream type: in this group of fishes litein and carotene remains in the tissues and cannot be transferred in any other form inside the bodies. 3. Prawn type: the beta-carotene molecule can be converted into astaxanthin molecule. Carotenoid occur in several isomeric forms, such as alpha (α), beta (β), gamma (γ), delta (δ), epsilon (ε), and zeta (ζ). Among the various carotenoids, α- and β-carotene are the two primary forms of carotenes. There are more than 600 types of carotenoids. The most common ones in the Western diet and the most studied, are alphacarotene, beta-carotene, beta-cryptoxanthin, lutein, zeaxanthin and lycopene.
IMPORTANCE OF CAROTENOIDS: 1. Vitamin A precursors: It is well-know that carotenoids have an unsubstituted – end group, such as -carotene, and the cryptoxanthin precursor of vitamin A in animals. Furthermore, canthaxanthin was also converted to retinol in some fish. 3- Hydroxy carotenoids: lutein, zeaxanthin and astaxanthin, were also reported to be precursors of 3,4-dehydroretinol (vitamin A2) in some fish. Astaxanthin, canthaxanthin and isozeaxanthin in addition to carotene were precursors for vitamin A in both guppies and platies. Astaxanthin, canthaxanthin and zeaxanthin were precursors of both A1 and A2 in rainbow trout (Oncorhynchus mykiss). 2. Communication: Many animals accumulate carotenoids in their integuments. Integumentary carotenoids may contribute to photoprotection, camouflage and signaling such as breeding color. Fishes change their appearance in response to background coloration and also display color responses during excitement and courtship (Fujii, 1969). The color pattern can be viewed as compromises between the need to communicate with other members of the species and the need to avoid being eaten. The internal control of color changes is complex and involves both hormones and nerves where the initiation comes from visual cues. 3. Reproduction and fertility: Aquatic animals also accumulate carotenoids in their gonads. Carotenoids are assumed to be essential for reproduction in aquatic animals. Astaxanthin supplementation in cultured salmon and red sea bream increased ovary development, fertilization, hatching and larval growth. In the case of the sea urchin, supplementation with -carotene, which was metabolized to echinenone, also increased reproduction and the survival of larvae. Marine pelagic cold water fish spawn large numbers of small eggs without visible carotenoid depositions, while demersal fish often have eggs containing high levels of carotenoids. The lack of visible carotenoids in transparent eggs may be an adaptation to minimize predation pressure. 4. Improvement of color in fish: Dietary supply of carotenoids can improve the skin color as well as market value of ornamental fish. The pigmentation of gold fish and koi carp is improved by addition of carotenoids and these fishes are found to be capable of metabolizing zeaxanthin to astaxanthin. However, gold fish lack the ability to metabolize lutein and have limited ability to convert β-carotene to astaxanthin. Skin pigmentation in tiger barb has been reported to increase when fed with diet containg carotenoids from shrimp meal, marigold and annatto seed extract. The blue green algae has also been used as a source of pigmentation for koi carp. 36-37 mg/kg astaxanthine in diet for intense colouration in gold fish found to be optimum and the supplementation significantly improved the survival rate. In red velvet swort tail, rainbow fish and topax cichlids the intensity of the coloration significantly improved when fed a diet containg 1.5-2% of a carotenoid rich strain of Spirulina platensis. A variety of carotenoids both synthetic and naturally occurring products are available or are being developed for use in aquaculture. Carotenoids developed from natural sources contain mixture several carotenoids like α-craotenoids, β-carotenoids, zeaxanthin, lutein, cryptoxanthin, etc. whereas synthetic precesses provides only specific carotenoids like β-carotenoids. Synthetic carotenoids are expensive and it has limitation to be used in aqua feed formulation depending upon the species. If used in excess synthetic carotenoids lead to deteriorating effect on the environment.
COLOURATION OF ORNAMENTAL FISHES: The fishes with colourful and diverse pigmentation patterns are called ornamental fishes and they are one of the most sought after pets of the world. However, colours and even its absence can have ornamental value e.g. Albino fish. Albino varieties of ornamental fishes have less melanin pigment or they lack melanin. Albinism in animals is considered as a pigmentation abnormality. The manipulation of colour in ornamental fishes has always attracted researchers. The methods used for the improvement in colouration are genetic engineering and nutritional supplementation of pigments.
CONCLUSION:
The most pressing issue for ornamental fish keepers and aquaculturists is the maintenance of the obtained skin colour once the fish are no longer fed. In 2017, Dananjaya et al., discovered that skin coloration of gold fish was unstable after 90 days of upbringing. There is a traditional approach for readily promoting skin coloration (Eslamloo et al., 2015), which involves growing ornamental fish in a tank or pond with carotenoid-rich algae and allowing the fish to develop the desired skin coloration. Although this procedure is straightforward, it does not ensure colour stability and can occasionally result in water quality issues. Fish skin colour may be modified by adjusting environmental factors such as light intensity, temperature, handling stress, and nutritional requirements (Gouveia et al., 2003). To completely understand the stability of fish coloration, more study is required. There is a scarcity of research on ornamental fish diet and colour enhancement. According to the findings, carotenoids are an essential component of the commercial ornamental fish sector. Natural plant sources can be harnessed and integrated in formulated diets for colour preservation or augmentation in confined environments due to the negative effects of synthetic carotenoids on aquatic environments. It will open up opportunities for the ornamental fish sector, as well as the colour enhancer feed industry and job creation.
Carotenoids are widespread and important pigment classes in the organisms as well as contributing characteristic quality criterion for marketing and consumer demands of aquaculture products. Appearance of an animal product, especially color plays an important role on the marketing. Color, nutritional value, healthy appearance, freshness and sensory test components are the elements to choose the product.
Compiled & Shared by- This paper is a compilation of groupwork provided by the
Team, LITD (Livestock Institute of Training & Development)
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