Effects of supplementing the rainbow trout (Oncorhynchus mykiss) diet with Spirulina and Chlorella on the tissue's cadmium detoxification capacity, growth performance, fatty acid composition, antioxidant defense system and liver histology

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This study aimed to determine the effects of the addition of Spirulina and Chlorella of the diets of rainbow trout (Oncorhynchus mykiss) on their growth, nutrient composition, the parameters of their antioxidant defense systems, liver histology, and the cadmium removal process of their tissues. Fish with an average weight of 84.25 ± 3.55 g containing Cd in their tissues were distributed in 15 tanks with 18 fish per tank. The fish were fed diets consisting of 0 % (Control-1), 0 % (Control-2), 4 % Chlorella, 4 % Spirulina and 2 % Chlorella +2 % Spirulina twice a day until they were satiated for a period of 80 days. At the conclusion of the experiment, it was determined that diets containing microalgae demonstrated increased growth rates, and that the growth values obtained from the 4 % Spirulina and the Control-1 were similar (p > 0.05). Regarding the fatty acid content, with the addition of microalgae to the diet, a significant (p < 0.05) decrease in SFA values and a significant (p < 0.05) increase in PUFA values were observed compared to the groups Control-1 and Control-2. On days 40 and 80, Cd levels in the muscle and liver tissue of the fish were found to be significantly (p < 0.05) lower in the groups that were fed diets containing microalgae in comparison with the Control-2 group. On days 40 and 80, the SOD, CAT, GSH, GST, and GPx values of liver tissues were higher (p < 0.05) than those of the Control-2 group. As a result of the semiquantitative histopathological evaluation of the liver tissues, improvements were observed in all groups containing microalgae; however, the most remarkable improvement was achieved in the Spirulina group. The results obtained in the study revealed that the addition of microalgae to rainbow trout feed removed Cd from liver and muscle tissues, reinforced the antioxidant defense system parameters, and increased growth. However, when the groups containing microalgae were compared among themselves, the diets containing 4 % Spirulina and 2 % Chlorella +2 % Spirulina were found to be more effective on these parameters.