Accurate fish Measurments- do fish shrink?

[vanstaal]

was the water cold ??

[vanstaal]

Although the information given refers mainly to cod, all white fish behave in a similar way, and the advice should prove of value to all fishermen and processors who are concerned with the processing of newly caught white fish, either at sea or on shore.

Rigor is only one factor among many that can affect the quality of fish frozen very soon after capture; other factors, for example blood discoloration, are not discussed here. General advice on the freezing of fish at sea is given in Advisory Note 34, and on the handling of blocks of sea-frozen fish in Advisory Note 2.

What is rigor?

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,

Rigor in fish usually starts at the tail, and the muscles harden gradually along the body towards the head until the whole fish is quite stiff. The fish remains rigid for a period which can vary from an hour or so to three days, depending on a number of factors described later, and then the muscles soften again.

What causes rigor?

Rigor results from a series of complicated chemical changes in the muscle of a fish after death; the process is not yet fully understood, and research is still going on, but it is known that factors like the physical condition of the fish at death, and the temperature at which it is kept after death, can markedly affect the time a fish takes to go into, and pass through, rigor.

While the fish is alive, cycles of chemical changes take place continuously in the muscle; these provide energy for the muscle while the fish is swimming, and also produce substances necessary for growth and replacement of worn-out tissue. The compounds that bring about, and control, these changes are known as enzymes.

The enzymes in the flesh go on working even after the fish is dead, and some of them act on those substances that normally keep the muscle pliable and lifelike. During life the muscle would contract and become rigid if its two main protein components were allowed to interact and bond together, but the bonding is prevented by the presence of substances that keep the muscle pliable, rather like the way in which oil lubricates the moving parts of a machine and prevents it from seizing up.

For so long as the muscles contain a reserve of energy, these substances can be replaced by one set of enzymes as fast as they are destroyed by another; thus the muscles stay pliable for a time after death. But once the energy reserves are used up, the replacement stops and depletion results. The protein components are then able to interact, the muscle attempts to contract, and it eventually becomes hard and rigid.

The interaction of the protein components is also influenced by the accumulation of lactic acid, which is produced in the muscle when the energy reserves break down. The relative importance of the two factors, depletion of one set of substances and accumulation of another, is not fully understood, but they are known to vary with the type of animal and with how well nourished and rested it was at the time of death.

How long docs a fish stay in rigor?

The time a fish takes to go into, and pass through, rigor depends on the following factors: the species, its physical condition, the degree of exhaustion before death, its size, the amount of handling during rigor and the temperature at which it is kept.

Species: Some species take longer than others to go into rigor, because of differences in their chemical composition. Whiting, for example, go into rigor very quickly and may be completely stiff one hour after death, whereas redfish stored under the same conditions may take as long as 22 hours to develop full rigor. Trawled codling, 18-22 inches long, gutted and stored in ice, usually take 2-8 hours to go into rigor.

Condition: The poorer the physical condition of a fish, that is the less well nourished it is before capture, the shorter will be the time it takes to go into rigor; this is because there is very little reserve of energy in the muscle to keep it pliable. Fish that are spent after spawning are an example.

Degree of exhaustion: In the same way, fish that have struggled in the net for a long time before they are hauled aboard and gutted will have much less reserve of energy than those that entered the net just before hauling, and thus will go into rigor more quickly.

Size: Small fish usually go into rigor faster than large fish of the same species.

Handling: Manipulation of pre-rigor fish does not appear to affect the time of onset of rigor, but manipulation, or flexing, of the fish while in rigor can shorten the time they remain stiff.

Temperature: This is perhaps the most important factor governing the time a fish takes to go into, and pass through, rigor because the temperature at which the fish is kept can be controlled. The warmer the fish, the sooner it will go into rigor and pass through rigor. For example, gutted cod kept at 32-35°F may take about 60 hours to pass through rigor, whereas the same fish kept at 87°F may take less than 2 hours.