Sustainable Approaches Towards Aquaculture: Microalgal Circular Economy Perspectives

Microalgae have higher nutritional value as they are abundant in protein, carbohydrates, lipids, and vitamins. Hence, they play several important roles in aquaculture and are known as a major source of the food chain for aquaculture organisms. Furthermore, they are also used indirectly or directly by humans as food supplements and medicines to improve health by strengthening the immune system. Microalgae are used as biocontrol agents because they have biocidal properties, produce biomolecules (beta carotene, PUFA, and astaxanthin), wastewater, are a renewable resource of biofuel, and are used in wastewater treatment. Due to the overexploitation of wild sh and pollution, aquaculture faces serious issues. Ecofriendly methods are required to overcome this problem, so, microalgae are in practicing, that control the water pollution. Fishmeal is a rich source of protein in aquaculture but it is decreasing over time and has become cost-effective, so, to solve the problem, microalgae are used to replace the shmeal which (microalgae as aquafeed) is cheap and not required large area to grow. Microalgae are seemed to be very useful in the growth enhancement of aquatic organisms.


Introduction
Aquaculture is derived from 'aqua' means 'water' and 'culture' means 'cultivation'. It is the process to cultivate the aquaculture of organisms or animals. Aquaculture is one of the fastest-growing industries and even three times faster than the land animal industry, which feeds about 47% of human sh consumption so, its production growing continuously (Ansari et al., 2019). This growing industry improves the economic condition due to its high global demand and helps to reduce hunger, poverty, and many other things (Halima, 2018).
It is reported that 4.8 billion pounds earned annually by Americans from seafood and 90% of sh imported from China in the USA (Healey et al., 2016). Apart from that, as sh farming increasing, some serious problems related to that also increasing like an overpopulation of wild sh and pollution in aquaculture. To overcome this problem, the practice of eco-friendly sh farming is in use for example, microalgae are used as sh feed (Tossavainen et al., 2018).
Algae are photosynthetic organisms and living as unicellular or as multicellular organisms. They are present everywhere around the world (water), they provide food for many aquatic animals, and so, they are known as primary producers (Brown et al., 2013). The more important algae are belonging to green algae (Chlorophyceae), red algae (Rhodophyceae), diatoms (Bacillariophyceae), and brown algae (Phaeophyceae) groups. Algae are divided as macroalgae and microalgae. Macroalgae (seaweeds) are multicellular, and they are very long and extend for more than a few meters long (Markou et al., 2012) while microalgae are single-celled, microscopic plants present in freshwater and marine water (Brown et al., 2013). Most of the microalgal species are autotrophic but some of the species are heterotrophic such as Polytoma sp. and Polytomella sp. and having degenerated chloroplast (Talero et al., 2015).
Microalgae known as the earliest life form on the earth, they acclimatize themselves as well as their metabolism in several environments. Microalgae have a high growth rate in appropriate conditions, and they can grow in wastewater or sewage water (Han et al., 2019). Microalgae are rich in nutrients (protein, carbohydrate, and lipids) and it is considered as the base of the food chain in aquaculture. They are used as food supplements by aquaculture organisms, direct or indirect way. All stages of bivalve mollusk and the larval or juvenile stages of sh eat the microalgae (Brown et al., 2013). Reported that microalgae are also a rich source of vitamins and minerals like vitamin A, B1, B2, C, and E; folic acid, magnesium, iron, iodine, and calcium, etc. (Sathasivam et al., 2017a) thus all these quality make them edible or bene cial and reduce the traditional feed materials that may not have su cient nutrient and growth rate on aquatic organisms as microalgae have (Shah et al., 2018).
Microalgae use sunlight, nutrients, and carbon dioxide or carbonate for their growth and lipids synthesis (Sirakov et al., 2015). By xing CO 2 , they can transform solar energy into chemical energy which is more e cient than any land plant (Sathasivam et al., 2017). Microalgae as aquatic food are getting popular due to their high nutritional values. Microalgae are also having the antioxidant property, the capacity to resist disease as they have antimicrobial (antibacterial, antiviral, and antifungal) activity, and high growth rate (Roy et al., 2014). They play an important role in wastewater remediation, by removing carbon, nitrogen, phosphorus and heavy metals from the environment. Microalgae like Chlorella, Nitzschia, and Scenedesmus are present in the wastewater that is highly polluted, apart from that other species like Cyanophyta cocal, Dactylococcopsis sp., Microspora, etc. used to treat the waste of sh in the water while Teilingia sp., Anabaena sp. Pinnularia sp. and Nitzschia sp. help to treat slaughterhouse wastewater (Salces et al., 2019). Microalgae produce high biomass and have high oil content so, for this, it is used as biofuel production, etc. (Sirakov et al., 2015). Apart from lipids, microalgae are also rich in protein and carbohydrate which is essential for good health, for an example protein or pigments used in the pharmaceutical industry for the treatment of speci c diseases while carbohydrate used in the fermentation process and long-chain fatty acids used as health supplements (Chew et al., 2017). Figure 1 elaborated the diverse application of microalgae.
Prawn industries have also become very popular all over the world. Its high productivity has become a major aim and goal to improve its production. By modulating aquafeed, the aim is to improve the growth of prawns, their quality and their successful production and survival has become major interest among the researchers and for that microalgae play a major role to feed the aquatic animals (Li et al., 2015). So, aquaculture will go to become the main interest of focus by industry to facilitate the aquatic products (Han et al., 2019). Another application of microalgae is that they are used as immunostimulants. They improve the immune system and the survival rate of larvae. It is reported that in Rohu sh, Euglena viridis work as antibacterial agent against A. hydrophila (Shah et al., 2018). Due to their number of application algae is used as food for aquaculture organism and at the same time it is indirectly consumed by other animals, used to kill harmful microorganisms by producing some antimicrobial compounds, also used in biofuel production as it is a renewable resource and replacement of fossil fuel because fossil fuel is limited and expensive and contribute in the greenhouse effect, microalgae balance the nitrogen in the environment, they are easily digestible thus it contributes to improving the growth rate of aquatic organisms and also useful to enhance the reproduction of aquatic organisms (Khan et al., 2018). The bioactive compounds derived from cyanobacteria have a broad range of biological activities such as antibacterial, antifungal, antiviral, anti-neoplastic, antifouling, antioxidant, anti-in ammatory, anticoagulant, and anti-enzymatic (Babu et al., 2017). This review elaborates the multifaceted applications of microalgae in aquaculture in aquaculture wastewater remediation, nutritional potential as aquafeed, biofuels, disease control, and other prospects.

Aquaculture Wastewater Treatment Using Microalgae
Water is one of the natural and important resources to survive on the planet. But by the time water is getting polluted by discharging waste into the water bodies, like an industrial, domestic, dairy, and agricultural waste. Wastewater contains organic (carbohydrates, fats, proteins, and amino acids) and inorganic pollutants (sodium, calcium, potassium, magnesium, chlorine, sulphur, phosphate, bicarbonate, ammonium salts, and heavy metals) (Raouf et al., 2012;Mahmoud et al., 2016a). This needs to be treated before discharging into water bodies (Mahmoud 2020b). A plethora of aquaculture pollutants can be remediated by the unique potential of microalgae (Table 1). To rearing sh in aquaculture the water quality is considered one of the major factors. The pollutants or toxic contaminants in aquaculture can be accumulated in sh, crustacean, mollusks, and bivalves, which can become serious problems who consumed these aquatic organisms (Justino et al., 2016). One of the major issues is the overpopulation of shes that can make the least genetic diversity in water bodies. This low genetic diversity can cause an imbalance of the ecosystem via leading the marine life extinction.
Genetic diversity is required for long-standing evolution towards environmental changes. So, aquaculture promotes those species which are exactly needed to grow for consumption without disturbing the natural environment (Healey et al., 2016).
The aquaculture wastewater contains nutrients because of wastes from sh ( sh excreta) farming that contain nitrogen and phosphorous, which are harmful to the environment and can cause many serious problems like hypertrophication (Khatoon et al., 2016). Apart from sh excreta, there is another reason of aquaculture water pollution that is traditional methods to feed aquatic animals, the feed is rich in nutrient mainly lipid and protein but this amount left by the aquatic animal which can slowly convert into a soluble form by bacterial activity, thus it can become the reason of oxygen depletion in the water. In addition, harmful algal blooms cause oxygen depletion in the closed aqua ecosystem and can consume oxygen at the same time, producing some toxic elements so; this is a serious problem for the health of Rong et al. demonstrated that the sea cucumber was in demand as it has nutritional value like good protein production and increase the nutritional value of human diet but it produces a huge amount of waste in aquaculture that rich in phosphorus and nitrogen. And to overcome these problems, microalgae Nitzschia sp. was used in aquaculture wastewater remediation (Xing et al., 2018).

Microalgae As Biofuel Resource
As industries are increasing rapidly, the requirement of sustainable energy sources is urgent because the availability of fossil fuel is very limited and depleting rapidly. Using fossil fuel or petroleum-based fuel is hazardous as it is contributing to global warming and release toxic gases into the environment.
Renewable energy sources as biofuel and biogas are better replacement of fossil fuels (Amit et al., 2018). Reported that Botryococcus sp. contain half of the long-chain hydrocarbons of the total dry mass. Many researchers are focusing on improving the production of algal strains for biofuel production by modifying their genetic (Hannon et al., 2011). Many countries are promoting and performing sustainable energy sources like biofuel and biogas. These renewable resources can overcome the problem because it is less expensive than fossil fuel and also more lubricate (Amit et al., 2018).
Biofuel is eco-friendly due to its lower release of CO 2 or CO and sulfur content (Sathasivan et al., 2014b).
But the biofuel (biodiesel and bioethanol) consumption is also depending on the sources of it. Biofuel obtains from fermented sugar and oleaginous plants need more energy and arable land which is limited and cost-effective.
Using microalgae are very effective way as sources of renewable biofuel because of its number of application and do not need farming land, they can grow in very less amount of water or area, required nutrient, and high CO 2 mitigation rate. Biodiesel production by using microalgae is one of the best ways as it has high oil production because of high lipid content and it can be cultivated or manage easily (Amit et al., 2018). And it is known that microalgae can produce more than 60% of oil content by dry weight biomass.
In microalgae, lipids are crucial metabolites and important for the growth of aquatic organisms. The

Downstream processing of biofuel
Microalgal biomass is required to convert into biodiesel where cultivation, harvesting, oil extraction, and conversion of lipid into the biofuel process are required (Fig. 2). The downstream process cost approx. 60% of the total biodiesel production. The oil extraction process from dried biomass needs several techniques like cell rupture via ultrasound, autoclave, bead milling, and homogenization. Chemical and biological treatment is needed to break the cell wall using organic solvents, acids, and enzymes. In physical treatments, freeze-thawing and osmotic shock are used to extract oil. Once the oil is extracted, the transesteri cation process in methanol was done for biodiesel production (Kim et al., 2013a). Reported that the downstream processing depends on the microalgal cell wall, like the cell wall of red algae Cyanidioschyzon merolae can be easily broken to extract cell components, these algae normally found in hot spring season in a metal-rich condition. In contrast Scenedesmus sp. that has multilayer cell wall structure is highly resistant towards biological and chemical disruption (Yew et al., 2019).

Microalgae As Aqua Feed
Fishmeal is the source of aquaculture feed that is rich in protein, fatty acids, vitamins, and minerals.
Fishmeal is the brown our that is procured from the whole sh by cooking, drying, and pressing it. But shmeal is limited and cost-effective that can rise up to 30 to 60%. So, these problems need to solve and need to nd out a new source of nutritious sh food.
Production of algae is the best source and inexpensive source for aquafeed and better replacement of shmeal that can save about 40% of feeding cost than shmeal which cost is known two-third of aquaculture costs [37]. Algae or microalgae are important for aquatic life because they are eaten by zooplanktons and basic in the aquaculture food chain. The use of algae is considered as the main ingredient for sh in aquafeed and it has been reported that a very few amounts of algae are su cient for the sh diet that gives better growth rate, feed utilization e ciency, intestinal microbiota, physiological activity, give strength to ght against diseases, and capacity to hold the protein in the winter season to decrease the chance of feed intake and control the stress response (Norambuena et al., 2015). The nutritional value of microalgae depends on various factors that are cell size and shape, digestibility, biochemical contents, and animal feeding requirements of microalgae (Guedes et al., 2015). Microalgae are considered a rich source of nutrition as a report by Alberto that microalgae are the source of carbohydrate, protein, lipid, and dietary ber (Niccolai et al., 2019). It is reported that microalgae have 30-40% protein, 10-20% lipids, and 5-15% carbohydrate in late log phase (Shah et al., 2018). All stages of bivalve mollusk and the larval or juvenile stages of sh and crustacean species eat the microalgae (Brown et al., 2013). The nutritional value of microalgae is varying from species to species; some may be rich in carbohydrates while some of them are rich in protein, vitamins, or lipids ( Table 2). Among the other microalgae, Spirulina is used as sh feed which is known to have better growth. It has been predicted that the demand for sh production will be increased day by day so that algae or microalgae will be high on demand for sh food, thus, it will provide a great amount to the algal and aquaculture industry. And for that high production of the bioactive compound is required that can get from selective strain or by genetic modi cation while some of the chemicals as metabolites can modulate the cellular metabolism that can activate the high yield production of bioactive compounds for as example epigallocatechin gallate and cyclin-dependent kinase 2 inhibitors can trigger the production of intracellular lipids in Nannocloropsis and Phaeodactylum tricornutum (Talero et al., 2015). Figure 3 elaborates the diverse applications of algal biomass.

4.1Protein
Protein is the major metabolite of microalgal biomass, and their productivity depends on several factors such as different species, culture conditions (temperature, pH, and light) and

Carbohydrate
The carbohydrate content is less than protein and lipids but it is known as the main substrate for various biofuel productions such as bioethanol, biohydrogen, etc. Photosynthetic microalgae convert solar energy into chemical energy via several complex reactions called photosynthesis. These two photosynthetic reactions are including light and dark reactions. In the light reaction chlorophyll pigment capture the solar energy and used to break the water molecules into electron, proton and oxygen and then this proton and electron produce energy transporter i.e. NADPH and ATP while in dark reaction, the NADPH, and ATP are used to reduce carbon dioxide to carbohydrate via Calvin cycle.
Carbohydrate production in algae, ful ll two requirements; rst in cell wall as a structural component and second for storage purpose in cell. As the storage component, carbohydrate gives the required energy during metabolism. The storage compounds (carbohydrates, protein) in algae helps in growth adjustment when the environmental conditions change.
The carbohydrate is species-speci c such as cyanobacteria synthesize glycogen, red algae synthesize oridean starch and green algae synthesize amylopectin-like polysaccharides (starch), etc. (Markou et al., 2012;Khan et al., 2018). Microalgal Polysaccharides can adjust the immune system and in ammatory reactions, so, this quality makes them a more attractive source as biologically active molecules for example used in cosmetics, as natural curative agents, and used in food products.

Vitamins and minerals
Microalgae are also rich in vitamins and minerals that are necessary organic micronutrients. In microalgae, vitamin production depends on the presence of nitrogen. At a low concentration of nitrogen, cyanobacteria produce the least vitamin B 12. So, the concentration of nitrogen in the culture medium affects the content of vitamins. For aquaculture animals, vitamin ribo avin is important that is found in microalgae (Chew et al., 2017). Chlorella and Spirulina species (beta carotene and B 12) have more vitamins than plants and animals. Most of the microalgae contain an active form of vitamin E i.e. α-/βtocotrienol or α-/β-tocopherol (vitamin E) at a very high concentration that has antioxidant property (Guedes et al., 2015). And vitamin E is also used to treat heart and eye disorders, Alzheimer's disease, and cancer. Vitamin C is stored by a few algal species that have antioxidant activity (Sathasivam et al., 2017a).
The algae have the potential to replace inorganic salt with vitamins and minerals. Vitamins cannot be directly synthesizing in su cient amounts only it can be obtained from the diet. If there is de ciency of vitamins then it can lead to several diseases such as beriberi (de ciency of vitamin B), pellagra (niacin), and scurvy (ascorbic acid, vitamin C). Ascorbic acid is found to (Vitamin C) has maximum variation among all vitamins because it is heat sensitive. Algal food such as sea spaghetti (Himanthalia elongata), Gracilaria changii, and laver (Porphyra umbilicalis) contain more Vitamin C than any vegetables (Wells et al., 2017).

Pigments
Microalgae are highly exposed to oxygen and radical stress due to their phototrophic nature. As they produce valuable bioactive compounds that have various important roles like protecting against oxidative and radical stressors (Tan et al., 2018a). Pigments are one of the important compounds that have number of applications like antibacterial and antioxidant activities (Fig. 4).
Phycocyanin pigment secreted by Spirulina help treat damage bone marrow stem cell by controlling the production of White blood cell (WBC). The astaxanthin which is a keto-carotenoid synthesized from microalgae is reported to essential for the survival and growth of shrimps, salmon, and trout. Astaxanthin protects the algae from the damage of UV radiation and photooxidation of polyunsaturated astaxanthin. Nguyen et al. reported that the algae which synthesized this astaxanthin are Haematococcus pluvialis, Chlorella zo ngiensis, and Chlorococcum sp., the red yeast Pha a rhodozyma (Nguyen 2013).
Carotenoids are a class of natural fat-soluble pigments found principally in algae where they play a critical role in the photosynthetic process. In human beings, carotenoids can serve several important functions. The most widely studied and well-understood nutritional role for carotenoids is their provitamin A activity. Carotenoids are found to be powerful antioxidants. Beta-carotene is an essential carotenoid as it is the form of provitamin A and is used in many food products. β-Carotene is a natural pigment derived from green algae, is used as a yellow-orange food coloring agent and may help prevent certain types of cancers. It is reported that few species of Dunaliella produce beta-carotene at a very high amount under extreme temperature, high light intensity and high salinity; it has very effective values as it is used as anticancerous and as antioxidants (Sathasivam et al., 2012c). For the production of beta carotene, proper environmental conditions are required. There are cis and trans isomers of beta carotene, where cis isomer of beta carotene has effective role as it protects the cell from oxidative damage (Sathasivam et al., 2017a).

Omega 3 fatty acids
The Omega-3 fatty acid is one of the most important fatty acids that have health bene ts because of its anti-in ammatory, anti-blood clotting property as well as help in regulating blood pressure and diabetes.
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are the two main types of omega-3 fatty acids. Algae are the novel source of omega-3 fatty acids (Ji et al., 2015). It is reported that at the logarithmic phase, phospholipids are high in microalgae while at the stationary phase they are rich in triacylglycerols. Eicosapentaenoic acid (EPA), arachidonic acid (AA), docosahexaenoic acid (DHA), and αlinoleic acid (ALA), are reported to essential for larval growth. Omega-3 fatty acid or polyunsaturated omega-3 fatty acid (PUFA) is secreted by microalgae at very high amount (Han et al., 2019). PUFA regulates the membrane uidity, electron or Oxygen transport, and thermal adaptation of cellular and tissue metabolism.
It is known that different species are rich in a different amount of Omega-3 fatty acid or polyunsaturated omega-3 fatty acid (PUFA) like docosahexaenoic acid (DHA) and Eicosapentaenoic acid (EPA). Diatom Bacillariophyceae and Chrysophyceae are rich in EPA and DHA while more amount of DHA found in Dinophyceae, Prymnesiophyceae, and Euglenophyceae whereas EPA found at a very high amount in Cryptophyceae, Prasinophyceae, Rhodophyceae, Xanthophyceae, and Glaucophyceae (Shah et al., 2018).

Microalgae As Biocontrol Agents
The Aquaculture industry is the fastest growing industry and a report suggested that in 2014, world aquaculture production earned approx. 160 billion from n sh, mollusks, and other aquatic animals but there is a problem to get infection of aquaculture animal from bacteria, virus, and fungus. Examples of infectious diseases in shrimps from viral pathogens are the White Spot Syndrome Diseases (WSSD), Yellow Head Disease (YHD) and the bacterial infection in shrimps is Early Mortality Syndrome (EMS) (Charoonnart et al., 2018). Table 3 highlights the antimicrobial potential of microalgae. Microalgae are available all around the world and they are consumed and exposed to disease-causing microbes such as bacteria, fungi, and virus. So, to protect themselves from the pathogens they need to develop a defense mechanism against these pathogens. Several studies elucidated that microalgae or algae posse antioxidant, anti-in ammatory, and antimicrobial properties (Fig. 5). The microalgae or algae which live in an environment where the bacterial population is dense can synthesized the antibacterial metabolites to kill the bacteria than those who live in a bacteria-free environment. The antimicrobial property of microalgae is depending on the species, their culture condition and their growth conditions.
The Vibrio species are the target pathogen to test the antibacterial effect of microalgae. Microalgae, Tetraselmis suecia exhibit antibacterial effect against Vibrio alginolyticus, vibrio anguillarum, Vibrio parahaemolyticus and Vibrio vulni cus.
The Antibacterial activity was tested against sh pathogen Aeromonas by using diatom species Skeletonema, Thalassiosira, and Chaetoceros where it showed growth inhibition of bacteria (Fig. 6). The clear zone of inhibition was observed and diatom Thalassiosira inhibiting maximum growth of Aeromonas (Bhattacharjya et al., 2020).

Viral disease
Diseases in sh also caused by viral pathogens, on that number of the study was done, one of the reports to overcome this problem vaccines are developed which is e cient against bacterial pathogens as well as viral pathogens but there is also a challenge to inject the vaccine into the intramuscular which can hurt the shes and aquaculture animals. This vaccine needs to store at a cold temperature which is very expensive. So instead of injecting the vaccine there was found another method that is direct spray the vaccine but doing this method needs more amount of vaccine and it can become a stressful situation for the sh (Charoonnart et al., 2018). Many compounds are found in algae, bacteria and other marine organisms and few of them have shown the antiviral property. Antiviral property from Gelidium cartilagenium algae exhibited protection from in uenza B and mumps viruses to embryonated eggs. Cyanobacteria are considered a better source of the antiviral compound. A compound sulphated polysaccharide from cyanobacteria is considered to have antiviral e cacy against human immunode ciency virus type 1 (HIV-1) and herpes simplex virus type 1 (HSV-1).
Previous studies showed that many antibiotic compounds have been isolated from the cyanobacterial and microalgal extracts, observed that cyanobacteria have antiviral and antineoplastic compounds (Falaise et al., 2016).
Terpenes are one of the bioactive compounds that are produced by algae. Terpenes such as diterpene neophytadiene, sesquiterpenes cartilagineol, obtusol, and elatol isolate from seaweed have antiviral property (Perez et al., 2016).

Antifungal activity
Apart from the bacterial and viral disease, fungal disease in shes is the major concern to get over it

Outlook For Circular Bioeconomy
The circular economy is ideal of production and consumption in which the idea of material is reused, repaired, and recycled as much as possible. Algae are bene cial for circular bioeconomy as they do not require very compound media; they only just need light, basic nutrients to grow. Microalgae can be cultivated in wastewater like sewage wastewater, aquaculture wastewater, etc. as a nutrient (Abidizadegan, 2020).
Amongst that wastage of food is generating a huge amount of bio-waste all around the world. And this may be generated during manufacturing, handling, packing, and consumption. Wastage of food is the big problem; this food contains carbohydrates, lipid, and proteins that can degrade into a simple form such as glucose, fatty acid, and amino acid respectively. To manage the wastage of food, the waste food can be converted into algal bio-fertilizer, biodiesel, and other useful things by bioprocessing. And food waste and wastewater are the best way to utilize to cultivate algae that work as algal nutrients. When algae or microalgae grow in the wastewater it gives a maximum quantity of lipids and biomass. Reported that Chlorella pyrenoidosa and Schizochytrium mangrovei when cultivated in canteen waste like vegetable, rice, and meat, etc. produce more lipid while Chlorella sorokiniana give approx. 23% of intracellular lipid when it cultured in food and municipal wastewater. So, algae produce large number of life supportable bioproducts. As microalgae can be cultivate in wastewater and waste food as a source of nutrient that is the solution of circular bioeconomy over environmental waste and agriculture by lowering the greenhouse gas emission, deforestation, and nutrient pollution (Dahiya et al., 2018).
Microalgae are the primary producer in the food chain for aquatic animals that are rich in nutrients. The carbohydrates, protein, and lipid content are dependent on the algal species and also produce hormones, pigments, and secondary metabolites that work as immunostimulants, anti-in ammatory, antimicrobial, antioxidant for aquatic organisms. The microalgal production did not require any arable land, excess of water. Microalgae convert atmospheric carbon dioxide into high nutrient products. This provides better circular bioeconomy via general circular aquaculture industry (Yarnold et al., 2019).

Conclusions
The progress of aquaculture industry is greatly in uenced by the signi cant challenges like the accessibility of resources which are natural in origin and the environmental impact. The sustainable utilization of resources, high productivity and good pro t can accelerate this industry and help in achieving the SDG targets wherein the objectives can help in eradication of poverty(SDG 1), providing adequate nutrition (SDG 2) and aid in substantial growth (SDG 8) for a better tomorrow. In this regard microalgae can play a lead role in the improvisation of feed quality and enhanced feed utilization promoting better sh health concomitant with utilization of minimal ecofriendly resources.    Inhibitory effect of Algal extracts against pathogenic organisms.