Algal Biotechnology in Aquaculture

Kanti Meena*, Dharmendra Kumar Meena¹ and Daryab Singh²

*Central Research Institute on Jute & Allied Fibres, Barrackpore, 700121

¹Central Inland Fisheries Research Institute, Barrackpore, Kolkata, 700120

²Project Directorate on Poultry Rajendranagar, Hyderabad, 500030

Corresponding Author: Kanti Meena

Email: Dkmeenafnb@gmail.com

Microalgae are a highly diverse group of unicellular organisms comprising the eukaryotic protists and the prokaryotic cyanobacteria or blue-green algae. The microalgae have a unique environmental status; being virtually ubiquitous in euphotic aquatic niches, they can occupy extreme habitats ranging from tropical coral reefs to the Polar Regions, and they contribute to half of the globe's photosynthetic activity. Furthermore, they form the basis of the food chain for more than 70% of the world's biomass. Microalgae are a valuable environmental and biotechnological resource, and the aim of this review is to explore the use of in vitro technologies in the conservation and sustainable exploitation of this remarkable group of organisms. The first part of the review evaluates the importance of in vitro methods in the maintenance and conservation of microalgae and describes the central role of culture collections in applied algal research. The second part explores the application of microalgal in vitro technologies, particularly in the context of the aquaculture and biotechnology industries. Emphasis is placed upon the exploitation of economically important algal products including aquaculture feed, biomass production for the health care sector, green fertilizers, pigments, vitamins, antioxidants, and antimicrobial agents. The contribution that microalgae can make to environmental research is also appraised; for example, they have an important role as indicator organisms in environmental impact assessments. Similarly, designated culture collection strains of microalgae are used for ecotoxicity testing.

Introduction

Microalgae are microscopic freshwater or marine organisms (e.g. see figure 3) that play a key role in nature as a food source for higher animals (zooplankton, fish), for transferring nutrients in aquatic food webs and for balancing the exchange of CO2 between the ocean and the atmosphere. Microalgae are microscopic freshwater or marine organisms. They are a highly diverse group, ranging in size from several hundredths of a mm to several tenths of a mm, taking many different shapes and existing singly or in chains or groups Microalgae occupy a very wide range of habitats, including forms that live in open water (phytoplankton) or on surfaces (benthic), and are adapted to extreme physical and chemical conditions (extremes of temperature, salinity, pH). Well known natural phenomena involving microalgae include blooms of green algae in freshwater ponds or lakes during summer and "red tides" in the sea.

The diverse end user applications for microalgal biotechnology include:

• Carbon neutral Biofuel production and Bioenergy generation;

• Capture and bioconversion of carbon dioxide (CO2) from industrial processes;

• Ingredients for human health and wellbeing products, including essential omega 3 oils, antioxidants and pigments;

• Ingredients for aquaculture and agriculture feeds;

• Bioremediation and valorization of agricultural and industrial effluents.

• Energy producers and heavy industry generating CO2 as a by-product (including both fossil fuel and biomass power plants)

• Municipal waste water treatment companies;

• Intensive livestock producers releasing "point source" effluents (both agriculture and aquaculture sectors).

• Food processors releasing nutrient-enriched

• waste waters

Application of micro algae

1. Aquafeed

Microalgae are used ubiquitously as a feed source in the commercial hatchery production of juvenile marine fish and shellfish. There are thousands of marine hatcheries globally, producing billions of juvenile fish and shellfish annually. A relatively small number (~6-10) of easy-to-rear microalgae species have been adopted for this purpose. In most cases, the microalgae are cultured on site by hatchery personnel and presented live to the fish / shellfish larvae. Under this scenario, sales opportunities to hatcheries mainly consist of the equipment and consumables required for microalgae production: photo bioreactors, pumps, lights, nutrient mixes, etc. However, there is a growing trend for hatcheries to buy proprietary microalgae concentrates in order to simplify on-site operations. These concentrates are supplied by companies specialising in the large scale production and processing of microalgae.

Problems in using micro algae as an aquafeed

The high costs associated with algal production, the risks for contamination, and temporal variations in the algal food value still pose problems for any aquaculture operation depending on the mass-cultures of unicellular algae. In order to overcome or reduce the problems and limitations associated with algal cultures, various investigators have attempted to replace algae by using artificial diets either as a supplement or as the main food source. Different approaches are being applied to reduce the need for on-site algal production, including the use of preserved algae, micro-encapsulated diets, and yeast-based feeds. There is further scope to develop the sector by introducing better quality products, since it is widely acknowledged that existing concentrated microalgae products still do not match live microalgae for hatchery applications.

2. Nutraceuticals

The most important microalgae species for this purpose are Dunaliella salina, Arthrospira sp, Chlorella sp and Aphanizomenon flosaquae. These are mainly produced in outdoor ponds or shallow raceways, but also in closed photo bioreactors at more northerly latitudes including Europe. Certain cyanobacteria, for example Arthrospira platensis and A. maxina are also marketed as whole food, being particularly protein-rich (up to 77% dry mass) and containing all essential amino acids, a number of important essential fatty acids (EFAs) and vitamins of the B, C, D and E groups.

3. PUFA and HUFA

Omega 3s are natural oils of marine origin containing n-3 series long chain fatty acids such as DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid). These fatty acids are referred to as being essential in nutritional terms, since they cannot be synthesised by humans and have crucial physiological functions. Microalgae are the main source of omega 3 oils in the marine food chain, where they become accumulated especially in the tissues of oily fish such as anchovies and sardines. The major source of commercially available omega 3 oils is currently from captured marine fish such as, cod liver oil, contributing about 85% of the market by volume. However, the supply of marinesourced omega 3 is being threatened by adverse environmental conditions that have contributed to lower DHA levels in fish oil especially from fish species from South American waters which are the major suppliers of fish oil and also depleting global fish stocks. These adverse environmental factors coupled with depleting fish stocks is aiding the global market growth of algal based omega 3, which is currently contributing about 3% of the total omega 3 market. Microalgae based omega 3 oils furthermore appeal to vegetarian consumers and this sub-sector of the algal oils market is growing.

Effluent remediation

It is now well known that microalgae have high potential to reduce nutrient, and organic loads from wastewaters. it is widely used for Phytoremediation in aquaculture. Removal percentages of 75%, 84% and 89% for ammonia, nitrite and phosphorous respectively have been reported. A combination of wastewater treatment and algal carbon dioxide fixation provides incentives in the form of saving in water treatment chemicals and the subsequent environmental benefits. Furthermore, a pathway for removal of nitrogen, phosphorous and metal ions from wastewater is provided and the pathway provides algal biomass which can further be exploited for biofuel production or for other innovative products.

Probiotics in aquaculture

Probiotics generally includes bacteria, cyanobacteria, micro algae fungi, etc. Probiotics are a cultured product or live microbial feed supplement, which beneficially affects the host by improving its intestinal balance and health of the host. The first probiotic discovered long time ago was Lactobacillus sp., the lactic acid producing bacteria.

Conclusion

Though there is burgeoning interest globally about biofuels from microalgae, this has been surrounded by much hype. It is becoming clearer as the sector develops that the biofuel component of microalgae will only become commercially viable if the biomass is fully exploited to utilise all of the value added components. However, at present the field of natural product processing from microalgae is underdeveloped and aside from a handful of components, there is little in the way of full cost analysis on the best products to isolate, upgrade and commercialise. This is an area which needs to receive concerted support in the short term.

References

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