Behavioral response and tolerance limits of red seabream Pagrus major fingerlings follow sudden low salinity exposure

Abstract

n this study, using a continuous behavior measurement technique, the eco-physiological changes of the fingerlings of red seabream Pagrus major caused by sudden exposure to low salinity in a controlled environment were observed, and the sub-lethal and tolerance limits of the test organism were investigated. As a result, the activity of the fingerlings suddenly exposed to 21.4, 17.3, and 9.8 psu increased temporarily at the initial exposure to show irregular swimming behavior, but then recovered a stable activity pattern through rapid salinity adaptation. These results indicate that red seabream fingerlings have a control mechanism that can adapt to various salinity changes through a temporary behavioral disturbance process as a method to adapt to osmotic stress at salinity concentrations within the tolerance limit. However, the organisms suddenly exposed to 7.3 and 4.3 psu could not withstand the salinity stress and their swimming behavior severely disturbed, and all individuals died with in 48 hours. According the results of this study, it was juged that red seabream fingerling underwent a temporary salinity stress process at the beginning of exposure at a concentration of 10.0 psu or higher, but osmotic control was possible within at least 11 hours, so that stable metabolic activity possible. However, it was analysed that the organisms that were suddenly exposed to the concentration below 5.0 psu exceeded the tolerance to low salinity and the sub-lethal limit. In red seabream fingerlings exposed to this concentration range, severe behavioral and metabolic disturbances was observed, and death was observed due to osmotic control failure. Therefore, it may be predicted the eco-physiological tolerance limit of red seabream fingerlings exposed to low salinity exists around 10.0 psu. In addition, it can be determined that the salinity range of 5.0 to 10.0 psu corresponds to the concentration range in which the osmotic control ability of the organism is lose and sub-lethal reaction occurs.