Minute tubercles development and function on the skin surface of the bitterling larvae

Abstract

Bitterlings are small freshwater fish that use ovipositors to spawn their eggs in host mussels, and they have morphological adaptations to increase larval survival. The most well-known adaptation is the minute tubercle on the skin surface of larvae. In Rhodeus pseudosericeus the minute tubercles of larvae began to develop 1 day after hatching (formation stage), grew for 2–5 days (growth stage), reached the peak height after 6–7 days (peak stage), abruptly reduced in height after 8–10 days (abrupt reduction stage), and gradually reduced in height (reduction stage) until completely disappearing 27 days after hatching (disappearance stage). At the same time, the larvae remained in the mussels’ interlamellar space of the gills until 10 days after hatching (formation to abrupt reduction), and began to migrate to the suprabranchial cavity 11 days after hatching (reduction to disappearance). The results presented herein elucidate that the minute tubercles are the developmental dynamic structures that the bitterling larvae have morphologically adapted to prevent premature ejection from the mussel.