How Does Light Affect Shrimps?

Light is also an important biological factor for shrimp. Photoperiod parameters such as intensity, duration and spectra have important effects on shrimp growth, survival, maturation and reproduction.

There have been several studies on the effect of light on growth performance, survival rate and stress resistance of shrimp. Although all of these studies and tests were mostly done on other types of shrimp, we can still use these results for our own shrimp.

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1. Light and molting rate of shrimp 

In one experiment, the biologists compared different light-dark conditions: growth, survival, and shedding. For 80 days, 150 shrimp of both sexes were maintained under three light-dark conditions:
– 24 hours (without light)
– 10 hours (partial light interval)
– 13 hours (long light time)
As a result, the molting rate at long light cycles (Moult Ratio = 1.7) was significantly higher than in partial light conditions (Moult Ratio = 0.6) or conditions continuous darkening (Moult ratio = 0.3).

Note: Biologists believe that darkness alters the relationship between the hormones that inhibit molting in shrimp.

2. Light and weight of the shrimp

Another experiment, lasting 84 days, showed that in full light system (24 h) shrimp were significantly larger (because of the molting rate). Full light (24h) is superior:

Partial lighting system (12h) increased by 33%.
No lighting system (0h) increased 48%.
The growth rate and final body weight were significantly greater in the total and partial treatments.

Almost the same result showed the first experiment. Under similar conditions, good weight gain was obtained with the three treatments, finding a positive correlation between mean weight and time.

These results show that growth and survival is best with a light-dark cycle (10 am, 14 pm). In addition, it shows us that growth is directly correlated with molting rate and survival.

The study's subjective observations showed an increase in algae growth on the tank walls. Algae is one of the main food sources of shrimp in the wild. Therefore, shrimps have regular access to food.

3. Light and survival rate of shrimp

Higher survival was observed under no-light (no light) and at 10 h (partial light period).

Read more: Ideal Parameters For Shrimp and Fish Farming

Explanation: Long light time increases molting rate, and frequent molting rate increases shrimp mortality. There are two main reasons for that:

The long light duration reduces the time between shell changes. During these molting stages, shrimp have a lower mass due to the high energy requirement per molt.
Note: Although in the long run, the overall mass of the shrimp will be larger due to the speed of molting. Because with each molt the shrimp grows.

Shrimp molting is always a risk. The higher the replacement rate, the higher the chance of failure. The increase in light duration produced an increase in lactate hemolymph similar to that produced by exercise and other factors that are considered stressors for shrimp. It allows biologists to think that the main cause of death is often stress caused by the high molting rate at 13:11 (light-dark) conditions.
Note # 1: This is a very interesting part. On the one hand, no-light conditions and partial light periods showed higher survival. On the other hand, the no-light condition had the lowest shedding and growth rates. This means that in the wild, shrimp under longer light time will grow larger and mature faster. So they can reproduce at a higher rate and compensate for the slight loss in their survivability compared to the absence of light.

Note # 2 : It does not mean that opening the lamp for a long time will kill the shrimp. This is not true! However, too much light will stress the shrimp and make them more vulnerable.

4. Shrimp's vision when feeding

There is a common belief that shrimp really don't need a light for them to be able to feed even without a light. Shrimps mainly use scent, not vision, to find food. However, it is not.

According to the results of the experiment, to determine the role of vision in feeding, in an experiment the eyes of the shrimp were painted over (loss of vision). The feeding response of the shrimp to the feed was significantly reduced.

Shrimps with normal vision detected and approached the pellets immediately, but those lost sight by the coating on their eyes only discovered the pellet after accidentally touching the walking foot while walking. wandering on the bottom of the tank.

Eating behavior includes finding, detecting, navigating, grasping, and digesting food. Vision is involved in early steps but is not considered the primary sense in crustaceans. After all, shrimp are usually scavengers. They are well adapted to foraging in rivers and pond beds where light is scarce. However, visibility and light can make all the difference in competition for food. As a result, shrimp growth and survival rate are affected.

5. Light and Shrinkage Color Variations 

In the fourth experiment, the biologists found that rhythmic light color fluctuations also had different effects on shrimp molting and growth. The light spectrum also significantly affects ovary maturation, reproduction and growth of shrimp.

The molting and growth performance of shrimp were tested according to the following treatments: three treatments of constant light color:
– Yellow light – “Y”;
– Green light – “G”;
– Blue light – “B”

Three methods of dealing with rhythmically oscillating light colors:
– Green light to Yellow light – “BY”;
– Green light to Green light – “BG”;
– Green light to Yellow light – “GY”.

Refer: Breeding: Inbreeding in Shrimps

The initial wet body weight of shrimp was 1.212 ± 0.010 g. After 45 days of experiment, the specific weight gain and growth rate of shrimp in treatment “B” were the smallest. This is likely due to the lowest energy allocation for growth and the highest energy allocation for excretion. Contrary to what was observed in treatment “B”, shrimp in treatment “BG” showed the highest growth and weight gain. This may be due to the high allocation of energy to growth rather than excretion.

Another experiment also showed the specific growth rate of shrimp for 45 days under different light colors. As follows: Natural light > green > yellow > blue light.

The growth rate of shrimp under blue light was only 73.0% and 85.8% compared to shrimp under natural light and green light. Therefore, it can be concluded that suitable light color variation can promote shrimp growth. 

6. Light and dark place in shrimp tank

Shrimps need both light and dark places in your tank. Light is the main reason for the growth of algae, which the shrimp rely on for food. When not feeding, however, they tend to prefer darker places to hide. It makes the shrimp feel more comfortable and less stressed.

There is a simple test that can be done by anyone. You need to put the shrimp in a transparent tank under direct light. After a while, you need to cover one end of the tank to block the light. As a result, the shrimp will begin to move to the darker part of the aquarium.

Thus, on the one hand, the shrimp benefit from the light, as it provides them with more food. On the other hand, shrimp prefer darker places to hide.

7. Shrimp and light

Again, when it comes to shrimp seed, plants, dark places and privacy are very important. Females are extremely vulnerable after shelling and they will try to find any place where they will be safe. It is not uncommon for female shrimp that have molted to die because of excessive attention from the male. 

8. Light enhances the color of the shrimp

Shrimp farmers have noticed that light also affects the color of shrimp, especially on dark backgrounds. Because they are trying to blend in with their surroundings. 

Conclude
In the wild, light increases algae growth, so shrimps start to grow faster. In general, the faster they grow, the more often they molt, and the faster they mature. However, to be safe, shrimp also like to hide.

All results indicated that light affected shrimp survival and growth. Light is considered the main physical factor for all aquatic organisms. Several studies have demonstrated that shrimp specifically exhibit different behaviors, food intake, growth rates, and survival under different lighting conditions. Of course, shrimp can live even without light or under constant light, but they will be very unhappy in such tanks.

The results indicated that supplemental light could improve shrimp fertility and have an effect on the nutritional characteristics of shrimp. 

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