| dc.description.abstract | The effects of temperature acclimation in a tropical fish,
Oreochromis niloticus have been investigated. Fish of the genus O.
niloticus were accli 111(1 ted to either (mean +/-S.D) 26.5 ± 0.3 OC or 20.5 ± 0.5
oC for three months in the laboratory.
On staining serial sections for myosin ATPase, succinic
dehydrogenase, a - glycerophospate dehydrogenase and periodic acid
Schiff three muscle fibre types were identified. The bulk of the fish
crossection was occupied by white fibres whose stnining characteristics
were similar to those reported for FG fibres in other vertebrates. Slow
oxidative fibres occupied a wedge shaped area near the lateral line.
Sand-witched beLween the red and whiLe fibre types was a layer of
intermediate or rOG fibres.
The standard oxygen consumption of fish acclimated to either 20.5 ±
0.5 oc or 26.5 ± 0.3 «: was determined at 20 oc. 25 «: and 30 0C. At all
the experimental temperatures, the oxygen consumption of fish acclimated
to 20.5 ± 0.5 oC W(lS higher than that of the 26 oC acclimated fish. At 20
oC, the oxygen consumption of the two groups of fish was 38.8 ± 7.3 and
69 ± 8.9 mg/kg/hr for the 26 OC and 20.5 oC acclimated fish respectively.
At 25 oC, the oxygen consumption of the two groups increased to 64.5 ± 3.6
lng/kg/hr and 10J.O ± 5.9 111g/kg/hr respectively. At 30oC, the oxygen
consumption of the 26 oC acclimated group was 84.4 ± 5.0 lng/kg/hr while
that of 20 oC acclimated fish was 130.0 ± 6.4 mg/kg/hr. The oxygen
consumption for the two groups of fish was significantly different at all
temperaturest P<O.Ol) and had a Q10 value of 1.88 for the 20.5 oC
acclimated fish and 2.16 for the 26 oC acclimated group.
In order to dH'l.'k if tho oxygen C()J)<:tllllrlion recorded above was
accompanied by ch;,ngcs in the energy supply system, the activities of
citrate synthase (CS), creatinine phosphokinase (CPK) and lactate
dehydrogenase (LOI I) were investigated at 25 0C. The levels of CS were
7.1 ± 0.82 and 3.16 ± 0.3 111n-LOofI substrate utilized/g wet weight/minute in
red muscle isolated Irorn both the 20.5 oC and 26 oC acclimated groups
respectively. While the activity of the same enzyme in white muscle
isolated from the two groups was 1.74 ± 0.21 and 0.56 ± 0.1 mrnol of
substrate utilized / g wet wcight /fninute for the 20.5 oC and 26 oC
acclimated fish respectively. In all the cases, the activity of CS in muscles
isolated from the 200C acclimated fish were significantly different from
that of muscles isolated from the 26 oC acclimated fish (p<0.01).
Similarly, the activity of CPK in white muscle from 20.5 oC
acclimated fish (584.9 ± 20.3 'lnnl01 of substra:..t~e.....• utilized/ g wet
weightz'minute) was significantly higher (p<0..01) than that of the same ~
muscle isolated from the 26 oC acclimated group (351.1±27 mmol of
substrate utilized / g wet weight/minute). IIowever, the activity of CPK in
red muscle isolated from both groups showed no significant differences t _
(p>0.1). The acti viti of CPK in red muscle isolated from 20.5 oC
acclimated fish was 176 ± 35 mmol of substrate utilized/ g wet weight/
minute while that of red muscle from the 26 oC acclimated group was 202
± 25.4 mmol of substrate utilized/g wet weight/ minute.
The LOB activity of 152 ± 20.8 mmol of substrate utilized / g wet
weight/minute in white muscle of 26 oC acclimated group was
significantly higher than the 108 ± 8.41 111Inolof substrate utilized /g wet
weight/minutc observed for white muscle from the 200C acclimated fish
(p-cu.l). TIH' LOB activity in red muscle was 34.3 ± 7.62 and 38.9 ± 5.3 mmol
of substrate utilizl'd/g wet weight/minutc for the 200C and 26 OC
acclimated groups respectively. This was not statistically different (pc-OI).
It is concluded that the increase in aerobic metabolism in O. niloiicus
on acclimation to a lower temperature, suggests that a tropical fish can
undergo temperature adaptation although it is exposed to narrow
temperature range in nature. | en |
