BODY PIGMENTATION AND SHRIMP HEALTH STATUS
In practice, we can somewhat assess the health status of shrimp through their body color. For example:
- Shrimp exposed to heavy metal toxicity often appear darker, more opaque than usual.
- Shrimp experiencing shock or stress may gradually turn pink.
- Shrimp suffering from prolonged chronic diseases become yellowish and paler.
From a scientific perspective, we can explain these issues. Shrimp body pigmentation is determined by the pigment cells present in their bodies. These pigments include the following main types:
- Melanin: a black or brown pigment. This is an important pigment, playing a significant role in shrimp protection. When shrimp are injured, the body reacts defensively by secreting a layer of melanin to protect the wound. The black color of melanin helps conceal the wound and creates a protective layer for the injured area, reducing the risk of infection or attack by other competitors in the living environment. This is commonly observed in ponds and is often referred to as black spot disease.
- Carotenoid: this is a pigment ranging in color from yellow to red and plays an important role in attracting mates, protecting shrimp from UV rays, and providing nutrients. There are many types of carotenoids in shrimp bodies, and astaxanthin is one of the most important pigments.
Astaxanthin plays many important roles such as boosting immunity, providing nutrition, helping to cope with the environment, and creating body coloration for shrimp. Normally, astaxanthin binds with a protein called crustacyanin to create the characteristic blue-black color of shrimp. When exposed to high temperatures, this bond breaks, proteins are denatured, but astaxanthin remains intact, resulting in the red-orange color in shrimp. Shrimp can change their body color according to the environmental color by regulating the expansion/contraction of pigment cells. In a darker environment, pigment cells expand more, making shrimp appear darker blue and also redder when cooked. That is why shrimp farmed in lined ponds have better coloration. And we also apply this at the end of the culture cycle, near harvest, by creating a dark green water color to make shrimp more appealing and fetch a better price.
When shrimp are stressed by environmental factors, oxidative radicals form and gradually weaken the shrimp. Simply put, these radicals create a chain reaction that destroys healthy cells. The role of astaxanthin and carotenoids is to inhibit this chain reaction. At that point, stored carotenoids and astaxanthin from the hepatopancreas are released throughout the body. In cases of severe illness, shrimp body color will turn pink, which we often call 'pink body' or 'red body'. Similarly, in the intestine, when damaged, pigment cells expand, releasing astaxanthin to prevent the destructive process of oxidative radicals. At this time, the intestine will appear orange-red.
In addition to the pigments above, there are still some other important pigments:
- Biliverdin: A green pigment produced during the release of bilirubin, a catabolite of hemocyanin, in the shrimp's liver.
- Porphyrin: this is a type of pigment that is blue or red and plays a role in gas exchange.
- Xanthophylls: A group of yellow-orange carotenoids found in the yellow tissues of shrimp, such as ovaries and liver.
Pigments are distributed throughout the shrimp's body, but the external color we observe is primarily determined by the shell's color. When the shrimp's shell is thicker, the amount of pigment is also greater, giving them a more appealing color. Therefore, in addition to supplementing the aforementioned coloring pigments in the diet, to achieve better shrimp coloration, a diet that helps shrimp develop a thick shell can be provided. Furthermore, creating dark water color or using shade nets are also measures to help shrimp achieve better coloration, because if they live in a dark environment, shrimp will be darker than in clear, brightly lit water.
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