Bloom of a freshwater green alga <i>Botryococcus braunii</i> (Botryococcaceae, Trebouxiophyceae) and the associated mass fish mortality in a man-made lake, Sarawak, Malaysia

Mass mortality of fish (∼8,500 fishes), mainly Oreochromis placidus, was noted in a man-made lake located at Kuching, Sarawak (Malaysia). A field investigation conducted to collect water samples and fishes. Patches discoloration brick red were observed the clear oil layer found on surface water. Microscopic observation enumeration showed that plankton composition dominated by green algal species Botryococcus sp., with colony densities ranging 1.2×103–7.4×106 colonies L−1. Detailed morphological assessment light microscopy revealed dominant as braunii Kützing. Molecular characterization using an rDNA marker further supported identity B. L race. Fish gill cells oily substances dead gills. The race-L bloom reported, for first time, be associated kill event freshwater Malaysia confirmed one types causing harmful effects environment.