Aquaculture: Water Quality Management

• Lecture 5 focuses on Water Quality Management in Aquaculture Technologies

Part 1: Pond Filling + Stocking

• Table 10 provides milkfish culture practices in earthen ponds, detailing the stocking density, food supply, pond size, pond depth and water management for extensive, modular, plankton, semi-intensive, and intensive culture systems.
• Table 4.5.2 outlines culture systems for shrimp production, listing stocking density, pond size, feeding habits, water management, and water depth for traditional extensive, modified extensive, semi-intensive, intensive, and super-intensive systems.

Part 2: Water Quality

• Key water quality parameters include salinity, temperature, light, turbidity, dissolved oxygen, pH, alkalinity & hardness, ammonia, nitrogen, phosphorus, hydrogen sulfide, and heavy metals.
• "Good water quality" enables successful propagation of the culture while requiring a strategic approach due to the complex interrelationships of many parameters.

Temperature

• Temperature fluctuation should be minimal, and abrupt changes of ≥ 5°C are stressful or lethal.
• Dissolved substances, suspended particulate matter and plankton influence increase of heat in water.

Salinity

• Salinity can be determined by measuring the refractive index using a refractometer.
• Fresh Water (FW): < 0.5 ppt
• Brackish Water (BW): 0.5 – 34 ppt
• Marine Water (MW): >35 ppt

Light

• Light provides illumination for efficient feeding and productivity in the system.
• Dissolved substances, suspended particulate matter, and plankton affect the penetration of light in water.

Turbidity

• Turbidity describes the degree by which the transparency of water is reduced.
• In general, water transparency is < 2,000 ppm and ideal Secchi disk: 30-40 cm

Dissolved Oxygen

• Dissolved oxygen is needed for respiration and bodily processes like metabolism.
• Dissolved oxygen aids the oxidation of metabolites in the environment, such as converting NH3 and H2S into nitrates and sulfates.
• Ranges of Expected Gains and Losses of Dissolved Oxygen Caused by Different Processes in Fish Ponds includes:
  • Gains through photosynthesis by phytoplankton (5-20mg/liter) and diffusion (1-5mg/liter).
  • Losses via plankton respiration (5-15mg/liter), fish respiration (2-6mg/liter), respiration by organisms in mud (1-3mg/liter) and diffusion (1-5mg/liter).
• Dissolved oxygen declines include high temperatures, increased salinity, or high altitude.
• Manage low dissolved oxygen in culture systems by:
  • Monitoring dissolved oxygen at critical times like dawn to 6 AM; avoiding overstocking, overfeeding and over fertilization are all key.
  • Install aerations if dissolved oxygen concentration remains at less than 3 or 4 ppm for prolonged periods.

pH

• pH refers to the quantity of hydrogen ions in the water.
• Natural waters are generally high in pH during the day and low at night.

Total Alkalinity

• Total alkalinity refers to the total concentration of bases (e.g., CO3(2-) and HCO3) present in the water expressed as mg/L or ppm of equivalent CaCO3.
• CO3(2-) and HCO3- ions serve as buffers in water, resisting sudden changes in pH.

Total Hardness

• Total hardness describes the concentration of metal ions, primarily calcium and magnesium, expressed in mg/L of equivalent calcium carbonate.
• Soft Water exhibits "temporary hardness' caused by dissolved calcium and magnesium bicarbonate ions, and measures <60 ppm.
• Hard Water exhibits “permanent hardness”, caused by dissolved calcium and magnesium sulfates or chlorides, and measures >120 ppm.

Ammonia

• Ammonia comes from organic Nitrogen of fecal material and dead remains broken down by microorganisms in a process called ammonification.
• Total ammonia is the sum of ionized (NH4+) and unionized (NH3) ammonia.

Nitrite

• Nitrite is prevalent at high pH levels and should be maintained within the limit of 0.1 ppm or lower for hatchery purposes.
• Nitrite toxicity converts hemoglobin into methemoglobin, which cannot carry oxygen effectively, potentially leading to hypoxia (lack of oxygen).

Nitrate

• Conversion from nitrites occurs at the ideal pH range of 7-8.5.
• Nitrate is the less toxic form of nitrogen in water.
• Maintain nitrate within a limit of 100 ppm or lower.

Hydrogen Sulfide

• Hydrogen sulfide is also known as H2S, originating from sulfide deposits in soil.
• When hydrogen sulfide is released in the water, it forms sulfuric acid and lowers the waters' pH.

Heavy Metals

• Heavy metals are metallic elements with high density.
• Heavy metals bioaccumulate and can prove toxic at high concentrations.
• Heavy metals include the following, with their respective values:
  • Copper (0.006 ppm)
  • Zinc (0.05 ppm)
  • Chromium (0.1 ppm)
  • Iron (0.5 ppm)
  • Cadmium (0.003 ppm)
  • Lead (0.03 ppm)
  • Manganese (0.01 ppm)
  • Nickel (0.100 ppm)
  • Mercury (0.002 ppm)
  • Polychlorinated biphenyls (PCB) (0.002 ppm)

Assignment

• Water quality assignment instructions state to refer to the water quality requirements for shrimp culture and identify the corrective measures needed for each parameter for levels outside the suitable range.