Histopathological Analysis And Heavy Metal Concentration of Tilapia Fish (Orechromis mosambicus) Harvested From Rivers Used For Mining Activities

Abstract

This research work was aimed at determining heavy metal concentrations and histopathological assessment 
of selected parts of Tilapia fish (Orechromis mosambicus) as a biomarker for heavy metal pollution of the 
rivers located in Anka and Maru LGAs of Zamfara state used for gold mining activities at two different 
season. Twelve (12) pieces of average size tilapia fish, three from each river were harvested and sacrificed, 
parts such as the gills, liver and skin (muscle) of the fish samples were processed and digested using 
standard method for AAS heavy metal determination. Histopathological analysis was also conducted the 
selected parts using gold standard method. The concentrations of all the heavy metals are generally higher 
during the dry season than in the wet season. However, Zn and Cr concentrations in the fish were within 
international safe limits of 5mg/l and 0.1 mg/l respectively, while the highest concentrations were recorded 
in the dry season for Cd, Pb and Hg (0.963±0.001 – 0.275±0.002), (0.828±0.001 – 0.187±0.002) and 
(1.349±0.003 – 0.219±0.002) respectively. These recorded values far exceed the WHO and USEPA limits 
of 0.01mg/l, 0.01mg/l and 0.001mg/l for Cd, Pb and Hg levels respectively in water. Pollution load index 
were greater than 1 indicating severe contamination. The histology assessment of tissues such as gills, liver 
and skin (muscle) showed that most common gill abnormalities observed in the fish sample inhabited in all 
the locations have desquamation of lamellar epithelium, hypertrophy of epithelial cells, lifting up of 
lamellar epithelium, intraepithelial oedema, aneurysm, hyperplasia, and haemorrhage in the gill filament. 
Histology of liver revealed the presence of heterogeneous parenchyma characterized by vacuolization, foci 
of necrosis, hypertrophy of nuclei and degenerated hepatocytes. Histology changes of the skin (muscle) 
were mostly at the level of the epidermis, without major changes in the dermis and hypodermis. The result 
of the heavy metal concentration particularly those of Pb, Cd and Hg are exceptionally high and should 
cause trepidation to regulatory authorities as continuous consumption of both water and fish from this river 
will cause public health issues.