which is related to the maturity of fish and
interspecific genetic factors. The oxygen
consumption rate increases with the rise of water
temperature. As the water temperature rises, the
activity performance and biochemical reaction speed
of animal tissues and organs also increase, which
leads to the acceleration of respiration and excretion.
This is the common feature of ectotherm (Wang
2010). The external temperature at which the
maximum respiratory metabolism occurs is the
optimum living temperature of the organism. The
fitted curve of the effect of water temperature change
on the respiratory metabolism of Acanthopagrus
schlegelii studied in this paper basically leveled off at
28℃. At this temperature, the physiological activity
of Acanthopagrus schlegelii reached its peak and the
respiratory metabolic rate was fast, indicating that the
temperature at around 28℃ might be the optimum
temperature for Acanthopagrus schlegelii. In the
experiment of Acanthopagrus schlegelii, the results
are similar to those of Zheng Jianmin et al. on juvenile
acanthopagrus schlegelii at 17.5 to 21.0℃, and the
experimental subjects are farmed Acanthopagrus
schlegelii (Zheng 1991). We can speculate that there
is little difference in oxygen consumption rate
between farmed and wild Acanthopagrus schlegelii.
The change of ammonia excretion rate of
Acanthopagrus schlegelii with water temperature is
similar to that of oxygen consumption rate, which
indicates that the change of metabolism in
Acanthopagrus schlegelii caused by temperature is
also influenced by enzyme activity and activity of
internal body organ. As the water temperature rises,
the basal metabolism of Acanthopagrus schlegelii
also increases, showing the enhancement of body
excretion. In the excretion study of hybrid
Acanthopagrus schlegelii and juvenile
Acanthopagrus schlegelii, Yan Fuyun et al. found that
the ammonia excretion rate increases with the rise of
water temperature in juvenile hybrid Acanthopagrus
schlegelii and juvenile Acanthopagrus schlegelii at
water temperature from 13 to 28°C (Yan 2010).
Organisms control energy metabolism through the
regulation of biological functions by weight. The
results show that the oxygen consumption rate of
Acanthopagrus schlegelii decreases with the increase
of weight, which may be related to the change of the
proportion of tissues that sustain the life of fish in the
body. Tissues are used to sustain the life of fish, such
as: brain, kidney, and gonads, have high oxygen
consumption. While tissues do not directly sustain
life, such as bones, muscles, and fats, have low
oxygen consumption (Li 2009). Small fish under
growth and development stage usually has large
proportion of tissue in the front part and small
proportion of tissue in the back part. In contrast, large
fish often has small proportion of the front part and
large proportion of the back part. For this reason, the
metabolic activity of small fish is more vigorous than
that of large fish (Wang 2011). The oxygen
consumption rate of Acanthopagrus schlegelii
decreases successively with the increase of weight,
which is similar to that of the fry of Fugu obscurus
(Wang 2002) and Perca fkuviatilis (Zakęś 2003).
There is a negative correlation between ammonia
excretion rate and the weight of fish. Since mature
fish are well-developed with strong anti-interference,
external changes have less impact on them than that
of juvenile fish. This was also found in other aquatic
organisms such as Strongylocentrotus intermedius
(Bi 2000), Penaeus japonicas (Zhu 2001),
Oratosquilla oratoria (Jiang 2000) and Apostichopus
japonicas (Sun 2012), suggesting a more pronounced
effect of weight on respiratory metabolism.
The value of Q
10
reflects the extent to which the
metabolic intensity is affected by temperature (Bayne
1983), which indicates the change in oxygen
consumption rate caused by every 10°C increase in
water temperature. The Q
10
value of oxygen
consumption rate of Acanthopagrus schlegelii varies
from 1.31 to 1.69. The larger the Q
10
value, the more
sensitive it is to the change of water temperature
within such temperature range, and the oxygen
consumption rate changes significantly. The Q
10
value of ammonia excretion rate varies from 1.05 to
1.78, and high Q
10
values indicates that there is an
upper limit exceeding the temperature tolerance
threshold of experimental fish in this temperature
range, which affects its physiological activities.
The energy substances metabolized by animals
are proteins, fats and carbohydrates, which are
eventually metabolized into CO
2,
water and nitrogen
while releasing energy. Excretion is one of the basic
physiological activities of energy metabolism in
organisms. The ratio of metabolic substrate O: N can
be used to deduce the source of energy substances.
Changes in O: N ratio are closely related to the
environmental factors to which the organisms are
subjected and can be used to determine the growth of
organisms under specific conditions (Widdows
1978). When the energy supply of the body is
provided by proteins, the O: N ratio is about 7 to 10.
When proteins and fats are oxidized for energy
supply, the O: N ratio is about 24. An infinitely
increasing O: N ratio is presumed to be a combined
energy supply of fats and carbohydrate (Mayzaud
1978, Ikeda 1974, Conover 1968). In the
experimental results, the O: N ratio of metabolic