Effect of transport stress on physiology of spotted knifejaw (Oplegnathus punctatus) reared in different culture systems

Standard technologies and models were applied to guarantee the production and supplement of high-quality protein in aquaculture. Recirculating aquaculture systems (RAS) have advantages on the level of intensive use, utilization of water resources, and command of environmental factors, and it was widely used in marine fish aquaculture. However, the higher energy consumption and more serious choices and management in fish. Offshore sea cage systems (OSCS) and offshore aquaculture nets (OANPS) take efficiency advantages of the natural environment to obtain optimal growth performance and flesh quality. Therefore, it is an efficient way to develop offshore aquaculture, promote the high-quality development of fisheries and alleviate the offshore pressure which relies on offshore facilities and pieces of equipment. Most fish find it difficult to resist severe winter in northern of China, and the ingestion and growth will be significantly influenced even if they can tolerate the low temperature. Therefore, it is an efficient way to conduct continuous aquaculture during land-sea relay. The method was applied to most marine fishes, which were cultivated in RAS and transported to OSCS and OANPS. Besides, the new aquaculture model during land-sea relay aimed to promote developments, utilization of natural resources and extension of culture spaces. Oplegnathus punctatus was popular with high economic value and broad prospects. According to previous researchers, transport stress significantly influenced the cortisol and glucose concentration in Ictalurus punctatus, Pelteobagrus fulvidraco, and Thunnus orientalis. Our research group had confirmed that handling stress as the primary stressor would influence the physiology function of O. punctatus. Meanwhile, O. punctatus of OSCS had better growth performance, physiology condition and immunity activity than RAS cultured in OANPS. So, we predicted that they would obtain optimal tolerance to stress after transport to OSCS. The study compared and explained the physiological response mechanism of O. punctatus subjected to transport stress under RAS and OSCS, aiming to explore the physiological response features and mechanisms during land-sea relay under different two kinds of culture models. Plasma cortisol (Cor), glucose (Glu) concentration, white blood cell numbers (WBC)and red blood cell numbers (RBC), hemoglobin (Hb) content, hematocrit (Hct) were analyzed by the automatic hematology analytical method. Hepatic and muscular glycogen content, hepatic superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), alanine transaminase (ALT), aspartate aminotransferase (AST) activity, malonaldehyde (MDA) content were detected by commercial kits. The hepatocyte apoptosis rate was evaluated using the TUNEL technique with a commercial kit of Fluorescein Tunel Cell (FITC) apoptosis detection. The results showed that RBC numbers, Hb content, and Hct under OSCS were significantly higher than RAS before transportation, whereas other parameters indicated no significant differences under OSCS and RAS. During transportation, plasma Cor and Glu concentration, plasma and hepatic ALT and AST, hepatic CAT and GSH-Px activity, MDA content, and hepatocytes apoptosis significantly increased under two kinds of models, whereas hepatic glycogen was significantly decreased and muscular glycogen and SOD activity had no significant changes during the whole experiment. The rate of changes of RBC number, Hb, hepatic MDA and glycogen content, Glu concentration, plasma and hepatic ALT and AST, CAT, GSH-Px and hepatocytes apoptosis rate in O. punctatus of OSCS was significantly lower than RAS. The above significant parameters accounted for 70.59% of the total indexes. The different changes of physiological indicators would recover after transportation 48 h, while RAS needed 72 h. Simultaneously, O. punctatus under OSCS had better physiological performances and stronger anti-stress characteristics than RAS during transportation and recovery. These findings offer important references and data support to optimize transportation and model during land-sea relay.