الفهرس 
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Abstract
In present study, about 90 samples of three farmed freshwater fish species (Common Carp, Nile Tilapia and Mugil cephalus) classified into 30 samples of each species. (10 of each) were collected from different locations as (Damanhour, Kafr El Dawar and El Mahmoudia) fish market along Al-Boheira governorate, and we have chosen this species for this study because of their economic importance in Egypt, also this species consider the most vital farmed fish in many countries of the middle and orient east.
7.1. The concentrations of heavy metals in the muscles and livers of investigated fish species:
The result of present study point to presence of significant difference in the concentration of chromium, cadmium, mercury, zinc, iron, lead, selenium and nickel in between the muscles samples of investigated fish species(Common Carp ,Nile Tilapia ,Mugil cephalus) from different location of this study.
In a comparison between each fish species in different region of the study for chromium (Cr) levels in the muscles it was found that 100% of Common Carp and Mugil cephalus fish in three regions (Damanhour- Kafr El Dawar and El Mahmoudia) have concentration of chromium within the allowed limits, while in Nile Tilapia the result was 80,100 ,100% in ( Damanhour -Kafr El Dawar and El Mahmoudia), respectively, with an overall 93.3%, but it was noted that the levels of chromium in the liver samples of (Common Carp, Nile Tilapia and Mugil cephalus) in three regions were 100% higher than the permissible limits.
With regard to the cadmium level in the muscles it was found that 100% of Common Carp fish from three regions (Damanhour -Kafr El Dawar and El Mahmoudia) have concentration within the allowed limits, though in Nile Tilapia the result was 80,60 and 60% in three regions (Damanhour and El Mahmoudia) respectively, with an overall 73,3%.On the other hand in Mugil cephalus the result was 20,40 and 10% in three regions (Damanhour- Kafr El Dawar and El Mahmoudia), respectively with an overall 23,3% ,also it was found that the levels of cadmium in the livers where in a rate 100% higher than allowed limits in all fish species except Nile Tilapia species from Kafr El Dawar where the level of cadmium was higher than the permitted limit by 90%.
With reference to the following heavy metals ( mercury Hg and zinc Zn) it was found that all samples of three fish species from three regions 100% within the permissible levels either muscles or livers samples.
Regarding to iron (Fe) levels in the muscles it was noted that 100% of Common Carp and Nile Tilapia fish from three regions (Damanhour- Kafr El Dawar and El Mahmoudia) have a concentration within the allowed limits, while in Mugil cephalus the result was 100% higher than permissible limit in Kafr El Dawar, 20 and 30% accepted samples in(Damanhour and El Mahmoudia) respectively with an overall 16, 6%, in three regions, but it was noted that the levels of iron (Fe) in the liver samples were in a rat 100% higher than allowed limits in all fish species except Tilapia fish from( Damanhour and El Mahmoudia) where the level of iron was within the permissible limits by 50 and 20% respectively with an overall 23,3%, in three regions.
Referring to copper (Cu) it was noted that the muscles of Common Carp and Nile Tilapia fish from three regions (Damanhour- Kafr El Dawar and El Mahmoudia) contain 100% concentrations within the allowed limits, while the levels of copper (Cu) in muscles samples of Mugil cephalus were in permissible limits by 60,20 and 40% in (Damanhour- Kafr El Dawar and El Mahmoudia), respectively, with an overall 40%, but it was noted that the levels of copper (Cu) in the liver samples were in a rat 100% higher than allowed limits in all fish species except Nile Tilapia fish from( Damanhour and El Mahmoudia) where the level of copper was within the permissible limits by 50 and 30%, respectively with an overall 26,6%, in three regions.
With regard to lead (Pb) it was noticed that the muscles of Common Carp and Nile Tilapia fish collected from (Damanhour- Kafr El Dawar and El Mahmoudia) contain concentrations 100% within the allowed limits. On the other hand muscles samples of Mugil cephalus were in permissible limits by 80, 50 and 40% in (Damanhour- Kafr El Dawar and El Mahmoudia), respectively, with an overall 65,6%, but it was noted that the levels of lead (Pb) in the liver samples were in a rat 100% higher than allowed limits in all fish species except Nile Tilapia and Mugil cephalus fish collected from Kafr El Dawar where the level of lead (Pb) was permitted limit by 40 and 10%, respectively.
With reference to selenium it was found that all samples of three fish species from three regions 100% higher than allowed limits either muscles or livers samples.
Referring to Nickel (Ni) levels in muscles of fish species it was found that 100% of the fish have concentrations within permissible limited, but it was noted that the levels of Nickel (Ni) in the liver samples of Common Carp fish collected from (Damanhour- Kafr El Dawar and El Mahmoudia) and Nile Tilapia collected from (Kafr El Dawar - Elmahmodua) contain concentrations 100% within the allowed limits, Tilapia collected from Damanhour contain levels of Nickel (Ni) in the liver samples within permissible limited by 60%, also it was found the levels of Nickel (Ni) in the livers samples of Mugil cephalus fish were in a rat 100% higher than allowed limits in all regions except Mugil cephalus fish from Damanhour where the level of Nickel (Ni) was higher than the permitted limit by 90%.
It was clear that the pollution of environment with heavy metals is reflected on the fish species but it was concentrated in the livers of the fish and not in the muscles therefore it is not recommended to use the livers of these fishes for human consumption.
7.2. Proximate composition analysis of fish species:
The result of this study point to the existence of significant differences between the three species and no significant difference within the same species in the analysis of protein, fat, fiber, ash and moisture.
The results of overall protein analysis in the three regions in Common Carp; Nile Tilapia and Mugil Cephalus were 18.64±0.12c, 19.71±0.17b and 20.87±0.16a in the three species, respectively. Results clarified that the three species were rich in crude protein and within the permissible limits. It was noted that the protein percentage was in the order of Mugil cephalus ˃ Tilapia˃ Common carp.
The overall fat content in the three fish species (Common Carp, Nile Tilapia, and Mugil Cephalus) were 4.62±12a, 1.80±0.10c and 3.17±0.05b in the three species, respectively.
The overall fiber content in the three fish species (Common Carp, Tilapia, and Mugil Cephalus) were 2.87±0.05a, 1.11±0.02c, and 1.29±0.04b in the three species respectively.
It was prominent that the fiber percentage was in the order of Common carp ˃Mugil cephalus ˃ Tilapia.
The overall ash content in the three fish species (Common Carp, Nile Tilapia, and Mugil Cephalus) were1.12±0.01c, 1.33±0.02b and 1.39±0.02a in the three species, respectively.
The overall moisture content in the three fish species (Common Carp, Nile Tilapia, and Mugil Cephalus) were 72.33±0.44c, 76.05±0.20a and 73.30±0.19b in the three species, respectively.
Finally, the influence of heavy metals on public health, as well as recommendations to applied for protection consumers and the affected fish were discussed in this study.