Copyright @ 2016, Indonesian Aquaculture Journal, p-ISSN 0215-0883, e-ISSN 2502-6577 75 Indonesian Aquaculture Journal, 11 (2), 2016, 75-79 # Correspondence: Institute for Freshwater Aquaculture Research and Development. Jl. Sempur No.1, Bogor 16154, West Java, Indonesian. Phone: + (0251) 8313200 E-mail: vitas.atmadi@gmail.com Available online at: http://ejournal-balitbang.kkp.go.id/index.php/iaj EFFECTS OF DIFFERENT SALINITY LEVELS ON PHYSIOLOGICAL AND HEM ATOLOGICAL RESPONSE OF ROCK BREAM Oplegnathus fasciatus Vitas Atmadi Prakoso *)# , Jun Hyung Ryu **) , Byung Hwa Min ***) , Rudhy Gustiano *) , and Young Jin Chang **) *) Institute for Freshwater Aquaculture Research and Development **) Department of Marine Bio-materials and Aquaculture, Pukyong National University, Korea ***) National Fisheries Research and Development Institute, Korea ABSTRACT Rock bream Oplegnathus fasciatus is one of economically important marine fish species in East Asia. However, lack of information about the salinity tolerance of rock bream related to its physiological response made this issue were needed to be studied. The present study was conducted to determine the effects of different salinity levels on physiological and hematological response of rock bream in order to obtain its salinity tolerance. Twelve rock breams (total length: 26.9 ± 0.6 cm, body weight: 477.3 ± 61.9 g) were used for experiments. Four experimental groups with three replications were conducted to measure the effects of salinity (5, 15, 25, and 35 practical salinity unit (psu)) on physiological and hematological response of rock bream. Fish were stocked into the chamber inside the closed recirculation system. At the end of each experiment, blood samples were collected. The study revealed that lower salinity exposure had tendency to decrease the physical and chemical properties of blood in rock bream. 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. KEYWORDS: Oplegnathus fasciatus ; salinity; physiological response; hematology INTRODUCTION Stress can be defined as a state of threatened homeostasis that is reestablished by a complex suite of adaptive responses (Chrousos, 1998). Stress response of fish is an adaptive mechanism which provides fish to overcome real or perceived stressors for keeping it in normal or homeostatic state. Environmental stressors had been studied by researchers because of its effects on metabolism and growth, disease resistance, reproductive capa- city, health, condition, and survival of fish popula- tions (Barton et al ., 2002). Blood parameters can be one of the methods to determine the stress response of fish. Several studies have observed the effects of stres- sors to the stress of fish, such as temperature (Hous- ton & Rupert, 1976), salinity (Chang & Hur, 1999; Choi et al ., 2007), and high stocking density (Tapia et al ., 2012). According to several studies, the popular meth- ods to evaluate fish physiological responses related to environmental disturbances are by blood proper- ties measurements (Barton et al ., 2002). The effect of salinity on stress response have already investigated in several fish species, such as pejerrey Odontesthes bonariensis (Tsuzuki et al ., 2001), euryhaline flounder Paralichthys orbignyanus (Sampaio & Bianchini, 2002), sturgeon Acipenser naccarii (Martinez-Alvarez et al ., 2002), and chinook salmon Oncorhynchus tshawytscha (Morgan & Iwama, 1991; Stewart et al ., 2016). The metabolic responses of fish to salinity changes showed inconsistent patterns, and the optimal salinities for growth are different within species, life stage, and season (Morgan & Iwama, 1991). Other species need to be observed their phy- siological response related to salinity changes.