Effects of Salinity and Temperature on Oxygen Consumption and Blood Properties of Young Grey Mullets Mugil cephalus

Abstract

The effects of salinity and temperature on oxygen consumption (OC) and blood properties of grey mullets Mugil cephalus (TL: 27.3±2.1 cm, BW: 187.9±45.8 g) were studied by using respiratory chamber. Seven experimental groups were conducted to measure OC according to salinity (30→15→0 psu, 0→15→30 psu) and temperature changes (15→20→25oC), and two groups were conducted to measure the lethal dissolved oxygen (DO); SDS: fish reared in seawater (SW, 30 psu) directly shifted to SW, SDB: SW fish directly shifted to brackish water (BW, 15 psu), SGF: SW fish gradually shifted to freshwater (FW, 0 psu), SDF: SW fish directly shifted to FW, FDF: FW fish directly shifted to FW, FDB: FW fish directly shifted to BW, FDS: FW fish directly shifted to SW, LOS: lethal DO in SW, and LOF: lethal DO in FW. OC was tended to decrease in the groups of SW fish shifted to FW showing 194.5 mg O2/kg/h at 25oC in SDS to 82.4 mg O2/kg/h at 15oC in SGF. On the contrary, OC was increased in the groups of FW fish shifted to SW showing 80.5 mg O2/kg/h at 15oC in FDB to 184.0 mg O2/kg/h at 25oC in FDS. Likely, hematocrit (Ht) and hemoglobin (Hb) were shown with the highest values (30.6% and 7.4 g/dL) in SDS and SDB, while those were shown with the lowest values (16.2% and 4.2 g/dL) in SDF. However, Ht and Hb were shown with the lowest values (26.8% and 5.8 g/dL) in FDF, while those were shown with the highest values (47.9% and 8.5 g/dL) in FDS. Cortisol levels at the end of experiments were rapidly increased with the lowering salinities in SW fish shifted to FW showing 20.6 ng/mL in SDS to 316.2 ng/mL in SDF, while those were decreased with the increasing salinities in FW fish shifted to SW showing 40.2 ng/mL in FDF to 10.3 ng/mL in FDS. However, glucose levels showed no significant differences among all experimental groups. Lethal DO in SW and FW showed the same DO of 0.3 mg/L in both environments. The blood factors including Ht, Hb, osmolality, cortisol, and glucose in LOS were totally higher than those in LOF. In conclusion, salinity and temperature clearly affected the OC, behavior, and blood property of grey mullets. Grey mullet must be an excellent osmoregulator species which can be applied for increasing aquaculture productivity by culturing this species in freshwater.