Vol.2, No.11, 1302-1311 (2010) Natural Science
http://dx.doi.org/10.4236/ns.2010.211158
Enzymatic and histopathologic biomarkers as indicators
of aquatic pollution in fishes
Alaa G. M. Osman1*, Abd-El –Baset M. Abd El Reheem1, Khalid Y. AbuelFadl2,
Ali G. GadEl-Rab1
1Department of Zoology, Faculty of Science, Al-Azhar University (Assiut Branch), Assiut, Egypt; *Corresponding author: os-
2The Egyptian Environmental Affairs Agency (EEAA), Assiut, Egypt
Received 6 August 2010; revised 20 September 2010; accepted 25 September 2010.
ABSTRACT
In the present study we investigated the altera-
tion in the activity of two metabolic enzymes
[Glucose-6-Phosphate Dehydrogenase (G6PDH)
and Lactate Dehydrogenase (LDH)] and the his-
tological changes on liver and gills of the African
catfish Clarias gariepinus collected from 6 sites
along the river Nile, from its spring at Aswan to
its estuary at Rosetta and Damietta branches.
The results showed that the physical and chem-
ical parameters of the water collected from Da-
mietta and Rosetta branches were higher than
those of the water collected from other sites.
Remarkable alterations in the activity of the se-
lected enzymes in the liver and muscles of the
African catfish were detected. These alterations
go in parallel with the elevation in the levels of
chemical parameters detected in the water of
Damietta and Rosetta branches as a result of
pollution stress in these areas. The activity of
G6PDH was significantly (p < 0.05) decreased
from Aswan to Rosetta and Damietta recording
the highest value at Rosetta followed by Dami-
etta water. The activity of LDH showed a signifi-
cant elevation (p < 0.05) in activity in the liver
and muscles of fishes collected from Rosetta
and Damietta branches comparing to other sites.
These alterations in enzymatic activities were
followed, in the present study, by the occurrence
of histological lesions and clear damage in liver
and gill tissues of the African catfish collected
from the same sites. Thus we may conclude that,
the altered activities of G6PDH and LDH could
be useful biomarkers of water pollution. At the
same time, histopathology provides a reliable,
easily quantifiable index of low-level toxic stress
to a broad range of environmental pollutants.
Keywords: Metabolic enzyme; Histopathology;
Biomarker; aquatic pollution; Rive Nile; African
catfish
1. INTRODUCTION
Contamination of fresh water with a wide range of
pollutants has become a matter of concern over the last
few decades [1,2]. Water pollution is one of the principal
environmental and public health problems that Egyptian
River Nile are facing [3]. The Nile represents the main
freshwater resource for the country, meeting nearly all
demands for drinking water, irrigation, and industry.
During its transit through Egypt, the river Nile receives
numerous non-point and point source discharges[4].
Even with the presence of numerous studies on aquatic
pollution [5-17] information about the biological effects
of pollution on the aquatic organism is lacking and show
many gaps. Fish have been the most popular choice as
test organism and for monitoring aquatic toxicity be-
cause they are presumably the best-understood organ-
isms in the aquatic environment, their large mobility
allows them to assess large –scale regional affect, and
also due to their importance to man as a protein source
[18,19].
Biochemical and physiological indicators such as en-
zymes, could be used (as biomarkers) to identify possi-
ble environmental contaminations before the health of
aquatic organisms is seriously affected [20,21] and to
develop water quality indices [22-26]. Such a biochemi-
cal approach has been advocated to provide an early
warning of potentially damaging changes in stressed fish
[27]. In toxicological studies of acute exposure, changes
in concentrations and activities of some enzymes may
reflect cell damage in specific organs [27,28]. Glu-
cose-6-Phosphate dehydrogenase (G6PDH) has long
been recognized as an antioxidant enzyme [29-31] and is

A. G. M. Osman et al. / Natural Science 2 (2010) 1302-1311 1303
relevant as a marker for carcinogenesis in mammals and
also as a biomarker of pollution-induced carcinogenesis
in fish. The cytoplasmic enzyme lactate dehydrogenase
(LDH) is widely used as marker of organ or tissue le-
sions in toxicology and in clinical chemistry [32-34].
This enzyme commonly reflects the metabolic capacity
of a tissue. G6PDH and LDH are key factors in the me-
tabolism with high sensitivity to pollutants [25,35-38].
Altered morphology, or altered structure, is the ex-
pression of the disease process that is examined by the
pathologist. Histopathology is the microscopic evalua-
tion of these disease processes [36,39,40]. It is a very
powerful, subjective tool which may be used to establish
primary and secondary disease patterns in populations of
fish. Most biomarkers are narrow in their expression
whereas pathology is broad in its evaluation [41]. There
is a dearth of literature concerning the critical evaluation
of fish histopathology in environmental effects monitor-
ing.
The present paper is a part of a detailed investigation
entitled (Biomonitoring of the river Nile pollution using
biomarker responses in fishes). The present part aimed
to study the alteration of the selected metabolic enzymes
(G6PDH and LDH) and the histological changes on the
liver and gills of the African catfish (Clarias gariepinus)
as biomarkers in combination with chemical analysis of
the water from six different sites along the whole course
of the river Nile from its spring at Aswan to its estuaries
at Rosetta and Damietta.
2. MATERIALS AND METHODS
2.1. Study Area
The program of monitoring had been planned and im-
plemented to evaluate the quality of water and the influ-
ence of the drained water on the aquatic biota. Eighteen
different sampling points from six sites (three points for
each site) were selected along the whole course of the
river Nile from its spring at Aswan to its estuaries at
Rosetta and Damietta (Figure 1).
Sites Corresponding points
Aswan Aswan city, Aswan dam, and Kom-Umbo.
Qena Armant, Qena, and Naj-Hamadi.
Assiut Sedfa, Assiut, and Qusia.
Beni-Suef Al-Fashen, Beni-Suef, and Al-Wasta.
Damietta Zefta, Mansoura, and Damitta.
Rosetta Cairo, Kafr-Elzeyat, and Rasheed.
2.2. Water Analysis
Four water samples were collected using polyvinyl
chloride Van Dorn bottle (5 L capacity) at two meters
depth from the selected points along the main course of
Figure 1. Map showing the sampling sites along the whole
course of the river Nile from its spring at Aswan to its estuary
at Damietta and Rosetta branch.
the river Nile. Water samples were kept in a one-litre
polyethylene bottle in ice box and analyzed in the labo-
ratory. Some of the physicochemical parameters includ-
ing the electrical conductivity of the water samples
(mScm-1), pH, water temperature (° C) and Turbidity
(NTU) were measured by using water checker U-10 Ho-
riba Ltd. The other water criteria [Chemical oxygen de-
mand (COD), Total Organic Compound (TOC), Total
solids (TS), ammonia (NH3), Nitrate (NO3) Orthophos-
phate (O-PO4) Chloride (CL) Florid (F) Sulfate (SO4),
Phenolics (Phenol)] were measured according to the
traditional manual methods [42].
Total Pb, Cu, Cr, Mn, Zn, Hg, Fe, Cd were measured
after digestion using Graphite Furnace AA (GFAA) spec-
troscopy. A mixture of nitric acid and sample was re-
fluxed in a covered Griffin beaker. After the digestate has
been brought to a low volume, it was cooled and brought
up in dilute nitric acid (3% v/v). The sample was filtered,
allowed settling and prepared it for analysis.
2.3. Measurement of Enzyme Activity
The activities of the selected enzymes were measured

A. G. M. Osman et al. / Natural Science 2 (2010) 1302-1311 1304
according to a modified protocol based on [25,43]. Liver
and muscles samples of 24 African catfish collected
from the selected sites were pulverized under liquid ni-
trogen and about 100 mg of ground tissue powder was
added to 5 vol. of buffer (50 mM Tris, pH 7.4, 1 mM
EDTA and 2 mM MgCl2). Tissue was homogenized
briefly with an Ultra-Turrax (temperature was main-
tained at 4 ºC during homogenization). The homogenate
was centrifuged for 15 min at 10,000 Xg and 4º C and
supernatants were used for the enzyme activity assays
using spectrophotometer (Micro Lab 200 Vital Scientific,
Dieren, The Netherlands) at a wavelength of 340 nm and
at 37 ºC using kits, Stanbio LDH (UV-Rate) procedure
no. 0940 USA for the quantitative determination of lac-
tate dehydrogenase and RANDOX Laboratories Ltd.,
PD410, UK BT294QY, for the quantitative determination
of glucose-6-phosphate dehydrogenase [44]. The catalytic
activities of the selected enzymes was calculated in ac-
cordance with the recommendations of the French Society
of Clinical Biology and was expressed as U/g tissues.
2.4. Histological Investigations
Liver and gills of 24 African catfish were collected
from the selected sites. The organs were fixed in Bouin’s
solution, dehydrated, embedded in paraffin wax and sec-
tioned at 4-7 μm. Slides were stained with haematoxylin
and eosin and examined microscopically [45].
2.5. Statistical Analysis
All values from chemical analyses and enzyme activi-
ties are presented as mean ± SD. Data obtained from the
experiment were subjected to one way analysis of vari-
ance (ANOVA) test using the Statistical Package for the
Social Sciences [46].
3. RESULTS
3.1. Water Analysis
The results of means and SD of the studied physical
and chemical parameters for water samples are given in
Table 1. According to the present results the pH seems
to be constant all over the river Nile. All the pH values
were in alkaline side (7.8 to 8.4). Electrical conductivity
showed lowest values at Aswan (0.257 mScm-1) and the
highest value were recorded at Rosetta (0,576 mScm-1)
followed by Damietta (0.379 mScm-1) with a significant
(p < 0.05) increase from Aswan to Damietta and then
Rosetta branch (Table 1). Chemical oxygen demand
(COD) and Total organic compound (TOC) were sig-
nificantly (p < 0.05) higher in the water of Rosetta
branch comparing to the other sites. The lowest values of
such parameters were detected in the Aswan and Qena
(Table 1). The value of COD in Rosetta branch, Assiut
and Aswan was higher than the permissible limits. The
highest concentration of the total solid (TS) was detected
in the water of Rosetta followed by Damietta branch.
The lowest value of TS was recorded in the water of
Aswan followed by Qena (Table 1). The concentration
of ammonia and nitrate were lower than the permissible
limits along the whole course of the river Nile but they
still higher in the water of Rosetta and Damietta branch
comparing to Aswan site (Table 1). The value of fluoride
was higher in Assuit and Rosetta branch than other sites
(Table 1). The level of Cholride and Sulphate exhibited
higher values in the water of Rosetta and Damietta
branches comparing to other sites (Table 1). The level of
Orthophosphate in the Rosetta branch was higher than
other sites (Table 1). The concentration of phenolics was
higher than the permissible limits in Rosetta and Dami-
etta branches (Table 1). The values of the selected met-
als in the water of the River Nile were lower than the
permissible limits nearly in all sites (Table 1). The lead
and chromium concentrations were higher than the per-
missible limit in the Rosetta branch. The cadmium and
mercury levels were higher than the permissible limits in
Rosetta and Damietta branches (Table 1).
3.2. Metabolic Enzyme Activities
The results of the two metabolic enzymes (G6PDH
and LDH) in the liver and muscles of the African catfish
Clarias gariepinus collected from the selected sites are
presented in Table (2). The activities of G6PDH and
LDH in the muscles were always higher than that in the
liver of fish collected from the same site (Table 2). The
activity of G6PDH in the liver and muscles tissues of the
African catfish decreased significantly (p < 0.05) from
Aswan to Damietta and Rosetta branch (Table 2). The
highest G6PDH activity was recorded in the tissues of
fish collected from Aswan comparing to other sites (Ta-
ble 2). On the other hand the lowest G6PDH activity was
recorded in the tissues of the African catfish collected
from Rosetta (Table 2).
The activity of Lactate Dehydrogenase (LDH) in the
muscles and liver of African catfish increased signifi-
cantly (p < 0.05) from Aswan toward Rosetta and Dami-
etta branches (Table 2). The lowest LDH activity was
recorded in the tissues of fish collected from Aswan
(Table 2). The highest value of LDH activity was in liv-
er of fish collected from Damietta (1388.5 U/g) and in
the muscles of fish collected from Rosetta (1529.2 U/g)
(Table 2). The activity of LDH in the muscles of the
African catfish seemed to be constant between Aswan
and Qena (Table 2).

A. G. M. Osman et al. / Natural Science 2 (2010) 1302-1311 1305
Table 1. Physical and chemical parameters of the water collected from different sites along the whole course of the river Nile, Egypt.
Aswan Qena Assiut Beny-Suef Damietta Rosetta
Sites
Parameter (unit) Mean ± SD Mean ± SD Mean ± SD Mean ± SD Mean ± SD Mean ± SD
Permissi
b
le
limit
PH (Unit) 7.858 ± 0.248 8.009±0.405 8.152±0.187 8.27±0.273 8.402 ± 0.442 8.225±0.449 7-8.5
Conductivity ( Ms/cm) 0.257 ± 0.029 0.270±0.0701 0.285±0.086 0.336±0.0722 0.379±0.099 0.576±0.115 -
Temperature ( °C ) 22.683 ± 2.218 23.7167±3.15223.33±4.671 23.644±4.239 25.292±5.661 24.525±4.441 Over 5 ºC
Chemical oxygen
demand (ppm) 10.583±3.616 9.167±3.0419 10.63±2.179 7.875±2.153 8.592±2.509 18±10.375 10
Total organic carbon
(ppm) 5.651±2.876 5.893±1.925 5.738±0.918 4.93±2.575 5.209±2.635 8.61±6.055 -
Total solid (ppm) 198.875±14.088 212.667±23.70227.75±16.297259.5±44.33 305.25±55.95 411.25±85.66 500
Ammonia (ppm) 0.1058±0.158 0.0086±0.00140.0198±0.0110.0125±0.0098 0.0447±0.048 0.146±0.091 0.5
Nitrate (ppm) 0.8084±0.396 0.765±0.3868 0.506±0.205 0.7233±0.627 1.1341±1.131 2.049±2.271 45
Chlorides (ppm) 7.0524±1.443 8.56±1.896 10.032±2.58 15.28±5.103 22.4199±4.92 40.546±6.722 -
Florid (ppm) 0.2836±0.146 0.319±0.1383 0.388±0.163 0.314±0.125 0.301±0.0971 0.372±0.0737 0.5
Ortho phosphate
(ppm) 0.014±0.0198 0.0367±0.03810.0937±0.0900.0334±0.034 0.132 ± 0.066 0.211±0.1871 -
Sulphate (ppm) 34.167±13.299 45.33±15.37 47.957±14.1145.25±15.81 51 ± 12.759 68.125±11.42 200
Phenol (ppm) 0.0234±0.0227 0.0213±0.01980.016±0.01570.0155±0.0098 0.0287±0.017 0.0401±0.022 0.02
Pb (ppm) 0.0177±0.015 0.02128±0.0140.0248±0.01740.01618±0.009 0.0335±0.04 0.0562±0.078 0.05
Cd (ppm) 0.00379±0.004 0.002124±0.000.00644±0.0070.00236±0.002 0.01586±0.02 0.0124±0.017 0.1
Zn (ppm) 0.2107±0.173 0.1237±0.101 0.3091±0.46 0.33659±0.45 0.45057±0.68 0.695±0.955 1
Cu (ppm) 0.0305±0.027 0.0274±0.024 0.03022±0.0260.03197±0.027 0.03206±0.03 0.0544±0.027 1
Cr (ppm) 0.00352±0.002 0.00653±0.0050.00558±0.0050.0060359±0.0050.04548±0.06 0.088±0.154 0.05
Fe (ppm) 0.197±0.1762 0.2205±0.195 0.3449±0.32 0.45957±0.39 0.40742±0.27 0.4973±0.44 1
Hg (ppm) 0.00099±0.001 0.00041±0.0000.00053±0.0010.00096±0.00090.0021±0.001 0.0034±0.001 0.001
Mn (ppm) 0.03319±0.02771 0.0651±0.06850.04511±0.02160.0589±0.060580.071±0.0851 0.0996±0.1466540.5
Table 2. Activities of Glucose-6-Phosphate Dehydrogenase (G6PDH) Lactate Dehydrogenase (LDH) in the liver and mus-
cles of the African catfish Clarias gariepinus collected from different sites along the whole course of the river Nile, Egypt.
LDH (U/g) G6PDH (U/g) Sites
Muscles Liver Muscles Liver
1389.8±11.4 1191.7±95.91 71.9±0.96 71.6±2.4 Aswan
1389.4±2.5 1199.4±51.25 71.9±0.97 60.7±1.3 Qena
1416.3±4.7 1245.6±106..7 66.7±2.34 55.8±2.2 Assiut
1431.0±59.5* 1340.7±1.29* 61.4±0.95 57.2±0.8 Beny-Suef
1513.7±4.6* 1388.5±7.15* 51.0±11.00* 46.9±8.8* Damietta
1529.2±52.7* 1378.7±6.85* 49.7±2.38* 46.7±1.2* Rosetta
Results are expressed as means ±SD. Significant comparing to Aswan site at 0.05 levels.
3.3. Histopathology
Remarkable structural changes were detected in the
tissues of the African catfish collected from the whole
course of the rive Nile. Significant differences in the
degree of such changes were recorded according to the
degree of pollution in the site. Figure 2 (a,b) shows the
normal histological structure of the liver. The photomi-

A. G. M. Osman et al. / Natural Science 2 (2010) 1302-1311 1306
crograph of the normal liver shows the parenchyma cells
(C) arranged to form a lattice network. The interspaces
are the sinusoid (S) of thin strip with sparse connective
tissue. The sinusoids made continuous communication
as they were seen converging into the central vein (V).
Also the hepatopancrease (hp) was clearly distinguished
between the liver tissues (Figure 2(b)). The histopa-
thological changes found in the liver of the examined
fish included irregular arrangements of hepatocytes,
vacuolation (va) and necrosis (ne) of the cytoplasm
(Figure 2(c)). In the fishes collected from Damietta and
Rosetta, patchy degeneration and isolated degenerated
elements around the parenchyma cells were observed
with progressive increase of fibro-connective tissue (fct)
(Figure 2(d)). Leukocyte infiltration (inf) and hemor-
rhage (hem) were also detected in the hepatic tissues of
some fish (Figure 3(a,b)). Also, acute and extensive
vacuolization (vac) and necrosis (nec) of liver cells was
observed (Figure 3(c)) in the liver of fish collected from
Damietta and Rosetta branches. Dilation of the central
vein accompanied by blood congestion (bc) (Figure 3(d))
was detected.
Light microscopic examination of photomicrograph of
the normal gills (Figure 4(a)) shows the arrangement of
the lamella. In the core was a cartilaginous supporting
rod and blood vessels with traces of sinusoidal blood
spaces. The primary lamella (P) was rounded at the api-
ces while the projecting secondary lamellas (S) were
clearly interspaced. The histological alteration of the gill
of fish collected from the river Nile included primary
and secondary lamella overlapping (Figure 4(b)). Thus
there was occlusion of inter lamella spaces. The core
Figure 2. Photomicrograph of liver tissue showing a, b) nor-
mal liver of Clarias gariepinus collected from Aswan, c, d)
histopatholoical changes in the liver of Clarias gariepinus
collected from Damietta and Rosetta branch. Stained with
H&E. (C) parenchyma Cells (S) Sinusoid (V) central Vein (hp)
hepatopancreas (ne) necrosis (fct) fibro-connective tissues
apparent.
Figure 3. Photomicrograph of liver tissue showing deformi-
ties in the tissue of Clarias gariepinus collected from Dami-
etta and Rosetta a, b) liver tissues with leucocytes infiltration
and haemorrhage, c) liver tissues with extensive vacuoliza-
tion and necrosis, d) showing dilation of the central vein with
blood congestion. Stained with H&E. (inf) infiltration, (hem)
haemorrhage, (va) vacuolization, (bc) blood congestion.
Figure 4. Photomicrograph of gills of Clarias gariepinus
showing a) normal gills of the fishes collected from Aswan
with regular arrangement of the Primary (P) and Secondary
(S) lamella, b) histological alteration of the gill showing
primary and secondary lamella overlapping, c) shrinkage of
cartilaginous supporting mass, d) showing lysis in the epi-
thelium cells. Stained with H&E.
was thin and indistinct. There was shrinkage of carti-
laginous supporting mass resulting in decrease in size of
the gills (Figure 4(c)). At Rosetta and Damietta, the ep-
ithelium was disrupted owing to the lysis of the cells
(Figure 4(d)). Sever degeneration and necrotic changes
in gill filaments were recorded (Figure 5(a,b)). The in-
crease in intracellular vacuolation (Figure 5(c)) signals
onset of oedematous changes. Frequently, alterations
such as dilation and congestion in blood vessel of gill
filaments were detected (Figure 5(d)). The gills show
further shrinkage making the cartilaginous core absolutely

A. G. M. Osman et al. / Natural Science 2 (2010) 1302-1311 1307
Figure 5. Photomicrograph of gills of Clarias garie-
pinus shows the deformation a, b) Severe degeneration
and necrotic changes in gill filaments, c) intracellular
vacuolation and edema, d) dilation and congestion in
blood vessel of gill filaments. Stained with H&E.
obscured. Table 3 show the distribution of the detected
lesions in the liver and gills of the African catfish. From
such table we concluded that all of the detected histopa-
thological lesions were recorded in the tissues of the
African catfish collected from Rosetta and Damietta
branches. Some of them were recorded in the tissues of
fish collected from other sites (Table 3).
4. DISCUSSIONS
According to the results of the present work most of
the detected physical and chemical parameters were sig-
nificantly higher in the water collected from Rosetta and
Damietta branches comparing to other sites. The values
of the selected metals in the water of the river Nile were
less than the permissible limits nearly in all sites but they
still higher in the water of Rosetta and Damietta com-
paring to other sites. Lead, cadmium, chromium and
mercury concentrations were higher than the permissible
limit in the water collected from Rosetta and Damietta
branches. Such results prove the presence of large quan-
tities of organic and inorganic pollutants and disposal of
domestic and industrial effluent in the water of Rosetta
and Damietta branch. This was expected due to the fact
that the water of such branches receives large quantities
of domestic, agricultural and industrial effluents without
sufficient treatments.
The alteration in enzyme activity has been advocated
to provide an early warning of potentially damaging
changes in stressed fish [25]. The altered activities of
G6PDH and LDH could be useful biomarkers of water
pollution [25]. The results of the present work recorded
a remarkable alteration in the activity of the selected en-
Table 3. Distribution of the detected histopathological lesions in the tissues of the African catfish Clarias gariepinus col-
lected from different sites along the whole course of the river Nile, Egypt.
Organ Histopathological changes AswanQena AssiutBeny
Suef Damietta Rosetta
Irregular arrangements of hepatocytes + + + + + +
Vacuolation + + + + + +
Necrosis + + + + + +
Degeneration and increase of
fibro-connective tissue + +
Leukocyte infiltration + +
Liver
Dilation of the central vein with blood
congestion + +
Primary and secondary lamella overlap-
ping + + + + + +
Shrinkage of cartilaginous supporting + + + + + +
Cell lysis + +
Sever degeneration and necrotic changes
in gill filaments + +
Gill
Oedematous changes + +
zymes in the tissues of African catfish. These alterations
goes in parallel with the elevation in the levels of water
chemical parameters detected in the water of Damietta
and Rosetta branches as a result of pollution stress in
these areas. These overall changes in the metabolic key
enzymes in the tissues of fishes collected from Rosetta
and Damietta branches indicate that major changes occur
in carbohydrate and protein metabolism. Glutathione
(GSH) serves to protect the cell against oxidative dam-
age as it conjugates with compounds of exogenous and
endogenous origin [47]. GSH production requires
NADPH to be synthesized in the pentose phosphate me-
tabolic pathway in which G6PD participate. For this
reason, G6PD is considered as antioxidant enzymes [26].
The activity of G6PDH was significantly decreased from
Aswan to Rosetta and Damietta recording the lowest

A. G. M. Osman et al. / Natural Science 2 (2010) 1302-1311 1308
value at Rosetta followed by Damietta water. Such re-
duction in G6PDH activity in the liver and muscles of
the African catfish was also previously observed in some
fishes exposed to toxicants [48,49]. Thus the observed
decrease in activity of G6PDH in the present work may
reflect metabolic imbalance after pollution stress in di-
rect relation to the limited availability of NADPH.
LDH is an important factor in the ability of some fish
to produce sudden bursts of swimming and is found in
large quantities in red muscle when a metabolic invest-
ment in locomotion capacity makes good adaptation
sense [50]. Anaerobic capacity was estimated by the
activity of lactate dehydrogenase (LDH), the terminal
enzyme of anaerobic glycolysis located in the cellular
cytoplasm. This enzyme commonly reflects the meta-
bolic capacity of tissues after long – term exposure to
contaminated water bodies [51,52]. LDH catalyses the
conversion of pyruvic acid to lactic acid under stressed
conditions. The activity of LDH, which is a cytoplasmic
enzyme, showed a marked elevation in the tissues of
fishes collected from Rosetta and Damietta branches
comparing to other sites. LDH activity is generally asso-
ciated with cellular metabolic activity which acts as a
pivotal enzyme between the glycolytic pathway and the
tricarboxylic acid cycle [53]. Thus, elevation of LDH
may suggest a bias towards the anaerobic glycolytic
pathway. By other meaning, changes in the lactate dehy-
drogenase activity may indicate the facility with which
the African catfish can shift to anaerobic metabolism
under stressed conditions. Liver is one of the richest
sources of LDH and the leakage of enzyme from even
small mass of damaged liver tissue can increase the ob-
served level to a significant extent. The increase in the
activity of enzymes after exposure to some pollutants
was explained as a result of destruction of liver cells and
increased cell permeability leading to a leakage of the
enzymes from the damaged liver cells into the serum
[28,54,55].
These alterations in enzymatic activities were con-
firmed, in the present study by determination histopa-
thological alterations and clear damage of liver cells of
the African catfish which collected from the same sites
of the Rive Nile. The results of the present work mani-
fest histopathological changes in the liver and gills of the
African catfish collected from different localities along
the whole course of the river Nile. Histopathological
biomarkers of toxicity in fish organs are a useful indica-
tor of environmental pollution [56]. In fact, the histo-
logical studies are considered as direct indication of any
adverse effect on fish. Numbers of histological lesions
have been detected in the tissues of the African catfish.
Liver of the African catfish showed degeneration in the
hepatocytes, necrosis and aggregation of inflammatory
cells, dilatation and congestion in blood sinusoid and
fibrosis. These changes may be attributed to the direct
toxic effects of pollutants on hepatocytes, since the liver
is the principal organ responsible for detoxification in
vertebrates generally and in fish particularly. One of the
most important functions of liver is to clean pollutants
from the blood coming from the intestine, so it is con-
sidered as indicator of aquatic environmental pollution
[57]. The vacuolization of hepatocytes might indicate an
imbalance between the rate of synthesis of substances in
the parenchyma cells and the rate of their release into the
circulation [58]. The present results are in agreement
with those observed by many authors who studied the
effects of different pollutants on fish liver [59-61].
Gills remain in close contact with the external envi-
ronment and particularly sensitive to change in the qual-
ity of water are considered the primary target organ of
the contaminant [62]. The cellular damages observed in
the gills in term of epithelium proliferation and necrosis
can adversely affect the gas exchange and ionic regula-
tion [62]. The observed edematous changes in gill fila-
ments probably due to increased capillary permeability
[61]. Alterations like fusion of some secondary lamellae
are examples of defense mechanisms, since; in general,
these result in the increase of the distance between the
external environment and the blood and thus serve as a
barrier to the entrance of contaminants [63,64]. Similar
lesions have been previously reported by some authors in
some fish species exposed to different kind of pollution
[65,66] {Rosety-RodrÃ-guez, 2002 #2696} [60,63,67,68].
This means, such alterations are non-specific and may be
induced by different types of contaminants As a conse-
quence of the increased distance between water and
blood due to epithelial lifting, the oxygen uptake is im-
paired. However, fishes have the capacity to increase
their ventilation rate, to compensate low oxygen uptake
[69]. According the results of the present work altered
metabolic enzymes activities can provide a tool to assess
the geographical areas impacted by aquatic pollutions.
The altered activities of G6PDH and LDH can provide a
useful biomarker for fish farms and for environmental
managers in investigating the exposure of fish to con-
taminated waters. All of the above mentioned histopa-
thological lesions were recorded in the tissues of fish
collected from Rosetta and Damietta branches. Some of
them were recorded in the tissues of fish collected from
other sites. So, histopathology provides a reliable, easily
quantifiable index of low-level toxic stress to a broad
range of environmental pollutants. It is possible that the
enzymatic and pathological alterations in the selected
tissues could be a direct result of the industrial, agricul-
tural, domestic waste products which are entered to the
Nile with the drainage water.

A. G. M. Osman et al. / Natural Science 2 (2010) 1302-1311 1309
5. ACKNOWLEDGEMENTS
This work was supported by Science and Technology development
fund (Project ID 448).
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