Detection of microcystin toxin from Microcystis aeruginosa Kutz collected from Laguna de Bay [Philippines] and its effects on tilapia (Oreochromis niloticus L.)

Laguna de Bay [Philippines] is extensively being used for aquaculture and is considered an important source of livelihood for families living along its coastline. At present, the lake faces problems such as runoff and siltation. Moreover, dumping of municipal wastes contributes to the formation of blooms of cyanobacteria which may be capable of producing toxins in the lake. The most common cyanobacterial toxin encountered in fresh water is the cyclic heptapeptide microcystin which inhibits protein phosphatase type 1 (PP1) and type 2A (PP2A), which can both be found only in eukaryotic organisms. Microcystin is also a hepatotoxin which can cause severe hepatic hemorrhage and possibly liver cancer. In this study, crude extracts of Microcystis aeruginosa were assayed for the presence of microcystin. Moreover the pathologic effect of the cyanobacteria on tilipia fingerlings (Oreochromis niloticus L.) was also determined. Masses of the cyanobacterium were collected and extracted using absolute methanol. Microcystin was then detected by intraperitoneal injection on ICR strain laboratory mice. The mice showed classical symptoms of microcystin intoxication which indicated the presence of the toxin. The presence of microcystin was confirmed by thin layer chromatography (TLC) with the elution of toxic spots having retardation factor (RF) values of 0.595 and 0.660 which are close to literature values. Meanwhile, three to four month-old tilapia fingerlings were fed with fresh cells of the M. aeruginosa for seven days. Deaths were observed after the 5th and the 3rd day of exposure to concentrations of 1g and 2g cyanobacterial cells per liter, respectively. Hotellings trace statistical analysis showed that the treatments had a significant effect on the accumulated deaths of the fingerlings. Histopathological examination revealed pronounced effects on the liver with the hepatocytes becoming enlarged and vacuolated, with the nuclei displaced at the periphery, and with lesions on all hepatic lobules