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International Journal of Aquaculture, 2014, Vol.4, No.20 118
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122
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to 80.8 µg/100g, maximum in
M. anguilloides
and
minimum in
P. annectens
, while the range in head was
91.25 µg/100g in
M. niloticus
and 74.4 µg/100g in
M.
anguilloides
.
Figure 1 The concentration of heavy metals in muscles of seven
commercial Nile fish
Figure 2
The concentration of heavy metals in heads of seven
commercial Nile fish
Results from this study revealed significant
differences (p<0.05) in the distribution of heavy
metals between muscles and head of the studied
species of fish. The head concentrates higher levels of
Mo, Ba, Mn and B in all species of fish than the
muscles. Ahmed et al.,
(
2010) also observed more
concentration of minerals and heavy metals in head of
of fish species. Accumulation of different heavy
metals depends on many factors such as the
physiological needs, feeding habits and genetic
composition, sex of each fish species and the
biochemical significant role of each metal
(Kamaruzzaman et al., 2010). Bo was the most
common heavy metals in both tissue and heads
followed by Mn, Ba and Mo. The level of Be and Si
was not significantly (P>0.05) different between the
tissues and heads of all species.
Protopterus annectens
was observed to contain the least level of most of
heavy metals in both tissues and head compared to the
other species. The main reason could be the different
habits and habitat of
P. annectens
because the fish is
found in marginal swamps and backwaters of rivers
and lakes. It normally lives on flood plains, and when
these dry up it secretes a thin slime around itself which
dries into a cocoon. So the fish is not continuously
exposed to pollutants in the Nile like other species.
Generally, heavy metal concentrations in the muscles
of freshwater fish vary considerably among different
studies (Papagiannis et al., 2004; Yilmaz et al., 2007;
Ahmed et al., 2010; Njogu et al., 2011; Opaluwa et al.,
2012; Mohammed and Osman, 2014), possibly due to
differences in metal concentrations and chemical
characteristics of water from which fish were sampled,
ecological needs, metabolism and feeding patterns of
fish, and also the season in which studies were carried
out. The variation in metal concentrations could also be
due to the presence of major sources of metal pollution,
intensive human activity and discharge of municipal
waste and industrial effluents.
Fish are often at the top of the aquatic food chain and
have the tendency to concentrate large amount of
some heavy metals from the water (Mansour and
Sidky, 2002). Bioaccumulation of heavy metals is
toxic to fish (Chattopadhyay et al., 2002; Ayotunde
and Offen, 2012). Be and Ba are considered as
potential toxic metals. Soluble Ba compounds are
poisonous due to release of the soluble Ba
. The
health risk limits established (HRLs) were 2.0 and
0.00008 mg/L for barium and beryllium, respectively
(WHO, 1985). Manganese is an essential element and
shows relatively low toxicity to aquatic biota. It is
rarely found at concentration above 1mg/L in natural
freshwater (Hellawal, 1986). The concentration of Mn
in water can increase due to the influence of industrial
wastes on the Nile. Adverse sublethal effect on fish
occurs at Mn concentration of 0.278 g/L. These metals
may alter the biochemical parameters in both blood
and other organ tissues and affect the physiological
activities and development of the fish (Bogut, 1997;
Mohamed and Gad, 2008). Metal stresses were
reported to cause reproduction failure and losses in
fish populations (Adham et al., 1999; Saeed and
Shaker, 2008). The gills serve as respiratory organs
through which ions are absorbed (Khan et al., 2011).