EFFECTS OF DIFFERENT SALINITY LEVELS ON BLOOD PROPERTIES OF ROCK BREAM Oplegnathus fasciatus  

Rock bream Oplegnathus fasciatus is one of economically important marine fish species in East Asia. A lot of information on the environmental and physiological factors should be observed for the successful rearing management of rock bream in culture farm. However, lack of information about the salinity tolerance of rock bream related to its physiological response were needed to be studied. The present study was conducted to determine the effects of different salinity levels on blood properties of rockbream in order to obtain its salinity tolerance.

Sixteen rock breams (total length: 26.9±0.6 cm, body weight: 477.3±61.9 g) were used for the experiments. Four experimental groups with 3 replications were conducted to measure the effects of salinity (5, 15, 25, and 35 psu) on the blood properties of rock bream. Fish were stocked into the chamber (dimension = 20 × 30 × 20 cm) inside the closed recirculation system. In order to observe the fish with lower salinity exposure (5, 15, and 25 psu), water salinity inside the closed recirculation system was declined slowly into the target salinity by adding the volume of freshwater on the day before experiment. Water temperature was maintained at 25±0.5^oC with 12:12 hour light:dark cycle. Each experiment lasted for 24 hours. At the end of each experiment, blood samples were collected. Fish were anesthetized and the blood samples were collected using heparinized syringes. Blood samples were centrifuged and analyzed the physical (hemoglobin and hematocrit) and chemical properties (Na⁺, K⁺, Cl^-, Ca, Mg, osmolality, cortisol, glucose, and total protein).

The study revealed that lower salinity exposure had tendency to decrease the physical properties of blood in rock bream Oplegnathus fasciatus (P<0.05) (Table 1). Similar tendency was also found in the results of chemical properties analysis of blood, except for total protein, cortisol, and glucose. The value of total protein did not have any special tendency since the values were fluctuated. The value of Na⁺, Cl^-, Ca, Mg, and osmolality showed tendency to decrease with lowering salinity, while cortisol and glucose showed tendency to increase from 35 psu to low salinity environment, indicating the enhancement of fish stress and resulted in fish mortality at 5 psu. The lowest cortisol value was 76.3 ng/mL in 25 psu, and the highest value was 188.8 ng/mL in 5 psu. Meanwhile, the lowest glucose value was 35.3 mg/dL and the highest value was 166.7 mg/dL (P<0.05). Results indicate that rock bream could tolerate lower salinity up to 15 psu.