Acetylcholinesterase activity and oxidative stress biomarkers in fiddler crabs (Austruca Occidentalis) from mangroves along the Coast of Dar es Salaam, Tanzania

The aquatic organisms such as crustacean serves as bio indicator to the environmental stressors, which affect the aquatic ecosystems. The main objective of this study was to generate information on the interactive effect of contaminants and salinity on Acetylcholinesterase (AChE) activity and oxidative stress biomarkers in fiddler crabs along the Dar es Salaam coast. The present study investigated the morphological parameters of fiddler erabs, concentration of heavy metals, oxidative stress responses and AChE activity in tissues (hepatopancreas, gills and muscles) of Austruca occidentalis crabs. Heavy metals concentrations in sediments and tissues samples were detected by using Atomic Absorption Spectrophotometer (AAS). The oxidative stress responses by tissues of fiddler crabs were determined by lipid peroxidation (LPO) assay and the AChE activity was determined by endpoint method. The Austruca occidentalis morphological parameters varied greatly among the sites with Kunduchi crabs having much lower morphological parameters. The variation of the parameters is reflected with the level of contamination variation among the study sites. The analysed heavy metals (lead (Pb), zinc (Zn), cadmium (Cd) and chromium (Cr) in Austruca occidentalis tissues concentration was in order of Cr > Zn > Pb > Cd. The concentration of heavy metals varied greatly in relation to the tissues and sites. The LPO levels in tissues of fiddler crabs was relatively high hepatopancreas and were affected by the interactions of factors i.e salinity, sites and tissues. The AChE activity is associated with heavy metals crabs gills are good indicator of heavy metal concentration, in this particular species. Furthermore, the lower AChE activity and relative high LPO level in hepatopancreas for fidder crabs collected from both sites potentiate its ability to be used as biomarker tissue in the particular species. However, futher studies under laboratory set up on biomarkers are needed to validate whether the impacts on MDA and AChE can be used to indicate exposure and effects of heavy metals to fidder crabs.