INTRODUCTION
Rigor or, to give it its full name, rigor mortis means the stiffening of the muscles of an animal shortly after death. The word rigor is used throughout this note because it is shorter and easier to use than either death stiffening or rigor mortis. Immediately after death the muscles of an animal are soft and limp, and can easily be flexed; at this time the flesh is said to be in the pre-rigor condition, and it is possible to make the muscles contract by stimulation, for example by means of an electric shock. Eventually the muscles begin to stiffen and harden, and the animal is then said to be in rigor. The muscles will no longer contract when stimulated, and they never regain this property. After some hours or days the muscles gradually begin to soften and become limp again. The animal has now passed through rigor, and the muscle is in the post-rigor condition. Sometimes rigor is said to be resolved; this is simply another way of saying that the muscle has passed through rigor to the post-rigor stage.
METHOD OF RIGOR ASSESSMENT
The continuous “Rigor-index” of fish was measured according to Bito et. al.,(1983). The fish was placed on horizontal table with half of its body (tail part) kept out of the table. At selected time intervals (per one hour), rigor was calculated by the following equation:
Rigor-index (%) = (D0-D)/D0×100
Where, D0 = the distances of the base of caudal fin from horizontal line of the table at the start of experiment that is in pre-rigor.
D = the distances of the base of caudal fin from horizontal line of the table at subsequent storage periods respectively.
Fish species
Local name: Taki
Scientific Name: Channa punctatus
Weight: 60g
Standard Length: 16cm
Time of death: 11: 05 am
D0 measurement time: 11:25 am
D1 measurement time: 12:25 pm
Table: Rigor-index (%) changes with the changes of time.
|
Time (hours) |
Rigor-Index (%) |
|
0 |
0 |
|
1 |
31.08 |
|
2 |
68.91 |
|
3 |
81.08 |
|
4 |
89.86 |
|
5 |
93.24 |
|
6 |
93.24 |
|
7 |
93.24 |
|
8 |
93.24 |
|
9 |
93.24 |
|
10 |
93.24 |
|
11 |
93.24 |
|
12 |
93.24 |
|
13 |
93.24 |
|
14 |
93.24 |
|
15 |
93.24 |
|
16 |
93.24 |
|
17 |
93.24 |
|
18 |
93.24 |
|
19 |
93.24 |
|
20 |
93.24 |
|
21 |
93.24 |
|
22 |
93.24 |
|
23 |
93.24 |
|
24 |
93.24 |
|
25 |
93.24 |
|
26 |
93.24 |
|
27 |
93.24 |
|
28 |
93.24 |
Fig.: Change in rigor mortis progress of Taki (Channa punctatus) at room temperature.
Table: Duration of different stages of rigor in Taki (Channa punctatus) at room temperature.
|
Stages
Conditions |
PR (pre rigor) hr |
SIR (start in rigor) hr |
FR (full rigor) hr |
SOR (start off rigor) hr |
OR (out of rigor) hr |
Duration before full rigor (hr) |
Duration of full rigor (hr) |
Duration of total rigor (hr) |
||||
|
Start |
End |
Start |
End |
Start |
End |
Start |
End |
|||||
|
Room Temperature |
0 |
1st |
1st |
4th |
4th |
|||||||
DISCUSSION
The fish (Channa punctatus) died at 11:05am and the method of rigor assessment was started at 11:25am. At selected time intervals (per hour) first rigor-index (%) was 31.08% when D1 was 5.1cm.At 4th hour the full rigor was started. But after the value (93.24%) of rigor-index occurred in full rigor, there was no change in rigor-index. The value remains constant for 24 hours. But the bad odour was felt which indicate that spoil already occurred inside the body. The procedure was done in winter season and we know that there is less humidity in this season and air absorbed more and quickly water from the fish body surface. But air could not absorb water from the center of the fish body as more as or as quick as from the surface of the fish body. So, the post rigor was not seen from the external view. For these problems, the rigor-index (%) for post rigor could not be measured and some values for some important terms were kept blank into the last table.
