In modern aquaculture, light and photoperiod play a crucial role in the management and productivity of various species. In shrimp farming, these environmental factors are essential for growth, reproduction, and overall well-being. Manipulating light exposure not only improves productive performance (Reis et al., 2019) but also directly influences the quality of the final product (Fang et al., 2024).
Thus, light exposure is fundamental in promoting optimal shrimp growth. Photoperiods with light, whether natural or artificial, generally result in higher growth rates, biomass, and survival. This article presents studies conducted on the effects of light and photoperiod on indoor farming of white shrimp Litopenaeus vannamei.
What is Photoperiod, and How Does It Affect Shrimp?
Photoperiod refers to the duration of light exposure within a 24-hour cycle. In aquaculture, it pertains to the length of light and dark periods that aquatic organisms experience daily.
As a fundamental environmental factor, photoperiod acts as a cue synchronizing the circadian rhythms of organisms. Circadian rhythms are 24-hour cycles influencing physiological and behavioral processes such as metabolism, locomotor activity, feeding, and reproduction.
Photoperiod affects the metabolism of aquatic organisms, including lipid metabolism and the nutritional quality of muscles. For instance, continuous light exposure can promote lipogenesis and the accumulation of fatty acids in shrimp (Fang et al., 2024).
Shrimp Biology and Its Relationship with Light
Shrimp, like Litopenaeus vannamei, possess light-sensitive receptors influencing their behavior and metabolism. Light directly impacts pigment synthesis, such as astaxanthin, which contributes to their coloration and, consequently, their commercial value.
Moreover, the light spectrum, intensity, and exposure duration affect shrimp hormone levels, influencing growth and reproductive development. These effects highlight the importance of carefully adjusting light conditions in controlled farming systems.
Nogueira et al., (2021) analyzed scientific studies on the performance of Litopenaeus vannamei under the influence of photoperiod and reported that results vary depending on the growth stage, farming system, and photoperiods used.
Effect of Light Color
The color of LED light significantly affects shrimp growth, influencing development, metabolism, and behavior. Studies show that different light wavelengths distinctly impact Litopenaeus vannamei growth and performance.
In this regard, Reis et al., (2023) evaluated different LED light colors on the growth of vannamei shrimp and obtained the following findings:
Green Light:
- Green light has been shown to have a positive impact on shrimp growth. Treatments with green light result in a higher final weight compared to treatments with blue, yellow, and white light.
- This positive effect may be related to metabolic adaptation mechanisms in crustaceans, which provide them with advantages.
- It has been observed that green light reduces stress and increases the ability to control osmotic pressure in shrimp exposed to stressful situations, such as salinity variations.
- Green light has also been found to favor the normal physiological metabolism in shrimp.
- Additionally, green light may influence the microbial community, increasing the abundance of bacteria such as free coccoid, free filamentous, attached filamentous, vibrio, and bacilli, as well as protozoa like flagellates, ciliates, rotifers, and nematodes. This increased microbial abundance may contribute to shrimp nutrition and, therefore, to their growth.
- In one study, the green light treatment showed a better nitrification process than the control treatment (white light), suggesting better water quality and, therefore, a more favorable environment for shrimp growth.
Red Light:
- Red light can also have a positive effect on shrimp growth, similar to green light, although the results may be less consistent compared to green light.
- Shrimp exposed to red light showed a similar result to the green light group but did not differ from other treatments.
- This positive effect could be related to metabolic adaptations that give them advantages in growth.
Blue, Yellow, and White Light:
- In general, blue, yellow, and white light have a lesser impact on shrimp growth compared to green light. Treatments with these wavelengths showed the lowest values in shrimp final weight.
- Blue light may inhibit the growth of L. vannamei and increase energy expenditure, which reduces feeding efficiency and, consequently, growth.
- These colors may not favor the same metabolic activity and feeding behavior as green light, leading to less growth.
Photosensitivity of Nitrifying Bacteria:
- Nitrifying bacteria are photosensitive, and their activity can vary depending on the wavelength of light. It has been observed that blue light can inhibit the activity of these bacteria, although to a lesser extent than other wavelengths.
- Green light might have lower photosensitivity for nitrifying bacteria, which could explain why a better nitrification process is observed in this treatment.
- Wavelengths in the blue and green spectrum showed lower values of photosynthetically active radiation in the water column, which could benefit the nitrification process.
Other Factors:
- The response to light color may depend on the shrimp species, its developmental stage, light intensity, and other environmental factors.
- In addition to wavelength, other factors such as light intensity, photoperiod, and the cultivation system also influence shrimp growth.
In summary, green light shows the best results for the growth of Litopenaeus vannamei, promoting a higher final weight and favoring both metabolism and microbial activity in the cultivation system. On the other hand, Reis et al., (2024) determined that green LED light with a photoperiod of 8 hours of light and 16 hours of darkness is the best choice for vannamei shrimp farming in a biofloc system, as it yields the best performance in terms of weight.
Effect of Ultraviolet (UV) Light
Ultraviolet (UV) light, particularly UVA, has various effects on aquaculture, influencing shrimp growth, immunity, oxidative stress, and gene expression related to apoptosis.
Wang et al., (2022) identified the main effects of UV light on indoor shrimp farming:
Growth:
- Supplementation with UVA light in specific photoperiods can improve growth and reduce the feed conversion ratio (FCR) in Penaeus vannamei shrimp.
- Specifically, photoperiods of 2 hours of UVA light and 22 hours of darkness (2L:22D) and 4 hours of UVA light and 20 hours of darkness (4L:20D) have been shown to be more beneficial for growth compared to other photoperiods, including the absence of UVA light.
- Longer UVA photoperiods (8 hours or more) may have a negative effect on growth and increase mortality.
Immunity:
- Exposure to specific UVA light photoperiods can enhance the immune response in shrimp.
- The 2L:22D and 4L:20D photoperiods increase the activity of immune enzymes such as catalase (CAT), superoxide dismutase (SOD), acid phosphatase (ACP), phenol oxidase (PO), and lysozyme (LZM).
- UVA light may promote the expression of immunity-related genes such as crustin, penaeidin 3a, Lc1, and LGBP, suggesting that it may increase resistance to pathogens.
UVA light has a complex and multifaceted effect on shrimp. Short and specific UVA light photoperiods (such as 2L:22D and 4L:20D) can be beneficial, improving growth and immunity while reducing oxidative stress. However, prolonged exposure to UVA light can be harmful, inducing stress, immunosuppression, and apoptosis. The choice of photoperiod and UV light intensity must be carefully considered to optimize shrimp health and production.
Photoperiod and Shrimp Nutritional Quality
Fang et al. (2024) reported that photoperiod significantly impacts shrimp’s nutritional quality, influencing muscle composition and lipid metabolism. However, the specific effects vary depending on the light duration and intensity, species, and farming conditions. The main findings of the study were:
Muscle Composition
- Protein: Exposure to light can influence the protein content in shrimp muscle. For instance, the study by Reis et al. (2019) showed that the group with a photoperiod of 12 hours light and 12 hours dark (12L:12D) had higher crude protein content compared to other photoperiods.
- Lipids: Photoperiod affects the fat content in shrimp muscle. Shrimp exposed to longer light photoperiods tend to accumulate more fat. For example, in one study, shrimp subjected to a 24-hour light cycle (24L:0D) showed the highest crude fat content, while those in continuous darkness (0L:24D) had the lowest.
- Amino Acids: Prolonged light exposure, such as in the 24L:0D photoperiod, can significantly increase the total essential amino acids (TEAAs), total hydrolyzed essential amino acids (THEAAs), and total non-essential amino acids (TNEAAs) in shrimp muscle tissue.
- Polyunsaturated Fatty Acids (PUFAs): Longer light photoperiods, like 24L:0D, can also increase the content of polyunsaturated fatty acids (PUFAs) in shrimp muscle. In contrast, continuous darkness can decrease PUFA content and metabolic activity.
Lipid Metabolism
- Lipogenesis: Continuous light exposure (24L:0D) can promote lipogenesis (fat production) in the shrimp hepatopancreas. This is evident through increased activity of enzymes related to lipogenesis, such as FAS (fatty acid synthase), CPT1 (carnitine palmitoyltransferase 1), and ACC (acetyl-CoA carboxylase). Additionally, there is higher expression of genes involved in lipogenesis, such as PPARα, PGC-1α, Rev-erbα, RORα, and SREBP1-C.
- Lipolysis: In contrast, continuous darkness (0L:24D) can reduce metabolic activity and lipolysis, resulting in lower fat content in shrimp muscle.
Fang et al. (2024) concluded that a 24-hour light photoperiod (24L:0D) can be beneficial for increasing essential amino acid and polyunsaturated fatty acid concentrations in shrimp muscle, thereby enhancing its nutritional value. However, a 16-hour light cycle is recommended, as the 24-hour cycle has some adverse effects on animal welfare.
Effect of Photoperiod on Growth
Reis et al. (2019) reported that using a natural photoperiod (12 hours light: 12 hours dark) for cultivating vannamei shrimp in a biofloc system allows for the best growth rate, likely because the lighting promotes a greater abundance of photoautotrophic flagellates, heterotrophic flagellates, ciliates, dinoflagellates, rotifers, and nematodes.
On the other hand, Fang et al. (2024) found that the 24-hour light photoperiod showed the best growth rate (3.69% per day) and feed conversion rate (1.68) in L. vannamei shrimp; however, it affects animal welfare.
Effect of Darkness
Total darkness has various effects on shrimp, which can be both negative and, in some cases, tolerable depending on the species and farming conditions. Below is the impact of total darkness on shrimp according to Jiao et al., (2021):
Negative Impact on Growth and Development
- Total darkness or light restriction can negatively impact shrimp growth and survival.
- The study showed that treatments with 24 hours of darkness result in lower final weight, biomass, and weekly growth rate compared to treatments with light exposure.
Effects on Metabolism and Physiology
- Total darkness can lead to lower metabolic activity in shrimp.
- Under constant darkness, decreased expression of genes involved in nutritional metabolism regulation, body coloration, circadian rhythm, immune function, and hormone levels has been observed.
- Serum levels of hepatic enzymes like ALT and AST increased under darkness, suggesting potential hepatocellular damage. Additionally, changes in glucose, albumin, and LDL levels were observed.
- Continuous darkness (0L:24D) resulted in a reduction in crude fat content in shrimp muscle, indicating that prolonged darkness can induce stress and nutritional depletion.
Impact on Gut Microbiota
- Total darkness can cause alterations in shrimp gut bacteria abundance. An increase in the relative abundance of genera such as Ruegeria, Vibrio, Actibacter, Roseovarius, Ilumatobacter, and Kriegella has been observed.
- This change in microbiota can increase susceptibility to pathogens, decrease nutritional metabolism, and influence the circadian rhythm.
- Notably, darkness promotes the proliferation of pathogenic bacteria such as Vibrio, a common pathogen in aquatic animals, and Roseovarius, associated with oyster disease.
Body Color Changes
- Exposure to total darkness can cause the shrimp’s body color to darken.
Finally, total darkness can have predominantly negative effects on shrimp, including reduced growth, metabolic changes, alterations in gut microbiota, and body coloration. While some studies suggest that cultivation in darkness is possible, results indicate that light exposure is essential for optimizing shrimp growth and health. Continuous darkness should be avoided due to its negative impacts on animal welfare and nutritional quality.
Types of Light Sources Used in Aquaculture
In shrimp farming systems, artificial light sources allow precise photoperiod control. The most common options include:
- LED Lights: With high energy efficiency, long lifespan, and the ability to emit different light spectra, they are ideal for aquaculture.
- Fluorescent Lights: Despite being less efficient, they are a cost-effective option for small systems.
- Controlled Natural Light: In semi-intensive systems, natural light is often supplemented with artificial sources to ensure consistent cycles.
Proper use of these sources not only reduces energy costs but also maximizes productivity.
Benefits of Proper Light and Photoperiod Management in Shrimp Production
Efficient lighting and photoperiod management offer multiple benefits:
- Improved Growth: Enhances body development and feed conversion.
- Higher Survival Rates: Reduced stress under controlled conditions increases survival rates.
- Superior Market Value: Controlled light exposure can improve shrimp coloration and size, boosting quality and market value.
These benefits translate into greater profitability and more sustainable production.
Challenges and Technical Considerations
Despite the benefits, implementing photoperiod control presents challenges:
- Initial Cost: Installing advanced lighting systems can be expensive.
- Training: Operators need training to manage automated systems.
- Environmental Impact: Energy use in intensive systems must be balanced with sustainable strategies.
Overcoming these challenges requires an integrated approach combining technology, research, and efficient management.
Future Research and Trends in Shrimp Lighting
Research in photoperiod and light in aquaculture continues to evolve. Emerging trends include:
- Smart LED Lights: Systems that automatically adjust intensity and spectrum based on biological needs.
- Photoperiod Impact on Microbiota: Further exploration of how light affects gut health and disease resistance.
- Energy Sustainability: Designing lighting systems that use renewable sources, such as solar energy, to reduce environmental impact.
These innovations promise to transform shrimp farming into a more efficient and environmentally friendly model.
Conclusion
Photoperiod and lighting management is an essential tool for maximizing efficiency in shrimp production. With advancements in technology and research, it is possible to implement more precise and sustainable strategies that benefit both producers and the environment. The future of aquaculture will largely depend on our ability to understand and optimize these fundamental factors.
References
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Jiao, L., Dai, T., Tao, X., Lu, J., & Zhou, Q. (2021). Influence of Light/Dark Cycles on Body Color, Hepatopancreas Metabolism, and Intestinal Microbiota Homeostasis in Litopenaeus vannamei. Frontiers in Marine Science, 8, 750384. https://doi.org/10.3389/fmars.2021.750384
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