INTRODUCTION
Metal contaminations of aquatic ecosystem have long been recognised as a serious pollution problem (Ayandiran et al., 2009). Heavy metal released into the environment find their way into the aquatic environment as a result of direct input, atmospheric deposition and erosion due to rain water which can be attributed to wide use of heavy metals in the environment for a lot of anthropogenic purposes (Kahay and Canli, 2000). This leads to elevated levels of metals in fishes due to uptake of these metals from their environment (Dupreez and Steyn, 1992; Seymore, 1994).
However, not all metals taken up by fishes accumulate due to their ability to regulate their body metal concentration to some extent (Romanenko et al., 1986). Excretion of metals has been reported via gills, bile/faeces, kidney and skin (Heath, 1987). There are five potential routes for pollutant to enter fishes – feed, non-food particles, gills, oral consumption of water and skin (Ayandiran et al., 2009). Subsequently, heavy metals are transported by the blood to either a storage point like the bones or to the liver for transformation and storage (Oronsaye and Ogbebo, 1995). Hence, contamination of fishes with heavy metals is a consequence of pollution of the environment and plays significant role in bioaccumulation of these metals in them.
In this study, assessment of bioaccumulation of some metals would be carried out in Momyrops rume, Momyrops caballus, Clarias gariepinus, Parachyna obscura, Hemisynodontis membranaceous fishes sourced from River Niger at Illushi, Esan South East Local Government of Edo State and those from River Null at Kiama, Kolokuma/Opokuma Local Government of Bayelsa State. The essence is to assess the level of contamination of the body water/environment of these fishes.
Illushi is an agrarian community. It is along the River Niger and fishes sold in their market are sourced from River Niger while fishes sold at Kiama are sourced from River Null in Niger Delta area where oil prospecting activities are taking place. This in some instances has been associated with oil spillage and other attendant problems. In this study, the level of different metals in different organs or tissue of similar species of fishes sourced from River Niger at the agrarian Illushi community and those obtained from River Null; in industrial or oil prospecting site at Kiama will be assessed. Many researchers have been concerned with the physiological effects and bio-concentration patterns of individual metals in aquatic ecosystems (Senthil et al., 2008).
1.1      JUSTIFICATION OF STUDY
Heavy metal contamination in our aquatic environment is constantly increasing principally due to industrial discharge of a considerable amount of untreated effluents into our rivers. The bio accumulation of heavy metals in tissues of aquatic organisms have been used as an indirect measure of abundance and availability of such metals in the aquatic environment (Grobler et al.,1991). Furthermore, heavy metals are seen as the most important toxic pollutants for aquatic organisms, as heavy metals are known to bio accumulate and concentrate to toxic levels at different stages of the food chain. Fish serve as an excellent biomarker of metal pollution in aquatic environment for many reasons; it occupies a higher trophic level in an aquatic ecosystem; therefore, they can normally accumulate heavy metals from food, water and sediments. Metal toxicity adversely affects the physical and physiological behaviour of fish. Heavy metals discharged into our aquatic environment can damage both the biodiversity and ecosystem, due to their toxicity and accumulative tendency in aquatic biota they pose a risk to fish consumers such as humans and wildlife because biomagnifications in tissue can lead to several clinical side effects (Senthil et al., 2008).
Fish is an important constituent of non-vegetarian diet of human, it is eaten to supply high quality protein rich in lysine and sulphur containing amino acids, it also provides calcium, iodine, trace elements (Fe, Mn, Zn, Se, Cu), vitamins and omega-3-polyunsaturated fatty acids.  In a situation where the fish is contaminated, the deleterious health effects that may be associated with the high content of toxic heavy metals in such fish can counteract the beneficial effects of consuming fish (Adeosun et al., 2015)
Oil prospecting activities releases a considerable load of heavy metals into our aquatic environment. The need to provide resource information on the effects of oil prospecting activities on aquatic life in Niger Delta area informs the need for this study. Presently, there is lack of information in this regard. Many researchers have been concerned with the physiological effects and bio-concentration patterns of individual metals in aquatic ecosystems (Villegas-Navarro and Villareal-Trevino 1989, Mohan and Choudhary, 1991; Peres and Pihan, 1991; Pelgrom et al., 1995; Senthil et al., 2008).
Hence, this study is designed to investigate the concentration of some heavy metals in the organs and tissues of Momyrops rume, Momyrops caballus, Clarias gariepinus, Parachyna obscura, Hemisynodontis membranaceous fishes sourced from River Niger at illushi and River Null at bayelsa in Niger Delta area of Nigeria.
1.2      AIM OF STUDY
The overall aim of the study is to provide animal model consequences of oil prospecting on aquatic animal life in Niger Delta.
1.3      SPECIFIC OBJECTIVES OF STUDY