LACTATE DEHYDROGENASE IN GUPPY FISH (Poecilia reticulata) AS A BIOMARKER FOR HEAVY-METAL POLLUTION IN FRESHWATER ECOSYSTEMS

Abstract

Heavy-metal concentrations and allozyme variations were determined in females of guppy fish (Poecilia reticulata) populations collected from polluted and unpolluted sites. The concentrations of Cu and Fe were significantly {P< 0.05) higher in guppies collected from polluted drainage compared to the unpolluted population. Higher concentrations of Cu, Fe and Zn (P< 0.05) were found in the surface sediment, indicating contamination by the three metals in the polluted drainage. The insignificant difference (P> 0.05) in the Zn concentrations between the polluted and the unpolluted populations indicated that Zn, as a major essential metal, was regulated in this freshwater fish. Seven enzyme systems EST, G6PDH, LDH, MDH, PGI, PGM and SDH were tested. Only LDH (lactate dehydrogenase) was found to be a good biomarker for the contamination of Cu and Fe in P. reticulata. The zymogram ofthe unpolluted wild population showed the same monomorphic allele as the unpolluted domesticated guppies from a pet shop, thus, further confirming LDH in P. reticulata as a good biomarker of contamination by Cu.