New technology for water quality monitoring in intensive aquaculture

Water quality monitoring for aquaculture

Aquaculture is increasingly considered as an integral component in the search for global world food security and economic development. The monitoring of farming processes can optimize the use of resources and improve its sustainability and profitability. The automation of aquaculture production systems will allow the industry to improve environmental control, reduce catastrophic losses, reduce production cost, and improve product quality. Equipment for measuring and recording various parameters is more and more commonly used in aquaculture, especially in intensive aquaculture. Such equipment can be used for controlling and monitoring environmental conditions so adjustment can be made to obtain optimal production results. The most important parameters to be monitored and controlled in an aquaculture system include temperature, dissolved oxygen, pH, ammonia, nitrates, salinity, and alkalinity, since they directly affect animal health, feed utilization, growth rates and carrying capacities.

Water temperature affects the feeding pattern and growth of fish. Fish generally experience stress and disease breakout when temperature is chronically near their maximum tolerance or fluctuates suddenly. Warm water holds less dissolved oxygen than cool water. Oxygen consumption is linked to size of fish, feeding rate, activity level and pond temperature. The amount of dissolved oxygen in water increases as temperature reduces and decreases when salinity increases. Low dissolved oxygen concentration is recognized as a major cause of stress, poor appetite, slow growth, disease susceptibility and mortality in aquatic animals. It is generally accepted that the minimum daily dissolved-oxygen concentration in husbandry systems is of the greatest concern. Not only is dissolved oxygen important for fish respiration, it is also important for the survival of phytoplankton, the organism which breaks down toxic ammonia into harmless forms.

The acceptable range of pH for fish culture is usually between pH 6.5 to pH 9.0. When water is very alkaline (>pH9), ammonium in water is converted to toxic ammonia, which can kill fish. On the other hand, acidic water (<pH5) leaches metals from rocks and sediments. These metals have an adverse effect on the fish’s metabolism rates and ability to take in water through their gills and can be fatal as well. Since failure of any component can cause catastrophic losses within a short period of time, the system must be reliable and constantly monitored. Thus, precise measurements and controls are necessary for the success of an intensive aquaculture system.

Information and Communication Technologies:

In recent years, the development of different Information and Communication Technologies (ICT) in conjunction with the creation of low-cost small sensors have made it possible to monitor many processes. Wireless sensor networks (WSN) are a clear example as they are often used for farming purposes. WSN have been used for monitoring the three vigor, greenhouses and citrus crops. Moreover, WSN are employed to monitor the state of farm animals such as goats or cows. Some systems have been proposed for monitoring fish farms. Most of them are based on monitoring water quality including just a couple of water parameters to be monitored. Moreover, they usually employ commercial probes. The commercial probes for underwater monitoring have a high cost. Thus, if a WSN were to be utilized to monitor several parameters using commercial probes in all the production tanks, the cost of the system would be unaffordable for the fish farms. Some of the latest technology available in water quality monitoring for aquaculture and potable reuse water will be described briefly below.

iTOXcontrol:

The iTOXcontrol is the most versatile screening and Water Quality Monitoring system in the world with unique options. Integrated and automated cultivation of the reagents inside of the instrument.
Information can be sent to an internet database to support decision making for alarm monitoring and modelling.
Integration of different optional sensors which creates a combined system for Early Warning and Water Quality Monitoring:

  • Option 1: UV-VIS sensor
  • Option 2: Algae sensor (for Chlorophyll-a and blue-green algae)

Option 1: addition of TOC/BOD/COD/DOC/UV254/SAC254/NO3-N/TSS

  • Optical UV/VIS sensor
  • Absorption spectrum range 204-900 nm
  • Automatic cleaning and 4 sample streams
  • Turbidity compensation
  • UV-Pro calibration software, UV spectrum management and calibration

Option 2: addition of Chlorophyll-a and Blue-green algae

  • Fluorescene detector with 7 wavelengths
  • Total chlorophyll: 0-200 µg/l (Chl.-a, green-algae + blue-green algae)
  • Cyano chlorophyll: 0-200 µg/l (Chl.-a, blue-green algae)
  • Turbidity and CDOM compensation
  • Range: 0-200 µg chl-a/l
  • Turbidity: 0-200 NTU
  • Transmission: 0-100%

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Author

  • Manager, Aquaculture, Department of Animal Sciences, Stellenbosch University

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