Possible involvement of microcystins in the unexplained mass mortalities of Lesser Flamingo (Phoeniconaias minor Geoffroy) at Lake Manyara in Tanzania

摘要

Frequent mortality of Lesser Flamingo (Phoeniconaias minor) in East African alkaline saline lakes is a tragedy to the conservation of this nearly threatened species of birds. The objective of this study was to investigate the cause of Lesser Flamingo mortality in Lake Manyara during August 2008 and to determine if microcystins were involved. Pathological, microbiological and microcystin analysis was done to 11 Lesser Flamingo carcasses using standard procedures. It was found that carcasses were emaciated, the visceral organs were enlarged, haemorrhagic and the livers had nodular lesions. Tissue histopathological sections revealed that there was diffuse chronic inflammation, perisinusoidal haemorrhages, portal mononuclear cell infiltrations, necrosis and degenerative changes in the liver. Corynebacteria spp., Pasteurella multocida, Proteus spp. and Escherichia coli were isolated from the visceral organs in all carcasses. All the Lesser Flamingo carcasses contained detectable levels of microcystins. Three microcystin variants: MC-LR, -YR and -RR were detected with MC-LR having a concentration of 22 ± 16 μg/g wet weight in livers. Low concentrations of microcystins were detected in the kidneys, lungs and heart samples. Simultaneously, the high concentrations of microcystins in the livers together with the opportunistic bacterial infections could synergistically have caused effects to the stressed Lesser Flamingo which lead to their mortality.