High levels of molecular metabolites formed as products of metabolic reactions can be toxic to aquatic organisms. In aquaculture, the most problematic metabolites are ammonia, carbon dioxide, nitrite and hydrogen sulfide. These substances enter culture water via excretions from culture animals and organic decomposition. As explained in this course, metabolites can be limited through controlled feeding, mechanical aeration and treatments to maintain oxygen at the sediment-water interface.
Liming of aquaculture ponds between cycles and during production is an important management tool. Liming materials neutralize acidity in soil and water, and increase the alkalinity of culture water. Fertilization improves conditions for healthy, managed growth of phytoplankton and other microorganisms. Students will review the different types of organic and commercial fertilizer products, as well as how to establish suitable rates of application based on practical tests and past research.
Still water tends to develop defined layers based on temperature and chemical composition, which reduces water quality with greater depth. This course outlines the dynamics of circulation and explains what affects stratification in ponds and larger water bodies. It compares various types of mechanical aerators and their best uses in raising oxygen levels and improving bottom conditions. Learn about proper siting and site management at cage sites in lakes and reservoirs, as well.
The nutrients aquatic species take in through feed support healthy metabolism and growth. However, feed waste products and uneaten feed are a major source of water quality deterioration in aquaculture. Enroll in this course and learn to judge feed quality and establish an effective feeding regimen that answers the nutritional needs of the culture species. Understand feed conversion and feeding methods that provide maximal diets while minimizing waste.
In aquaculture, water must provide a healthy environment for culture species, support feeding and handle waste products. This course introduces various traits and chemical properties of freshwater, brackish water and ocean water, as well as how they are measured and managed. It also explains osmotic pressure in aquatic animals and their need to live in environments with limited ranges of salinity. Alkalinity and hardness are also covered.
Phosphorus is an essential mineral for fish and shrimp, and also a key regulator of phytoplankton growth in aquaculture ponds. Phytoplankton supply natural food and oxygen through photosynthesis, but can cause thermal stratification and reduce oxygen levels at night. This course describes the phosphorus cycle, as well as how to measure phosphorus and phytoplankton levels. Phosphorus and phytoplankton must be managed through controlled pond fertilization, stocking and feeding.
Dissolved oxygen concentration is a primary water quality gauge in aquaculture systems. Low concentrations stress culture animals and increase susceptibility to disease. This course explains the typical daily peaks in dissolved-oxygen levels and what conditions affect how animals absorb oxygen from water. Learn how to measure dissolved-oxygen concentrations, as well as target and maintain appropriate DO levels through feed and fertilizer management, and use of aeration.
Fish and shellfish must maintain fairly specific internal pH levels. Chemical changes in water can shift pH and affect cell function and even survival. This course explains the pH scale is an index of the hydrogen ion concentrations in water, which can swing widely in ponds due to levels of vegetation, temperature, aeration activity and bottom soil composition. Learn to maintain pH between 7 and 8.5 with liming treatments and controlled fertilization, stocking and feeding.
Suspended solids from source water, erosion, excess feed and feces can lower dissolved-oxygen levels, contribute to water pollution and cause thermal stratification. This course discusses solids measurement and recommends management through eliminating sources of turbidity and using controlled applications of coagulants, if necessary. Learn to control erosion by applying stabilization construction methods and treat turbid conditions with organic fertilizers or inorganic flocculants.
Water quality in ponds is influenced by interactions between chemical compounds in the water and those in bottom soils. Decomposition of organic matter on pond bottoms removes dissolved oxygen and can lead to the release of toxic metabolites. As described in this course, inputs can be reduced to improve sediment quality. Mechanical aeration helps maintain conditions at the soil-water interface. Bottom dryout between crops oxidizes organic matter and lessens its accumulation.