An initiative of offshore salmon mariculture in the Yellow Sea Cold Water Mass (YSCWM) has been launched since 2012. One key step of the project is the ‘mountain-sea relay’ mode, meaning that salmons need to be transferred to seawater appropriately. Temperature is one of the most dominant environmental stimuli initiating the smoltification in salmonids. Besides, aquatic animals reared at constant temperature and diel-fluctuating temperature perform differently in growth and physiology. Hence, our purpose of this study focuses on salinity acclimation in juvenile rainbow trout Oncorhynchus mykiss inducing by different constant temperatures or diel-fluctuating temperature. Two trials were carried out at the Key Laboratory of Mariculture in Ocean University of China (Qingdao, China).
In trial I, rainbow trout were distributed to three treatments (9 °C, 12.5 °C and 16 °C) with three replicates, maintained in fresh water for four weeks. In trial II, fish were distributed to three treatments (13 ± 0.2 °C, ± 1 °C and ± 2 °C) with four replicates, reared for six weeks. The water temperature was adjusted according to sine function by AI controller. After that, the salinity in both trials were elevated from 0 to 15 immediately, then elevated to 30 gradually. After that, fish were sampled at the 1st, 4th, 7th, 14th and 21th day.
In trial I, final weight (FW), percent weight gain (WG) and specific growth rate (SGR) in rainbow trout at 12.5 °C were significantly higher than those at 9°C. Thermal growth coefficient (TGC) at 16 °C was significantly lower than other treatments (Table 1). In trial II, there is no significant difference in growth among treatments (Table 2). Since growth before salinity acclimation is usually poor indicator, hematology, enzymes, and metabolomics will be determined for select tissues in trial II.