International Journal of Aquaculture, 2017, Vol.7, No.9, 64-70
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3 Results
3.1 Trends in mortality and physicochemical parameters
Time to death was shorter in the higher concentrations (Figure 1). At the first 12 hours, there were no noticeable
effect on the test organisms even at higher concentrations. Few mortality were recorded at the first 24 hours of the
toxicant introduction but at 72-96 hours, mortality rate increases speedily. The mortality rate of the experimental
fish increased with increase in concentration of the toxicant. The 24, 48, 72 and 96 hours LC
50
was estimated to be
8.49, 6.36, 4.80 and 3.39 mg/l respectively which was analysed using probit analysis.
Figure 1 Trend in fish mortality with duration of exposure to selenium
3.2 Haematological variables
Table 1 showed the mean value of the haematology. PCV of untreated group is significantly higher (48.33±0.58)
than the treatment groups while that of the treatments decreases (22.67, 21.67, 19.00, 17.00 and 12.50) with
increase in concentration of selenium except for treatment 1 which is slightly higher than treatment 2 but showed
no statistical differences. The WBC of the treated groups were significantly lower than the control. No significant
difference between treatments 1 and 2. Also,no significant difference between treatments 3, 4, and 5. The
haemoglobin concentration was highest (25.71) in the unexposed fish while it was least (4.96) in the group
exposed to highest concentration of selenium (6 mg/l). There was a slight decrease with increase in concentration
of the treated groups while the unexposed fish had the highest RBC count. There were great variations in the
values of MCV, MCH and MCHC. Mean corpuscular volume (MCV) of treatments 4 and 5 were significantly
higher (p ˃ 0.05) compared to control group. Treatment 5 had the highest mean corpuscular haemoglobin (MCH)
value while mean corpuscular haemoglobin concentration (MCHC) was higher in the control than treatment
groups.
3.3 Water parameters
In Table 2, dissolved oxygen decreased with increase in concentration of selenium. However, all other parameters
showed no significant difference.
4 Discussions
The present study shows that
C. gariepinus
juvenile are susceptible to selenium toxicity; the LC
50
reduces with
increase in duration of exposure. Also, the higher the concentration of selenium, the higher the mortality rate
(Figure 2). The 96 hours LC
50
of selenium in this study (3.39 mg/l) has a close range with the 96 hours LC
50
of
