International Journal of Marine Science, 2017, Vol.7, No.29, 284-291
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in response to agricultural, sewage and industrial pollutants (Mohamed, 2003). There have been numerous reports
on histopathological changes in gill, kidney, and flesh of fish exposed to different toxicant (Olufayo and Alade,
2012; Vinodhini and Narayanan, 2008). Histopathological alterations have been used as indicators of the effects
of various pollutants on the organism including fish, and reflection of the overall health of the entire pollution.
Mohamed (2009) reported several pathological changes in different tissues of fish exposed to chemicals. The
exposure of fish to pollutants that is agricultural and industrial chemicals, were resulted in several pathological
changes in different tissues of fish. Alterations in histopathology were also reported in
Heterobranchus Bidorsalis
e
xposed to cypermethrin (Olufayo and Alade, 2012). Information on lethal exposure of selenium and its
compounds on the physiology of fish are limited and its effects on organs of
Clariasgariepinus
juveniles are
scarce. This paper therefore presented to the effects of selenium on the behaviour and some organs of
C.
gariepinus
juveniles.
1 Materials and Methods
Juveniles of African catfish (
Clarias gariepinus
) with average weight of 7.4±0.64 g were used for the study. 180
fish were purchased from a reputable fish hatchery 10 fish were acclimatized in 80L plastic container filled with
60 L of water each for a period of 4 weeks to the laboratory condition. During this period of acclimatization, the
fish were fed with artificial feed twice daily at 3% body weight and water was changed every other day. The fish
were not fed 48 hours prior to experiment in order to minimise ammonia production as a result of fish waste. The
selenium was in the form of sodium biselenite (NaHSeO
3
) which was purchased from a reputable scientific store.
Toxicant stock solution of the tested metal, a pure chemical: sodium bi- selenite was prepared by dissolving 5 g of
reagent equivalent to 1 g of selenium in 1000 mL tap water at concentration of 1000 mg/L. From the stock
solutions, different concentrations required were prepared after a range – finding test using a screening procedure.
The concentrations prepared for the experiment were: 2, 3, 4, 5 and 6 mg/L based on literature guidance (Burba,
1999; Vinodhini and Narayanan, 2008). This was prepared 24 hours before the experiment in other for the
chemical to properly dissolve. Water quality monitoring was done every 24 hours throughout the period of the
experiment. The pH, conductivity, dissolved oxygen, and temperature was done with the use of HI-769828
multi-parameter water analysis probe. Ammonia, nitrate and nitrite test was done with the use of NT LABS pond
water multipara meter test kit. The histological examination of
Clarias gariepinus
juvenile exposed to sodium
bi-selenite was done on the survived fish after 96 hours by the removal of the desired organ (gill, kidney, and
flesh). Three fish were randomly selected from each group after 96 hours for the histological extermination. The
tissues were fixed in 10% formalin and were processed (dehydrated in ascending grades of alcohol, clear in xylene,
and impregnated in molten paraffin wax) in Automatic tissue processor. These were then observed under
microscope.
2 Results
Behavioural response observed during the 96 hours experiment include: attempt escapement especially at the
point of death, erratic swimming, and irregular movement of the opercula. These behavioural changes were
observed more in group exposed to higher concentrations (5 and 6 mg/L). These responses indicated that the
culture environment containing selenium was unsuitable for the fish. No visible lesion was seen in the gill section
of the control group (Figure 1) which remained an ordinary structure and non-differentiated cell were found in the
lamellae. Damage to organs was more pronounced in the fish exposed to higher concentrations. The gill section of
C. gariepinus
exposed to 2 and 3 mg/L of selenium showed stunted secondary gill lamellae (Figure 2; Figure 3;
Figure 4). Degenerative changes were seen in the groups exposed to higher concentrations (5 mg/L and 6 mg/L) of
selenium (Figure 5; Figure 6). These showed many areas of mucosal erosion, lamellar necrosis and hyperplasia
which change the normal structure of the gill section. Sections of unexposed kidney of
C. gariepinus
showed no
visible lesion (Figure 7). Pathological changes were seen in the kidney sections of the exposed group. The kidney
section of
C. gariepinus
exposed to lower concentration (2 mg/L and 3 mg/L) of selenium shows few foci tubular
necrosis within the parenchyma cell (Figure 8; Figure 9). Kidney of
C. gariepinus
exposed to 4 mg/L selenium
revealed some blood stains in the glomerulus (Figure 10). The kidney sections of
C. gariepinus
exposed to the
highest concentration 5 mg/L and 6 mg/L of sodium selenium showed a severe interstitial congestion and blood
