**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].


*\*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.*

#### **Table 1.**

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

*Microalgae and Fish Nutrition DOI: http://dx.doi.org/10.5772/intechopen.105028*

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.
