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The Adaptation strategy for increasing survival rate of bitterling embryos

Hyeong Su Kim

Bitterlings are small freshwater with an unusual spawning character with freshwater mussel. They use ovipositors to spawn their eggs in host mussels and display remarkable morphological adaptations to increase larval survival. Their eggs vary in shape, size, and number and four types have been classified: bulb-like, pear-shaped, spindly, and ovoid. Some bitterling have small number of eggs but sticky, which is possible to prevent premature ejection from mussels. The most well-known adaptation structure is the minute tubercle on the skin surface of bitterling larvae. In bitterling groups, the changes in height and shape of minute tubercles of larva can be categorized as six stages: formation, growth, peak, abrupt reduction, reduction, and disappearance stage. The minute tubercles on the larval skin surface start to be grown after hatching and after that it were gradually decreased as the larvae grow and then disappeared at the free swimming stage. The previous study suggested that the minute tubercles are the developmental structures that the larvae have morphologically evolved to prevent ejection from the mussel for increase survival rate of embryos.