MS-222 toxicity in juvenile seabream correlates with diurnal activity, as measured by a novel video-tracking method

a r t i c l e i n f o Keywords: Sparus aurata Video-tracking Swimming activity Chronotoxicity MS-222 Anaesthesia Fish are frequently exposed to anaesthetics since their use is necessary in several aquaculture procedures. The aim of this study was to investigate the existence of day–night differences in the toxicity and effectiveness of a common fish anaesthetic (MS-222) in juvenile gilthead seabream (Sparus aurata), determining the induction time of anaesthesia and subsequent recovery by a novel video-recording system. Our results showed that MS-222 toxicity was significantly higher at ML (mid-light) (LC50 = 85.5 mg/L) than at MD (mid-darkness) (LC50 = 107.6 mg/L) (trimmed Spearman-Karber method). In addition, when fish were exposed to a sublethal but effective MS-222 concentration (65 mg/L), 7 min passed before a 50% reduction in swimming activity was observed at ML compared to the 9 min required at MD. As regards recovery, fish showed activity levels similar to basal levels 10 min after MS-222 removal at ML, but only 6 min at MD. These results indicated that both toxicity and effectiveness were higher during the day than at night, coinciding with the diurnal activity pattern displayed by seabream, which should be taken into account when designing and applying daily protocols for anaesthesia in aquaculture. The development of accurate methods to quantify behavioural changes in fish is of great interest in order to characterise the sublethal effects caused by exposure to xenobiotics. Besides traditional methodologies applied in ecotoxicology studies, there is a need to find systems which link toxicology data with swimming activity alterations (Vogl et al., 1999). Although several commercial tools are available for performing behavioural analysis, these expensive packages are designed for terrestrial animals and have serious constraints when used in fish, which resulted in the design of costumised alternatives by various research groups (Kane et al. Aquaculture fish species are exposed to several stressful conditions during handling and transportation (Gatica et al., 2010), as well as to a great number of xenobiotic substances (e.g. antibiotics, disinfectants, vaccinations and anaesthetics). The toxicity and effect of anaesthetics are of special interest since they are frequently used in research and routine aquaculture procedures to immobilise fish and minimise their stress responses (King et al., 2005). These operations include the grading of fish, measurement, sampling, labelling, injection of vaccines, medical treatment and spawning induction, among others (Park et al., 2008; Weber et al., 2009). An appropriate anaesthetic for …