**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.
