Aquaculture in brackish water refers to the cultivation of aquatic life in salinity levels that fall between freshwater and saltwater. It is an essential industry for both economic growth and global food security, especially in coastal areas. But two major obstacles in this industry are controlling pollution and preserving water quality. In order to preserve the environment and guarantee the well-being of cultivated species, efficient management techniques are crucial.
Water Quality Is Important
Aquatic species’ health, growth, and survival in brackish water aquaculture systems are largely determined by the quality of the water. Stress, disease outbreaks, and cultured organism death can all result from poor water quality. Salinity, dissolved oxygen (DO), pH, temperature, and the amounts of ammonia, nitrite, and nitrate are important factors that determine the quality of water. The ideal aquaculture environment requires careful monitoring and management of each parameter.
Important Water Quality Factors
- Salinity: For the particular species being cultivated, the salinity level needs to be kept within an ideal range. Osmotic stress, which is brought on by abrupt changes in salinity, can lower growth rates and make people more prone to illness.
- Dissolved oxygen (DO): Sufficient DO levels are necessary for aquatic creatures to breathe. Hypoxia brought on by low DO levels can result in stress and death. Stocking densities and aeration systems are two ways to regulate oxygen levels.
- pH: The metabolic processes of aquatic organisms are influenced by the pH level. An ideal pH range for most brackish water species is 7.5 to 8.5. In addition to being dangerous, extremely high or low pH levels can alter how deadly certain substances, like ammonia, are.
- Temperature: Growth and metabolic rates are impacted by temperature. For best growth, each species has a particular range of temperatures. In interior buildings, climate control systems, water exchange, and shade can all be used to regulate temperature.
- Ammonia, nitrite, and nitrate: These nitrogenous substances are released by aquatic organisms as a result of the decomposition of organic waste. High amounts of ammonia (NH3) and nitrite (NO2-) are hazardous, whereas nitrate (NO3-) is less dangerous but can cause eutrophication if it is released into natural water bodies.
Sources of Pollution in Brackish Water Aquaculture
There are several internal and external causes of pollution in brackish water aquaculture.
- Nutrient loading: Excess nutrients enter aquaculture systems through feed, fertilizers, and excreta, mainly in the form of nitrogen and phosphorus. Deterioration of water quality and nutrient accumulation can result from overfeeding and poor feed management.
- Organic Matter: The water’s organic load is influenced by decomposing plant matter, excrement, and uneaten feed. Oxygen depletion can result from high quantities of organic matter because microbial breakdown processes use up oxygen.
- Chemical Contaminants: Aquaculture-related pesticides, herbicides, and antibiotics can infiltrate the water system and build up, endangering the ecosystem and cultivated species alike.
- Heavy Metals and Industrial Pollutants: Aquatic life may be harmed by the introduction of heavy metals and other hazardous compounds into brackish water systems by industrial effluents, agricultural runoff, and other external sources.
Management Techniques for Controlling Pollution and Water Quality
For brackish water aquaculture systems to maintain water quality and reduce pollution, effective management strategies are crucial. Among these methods are:
- Water Exchange: Having regular water exchanges keeps contaminants at bay and water quality at its best. The stocking density and the particular requirements of the cultivated species determine the frequency and volume of water exchange.
- Sedimentation Ponds: These water features can be utilized to lessen the amount of organic and nutrient load in the water by settling out sediments. These ponds offer a practical means of controlling organic waste and suspended particles prior to water being released or cycled.
- Bio filters: Bio filters, also known as biological filtering devices, use advantageous bacteria to change toxic nitrite and ammonia into less toxic nitrate. Recirculating aquaculture systems (RAS) require bio filters as a necessary part to maintain water quality and minimize water exchange requirements.
- Integrated Multi-Trophic Aquaculture (IMTA): In IMTA, several species from various trophic levels are cultivated inside a single system. For instance, waste products from one species can be used as nutrients by another to develop algae, fish, and shellfish together. This method lessens nutrient accumulation and makes efficient use of resources.
- Probiotics: To outcompete harmful bacteria and break down organic matter, probiotics are good bacteria that can be given to aquaculture systems. They can enhance water quality and support a balanced microbial community in the water.
- Feeding Procedures: In order to minimize feed waste and nutrient loading, proper feeding procedures are essential. Feed conversion efficiency can be increased and uneaten feed can be reduced by using high-quality, nutritionally balanced feeds and proper feeding techniques.
- Aeration Systems: Aeration systems, which include diffusers, air stones, and paddlewheels, aid in keeping the water’s DO levels at a suitable level. To avoid hypoxia and meet the metabolic requirements of cultured organisms, proper aeration is crucial.
- Water Treatment Technologies: To eliminate pathogens, lessen organic matter, and enhance overall water quality, advanced water treatment technologies can be applied. Examples of these technologies are ultraviolet (UV) sterilization, ozone treatment, and bio char filtration.