treatments had significantly higher

treatments had significantly higher DO, ammonia, and pH than
the controls during 12–24 h, but failed to decrease un-ionized
ammonia content. In contrast, the clove oil treatment significantly
reduced the un-ionized ammonia but failed to improve
DO and pH during 12–24 h. These results have also been observed
in southern platyfish, where 2-phenoxyethanol, quinaldine
sulphate, metomedate, and MS-222 had different effects
on water quality (Guo et al. 1995).
Juveniles become agitated when transported at high density,
which leads to more oxygen consumption and metabolic waste
products (Berka 1986). This stress response may explain different
effects on water quality variables during different phases.
However, the anesthetic mechanisms that affect water metrics
and the differences between anesthetics, still are not clearly
understood.
Generally, mortality increases with time during juvenile
transport due to the deterioration of water quality (Pramod et al.
2010). Among the factors affecting fish mortality, DO is con-
sidered the most important (Berka 1986). Moreover, high concentration
of ammonia in water causes high ammonia levels and
pH in fish blood, which damage the red blood cells and gills,
affect osmoregulation, and increase the oxygen demand of fish
(Lawson 1995). Compared with ionized ammonia, un-ionized
ammonia is considered more toxic to fish. Though the maximum
safe concentration of un-ionized ammonia is unknown,
0.0125 mg/L is commonly accepted by fish culturists (Meade
1985). Sublethal un-ionized ammonia concentrations are known
to cause behavioral, physiological, and histologic changes in
fish; high concentrations directly result in mortalities (Evans
et al. 2006). Furthermore, water variables can act together; the
ability of fish to use oxygen depends on their tolerance to stress,
water temperature, pH, and concentrations of carbon dioxide
and metabolic products such as ammonia (Berka 1986). Furthermore,
un-ionized ammonia toxicity increases when DO is
low (Merkens and Downing 1957).
Compared with the control group, both MS-222 and clove oil
significantly improved survival of juvenile redtail culters at 6 h
and 18 h. This result was similar to that of Pramod et al. (2010),
who found that juvenile survival during transportation improved
when anesthetics were added. Higher survival of anesthetized
fish at and beyond 18 h can be attributed to the better water
quality maintained by the actions of the anesthetics.
Additionally, we found that mortality was higher in the control
group than in anesthetic treatments even at 6 h, despite the
fact that no significant differences in water quality were observed
between them. We speculate that this was the result of
physical damage avoidance due to stress suppression from anesthetics
because clove oil and MS-222 have been shown to reduce
fish stress (Iversen et al. 2003; Inoue et al. 2005). Regardless of
the mechanisms, our results demonstrate that MS-222 and clove
oil are useful in short-term and long-term transport of juvenile
redtail culters.
In conclusion, our study showed that MS- 222 and clove
oil reduced deterioration of water quality, thus improving juve-
nile redtail culter survival during transport. Although MS-222
and clove oil were equally effective, we recommend the use of
5 mg/L clove oil because that anesthetic and dose provide a
cost-effective means of improving fish survival during transport
in China. However, other countries may restrict the use of clove
oil for food fish, so further research into eugenol and other clove
oil derivatives is needed.
ACKNOWLEDGMENTS
We express our thanks to technician Xinnian Chen for
assistance in tagging operations. We also thank M. D. Klopfer
and two anonymous reviewers for their critical reviews of
this manuscript. This research was financially supported by
the National Natural Science Foundation of China (grants
30830025 and 30900182) and National Science and Technology
Supporting Program (grant 2012BAD25B08). Participation of
B. R. Murphy was supported by the Acorn–Alcinda Foundation,
Lewes, Delaware.
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