In modern shrimp farming, particularly with species like Penaeus vannamei (Pacific white shrimp), ensuring optimal water quality is paramount. This is even more critical in Recirculating Aquaculture Systems (RAS), where water reuse and biosecurity are at the forefront. Key parameters like temperature, dissolved oxygen (DO), and salinity must be rigorously monitored and controlled to prevent disease, optimize growth rates, and maintain overall shrimp health. Let’s explore these vital parameters in detail.
1. Importance of Water Quality in Shrimp Farming
Water quality directly impacts shrimp health, growth, and productivity. In intensive systems like RAS, poor water conditions can lead to disease outbreaks, slow growth, and increased mortality, severely affecting profitability. The closed nature of RAS means that any deterioration in water quality happens more quickly than in traditional open systems. Monitoring and managing water chemistry is essential to prevent catastrophic losses.
Critical parameters include temperature, dissolved oxygen (DO), and salinity. These factors directly affect shrimp metabolism, immune function, and overall growth. By maintaining these parameters within optimal ranges, shrimp farmers can promote healthier, faster-growing shrimp populations.
2. Critical Variables
Temperature
Temperature plays a major role in shrimp metabolism and growth. As poikilothermic animals, shrimp depend on the environmental temperature to regulate their body temperature, making consistent temperature management essential for health and growth.
- Optimal Range: The recommended temperature for Penaeus vannamei is between 28°C and 30°C for juveniles and adults. Deviations outside this range reduce growth and increase vulnerability to diseases like white spot syndrome virus (WSSV) and Vibrio bacterial infections.
| Life Stage | Effect | Temperature | Reference |
| Post-larval, 0.02 g | SGR affected | <26°C, >31°C | Ponce-Palafox et al., 1997 |
| Juvenile, 3.9 g to adult | SGR affected | <28°C, >30°C | Wyban et al., 1995 |
| Broodstock 48 g – Male | Reduced sperm count | >26°C | Perez-Velazquez et al., 2001 |
| P. vannamei | Thermal preference | 26°C | González et al., 2010 |
| Post-larval PL16, Juvenile | Lethal (LC50) | <12.9°C | Pontinha et al., 2017 |
- Risks of Deviations: Temperatures below 26°C or above 30°C affect growth and immune function. Temperatures below 32.3°C increase susceptibility to WSSV, while temperatures above 32°C make shrimp vulnerable to Vibrio infections.
- Measurement: Use calibrated digital thermometers or automated systems with a margin of error of ±0.5°C. Monitor every 6 hours or continuously in RAS systems.
Dissolved Oxygen (DO)
Dissolved oxygen is critical for shrimp health and growth. Oxygen demand in RAS is high due to biofilters and dense stocking densities, making it essential to maintain optimal DO levels.
- Optimal Range: The recommended DO range for Penaeus vannamei is 4-5.5 mg/L. Lower levels reduce shrimp growth rates and can lead to mortality.
| Life Stage | Effect | DO Level | Reference |
| Juvenile, 6-8 g | SGR affected | <4 mg/L | Nonwachai et al., 2011 |
| Juvenile, 6-8 g | Survival affected | <2 mg/L | Nonwachai et al., 2011 |
| P. vannamei | Immune function | <3 mg/L | Fawen et al., 2009 |
| Larval to Adult | Lethal (LC50) | 0.57–1.23 mg/L | Zhou et al., 2014 |
- Risks of Deviations: DO levels below 3 mg/L lead to stress, reduced feed efficiency, and weakened immune responses. Levels below 2 mg/L can cause mass mortality within hours.
- Measurement: Use optical or electrochemical DO probes with a margin of error of ±0.1-0.3 mg/L. Measure every 2-4 hours or continuously in RAS systems.
Salinity
Salinity directly influences shrimp osmoregulation, energy expenditure, and growth rates.
- Optimal Range: The ideal salinity range for Penaeus vannamei is 20-25 psu. Extreme fluctuations can harm growth and increase disease susceptibility.
| Life Stage | Effect | Salinity | Reference |
| Post-larval, 0.1 g | SGR affected | <3 psu | Laramore et al., 2001 |
| Juvenile, 1.6-2.2 g | SGR affected | >49 psu | Bray et al., 1994 |
| P. vannamei | Isosmotic point | 24.7 psu | Castille & Lawrence, 1981 |
| P. vannamei | Susceptibility to WSSV | <15 psu | Lin et al., 2012 |
- Risks of Deviations: Salinity below 5 psu or above 49 psu can severely affect shrimp health. Sudden drops in salinity increase susceptibility to WSSV and other diseases.
- Measurement: Use refractometers or digital salinity probes. Measure salinity daily, especially in RAS systems where fluctuations can occur rapidly.
3. Measuring Tools and measurement frequency
Temperature Monitoring
- Types of Probes: Digital thermometers and automated probes are the most common tools in modern RAS systems. Automated systems integrate with monitoring software to provide real-time data.
- Approximate Cost:
- Digital handheld thermometers: $50 to $100 USD.
- Automated systems: $500 to $3,000 USD.
- Maintenance: Requires periodic calibration and regular cleaning to prevent fouling. Calibration is recommended every 3 months.
- Reliability: In intensive systems, real-time monitoring is essential for preventing temperature deviations. Automated systems can provide alerts for immediate action.
Dissolved Oxygen Monitoring
- Types of Probes: Optical DO probes (using luminescence technology) offer more precise measurements and lower maintenance than electrochemical probes.
- Approximate Cost:
- Optical DO probes: $1,500 to $3,500 USD.
- Electrochemical probes: $500 to $1,000 USD.
- Maintenance: Optical probes require calibration every 6 months and are resistant to fouling. Electrochemical probes need more frequent calibration and cleaning (every 2-4 weeks).
- Reliability: Optical DO probes are highly reliable in intensive RAS systems due to their accuracy and low maintenance needs. Continuous monitoring helps prevent hypoxia and mass mortality.
Salinity Monitoring
- Types of Probes: Manual refractometers and digital salinity probes provide precise measurements. Digital probes are ideal for continuous monitoring.
- Approximate Cost:
- Refractometers: $50 to $200 USD.
- Digital salinity probes: $300 to $1,500 USD.
- Maintenance: Requires calibration every few months and regular cleaning to avoid fouling, especially in high-salinity environments.
- Reliability: Continuous digital monitoring allows for timely adjustments and better control of salinity in super-intensive RAS systems.
4. Importance of parameters recording and tracking
Recording water quality parameters is critical in intensive RAS shrimp farming. By logging temperature, DO, and salinity data, shrimp farmers can analyze trends, anticipate seasonal changes, and respond to issues before they escalate.
- Trend Analysis: Regular recording helps spot gradual shifts in water quality, such as rising salinity due to evaporation or oxygen depletion during feeding. This allows for proactive management.
- Optimizing Health and Growth: Accurate records allow for fine-tuning water conditions to promote faster growth and better shrimp health.
- Combined Effects: By correlating data across multiple parameters, farmers can detect cumulative stress, such as how increased temperature can reduce DO levels, and take corrective action.
- Proactive Risk Mitigation: Historical data helps predict future deviations and adjust system settings before conditions deteriorate. Minimizing environmental stress reduces the risk of disease outbreaks like WSSV.
Conclusion
Maintaining the right balance of temperature, dissolved oxygen, and salinity in RAS shrimp farming is essential for optimal growth and health. With the proper tools and consistent monitoring, shrimp farmers can ensure the long-term success of their operations while mitigating risks associated with water quality deviations.
