Aquaculture as Source of Environmental Contaminants: A Study of Earthen Pond versus Plastic Pond

Abstract

There is a need to meet up food demand by replenishing the continuously depleted population of fish stock available in natural water bodies as human population increases around the world. Man`s conscious attempt to increase fish production through aquaculture has played an important role in enhancing food security and human nutrition, especially in many developing countries. As a result, aquaculture provides controlled cultivation and harvest of aquatic organisms to ensure its year-round availability. Unlike land under cultivation, the world's oceans, lakes, rivers and streams are usually public, common resources and managing common resources could be problematic. In aquaculture, man-made water bodies are dammed for use, providing favorable conditions necessary for the survival of cultivated aquatic organisms. With key control on parameters such as water quality, stocking density, feed quality, aeration and mineral availability (Makori et al., 2017), the optimum condition for fish production has been achieved and the process has been explored for human benefits. The seemingly controlled environment for fish farming (the pond) presents a dynamic zone of activities. Its chemistry is expressed bythe physical, chemical and biological characteristics (Mwekaven et al., 2017; Makori et al., 2017) and assessed by pH, conductivity, alkalinity, acidity, hardness, chloride, sulphates, nitrates, phosphates, total solids, solid matters, dissolved oxygen, chemical oxygen demand, biochemical oxygen demand, and mineral composition (Imsland et al., 2007; Bhatnagar and Devi,2013). Also important is the pond's bottom zone, which may be composed of soil, organic solids, inorganic compounds and trapped gaseous components. It is a complex heterogeneous medium, which shows spatial variability in physical and chemical properties at micro and macro scales (Younis and Tesfamariam, 2017).Due to its adsorptive tendency, this bottom zone can be a carrier and potential source of contamination for the larger environment. The adsorption is strongly influenced by the prevailing pH, redox condition and relative concentration of ions present in the aqueous solution in contact with the zone. In aquaculture, aquatic organisms cultivated maybe plants, fish or shellfish (oysters), mussels, clams, shrimp, crabs, crayfish, etc. These organisms usually take-up minerals and trace metals from soil sediments and associated water. When fish are exposed to water laden with trace metals quantities above specified environmental standards, it becomes inimical to their growth and survival. This condition is also known to disturb the delicate balance of the aquatic