الفهرس 
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Abstract
The aim of the present study is to assess some heavy metals such as, Zinc, copper, lead, Cadmium and Nickel in muscles, liver, gills and gonads of fish cultured at Damietta Governorate, and to compare the obtained values with those of cultured fish in various regions of the world. from the health and economic point of view, the metal concentrations in fish edible organs will be compared with the maximum international permissible limits to ascertain the suitability of these fishes for human consumption.
To carry out this study, Fish were collected from four fish farms in Damietta Governorate during October and December, 2018:
Farm 1. Is the governorate farm ( called also El-Ratama fish farm), it has total area of 1856 acres, but 947 acres only are used in fish culture . The farm is divided into five basins. The following fish species were collected from this farm : Nile tilapia (Oreochromis niloticus), Thin-lipped mullet (Liza ramada), flathead grey mullet (Mugil cephalus), golden grey mullet (Liza aurata), leaping mullet (Liza saliens) and blue spot mullet (Valamugil seheli) , European sea bass (Dicentrarchus labrax) , gilthead sea bream (Sparus aurata) and The spotted sea bass ( Dicentrarchus punctatus) .
Farm 2. Is situated inside Lake Manzala, has an area of 12 acres and water depth of 1-1.5 m. The following fish species were collected from this farm: flathead grey mullet (Mugil cephalus) Thin-lipped mullet (Liza ramada), gilthead sea bream (Sparus aurata), the spotted sea bass (Dicentrarchus punctatus) and leaping mullet (Liza saliens).
Farm 3. Has an area of 30 acres divided into 6 basins. The following fish species were collected from this farm: flathead grey mullet (Mugil cephalus), Thin-lipped mullet (Liza ramada), European sea bass (Dicentrarchus labrax), gilthead sea bream (Sparus aurata), and the spotted sea bass (Dicentrarchus punctatus).
Farm 4. Nile tilapia (Oreochromis niloticus) and leaping mullet (Liza saliens) were taken from this farm.
The collected fish brought to the laboratory, weighed, measured and dissected. Part of epiaxial muscle, liver, gills and gonads were taken out, weighed, dried in oven at 105oC, digested by Nitric acid (HNO3) and Hypochloric acid (HCLO4), filtered and diluted by distilled water. Heavy metals (Cu, Zn, Pb, Cd and Ni) were measured using an Atomic Absorption Spectrophotometer at Faculty of Science, Damietta University.
The present results indicated the following:
Fish of Farm 1
Zn concentrations showed a highly significant differences between the organs of the investigated fishes. Gills was the major sites of Zn accumulation in all fish species containing the highest level of this metal (354.11) in V. seheli. While muscles of all the investigated fish had the lowest concentration of it fluctuating from 12.67 (M.cephalus) to 24.97 (O.niloticus).
Cu concentrations varied significantly (P < 0.001) between the organs of the investigated fishes. Liver was the organ which had higher concentrations of Cu with a broad range of 34.71(S.aurata) and 113.84 (L.saliens) .Cu concentrations in muscles had the least concentrations between the fish organs and ranged from 2.36 (M.cephalus) to 4.96 µg/g dry wt. (O.niloticus).
Ni concentrations showed a significant variations between the organs of the investigated fishes .The highest Ni accumulation (25.45) was recorded in the gonads of O.niloticus, while muscles had the lowest accumulation of it with a range between 1.62 (L.amada) to 5.08 µg/g dry wt. (O.niloticus).
The highest level of Cd was found in the gonads of S.aurata (6.62) µg/g dry wt. . Muscles contained the least concentrations of Cd and its levels ranged from 0.27 (V.seheli) and 0.72 µg/g dry wt. (L.amada).
Zinc showed positive significant correlation with Nickel (r=0.322) and cadmium (r=613). Nickel had positive correlation with cadmium (r=0.722).
Fish of Farm 2
Zn concentrations varied significantly between the organs of these fishes. S. aurata accumulated in their gills the highest concentration of Zn (337.61), while muscles of M.cephalus contained the lowest value of it (14.53). In muscles, Zn ranged from 14.53 (M.cephalus) to 33.72 µg/g dry wt. (L.ramada).
Cu concentrations showed a significant variation between the organs of the investigated fishes. Liver of all the investigated fishes accumulated the highest levels of Cu (46.01, 76.97, 129.21, and 43.08) µg/g dry wt. For M.cephalus, L.ramada, D.punctatus, S.aurata respectively. Fish muscles had the least concentrations of Cu fluctuating between 2.80 (M.cephalus) and 5.65 (Liza ramada) µg/g dry wt.
The highest levels of Ni (6.61) was found in the liver of L.ramada, while the least concentration (1.31) of it was detected in the muscles of L.ramada also. Ni levels in muscles ranged from 1.31 (L.ramada) to 1.77 µg/g dry wt. (D.punctatus).
Gills of L.ramada accumulated the highest levels of Cd (4.04) µg/g dry wt. Fish muscles had the least concentrations of Cd fluctuating between 0.68 (M.cephalus) and 1.28 µg/g dry wt. (D.punctatus)
Zinc showed positive significant correlation with cadmium (r=0.305). Nickel had significant positive correlation with Copper (r=0.787) and cadmium (r=0.750). There was a remarkable significant correlation between copper and cadmium (r=0.591).
Fish of Farm 3
Zn concentrations varied significantly between liver, gonads and muscles of fishes. L.ramada accumulated in their gills the highest concentration of Zn (234.60), while M.cephalus contained the lowest value of it in their muscles (11.12). Fish muscles had the least concentrations of Zn ranging from 11.12 (M.cephalus) to 35.59 µg/g dry wt. (D. labrax).
Cu concentrations in liver and gonads showed a significant variations. Liver of all the investigated fishes accumulated the highest levels of Cu (274.96, 181.71, 299.40, 115.82, and 84.24) µg/g dry wt. For M.cephalus, L.ramada, D.labrax, D.punctatus, S.aurata respectively. Fish muscles had the least concentrations of Cu fluctuating between 2.07 (M.cephalus) and 5.03 µg/g dry wt. (D.punctatus).
Gills of fish of this farm accumulated the highest levels of Ni which fluctuated from 5.01 (D.punctatus) to 6.50 µg/g dry wt. (L.ramada).
Gonads of D.labrax accumulated the highest levels of Cd (3.43) µg/g dry wt. . Fish muscles had the least concentrations of Cd fluctuating between 0.43 (M.cephalus) and 1.09 µg/g dry wt. (D.labrax).
Zinc showed positive significant correlation with nickel (r=0.611) and cadmium (r=0.540), while it had a significant reversal correlation with copper (r=0.245). There was a remarkable significant correlation between nickel and cadmium (r=0.594).
Fish of Farm 4
L. saliens accumulated in their gills the highest concentration of Zn (283.95), while O.niloticus contained the lowest value of it in their liver (13.36). Fish muscles had Zn levels ranging from 22.42 (O.niloticus) to 26.25 µg/g dry wt. (L.saliens). Liver of all the investigated fishes accumulated the highest levels of Cu (72.17, 59.07) µg/g dry wt. For L.saliens and O.niloticus respectively.
Ni concentrations varied significantly between liver, gills and gonads of fishes. Fish muscles had the least concentrations of Ni ranging from 0.73 (L.saliens) to 0.84 µg/g dry wt. (O.niloticus).
Gills of both O.niloticus and L.saliens accumulated the highest levels of Cd (2.12 and 2.30) µg/g dry wt. respectively. Fish muscles of the two fish species (O.niloticus and L.saliens) had the least concentrations of Cd fluctuating between 0.80 (L.saliens) and 0.83 µg/g dry wt. (O.niloticus).
In general, the concentrations of heavy metals in muscles of the investigated fish were as follow: Zn: 11.12 – 35.59, Cu: 2.07 – 5.65, Ni: 0.73 – 0.84, Cd: 0.27 – 1.26 µg/g dry wt. Accordingly, the metals levels in the muscles (the edible parts) of the investigated fish samples are in the safe limit for human consumption as reported by FAO.
Although, it is rarely to consume the liver and gill of fish by human, they represent a good bio indicator for the presence of heavy metal in the surrounding environment.