An improved cultivation device for appendicularians with notes on the biology of Fritillaria sp. collected in Sagami Bay, Japan

To cultivate zooplankton species with highly fragile mucoid structures, a new type of cultivation device was developed, which uses a novel method to gently circulate the water in the culture vessel. Using this device, a species of the fritillarid appendicularia (Fritillaria sp.) collected in Sagami Bay was successfully cultivated. This form resembles Fritillaria haplostoma or Fritillaria formica tuberculata, but some taxonomical characteristics differed from those of the latter forms. A novel device comprising a polycarbonate bucket with a motor-driven rotating cylinder inserted into the water in the bucket was developed and maintained Fritillaria sp. over ten filial generations in the laboratory. The animals reached trunk lengths of 1026 ± 85 μm (mean ± SD) four days after fertilization at 23°C. The instantaneous growth rates were calculated as 1.11–1.72 at 20–26°C, representing a 3.0–5.6-fold daily increase in body weight. The house constructed by this species is extraordinarily fragile, typically has a barrel-like or cylindrical shape, and accommodates its entire body and food-concentrating filter. At 23°C, the species produced houses at a rate of 28 ± 2.8 houses d−1. The new device is useful for the continuous cultivation of the fragile form of fritillarid appendicularia, and even for various other zooplankton. It also shows that Fritillaria sp. could be a significant secondary producer and transporter of organic matter in marine ecosystems due to its high growth and house production rates.