Aquaculture is one of the booming sectors. For enhanced productivity, higher stocking density in an intensive culture system requires exogenous feed to satisfy all the essential nutrients to the cultured animals. Nutrition is a complex and meticulous branch of science. In order to have a complete feed, certain additives are added to enhance the quality of feed, and one such additive is the carotenoids; you may be familiar with this if you are knowledgeable in Salmon farming.
Research Scholar
M.F.Sc, ICAR-Central Institute of Fisheries Education, Mumbai
Research Scholar
M.F.Sc, Department of Aquaculture, TNJFU-FCRI, Tuticorin, India
Studies on carotenoids started during the 19th century. Carotenoid was discovered long back from the roots of carrot (Daucus carota), and the word carotene was named after the carrot from which it was isolated. Beta–carotene was the first type of carotenoid discovered by Wackenroder during the year 1831, and later other types of carotenoids also came into the picture.
WHAT ARE CAROTENOIDS?
Carotenoids are lipid-soluble compounds also called tetraterpenoids which means they have eight isoprene units containing conjugated double bonds. Their structure lacks nitrogen. They are more than 750 types found in nature, with the availability of more than 100 million tons/year. Carotenoids can capture light within the range of 400-600nm (visible region) of the electromagnetic spectrum. The backbone for this structure comes from the C40 polyene chain. Colour intensity increases with the increasing number of double bonds ranging from yellow to red. Hence it should have at least seven conjugated double bonds in its structure to impart colour. Absorption spectroscopy is a powerful analytical instrument used for carotenoid analysis.
CLASSIFICATION:
Most of the compounds are found in trans configuration in natural foods. Based on the presence of oxygen in their structure, they are classified as (Major classification)
CAROTENOID -A SIGNIFICANT BACKBONE TO THE AQUAFEED INDUSTRY:
The sensory characteristics highly influence the price of the cultured fish, and people generally perceive comparing the overall quality with the wild stocks of the same species. One such prominent example is the texture colour of Salmon from the wild, which have pink-red colouration because of the rich natural food available in the ocean. In the case of cultured Salmon, it should be supplemented through diet in the form of Astaxanthin. Dietary supplementation to the Crustacean provides colouration to the cuticle during cooking.
Some species like Crustacean can convert beta-carotene to Astaxanthin, whereas species like sea bream are incapable of bioconversion but can use dietary supplementation. `Example Tuna-xanthin (Yellow) are common in fishes like scombrids, Freshwater fishes like pangasius flesh can be sometimes yellow in colour, mainly due to the accumulation of lutein and zeaxanthin, which is derived from the ingredients like corn in the feed. Generally, most consumers like the mild-white fillet of Pangasius over the yellow fillet. Crustacyanin is a combination of carotenoid+ protein (Carotenoprotein), which gives a blue colour to the live lobster, however heat applied during cooking, cleaves the caroteno-protein and gives a red appearance to the cooked meat.
Ornamental Fishes are globally admired for their fascinating colour; the Colour intensity of fishes determines the customer preference and value. For instance, Goldfish reared in the open pond are generally brighter than the Goldfish reared in captivity. It was found that astaxanthin supplementation @ 36-37mg/kg diet to Goldfish improved the colouration and survival rate. Hence whenever you are feeding your pet fish, make sure you provide carotenoid enriched feed or go for live feeds such as freeze-dried blood worms/Tubifex worms. It was reported that the inclusion of canthaxanthin @ 0.005 % improved the colour of Trichogaster leeri (Fey and Mayers 1980). Small fishes generally accumulate the carotenoids on their skin. As the fish ages, it gets stored in the muscle. Live feeds such as micro-algae, copepods are rich in carotenoids which shows they are the ideal feed for larval rearing. Nowadays, synthetic carotenoids, produced from petrochemicals, are used, which do not exist in a mixture like a natural one and possess only specific carotenoids; however, they are expensive and possess residual problems.
METABOLISM OF CAROTENOIDS:
Being a lipophilic compound, dietary lipid has a massive role in the digestion and absorption of carotenoids at the enterocyte brush border inside the animal’s body. It takes around 18-30 hours for 35% astaxanthin to be absorbed in salmonids. Hence increase in lipid in the diet improves the astaxanthin bioavailability. Carotenoids are transported across the body as LDL cholesterol. Carotenoids are generally accumulated in fish integuments and gonods; in salmonids, it accumulates in muscle. The digestibility coefficient is the greatest for the Astaxanthin than any other form of carotenoids.
CAROTENOID AS NUTRACEUTICAL:
Nutrition+ Pharmaceutical=Nutraceutical. Yes, carotenoids are added as the additive to the feed; however, these compounds can also be referred as Nutraceuticals because of their health benefits to the aquatic animal. Their robust antioxidant activity is mainly due to the presence of conjugated double bonds in their structure. It was found that Astaxanthin has a role in improving disease resistance, better egg quality and immune-modulator and offers protection against UV radiation.
CONCLUSION:
This evidence shows that carotenoids have an indispensable role in fish nutrition, and they are ecologically friendly functional feed additives. Hence, regular supplementation through diet is mandatory to attract consumers and offer health benefits to the cultured animal in captivity. The antioxidant is essential to protect all lipids, including carotenoids molecules, from peroxidation. Carotenoids are not just colouring agents. They have an in-depth role in the health and growth of the animal. Using natural carotenoids will be beneficial to retain sustainability in the longer run.
Reference:
1) Elkin Amaya, Philippe Becquet, Sergi Carne, Silvia Peris, Pilar Miralles, Carotenoids in animal nutrition, ISBN 978-2-9601289-4-9, Fefana publication.
2) Fey, M. and Meyers, S.P. 1980. Evaluation of Carotenoid-fortified flake diets with the pearl gourami,Trichogaster leeri. J. Aquicult Aquat. Sci. 1: 15-19.
3) G.H. Pailan*, Sujata Sahoo and D.K. Singh, Role of Carotenoids in Ornamental Fish Nutrition: A Review, Indian Journal of Animal Nutrition, doi: 10.5958/2231-6744.2019.00037.9
4) S K Gupta, A K Jha, A K Pal and G Venkateshwarlu, Use of natural carotenoids for pigmentation in fishes, Natural Product Radiance, Vol. 6(1), 2007, pp.46-49
About Sowmiya Chandru
Sowmiya Chandru is currently pursuing masters’s in aquaculture at fisheries college and research institute, Tuticorin. She has a strong interest in entrepreneurship and shrimp farming. She has published several articles in international magazines and presented her knowledge in aquaculture at several conferences. Being a creative head, Sowmiya foresee working on the farmers’ problem and would bring out a sustainable solution.
About Atshaya Sundararajan
Atshaya Sundararajan is currently pursuing master’s degree in fish nutrition and feed technology at ICAR – Central Institute of Fisheries Education, Mumbai. She has delivered several talks during prestigious national and international conferences and symposiums. Sundar believes that “Sharing knowledge is the most significant contribution to the scientific community”. Hence, she published several popular articles in international magazines and full-length articles in conference proceedings.
