Mass mortality of cultured ascidians Halocynthia roretzi associated with softening of the tunic and flagellate-like cells.

Since 2007, mass mortalities of cultured ascidians Halocynthia roretzi (Drasche) have occurred in Miyagi Prefecture, Japan. The mortalities occur from November through August, and the tunics of affected animals become abnormally weak and soft. The number of farming areas where mass mortalities have occurred has increased rapidly: 3 in 2007, 6 in 2008, and 14 in 2009. When an outbreak of the disease occurred, mortality reached 17 to 100%. Prominent histopathological changes in the diseased ascidians were found in the tunics; the tunics of affected animals were usually much thinner than those of healthy individuals, and the tunic matrix showed marked disintegration with irregular arrangements of fiber layers or the presence of hollow spaces. In addition, flagellate-like cells (10-14 microm x 2-3 microm) stained with hematoxylin were observed in the tunics of 31 out of 36 diseased animals (86%), but not in apparently healthy animals (n=38). Experimental infection with the disease was successfully conducted by immersing small pieces of tunic samples from diseased ascidians into aquaria with healthy ascidians. The flagellate-like cells were confirmed in the tunics of all the experimentally infected animals. These results indicate that the mass mortalities of ascidians accompanied by abnormally softened tunics were caused by an infectious agent, and suggest the involvement of the flagellate-like cells in the disease.

Mitochondrial genotyping of an endangered bitterling Acheilognathus typus (Cyprinidae).

Genotyping of endangered species is helpful for establishing and evaluating conservation strategies. Mitochondrial sequence data was analyzed from 541 individuals of a critically endangered fish, Acheilognathus typus from present-day range-wide localities to re-evaluate an in-progress restoration program around Lake Izunuma-Uchinuma, Miyagi, Japan. Acheilognathus typus showed low sequence diversity with only eight haplotypes and π and h values of 0.59129 and 0.00118 respectively. Genetic data suggests Acheilognathus typus is adapted to pulsed environments and prone to population flush and crash. Genotyping of populations in introduced localities revealed that their source is not from nearby localities.