International Journal of Aquaculture, 2017, Vol.7, No.25, 166-173
167
development and habitat transformation resulting from dam construction and human settlements are important
causes of molluscs’ population declines in many areas (Hunters et al., 1976; Yang et al., 2013). Most freshwater
molluscs species are highly sensitive to water quality because of their permeable skins and because they need a
good oxygen supply. Larval stages of unionids require fish as a host for development. As fish stock become
scanty, the parasitic larval stages of the molluscs lack host to complete their development. It therefore means that
loss of fin fish stock leads to loss of bivalve requiring the fin fish their development in an area. Continuing loss of
molluscs diversity is detrimental, not only to ecosystems around the world, but in the long run, to the welfare of
mankind itself (Svobodováet al., 1993). Indeed, molluscs are crucial to the integrity of ecosystems, the evaluation
of environmental health, and human well-being.
Some heavy metals have beneficial functions to the bodies of organisms while others are not and can be highly
toxic. They accumulate in the body tissue of organisms because they are rarely broken down (Ekpo et al., 2008).
However, large quantity of heavy metals and derivatives are discharged by industrial plants and municipal sewage
treatment plants into the aquatic ecosystems. They may also get into the water from polluted runoff in urban and
agricultural areas (Ayotunde et al., 2012).
Okpon River serves as a major source of drinking water and site of fishing activities. There are many fishing
landing sites along the river. These include: Ekurri beach, Okpon beach and Nsin beach. Where the river
transverse villages, there are sand mining activities. This forms a big industry in Ochon where the river
transverses Calabar-Ikom high way, English Sand beach and Men sand beach are equally found in Ochon. Other
sand beaches include those in Ekurri (Ekurri sand beach) and Nsin (Nsin sand beach), Onyen Okpon (Monkey
Agwu Okpa sand beaches). This equally provides livelihood for the inhabitants. There is relatively a high
population density along the river due to its reach resources (Ako and Salihu, 2004; Study.com, 2016). Logging
activities have been going on. As Rainforest Movement (2016) wrote ‘Logging has significantly reduced animal
habitat, shrinking the animal populations that serve as a traditional source of protein in Cross River State. Meat
obtained from feral animals commonly called bush meat that was once plentiful is now scarce (pers. observ.). The
plundering of trees which provide shelter has left whole areas without windbreakers or sufficient trees to check
the devastating rainstorms. Thus, the roofs of houses are often blown off by the slightest rainstorm.’ Because of
high anthropogenic activities, natural phenomenon like weathering and seapage of materials from surrounding
basements, there is likely to be inflow of metals into the river. In addition to indirect feeding of aquatic systems
with contaminants, humans feed the system with metal containing items like personal care products (Schueler,
2000; Burton and Pitt, 2007). Apart from metal pollution, climate change which is presently much talked about is
likely to affect the ecology of the river.
Due to the toxicity level of heavy metals concentrations in aquatic food items such as fish species, they have
received considerable attention in different places (Mohamed and Gad, 2008; Klavins et al., 2009; Ayotunde et al.,
2012; Ekpenyong et al., 2015). Many research interests have been generated on the integrity of aquatic
environment especially as it concerns heavy metal pollution (Rashed, 2001; Tawari-Fufeyin and Ekaye, 2007;
Yilmag, 2007; Yilmag et al., 2009). As Elder and Collins (1991) pointed concentration of metals in an organisms
cannot be extrapolated from place to place due to differences in individual organisms and environmental
characters, we work to investigate the concentration of some metals in
Malletia cumingii
in Okpon River.
2 Materials and Methods
2.1 Study area
Okpon River is a tributary of Cross River. It has its source from Etung Local Government Area of Cross River
State Hills. Okpon River flows from Ekurri in Etung Local Government Area and empties into Cross River. The
Okpon River is located in the southern part of Nigeria latitude 4°25”-7°0” North and longitude 7°15”-9°30” East.
The climate of the area is characterized by two seasons dry and raining. The raining season is (May-October) with
higher precipitation, while the dry season is (November-April) with low precipitation (Freund et al., 1995).
