Abstract
The use of anesthesia is a common practice in aquaculture to sedate fish and mitigate handling stress. Although the employ of anesthesia is considered beneficial for fish, as it reduces stress and improves welfare, at the same time it may induce hazardous side-effects. The aim of the present study was to investigate the effects of clove oil (CO) and tricaine methanesulfonate (MS222), two of the most used anesthetics, on several oxidative stress related parameters in gilthead sea bream (Sparus aurata), as these types of effects of anesthetics have been seldom investigated. To assess these effects, S. aurata juveniles were placed in a setup of mobile water tanks and were transported during 6 h with either 2.5 mg/L CO or 5 mg/L MS222. After transport, half of the fish were sampled, whereas the remaining fish were transferred to tanks without anesthetics where they were allowed to recover for 18 h before sampling. Changes in the expression levels of several target genes related with the antioxidant response and cell-tissue repair were evaluated in the gills, liver and brain. Those transcripts included glutathione peroxidase 1 (gpx1), catalase (cat), glutathione S-transferase 3 (gst3), glutathione reductase (gr), superoxide dismutase [Zn] (sod2), heat shock protein-70 (hsp70), and metallothionein (mt). Antioxidant enzymatic activities glutathione S-transferase, GST; catalase, CAT; and glutathione reductase, GR, levels of non-enzymatic antioxidants (non-protein thiols – NPT), and pro-oxidative damage, assessed as lipid peroxidation (LPO), were determined in gills, liver and brain. Acetylcholinesterase activity (AChE) was determined in plasma, gills, brain, muscle and heart as an indicator of neuro-muscular alterations. In plasma, the total antioxidant capacity (TAC) and total oxidative status (TOS) were also measured. Results showed that the use of both anesthetic agents, CO and MS222, interferes with fish antioxidant status. All tested biological matrices displayed alterations in antioxidant endpoints, confirming that these substances, although minimizing the effects of transport stress, may have long term effects on fish defenses. This result is of high relevance to aquaculture considering that the oxidative stress, may increase the susceptibility to different environmental or biotic stress and different types of pathologies.
Highlights
The use of light anesthesia or sedation on fish is a common practice in aquaculture to reduce the stress due to handling, transport, vaccination and blood sampling by depressing fish central and peripheral nervous systems
Fish exposed to MS222 enhanced hepatic sod2 and gr mRNA levels after 6 h of transportation, returning to control levels after 18 h of recovery; while no alterations were observed in mRNA levels of gpx1 (Figure 1) as well as cat and gst3
Respect to the assessed cellular stress indicators, no significant effects were detected after transportation, FIGURE 1 | Relative mRNA levels of target genes measured on gills, liver and brain of S. aurata sedated with tricaine methanesulfonate (MS222) or clove oil (CO) after 6 h transportation and 18 h recovery
Summary
The use of light anesthesia or sedation on fish is a common practice in aquaculture to reduce the stress due to handling, transport, vaccination and blood sampling by depressing fish central and peripheral nervous systems. Clove oil (CO) has been proposed as a natural alternative and safer anesthetic, available and less expensive than MS222 with demonstrated efficiency in several fish species, including gilthead sea bream, Sparus aurata (Tort et al, 2002; Vera et al, 2010; Bodur et al, 2018). This anesthetic is a natural essential oil obtained from the clove tree (Syzygium aromaticum) and has as active ingredients eugenol and iso-eugenol (Javahery et al, 2012). The two compounds, MS222 and CO, are administrated by immersion of fish in water with the dissolved anesthetic, and mainly absorbed through the gills (Sneddon, 2012), biotransformed by the liver and probably the kidneys and mainly excreted through the gills and, to a lesser extent, through the urine and bile (Carter et al, 2011; Javahery et al, 2012)
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