How Rigor Mortis Effect Physical and Chemical Parameters of Fish 

by Mark Clemons
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Fish is a highly degradable animal. As soon as it dies, many changes take place in its body. The changes in fish after its death depend upon many factors. Specie to specie shows variation in these effects and processes after death.

Fish condition deteriorates fastly after death. And now, if there is a question in your mind that why it happens so fast? The answer to this question is rigor mortis. 

What do you mean by rigor mortis?

Changes taking place during and after the death of an animal are collectively termed rigor mortis. Rigor mortis is the postmortem process that occurs in all animals. Many complex and complicated reactions are involved in rigor mortis.

These changes in fish happen rapidly. The time and nature of these changes vary from specie to specie. Scientists and researchers are still working to understand these changes and reactions happening before, during, and after the death of fish.

Physical Effects of Rigor Mortis

Numerous changes take place before and after the onset of rigor mortis. Both physical and chemical parameters get affected by rigor mortis. 

Alterations in physical characteristics without changing chemical composition states as physical effects. Time and temperature play an important in this aspect.

1- Overall Appearance

Rigor mortis causes the stiffness of muscles. It loses its elasticity and becomes rigid. This contraction of the muscles happens because of the bonding of two different types of protein present in fish. It becomes the reason for the hardness of fish.

And after completion of rigor mortis, the muscles reverse to soften. Eyes become bulging. Skin gets pale and light. Gills and other body organs bear slight changes. 

2- Texture

Before rigor mortis, the texture of fish is pale and soft. During rigor mortis, it starts to dry up. And after completion, it becomes firm, succulent, and elastic. The extent of change in texture changes from specie to specie. 

3- Color

Rigor mortis impact the color of fish. The range of color varies from specie to specie. Initially, it appears bright and transparent. In the absence of oxygen, it starts to appear darker in color.

4- Fillet size

Stiffness and rigidity of muscles reduce the size of the fillet. It will keep reducing the total fillet yield as long as, rigor does not stop.

5- Water holding capacity

Throughout rigor, the capacity of muscles to hold water in fish muscles decreases, Which causes moisture loss. It is the same reason behind the dry texture of fish

6- Flavor 

Poor handling and processing of rigor mortis lead to the development of flavor.

Production of lactic acid causes sourness in fish meat. The breakdown of glycogen can develop an ammonia-like flavor.

7- Smell and Odor

During rigor mortis, the release of chemicals like tetramethylene diamine in different reactions gives rise to smell and spoilage in fish. 

Chemical Effect of Rigor Mortis

These effects are the result of changes in the chemical composition of fish. Many quality parameters of fish get affected during rigor mortis because of the formation of new substances during different reactions.

1-Enzyme activity

In the beginning, there will be less enzyme activity. It can impact protein breakdown reactions. After the end of rigor mortis, the enzyme activates and starts causing autolysis because of the absence of glycolysis. 

2-Energy level

The ATP molecule providing energy to fish starts to get depleted without oxygen. All the energy reserves get used up. Aerobic respiration shifts to anaerobic respiration.

3- pH level

After death, all the oxygen gets used. Aerobic respiration gets replaced with anaerobic respiration. Anaerobic respiration results in the production of lactic acids causing acidosis in fish. Scientists have observed the pH falls below 6 in some fish. 

4- Quality of fish

Nutritional composition gets affected by rigor mortis. Drip and exudation losses happened in thawed fish causing weight loss. Rigor mortis causes gaping in fillets.

Connective tissues get weakened. Moreover, the longer the duration of rigor mortis larger its effect will be.

5- Shelf life

Exposure of the flesh to the atmosphere gives space for bacterial attack. A decrease in pH also favors this process. 

Bacteria and other insects deteriorate the organic matter rapidly. All these microbes and insects collectively lead to the spoilage of fish. The longer the duration of rigor mortis shorter will be the shelf life of fish. 

6- Nature of Protein

The protein undergoes a significant number of changes during rigor mortis. Denaturation and breakdown of protein take place. Aggregation of protein occurs. It massively affects the tenderness and chewiness of fish when cooked.

The safe handling and processing of fish can control the extent and range of these effects. The duration and outcome of rigor mortis vary differently from specie to specie.


Rigor mortis massively affects the quality, life, odor, taste, texture, and overall appearance of the fish. The range of these effects is different in different species of specie.

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