Acetylcholinesterase Activity and Oxidative Stress Biomarkers in Fiddler Crabs (Austruca occidentalis) along the Coastal Mangrove Areas of Dar es Salaam, Tanzania

The aquatic organisms such as crustaceans serve as bioindicators of the environmental stressors which affect the aquatic ecosystems. The present study assessed environmental health status through fiddler crabs (Austruca occidentalis) towards oxidative stress biomarkers and AChE activity in mangroves with different levels of salinity and environmental contamination. Fiddler crabs were collected from Mtoni Kijichi, Kunduchi and Mbweni, which experience different levels of contamination from high to low along the Dar es Salaam coastline. Malondialdehyde the biomarker of oxidative stress was analysed by lipid peroxidation (LPO) assay and AChE activity was tested using Ellman assay in the crab tissues (muscles, hepatopancreas and gills). To this end, the results showed a significant variation in the LPO levels in analysed tissues (p < 0.05) with relatively higher level observed in hepatopancreas, 1.799 μM MDA/mg w.wt than in muscles and gills 0.924 and 1.378 μM MDA/mg w.wt, respectively. Although there was variation of LPO levels in A. occidentalis among the studied sites as well as between salinity levels, the variation was not statistically significant (p > 0.05). The AChE activities in A. occidentalis were significantly different among the study sites (p < 0.05), with Mbweni having lowest (4.791 nmol/min/mg protein) activity followed by Kunduchi (4.965 nmol/min/mg protein) and lastly Mtoni Kijichi (5.321 nmol/min/mg protein). The AChE activity also varied significantly by tissue (p < 0.05), whereas hepatopancreas and gills had lowest enzyme activity (4.254 and 4.534 nmol/min/mg protein, respectively) as compared to muscles (6.290 nmol/min/mg protein). This field study provides information on the usefulness of A. occidentalis in assessing the health status of marine costal ecosystems through their responses against toxicants. Keywords: Fiddler crabsn; Oxidative stress; Bioindicators; Acetylcholinesteras