We take light for granted and cannot imagine our lives without it. However, do our shrimp need it as we do? Do the shrimp share the same necessity for the light? How does light affect them in our aquariums?
Light is an important biological factor for the shrimp as well. Photoperiod parameters such as intensity, duration, and spectrum have important influences on the growth, survival, maturation, and reproduction of the shrimp.
There have been done several studies about the effect of light on growth performance, survival, and stress resistance of shrimp. Although all these researches and experiments were conducted mostly on other types of shrimp, we can still use these results and extrapolate them to our dwarf (ornamented) shrimp.
I believe that this information can be very useful for any shrimp breeder. It can help us to understand how to better set up our shrimp aquariums.
Light and Molting Rate of the Shrimp
In one of the experiment biologists compared different light-dark conditions: growth, survival, and molting rate. During 80 days, 150 shrimp of both sexes were maintained under three light-dark conditions:
- 0:24h (no light period)
- 10:14h (partial light period)
- 13:11h (long light period)
As a result, the molting rate was significantly higher at a long-day photoperiod (Molting rate = 1.7) than at a partial light (Molting rate = 0.6) or continuous dark condition (Molting rate = 0.3).
Note: Biologists supposed that darkness alters the relationship between gland molting-inhibiting hormone.
Light and Weight of the Shrimp
Another experiment, which lasted 84 days, showed that the full light systems (24h) produced significantly greater shrimp biomass after all (because of the molting rate). Full light (24h) outperformed:
- Partial light systems (12h) by 33%.
- No light systems (0h) by 48%.
The growth rate and final individual weight were significantly greater in full and partial treatments.
Almost the same result showed the first experiment. Under similar conditions, good weight increment was obtained with the three treatments, finding a positive linear correlation between mean weight and time.
These results suggest that the best growth and survival result with a 10:14 light-dark cycle. In addition, it shows us that growth has a direct correlation with molting rate and survival. Which in its turn depends on the light.
Subjective observations of the research demonstrated a growth increase of algae on the tank wall. The algae are one of the main food resources for the shrimp in nature. Therefore, shrimp had constant access to food.
Light and Survival Rate of the Shrimp
Higher survival was recorded at complete darkness (no light period) and at 10:14h (partial light period) conditions.
The explanation is pretty simple. A long light period increased the molting rate and a frequent molting rate increased the mortality of the shrimp. There are two main reasons for that:
- Long light periods decrease the time between molt stages. During these inter-molt periods, shrimp have a lower mass due to the high cost of energy that the molt implies every time. Note: Although, in the long term, the general mass of the shrimp will be bigger because of the molting rate. Because with every molt shrimp grows.
- Molting is always a risk for the shrimp. The higher is the molting rate, the higher is the chance to fail. An increase of light periods produces an increase in the haemolymph of lactate similar to that produced by exercise and other factors considered as stressors to the shrimp. It allowed biologists to think that the main cause of death is usually the stress produced by the high molting rate at 13:11 (light-dark) conditions.
Note # 1: This is a very interesting part. On the one hand, complete darkness and partial light period showed higher survival. On the other hand, complete darkness had the lowest molting and growth rate. It means that in nature shrimp under longer light periods will become bigger and mature faster. So that they can reproduce at a higher rate and compensate for the slight loss in survival by a big margin compared to no light period.
Note # 2: It does not mean that a long light period kills shrimp. Absolutely not! There are too many variables in this equation. However, too much light stresses shrimp and makes them more vulnerable.
Vision and Feeding of the Shrimp
There is a popular thought that shrimp do not actually have to have a light that they can feed even without it. Well, shrimp do primarily use scent, not vision, to search for food. However, it is not that simple.
According to the results of the experiment, to determine the role of vision in feeding, the eyes of the juveniles shrimp were painted over (deprived of vision) with a white manicure. Their feeding response to commercial pellets was compared with those with untreated eyes.
The untreated eyed juveniles detected and approached a feed pellet right away, but the specimens blinded by the coating detected a pellet only after random accidental touch with the walking legs while roaming on the aquarium bottom.
Feeding behavior includes searching, detection, orientation, grasping, and ingestion of the food. Vision is involved in the initial steps but is not considered as the main sense in crustaceans. After all, shrimp are generally scavengers. They are very adaptive to find food on the river and pond beds where light is scarce. Nonetheless, vision and light can make a whole difference in terms of competition for the food. As a result, it affects the growth and survival of the shrimp.
Light color fluctuation and Shrimp
In the fourth experiment, biologists registered that rhythmic light color fluctuation also has a different effect on the molting and growth of shrimp. Light spectrum also significantly affects the ovarian maturation, reproduction, and growth of the shrimp.
Molting and growth performance of shrimp were tested under the following treatments: three constant light color treatments:
- Yellow light – “Y”;
- Green light – “G”;
- Blue light – “B”
Three rhythmic fluctuating light color treatments:
- Blue light to Yellow light – “BY”;
- Blue light to Green light – “BG”;
- Green light to Yellow light – “GY”.
The initial wet bodyweight of shrimp was 1.212 ± 0.010 g. After the 45-day experiment, the weight gain and the specific growth rate of shrimp in “B” treatment were the smallest. This might be due to the lowest energy allocation to growth and the highest energy allocation to excretion. Opposite to what was observed in the “B” treatment, shrimp in “BG” treatment showed the highest weight gain and growth rate. This might be due to the high energy allocation to growth rather than to excretion.
Another experiment also showed the specific growth rate of the shrimp over 45 days under different light colors. As follows: natural>green>yellow>blue light.
The growth rate of shrimp under blue light was only 73.0% and 85.8% of those under natural light and green light, respectively. Thus, it is reasonable to conclude that suitable fluctuation of light color can promote the growth of the shrimp.
Light and Dark Places in the Aquarium
Shrimp need both light and dark places in your tank. Light is the prime reason for the growth of algae, which the shrimp rely on for food. However, when they are not feeding, they tend to prefer darker places to hide. It makes them feel more comfortable and less stressed.
There is a simple experiment that can do anybody. You need to place your shrimp into a clear tank under direct light. After some time you need to cover one end of the tank to block the light. As a result, the shrimps will start moving to the darker side of the aquarium.
Thus, on the one side, shrimp benefit from the light, because it provides them more food. On the other side, shrimp are at the bottom of the food chain. They know that and prefer darker places to hide.
Breeding Shrimp and Light
Once again, when it comes to breeding shrimp, plants, dark and private places are crucial. Females are extremely vulnerable after the molt and they will try to find any place where they will be safe. It is not a rare case when molted female shrimp died because of the excessive attention from the males.
Light Enhance the Color of the Shrimp
Shrimp breeders noticed that light also affects the color of the shrimp, especially on the dark substrate. The theory is that by doing so, they are trying to blend in with its surroundings.
In nature, light increases the growth of algae thus shrimp start to grow faster. In general, the faster they grow, the more frequent they molt, and the faster they mature. However, in order to be safe, shrimp also prefer to hide.
All results indicate that light influences the survival and growth rate of shrimp. Light is considered as a main physical factor for all aquatic organisms. Several studies have demonstrated that shrimp express specifically different behavior, food intake, and growth and survival rates under various light conditions. Of course, shrimp can live even without light or under constant light, but they will be very unhappy in such aquariums.
The results indicate that supplemental lighting can improve shrimp breeding and have effects on shrimp nutritional characteristics.