CHAPTER ONE1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDYAlthough biologist have been studying the effects of human activities on aquatic systems and its effects on fish production for decades, their findings have only relatively recently being translated into methods suitable for monitoring the quality of water bodies. Mostly, bio-indicators such as benthic macro-invertebrates, phytoplankton and zooplankton are among the common bio-indicator organisms used during bio-monitoring of water to determine the suitability for fish production (Tassi, 2009). Artificial (and in some cases natural) changes in the physical and chemical nature of freshwaters can produce diverse biological effect ranging from the severe (such as a total fish kill) to the subtle (for example, changes in enzymes level or sub-cellular components of organisms) (Pagano et.al., 2006), changes like these indicates that the ecosystem and its associated organisms are under stress or that the ecosystem has become unbalanced (Masona, 2007). Because flora and fauna of various trophic levels can integrate the effects of water quality or habitat changes over time, they become effective pollution indicators (Fernando, 2002). The concentration of a pollutant in an organism is the result of many variables such as the concentration of the pollutant in the water, the physical-chemical form of the pollutant, the membrane permeability of the organism, the type and quantity of food and its degree of contamination, the physiological state of the organism and the characteristics of the physical environment influencing the organism as well as the pollutant (Rose et.al., 2003). The response of biological communities or of the individual organism can be monitored in a variety of ways to indicate effects on the ecosystem. The co-existence and abundance of certain species at a particular location can indicate for example whether that habitat has been adversely altered (Pearl et al., 2003). The reactions of individual organisms such as behavioral, physiological or morphological changes can also be studied as responses to stress or adverse stimuli (for example caused by the presence of contaminants (Bailey et al., 2001).