Abstract:
Histo-pathological biomarkers are widely used to elucidate potential
toxicological impact of contaminated sediments on organisms, including
fish. A controlled laboratory experiment of sediment toxicity was carried
out to qualitatively examine gill and liver histological alterations in juvenile
Oreochromis niloticus exposed to contaminated sediment from a fisheries
harbour. Four groups in duplicate, namely negative control (no sediment),
reference group (pristine sediment), and two exposure groups with single
(Tl) and triple (T2) levels of HC-contaminated sediment from a fishery
harbour were used. The study aimed at reporting the gill and liver histology
in randomly selected fish (n=6 per group in duplicate) from the four
experimental groups at the end of 16-week period. Gill histology was found
to be altered in all the examined fish in Tl and T2 groups when compared
to the gill histology found in the negative control and the reference groups.
Pathological alterations of the gills include epithelial hyperplasia and
hypertrophy, dilation of marginal canals, and hyperplasia in the interlamellar
space, and lamellar fusion apparently blocking the water flow
between lamellae. Major liver histo-pathological indications were observed
in all examined fish in Tl and T2 groups, including vacuolization of liver
cells and focal necrosis. The results reveal that long term exposure to
persistently contaminated sediment causes histological alterations in gill
and liver of fish, and highlight the bioavailability of sediment-associated
pollutants to the fish.
