Microalgae and Fish Nutrition

Abstract

Fish has long been a source of “rich food for poor people” and has played an important role in increasing food security and nutrition in developing countries. Because various chemicals in algae can have confusing effects, the results of experimental research can be difficult to understand. Algae has been associated with strengthening immune systems, lipid metabolism, antiviral and antibacterial action, improved gut function, stress resistance besides providing a source of protein, amino acids, fatty acids, vitamins and minerals, and other biologically active phytochemicals in cattle and aquaculture feeds, even when used in modest amounts. The addition of algae to the fish diet modified the growth performance of the fish, causing it to improve. Its use resulted in a decrease in feed conversion ratio expenses, which plays an important part in determining aquaculture costs, an increase in feed efficiency ratio, and a decrease in feed conversion ratio. In accordance with the findings of chemical composition, various statements were acquired wherein the high proportion of algae significantly affects the protein and fat ratio. The outcomes demonstrated that algae could be a decent option as an additive for fish feed.

1. Introduction

Diet supplementation is an important aspect of aquaculture management, especially in intensive or semi-intensive fish culture, and is promising for increasing fish production [1]. Protein, on the other hand, is required for normal tissue function, fish body protein maintenance and replenishment, and growth. Due to the high cost of protein, it is more cost-effective to use all of the protein for tissue repair and growth rather than catabolizing it for energy [2].

This cost is determined by a variety of factors, including the amount of protein in the product, the source and kind of ingredients sourced from plant or animal sources, and manufacturing techniques. Different feeding management solutions, such as on-demand feeding regimes, are in addition to generating low-cost diets and/or good husbandry and pond management [3] possibly aid in the growth of fish. One issue that fish farmers face is finding a balance between rapid fish growth and the most efficient use of available feed. Because managing their feed intake in accordance with their energy needs is expected to improve when fish are fed with a proper feeding frequency, growth and feed conversion ratio are expected to improve.

The concept of a feeding schedule was created to account for fluctuations in the protein requirements and digestibility of farmed fish. In terms of practicality, the ideal condition would maximize the utilization of dietary protein for growth while reducing the usage of proteins for functional protein synthesis, gluconeogenesis, lipogenesis, and energy production [4].

Algae are photosynthetic creatures that provide the ultimate source of cellular carbon as well as chemical energy to other organisms. As a result, they were frequently referred to as primary producers. Microalgae (seaweed) and macroalgae (seaweed) are the two types of algae (unicellular). Microalgae require light, carbon dioxide, and nutrients to grow. Microalgae are grown for food, to produce valuable compounds, as biofilters to remove nutrients and other contaminants from wastewater, in the cosmetic and pharmaceutical industries, and for aquaculture. Also, due to their high oil content and quick biomass production, microalgae could be a viable source of biofuel [5].

Because the fish expends energy to collect prey but gains no energy from ingesting it, some plankton pass through the gut of planktivorous fishes undigested. In this circumstance, the fish may detect and reject such undesirable creatures. In the early stages of a fish’s life, natural food is essential [6].

Cyanobacteria have been used in photosynthesis and its genetic control, photoregulation of genetic expression, cell differentiation and N2fixation, nitrogen, carbon, and hydrogen metabolism, resistance to environmental stress, and molecular evolution due to their benefits for humans, animals, and the environment (photosynthesis) [7]. When carp are removed, algal output decreases due to nutrient depletion, macrophytes grow due to reduced turbidity, and zooplankton increases due to increased macrophyte cover.

Spirulina is a cyanobacterium that has been commercially produced for over 10 years because of its high nutritional content, which includes protein, amino acids, vitamins, minerals, vital fatty acids, and carotene [8]. Spirulina can be used as a nutritional supplement for people, as well as a feed supplement for animals with economic benefits. For example, when fed to trout, sea bass, fancy carp, red tilapia, shrimp, and mollusk, it can be a good food supplement. The alga has been discovered to be a good source of protein as well as a way to improve the color, flavor, and quality of meat [9].

Spirulina has been shown to have therapeutic effects in animals, including fish, as a growth promoter, probiotic, and immune system booster [10]. Spirulina is used to help livestock, poultry, prawns, carp, canaries, and exotic birds develop faster [11]. Preclinical research indicates Spirulina possesses antimutagenic, hypocholesterolemic, immunological, and antiviral effects.

Spirulina’s chlorophyll functions as a purifying and cleansing agent against harmful chemicals. It is also utilized as a probiotic agent and as a food supplement to increase color in ornamental fish. Spirulina contains protein (60–70%), necessary amino acids and fatty acids, phycocyanin (14%), chlorophyll (1%) and carotenoid colors (0.37%), vitamin B-12, and minerals that play key functions in animals in a variety of ways [10, 12].

Spirulina is a source of linolenic acid (GLA), an important fatty acid with therapeutic effects. Iron, calcium, chromium, copper, magnesium, manganese, phosphorus, potassium, sodium, and zinc are among the minerals found in Spirulina. By breaking down indigestible feed components, Spirulina promotes the intestinal flora of fish, according to Bargey’s Manual of Determinative Bacteriology, Spirulina is an oxygenic photosynthetic bacterium that belongs to the Cyanobacteria and Prochlorales families. In this classification, the sequence of the rRNA subunit 16S is considered. In 1989, these microorganisms were classified into two genera, according to the suggestion by Gomont in 1892 [12].

Spirulina is becoming a popular health food all over the world. It is a filamentous Cyanobacterium that belongs to the Cyanophyte class of algae. Furthermore, Spirulina is a natural resource that is high in protein, amino acids, vitamins, minerals, essential fatty acids, B-complex, and -carotene [13].

Spirulina has been shown to be capable of breaking down indigestible feed components and improving the intestinal flora in fish in previous studies [12]. In fish, the creation and release of enzymes that transfer lipids for growth rather than storage. Furthermore, the -carotene in Spirulina helps to keep the mucous membrane in place, preventing hazardous materials from entering the body. Spirulina’s chlorophyll functions as a purifying and cleansing agent against harmful chemicals [14].

Phosphorus and nitrogen from agricultural and industrial effluents, as well as home wastewater, can produce major eutrophication in any aquatic body. These nutrients, on the other hand, can be used to boost plant growth, such as phytoplankton, which can be used as natural fish food or in pharmaceuticals. Due to its great nutritional content, Spirulina is one of the most promising microalgae for culture [15].

2. Importance of fish and aquaculture to alleviate poverty and malnutrition

The nutritional benefits of fish and fish oil consumption on human health, such as cancer, diabetes, and heart disease prevention, have long been known. The global demand for aquatic foods is predicted to continue to climb as public knowledge of the health advantages of fish intake grows [16].

Furthermore, by 2050, the world’s population is predicted to increase by more than 30%, resulting in an additional 2.3 billion mouths to feed, with the majority of this expansion occurring in developing countries where fish is the primary source of protein [17].

The progressive intensification of production systems has resulted in the aquaculture sector’s exponential rise during the last two decades. The use of manufactured feeds intended to fulfill the nutritional requirements of the targeted fish species is a major contributor to this intensive production system. For many fish species, feeds account for up to 70% of the variable cost of a commercial aquaculture operation [18].

The cost of fishmeal, an important protein source in fish diets, drives feed production prices. In recent years, the price of fishmeal has climbed more than twofold. It increased from around US$600 per metric ton in 2005 to around US$2000 in the first quarter of 2010 [19].

3. Using of algae as a supplement to enhance the nutritional value of fish

In place of artificial vitamin and mineral pre-mixes, 15% of mineral-rich seaweed has been included in commercial salmon meals [20]. Final testing revealed that salmon fed the “seaweed” diets were healthier and more energetic, with superior flavor and texture, possibly due to bromophenolic chemicals contained in seaweeds. In other studies, adding Enteromorpha prolifera and Cladophora sp. to laying hens’ diets improved egg weight and eggshell thickness.

The vitamin content of algal biomass varies a lot depending on the species. According to Brown and Miller [21], ascorbic acid has the most variability, which could be related to changes in algal processing, drying, and storage, as ascorbic acid is particularly heat sensitive. This demonstrates the disadvantage of obtaining essential micronutrients from natural sources: there is too much variability due to the combined effects of different algal species, growing seasons, culture conditions, and processing methods to reliably supply the required micronutrients in a pre-determined manner. As a result, algal biomass in animal diets is primarily used as a supplement rather than a complete replacement for produced minerals or vitamins.

Carotenoids are a group of pigments that exist naturally in the living world and are yellow, orange, or red in color. Only bacteria, fungus, algae, and higher plants can synthesize carotenoids from scratch; therefore, animals must rely on the pigment or a similarly comparable precursor being provided in their diets, which would otherwise have gone down the food chain.

Due to the inclusion of fishmeal and fish oil in formulated aquafeeds, farmed fish and shellfish are rich sources of long chain, highly unsaturated fatty acids (HUFA). HUFA are essential for human health since they aid in the prevention and treatment of coronary heart disease, hypertension, diabetes, arthritis, and other inflammatory and autoimmune diseases. Due to a global lack of fish oil and fishmeal, researchers are increasingly looking at other lipid sources, such as algal biomass [22].

Unlike terrestrial crops, algae can directly produce HUFA such as arachidonic acid (AA, 20:4n-6) (Porphyridium), eicosapentaenoic acid (EPA, 20:5n-3) (Nannochloropsis, Phaeodactylum, Nitzschia, Isochrysis, Diacronema) and docosahexaenoic acid (DHA, 22:6n-3) (Crypthecodinium, Schizochytrium). While most of these algae are not acceptable for direct human consumption, adding them to animal feeds could increase their nutritional value for people indirectly. However, only a few studies have been conducted to date to assess microalgal lipids in farmed fish meals [23].

Despite the low lipid content of seaweeds, Dantagnan et al. [24] found that including Macrocystis pyrifera meal in the diet at a rate of 6% increase the level of PUFAs in trout flesh. Micro- and macroalgae have also been investigated as potential alternatives to fish oil and flaxseed for increasing the HUFA content in hens’ eggs [25].

The Table 1 compares the usual nutritional profiles of commercially available animal feed ingredients with some selected micro- and macroalgae to aid in evaluating algae as a potential source of protein and energy in the form of carbs and fats.

	% Crude Protein	% Crude Lipid	% Crude Carbohydrate*	% Ash	Gross Energy MJ/kg
Fishmeal	63.0	11.0	—	15.8	20.1
Poultry meal	58.0	11.3	—	18.9	19.1
Corn-gluten	62.0	5.0	18.5	4.8	21.3
Soybean	44.0	2.2	39.0	6.1	18.2
Wheat meal	12.2	2.9	69.0	1.6	16.8
Spirulina	58.0	11.6	10.8	13.4	20.1
Chlorella	52.0	7.5	24.3	8.2	19.3
Tetraselmis	27.2	14.0	45.4	11.5	18.0
Gracilaria sp1	34.0	1.5	37.1	26.9	13.4
Gracilaria sp2	10.0	0.9	50.1	34.0	11.2
Ulva lactuca1	37.4	2.8	42.2	17.4	15.7
U. lactuca2	12.5	1.0	57.0	24.5	11.2
Schizochytrium3	12.5	40.2	38.9	8.4	25.6

Table 1.

Typical composition of commercially available feed ingredients and algae species (per dry matter).

*

Carbohydrates calculated as the difference % DM – (% protein + % lipid + % ash).

¹

Cultured in the effluent of fish tanks.

²

Collected from natural habitat.

³

Commercial product, Martek Biosciences.

4. Algae

Cyanobacteria (blue–green algae) are Gram-negative oxygenic photosynthetic autotrophs that are among the most successful and oldest living organisms on the planet [26, 27]. The majority of oxygen in the early atmosphere originated from cyanobacteria’s oxygenic photosynthesis [27]. They are important primary producers on a global scale and play important roles in nitrogen, carbon, and oxygen biogeochemical cycles (30% of the annual oxygen production on earth) [28, 29].

They are the organisms that deliver oxygen to the earth and hence played an important part in the evolution of life. Some cyanobacteria have a unique biological mechanism (which combines N2-fixation and oxygenic photosynthesis) and can be used as a model to research significant biological activities or capabilities. Unicellular, colonial, filamentous, and branched filamentous forms are all included [30]. They are broken down into five pieces [31].

Cyanobacteria are also responsible for the origin of eukaryotic plant life on the planet, as the chloroplast of eukaryotic cells is descended from a cyanobacterial predecessor. It is a filamentous Cyan bacterium that belongs to the Cyanophyta class of algae. Spirulina was deemed “the best for tomorrow” by the United Nations (UN) world food conference, and it has gained appeal as a nutritional supplement in recent years [32].

The utilization of cyanobacteria as a nontraditional food and protein source appears to be promising [33, 34, 35]. Extremophyles are cyanobacteria that live in severe settings, such as Spirulina (alkalophilic), Extremophyle mass cultures are expected to be free of microbial contamination due to their high needs, avoiding a serious problem in outdoor cultures [34].

Pigments, such as chlorophyll a, carotenoids, and phycobiliproteins, are abundant in cyanobacteria. Spirulina phycocyanin buffer extract is utilized in eye shadow, eyeliner, and lipsticks. Because the product is water-insoluble, it does not fade or irritate the skin when exposed to water or sweat [36]. Cyanobacteria manufacture carbohydrates, particularly the compatible solutes glucosyl glycerol, trehalose, and sucrose, under various osmotic conditions.

In both animals and people, cyanobacteria can help lower cholesterol levels. When a high cholesterol meal was supplemented with cyanobacteria, the levels of total cholesterol, low-density lipoprotein, and very low-density lipoprotein cholesterol in rat serum were lowered. Mollusks, fish, and crabs feed on cyanobacteria. It has been found that the cyanobacterium Spirulina not only increases protein content but also improves the color of fish flesh. Cyanobacteria, in conjunction with bacteria, perform a crucial function in regulating the water body’s O2 and CO2 balance, supporting aquaculture. Cyanobacteria assist in the removal of phosphate and nitrogen from polluted water while also producing biomass.

Cyanobacteria are vulnerable to unexpected physical and chemical changes in environmental factors, such as light, salinity, temperature, and nutrient constraint, in their native habitat. Spirulina is prokaryotic cyanobacteria that are spirally coiled or filamentous and have a lot of similarities morphologically (as shown in Figures 1 and 2) [37]. The loosely coiled trichomes of varied width with cross-walls, visible in light microscopy, are the most distinctive feature of Spirulina [31]. The morphology of these related strains has traditionally been used to distinguish them: helix type, distribution of pores in the cell wall, appearance of septa under light microscopy, and trichome diameter and fragmentation type [38].

Figure 1.

Spirulina in natural shape.

Figure 2.

Spiral shaped of Spirulina.

The cyanobacterium Spirulina platensis is cultivated commercially as a possible source of proteins and medicines. Diatoms, dinoflagellates, green and yellow–brown flagellates, and blue–green algae are all examples of phytoplankton.

These groups, as photosynthetic organisms, play a critical role in ocean productivity and form the foundation of the marine food chain. Spirulina and Chlorella are two alga genera that require special attention because of their value as human food and in vitro and/or in vivo antioxidant capacity. These algae can be widely farmed to produce a protein-rich material for alimentary (diet supplementation) or industrial usage (blue pigments, emulsifiers, thickening, and gelling agent) [39, 40].

Due to a wide spectrum of vital elements, such as vitamins, minerals, and proteins, Spirulina’s chemical makeup suggests that it has a high nutritional value [41]. Microalgae play a vital function in aquaculture as a source of zooplankton for fish and larvae to eat [42]. Spirulina may boost carotenoid and pigment levels, according to a study by Lu et al. [43].

Furthermore, the usage of Spirulina meal in the animal feed business is growing [44, 45]. Aquaculture of macro- and microalgae is a lucrative global business. Macroalgae are grown for both their hydrocolloids and their nourishment.

In the commercial rearing of many aquatic species, microalgae are an essential food source and feed supplement. Algae are the natural food source for these creatures, therefore their relevance in aquaculture is unsurprising, only a few algae species contain components that have antioxidant properties. It has been reported that including Spirulina in ayu’s feed produces in better flavor, firmer flesh, and brighter skin color. Other research has found that a 5% dietary Spirulina supplement reduces muscle lipids and improves the flavor and texture of striped bass jack.

Spirulina has been identified as a potential protein source for fish feed. Earlier research looked into how adding dry Spirulina powder to a diet changes the taste and quality of fish. Spirulina supplementation in freshwater fish feed has been shown to improve growth and promote gonad development and maturation, according to other studies.

Antioxidants from marine organisms, including alga extracts from several species, were studied. Many algae species have been shown to be powerful antioxidants. Due to a wide spectrum of vital elements, such as vitamins, minerals, and proteins, Spirulina’s chemical makeup suggests that it has a high nutritional value. Aztecs have been collecting and using Spirulina (now known as Arthrospira) [34].

Externally, Spirulina is used as a poultice to treat certain disorders. The International Association of Applied Microbiology designated Spirulina as a “great future food source” in 1967. While no microbe ever delivered on its promise of inexpensive protein, Spirulina continues to spur research and production, owing to its claimed nutritional benefits [46].

The ability of this microbe to use ammonia as a nitrogen source at high alkaline pH values may be due to a comparatively high cytoplasmic pH (4.2–8.5). Spirulina contains a higher percentage of high-quality protein (59–65%) than other regularly used plant sources such as dried soybeans (35%), peanuts (25%), or cereals (8–10%). Due to the absence of cellulose in its cell walls (as is the case for eukaryotic green microalgae, such as Chlorella, Ankistrodesmus, Selenastrum, Scenedesmus), Spirulina has a unique value: after 18 hours, more than 85% of its protein has been digested and assimilated.

Spirulina is also a common ingredient in ornamental fish feed, such as carp, because it improves coloration. Algal carotenoids may also operate as a growth factor, which could lead to yet another use for algae in aquaculture diets. Because of its incredible ability to generate high-quality concentrated food, cyanobacteria, particularly Spirulina, is being developed as the “Food of the Future.” Spirulina is said to offer a full protein content of 65–70%, with all essential amino acids in perfect balance.

When the necessary circumstances for producing Spirulina can be attained, culturing this organism is not difficult. Spirulina, on the other hand, has a high protein and vitamin content despite its low protein output by an order of magnitude. 20 g dried Spirulina offers 100% of the recommended daily allowance of vitamin B12, 70% of the recommended daily allowance of thiamine, 50% of the recommended daily allowance of riboflavin, and 12% of the recommended daily allowance of niacin. Spirulina also has a high level of p-carotene (provitamin A) and important unsaturated fatty acids, which are both beneficial nutritionally. For the feeding of artificially grown clams, a semi-commercial concept on Cape Cod, USA, uses three different and relatively pure algae cultures in unheated water. The three species employed enable seasonal changes in growing conditions to be compensated for. After that, the algae is diluted with seawater and circulated through the hatchery beds, where the clams filter feed to get the protein source. Algae has also been discovered to give a growth factor to the larvae’s culture media, improving their survival and growth.

The following are some of the primary advantages of using Spirulina in aquaculture, according to their promotional literature:

1. Because of Spirulina’s intrinsic palatability, better growth rates are achieved and less feed is lost. Fish fed this cyanobacterium have reduced belly fat, indicating that the energy has been transferred to growth. In feeding trials with Cherry salmon, this theory was tested and confirmed.

2. In terms of meat flavor, consistency, and color, fish-fed Spirulina has a higher quality. Henson [47] cites research in which Spirulina supplements improved the coloration of Sea Bream, Mackerel, Yellowtail, and ornamental koi carp.

3. Henson [47] also mentions research in which yellowtail was shown to have improved survival rates after being reared with Spirulina, with mortality rates lowering by 14%.

4. The blue pigment phycocyanin has been blamed for the reduced toxicity and greater effectiveness of fish medicines in Spirulina-fed fish. Spirulina reduced the hazardous effects of heavy metal poisoning in particular fish, according to Henson [47].

Due to the unpopularity of artificial dyes, one of the key areas of research into the aquacu1tural relevance of Spirulina has been the color improvement potential. Spirulina is used to improve the color of ornamental koi carp, trout, salmon, and shrimp, sweet smelt, red tilapia, and the striped jack [48].

The high production costs of pure-culture-produced biomass have hampered the use of Spirulina as a protein and pigment source in aquaculture. As a result, the algae are either utilized as a beginning feed for larvae or as a specialty diet for adults (e.g., for color enhancement in ornamental fish). Given Spirulina’s nutritionally complete nature, it appears that if production costs could be kept to a low, this cyanobacterium might provide a novel feed source for aquaculture creatures.

Spirulina was named “The Best for Tomorrow” by the United Nations World Food Conference, and it has gained appeal as a food supplement in recent years. Spirulina, planktonic blue–green microalgae, has been proposed as a future food source that is both acceptable and safe. Due to its antioxidant, anti-inflammatory, antimetastasis, and blood cholesterol-lowering properties, it has recently been considered a source for possible medicines. Spirulina, for example, increased interferon production and natural killer cell activity when given orally [49].

Aquacultural systems based on microalgae and their animal consumers, which can be considered an indirect use of microalgae in human food, have been far more successful thus far, however, the uptake of microalgal biomass by commercially important filter-feeders is very promising from an energetic standpoint. Microalgae are the biological starting point for energy transfer in most aquatic ecosystems and are, hence, the foundation of many aquaculture operations’ food chains.

Spirulina is also used in fish farming, primarily for colored fishes [50], as a good source of antioxidant pigments, such as carotenoids, lutein, astaxanthin, zeaxanthin, and others, for intracellular protection of fish larvae against various diseases as well as the bright coloration of fishes [50]. Spirulina supplementation has been shown to prevent ischemic brain damage [51].

Despite its widespread distribution and economic importance, little is known about the feeding ecology of the common carp in natural settings. The influence of this cyprinid species on macrophytes has been well described, as has the functional anatomy of its feeding mechanism.

However, the majority of diet research has been conducted in fish culture ponds. The risk of consuming Spirulina was evaluated, and after a subchronic therapy, mice showed no harmful effects. Spirulina maxima oil extract or defatted fraction feeding reduced carbon tetrachloride-induced fatty liver growth in rats, showing a hepatoprotective activity. This lower plant group contains a large range of vitamins, colors, and practically all-important nutrients, including PUFA (polyunsaturated fatty acid), and is also a good source of proteins and carbs. A lot of algae have been validated over time due to their remarkable impact on fish development and vitality, but only about 40 genera have gained widespread use in aquaculture.

Furthermore, some Spirulina species lack a cell wall, resulting in enhanced digestion and absorption. A number of studies have previously reported that dietary inclusion of Spirulina improves fish growth [13]. The ability of Spirulina to act as an antiviral, anticancer, hypercholesterolemia, and health improvement agent is receiving interest as a nutraceutical and a possible pharmaceutical source. When Spirulina alga is fed to young prawns and fingerlings, the fish have good coloring, a low death rate, and a high growth rate. These studies have also discovered an increase in the amounts of linoleic acid, GLA, protein, and an improved color in the meat of the fish when compared to fish fed on standard instant feeds [52].

The use of plant products as protein sources in fish meals has a lot of potential for aquaculture around the world. Spirulina is multicellular, filamentous blue–green algae that have grown in popularity in the health food sector and is increasingly being included in people’s diets. Because muscle protein deposition is the primary cause of growth in fish, the flow of amino acids (A.A) from diet to developing biomass must be maintained. Fish require a variety of essential elements, including protein, fat, carbohydrate, vitamins, and minerals, although these requirements differ depending on the species. In comparison to the basal diet, 1–10% Spirulina supplementation boosted growth rate (up to 1.5 times), survival rate, and feed efficiency. There was also evidence of illness resistance to bacterial infection.

Bermejo et al., [53] found that the biliproteins found in Spirulina, such as phycocyanin, are responsible for the majority of the antioxidant capacities of this microalga’s protean extract, and they suggested that Spirulina could be used to make a natural dietary antioxidant supplement or added to healthy food products like cereals, fruit bars, or drinks to prevent some chronic diseases involving free radicals.

Furthermore, Spirulina is gaining popularity due to its bioactive components, which have antioxidant properties [51]. Supplementing with live Spirulina enhanced fish growth and feed utilization, which could be related to improved feed intake and nutrient digestibility. Spirulina, on the other hand, contains a number of nutrients, including vitamins and minerals, that may aid in the development of growth.

Increased fish appetite may have resulted in higher feed intake and improved growth in Spirulina-enriched diets, leading to better feed intake and growth. Changes in protein and lipid content in the fish body, on the other hand, could be linked to changes in their synthesis, muscle deposition rate, and/or different growth rates. Additionally, it works as an immunomodulator [54]. Spirulina platensis is more extensively dispersed and found primarily in Africa, Asia, and South America. Several studies have been undertaken using dried Spirulina as a feed supplement [55]. Spirulina has been shown to have an accessible energy content of 2.50–3.29 kcal/gram and a phosphorous availability of 41%.

Spirulina typically contains only trace amounts of zinc (21–40 g/g), although it is easily enhanced [56] (Azina®: 6000 g Zn/g). There are simple methods for obtaining zinc-rich Spirulina [46]. Magnesium is abundant in Spirulina, and its bioavailability is excellent [57]. Spirulina has been designated a national food in China [58].

It is said to have been consumed as food in Mexico during the Aztec civilization 400 years ago. It is still eaten by the Kanembu tribe in the Republic of Chad’s Lake Chad region, where it is sold as dried bread known as “dihe.” [59].

Chlorella is a freshwater single-celled microalga with a grassy odor. Its distinctive emerald-green hue and lovely grass odor are attributed to its high chlorophyll concentration, which is the highest of any known plant. The name “Chlorella” comes from the Latin words “chlor” which means “green” and “ella” which means “little.” Its size ranges from 2 to 8 microns, making it only visible through a microscope. It is about the same size as a human red blood cell, but the shape is different: Chlorella is spherical, whereas human red blood cells are disc-shaped. Chlorella reproduces quickly, dividing into four new cells every 17–24 hours. This exceptional ability to reproduce indicates a high level of “qi,” or life energy [60].

Chlorella spp. is being investigated as a potential source of a wide range of nutrients (carotenoids, vitamins, minerals) that are widely used in the healthy food industry, as well as in animal feed and aquaculture Gastric ulcers, wounds, constipation, anemia, hypertension, diabetes, newborn malnutrition, and neurosis are all problems that Chlorella spp. can help. Glycolipids and phospholipids are also thought to have antiatherogenic and antihypercholesterolemic properties, whereas glycoproteins, peptides, and nucleotides have antitumor properties. However, a beta-1,3-glucan, which is a strong immunostimulator, a free-radical scavenger, and a blood lipid reducer, appears to be the most important component in Chlorella spp. [61]. These groups, as photosynthetic organisms, play a critical role in ocean productivity and form the foundation of the marine food chain. Spirulina and Chlorella are two alga genera that require special attention because of their importance as human meals and in vitro and in vivo antioxidant capacity. These algae can be widely grown to produce a protein-rich material for alimentary (diet supplementation) or industrial usage (blue pigments, emulsifiers, thickening, and gelling agent) [39, 40].

At technical medium, C. vulgaris grew satisfactorily. Up to 10% phyto-s, 57.63% crude protein, 5.84% fat, 6.44 mg/gram beta-carotene, 4.12 mg/gram vitamin C, and 1.32 mg/gram vitamin E Chlorella vulgaris has the potential to be a natural and ASUH feed additive, and Phyto-s can be employed for mass production nutrition [62]. C. vulgaris is a spherical, unicellular microalga that grows in fresh water and has a diameter of 2–10 M. It grows quickly under ideal conditions and is resistant to invaders and the harsh climate. In the aqueous medium, light and CO2 are the bare minimum conditions for algae formation. Their development is expedited and targets the synthesis of a specific set of compounds by changing the medium and changing the circumstances [63].

5. Chlorella as a feed supplement for humans

Microalgae are effective producers of high-protein biomass due to their quick growth rates and use of renewable resources. Microalgae are photosynthetic heterotrophic organisms that include vital amino acids, protein, minerals, vitamins, chlorophylls, antioxidants, and bioactive compounds [64]. Microalgae have been used in food and medicine because of their qualities. Researchers have recently become interested in the immunostimulating effects of microalgae.

The use of algae as animal feed is more frequent than the use of algae in human diets. A vast number of nutritional and toxicological studies revealed that algal biomass can be employed as a beneficial feed supplement that can effectively replace conventional protein sources (soy, fish meal, rice bran, etc.) [65]. Seaweeds are also high in minerals, including salt, potassium, and iodine, as well as fiber. Supplementation of seaweeds to improve the texture of foods is another potential area where their use becomes crucial [66]. Both national governments and intergovernmental organizations have a role to play in re-evaluating the potential of Spirulina to meet both their own food security demands as well as a tool for their international development and emergency response initiatives [39]. Algae are high in vitamins, minerals, proteins, polyunsaturated fatty acids, antioxidants, and other nutrients [67]. The enormous potential of microalgae arises from the fact that they are less thoroughly studied than agricultural crops, that they may be cultivated in conditions that are inappropriate for plants (requiring less or no seasonality), and that some species produce several times more than plants. Their potential for producing useful molecules or biomass is generally recognized, and they can be employed to improve the nutritional value of food and feed since they use sunlight energy more efficiently.

6. Feeding algae to fish

The utilization of Spirulina (Arthrospir platensis) as a growth and immunity enhancer for Nile tilapia, Oreochromis niloticus, was investigated (L.). Fish have been shown to benefit from Spirulina’s growth-promoting properties. Although Spirulina supplementation boosted protein deposition in the fish body, especially when fed a 1.25–5.0 g/kg diet, there were no significant differences in fish survival among the three treatments. When fish were provided a Spirulina supplement, their physiological indicators improved. With increased Spirulina levels in fish diets, total fish mortality 10 days after IP injection with A. hydrophila and its count following incubation with fish serum decreased. When fish were given 5.0–10.0 g Spirulina/kg, the lowest mortality and bacterial levels were observed. These findings suggest that Spirulina supplementation is effective in preventing disease in tilapia culture, with an optimum dose of Spirulina in the diet of 5.0 to 10.0 g per kg of food [68].

In the study of Al-Koye [69], replacing fishmeal with 10% Spirulina had a positive impact on all growth metrics, including weight gain, daily growth rate, specific growth rate, relative growth rate, and productivity, particularly food efficiency ratio and survival. The protein content of the fish carcass was also affected, as was the lipid content of the fish diet, and had a significant impact on blood parameters. Different Ulva levels in the diet of [70] were utilized, and the fish maintained at 10, 15, and 20% nutritional Ulva had the most significant (P 0.05) values of protein efficiency ratio (PER), protein production value (PPV percent), and energy retention (ER percent). Green seaweeds (Ulva sp.) could thus be added to the diet of red tilapia (Oreochromis sp.) at a rate of 15% to boost growth performance without affecting feed efficiency or survival rate.

The goal of [71]'s study was to see how a diet including Ulva lactuca, green macroalgae, affected the growth, feed consumption, and body composition of African catfish Clarias gariepinus. Weight gain, specific growth rate, and feed consumption all showed significant differences. Overall, the experiment revealed that African catfish-fed diets containing 20% and 30% U. lactuca had poorer growth and feed utilization than the control group and fish-fed diets containing 10% U. lactuca. Güroy et al. [72] demonstrated that adding dietary low-level Ulva meal to numerous fish species, including rainbow trout Oncorhynchus mykiss and tilapia O. niloticus [73], improved growth performance and lipid deposition.

The effects of two algal meals (Cystoseira barbata or Ulva rigida) on feed consumption, development, and nutrient usage in young Nile tilapia, O. niloticus, were examined in a 12-week feeding experiment. The fish fed the 5% Cystoseira diet, control diet, and 5% Ulva diet gained the most weight (156%, 151%, and 150%, respectively), but the values were not significantly different (P > 0.05) from the other treatments, with the exception of the fish fed the 15% Ulva diet (P 0.05), which gained the least weight. 15% of the diet is made up of fish. The feed change ratio of Ulva meal was poor (FCR). At the maximal supplementation level of 15%, protein and energy utilization contribute to a decline in the groups fed algal meals. Carcass lipid levels fell as Ulva meal concentrations increased, but carcass lipid levels increased as Cystoseira meal concentrations increased (P 0.05). According to the findings, C. barbata or U. rigida meals could be utilized in tilapia diets in small amounts [74].

Rybak et al. [75] investigated the ability of freshwater Ulva species (Ulvaceae, Chlorophyta) to serve as metal bioindicators in rivers and lakes. From June to August 2010, researchers looked at changes in heavy metal (Ni, Cd, and Pb) and alkaline earth metal (Ca and Mg) concentrations in freshwater Ulva thalli. Ni was detected in the highest concentration among the heavy metals studied in thalli, whereas Cd was found in the lowest concentration. Metal concentrations in macroalgae, water, and sediment had statistically significant connections. Ulva populations from freshwater habitats were more efficient in bioaccumulating nickel than those from marine ecosystems.

7. Nutritional considerations of algal usage

Algae must compete with similar feed ingredients, namely fishmeal and oilseed meals, to break into the animal feed market and be economically viable (soya, etc.). Green, blue–green, and colored flagellates have all been utilized as animal feeds in the past, with the benefit that artificially farmed algae are very efficient protein producers in terms of land and water utilization. In animal production systems, good nutrition is critical for producing a healthy, high-quality product at a low cost. Nutrition is crucial in fish farming since feed accounts for 40–50% of production costs. With the introduction of new, unbiased commercial foods that support optimal fish development and health, fish nutrition has evolved dramatically in recent years. The creation of new species-specific diet formulations aids the aquaculture (fish farming) business in meeting the rising demand for inexpensive, safe, and high-quality fish and seafood [76].

Abdulrahman [77] evaluated the effect of replacing fishmeal with Spirulina spp. at four different levels, 0, 5, 10, 15, and 20%, such as T1, T2, T3, T4, and T5 on carcass mean weight (CMW) with head and without peripheral organs and CMW without head and peripheral organs, where the third and fifth treatments give the higher value in CMW with head and without peripheral organs, and the fifth treatment gives the highest value in C When it comes to chemical composition, the T3 and T5 have a greater significant difference in crude protein than the other treatments, while the T5 has a greater significant difference in crude fat.

The purpose of [78] was to look into the effects of Chlorella powder (CHP) as a feed additive on the growth of juvenile Korean rockfish, Sebastes schlegeli (Hilgendorf). Chlorella powder (CHP) was added to six experimental diets at 0, 0.5, 1.0, 1.5, 2.0, and 4.0% (CHP0, CHP0.5, CHP1.0, CHP1.5, CHP2.0, and CHP4.0, respectively) of the dry matter basis. These findings imply that the optimum dietary CHP supplementation amount for juvenile Korean rockfish growth and feed utilization is around 0.5% of the diet, with no deleterious impacts on blood parameters or body composition.

Abdulrahman researched the effects of varying quantities of the alga Spirulina spp. in the fish laboratory of Sulaimani University’s Animal Production Department (2014). T1 was a control treatment with no Spirulina spp., T2 was a treatment with 1 gm Spirulina /kg diet, T3 was a treatment with 3 gm Spirulina /kg diet, and T4 was a treatment with 5 gm Spirulina /kg diet. Weight gain of 6.89, Daily growth rate of 0.17, Specific growth rate of 0.147, Relative growth rate of 15.31, and Food change ratio of 2.14 were all significantly higher in the fourth treatment than in the other treatments, while the Food effectiveness ratio was significant in T3 and T4 (62.48 and 62.47), respectively.

According to Abdulrahman et al., [79], adding Spirulina platensis to a fish’s diet as a feed additive or a partial replacement for expensive fishmeal results in significant improvements in growth, coloration, reproduction, and flesh quality. According to the findings of Sleman et al., [80], Chlorella supplementation in the diet may have an effect on blood and biochemical parameters.

According to Abid [81], it can also be added to the diets of common carp in various quantities to have an effect. (T4) algae as a feed additive in combination with a 7.5 gm Chlorella/kg diet had a positive impact on weight increase, daily growth rate, and relative growth rate. The findings of chemical studies (proximate analyses) revealed that common carp flesh had a positive impact on protein, lipids, ash, and moisture. Blood parameters, such as monocytes, granulocytes, RBC, HGB, and glucose, were also affected. The addition of (T3) algae as a feed additive to a diet containing 5 gm Chlorella/kg food had an effect on the relative growth rate. It also had a positive impact on feed utilization, such as the protein efficiency ratio. The condition factor had a significant impact on fish meat indices, as well as on fish weight without viscera. The effects of lipid and moisture on proximate analysis and some blood picture parameters were positive.