mortality, especially during long-d

mortality, especially during long-distance or high-density transportation
(Teo et al. 1989; Gomes et al. 2003).
Anesthetics are widely used before and during transport
to slow metabolism and reduce stress of fish (Harmon 2009;
Pramod et al. 2010). Anesthetics reduce the contractile force
of the ventricular myocardium and alter gill haemodynamics
(Hill et al. 2002) by depressing neuronal activity (Sp
¨
ath and
Schweickert 1977; Arnolds et al. 2002) and preventing plasma
cortisol elevation (Iversen et al. 2003). These neural and physiological
variations reduce fish activity and metabolic rate, thus
decreasing oxygen uptake and carbon dioxide and ammonia production
(Zhuang et al. 2009). Therefore, water quality does not
decline as rapidly during fish transport when some anesthetics
are added (Berka 1986; Park et al. 2009).
When anesthetics are used at proper doses, physical damage
may also be reduced because fish are calmer and less active.
Consequently, anesthetics generally reduce fish mortality
during transportation (Estudillo and Duray 2003; Pramod
et al. 2010). Somewhat paradoxically, anesthetics have also been
shown to cause an acute stress response immediately after sedation
(Trushenski et al. 2012; Zahl et al. 2012). During this
acute response, the stress hormone cortisol may increase, leading
to increased levels of glucose and lactate in the blood after
sedation. Compared with the levels of these chemicals that occur
after a fish is stressed by handling, the amounts released in
response to anesthesia are low (Zahl et al. 2012). Levels of cortisol,
glucose, and lactate in the blood return to normal within
6 h after sedation (Trushenski et al. 2012). A number of anesthetics,
including tricaine methanesulfonate (MS-222), benzocaine,
2-phenoxyethanol, quinaldine sulphate, metomidate, and
lidocaine have been used in juvenile fish transportation (Guo
et al. 1995; Park et al. 2009; Pramod et al. 2010). Among the
broad spectrum of anesthetics, MS-222 appears to be used most
frequently (Marking and Meyer 1985; Berka 1986). Clove oil
(major constituent eugenol: 2-methoxy-4-[2-propenyl] phenol),
is another common fish anesthetic due to its efficacy, affordability,
and short withdrawal period (Harper 2003). Although
many studies have assessed the effects of anesthetics on ornamental
fish transported in polyethylene bags (Teo et al. 1989;
Pramod et al. 2010) and on low-density transportation of cultivated
juvenile fish (Guo et al. 1995), the effects of anesthetics on
juvenile survival and water quality during high-density transport
in polyethylene bags are not well studied.
Redtail culter (or Mongolian culter) Culter mongolicus is an
important piscivorous fish in China, widely distributed in lakes,
rivers, reservoirs, and other freshwater bodies (CAS 1976). The
species is characterized by high price and high market potential
(Zhang 2008). However, its population has declined seriously
during recent decades, mainly due to overfishing, habitat destruction,
and water pollution (Zhang 2005; Ye 2007). To rebuild
the population, China’s Ministry of Agriculture initiated stock
enhancement programs in some lakes of the Yangtze River basin.
Furthermore, pond and cage farming of redtail culters has developed
rapidly, increasing the need for juvenile transportation.
However, high mortality has been observed during transport
for redtail culters (Xu et al. 2009). Our objective in this study
was to evaluate the effects of MS-222 and clove oil on survival
of redtail culter juveniles during transportation in polyethylene
bags. Furthermore, we monitored water quality parameters to
help define important mechanisms of anesthetic action.
METHODS
Experimental fish.—We obtained juvenile redtail culters
from Niushan Lake Fish Breeding Center, Wuhan, Hubei
Province, China. Juveniles were stocked in a cultivation pond
for 1 month prior to the experiment. They were fed a commercial
pelleted diet in the pond, but feeding was terminated 1 d before
the experiment. Juveniles were 41 d old when the experiment
began (mean ± SE: total length = 46.09 ± 0.91 mm, body
weight = 0.75 ± 0.04 g).
Anesthetics.—Two commercial anesthetics, MS-222 (Sigma
Chemicals, St. Louis, Missouri) and chemically pure clove oil
(Shanghai Feixiang Chemical Factory, Shanghai, China), were
used to lightly sedate the fish. Each anesthetic was tested at
three concentrations based on previous experience, MS-222 at
10, 20, and 40 mg/L of water and clove oil at 2, 5, and 10 mg/L.
Sodium bicarbonate was used in MS-222 solutions to adjust pH
to 7.0.
Experimental setup.—The experiment was conducted on 31
July 2010. Juveniles scoop-netted after being seined from the
pond were batch weighted and transferred to bags. Eighty-four
bags used in this experiment (7 treatments × 4 time samples
× 3 replicates). The clear plastic bags were 20 L (40 cm wide,
63 cm high) and were sealed to be airtight after adding 5 L of
water,15 L oxygen, the fish, and their anesthetic treatment dose.
Transport density was 50 g of fish/bag (average, 67 fish/bag) or
10 g of fish per 1 L of water (13 fish/L of water). This density was
based on actual transport practices and a previous experiment
to measure oxygen consumption of juveniles.
All the bags were put in a vehicle and transported for approximately
1 h to the laboratory of the Institute of Hydrobiology,
Chinese Academy of Sciences. Natural light was maintained
in the laboratory, and an air conditioner was used to maintain
the air temperature at 25
◦
C. The experiment lasted for 24 h,
and three bags from each treatment were examined at each 6-h
interval to assess water quality.
Transport water came from the cultivation pond: temperature
= 29
◦
C, dissolved oxygen (DO) = 6 mg/L, pH = 7.8,
conductivity = 325 µS/cm, ammonia = 0.47 mg/L). During the
experiment, DO (YSI Model 85 instrument, YSI Inc., Beijing,
China) and pH (YSI pH100) were measured immediately after
the bags were opened, and total ammonia was titrated within
6 h after the bags were opened. Total ammonia content was
determined by the Nessler reagent spectrophotometric method
(Huang et al. 1999). Concentration of un-ionized ammonia was
calculated by multiplying the total ammonia by the appropriate
conversion factor according to the measured water temperature