Growth performance, body composition and stress responses of olive flounder Paralichthys olivaceus held under different water pH levels

Abstract

The growth performance, body composition and stress responses of olive flounder, Paralichthys olivaceus (50.8 g mean body weight) reared under three different water pH levels (8.0, 7.5 and 6.5) were investigated. Fish in each pH level were stocked at a density 8 fish per rectangular aquarium (96 L) with triplicate, and were fed with a commercial diet (54.4% protein) to apparent satiation, two times a day for 6 weeks. At the end of experiment, blood sample was collected from 4 fish of each aquarium for haematological analysis and the other 4 fish were sacrificed for chemical body composition analysis. After blood sampling from each experimental fish, the fish were sacrificed for histological analysis of its gill, liver and kidney. Before the sampling, all fish were measured and weighed individually. There were no significant differences in weight gain, feed efficiency, specific growth rate and feed intake in fish exposed to 8.0, 7.5 and 6.5 pH levels (P > 0.05). Moisture and protein content of fish were not significantly (P > 0.05) affected by pH levels. However, decrease in the pH level provoked significant (P < 0.05) increase of lipid and decrease of ash content in fish. Hemoglobin (Hb) content of fish in pH 6.5 was significantly (P < 0.05) lower than those of fish in pH 8.0 and 7.5, but no significant difference was observed in Hb between the fish raised at pH 8.0 and 7.5. Although the histological changes of liverstocked at a density 8 fish per rectangular aquarium (96 L) with triplicate, and were fed with a commercial diet (54.4% protein) to apparent satiation, two times a day for 6 weeks. At the end of experiment, blood sample was collected from 4 fish of each aquarium for haematological analysis and the other 4 fish were sacrificed for chemical body composition analysis. After blood sampling from each experimental fish, the fish were sacrificed for histological analysis of its gill, liver and kidney. Before the sampling, all fish were measured and weighed individually. There were no significant differences in weight gain, feed efficiency, specific growth rate and feed intake in fish exposed to 8.0, 7.5 and 6.5 pH levels (P > 0.05). Moisture and protein content of fish were not significantly (P > 0.05) affected by pH levels. However, decrease in the pH level provoked significant (P < 0.05) increase of lipid and decrease of ash content in fish. Hemoglobin (Hb) content of fish in pH 6.5 was significantly (P < 0.05) lower than those of fish in pH 8.0 and 7.5, but no significant difference was observed in Hb between the fish raised at pH 8.0 and 7.5. Although the histological changes of liver