Exploring the potential of the sea cucumber Cucumaria frondosa as an aquaculture species

Sea cucumbers are a luxury seafood in China and the increasing demand is driving aquaculture initiatives towards new species worldwide. Cucumaria frondosa has been commercially harvested for decades in North America and has also been identified as a potential candidate for aquaculture. So far, captive-breeding methods have focused on tropical/temperate deposit-feeding species with planktotrophic development (small eggs, feeding larvae); however, C. frondosa is a cold-water suspension-feeder with lecithotrophic development (large yolky eggs, non-feeding larvae). The aim of this study was to explore the reproductive biology, larval development, and juvenile ecology of C. frondosa to identify optimum conditions for culture. In an experimental study, adults kept in ambient environmental conditions showed the best reproductive output and embryo survival relative to those in warmer water, advanced photoperiod, and constant light or dark conditions. An increase in food concentration did not enhance the reproductive output. When methods used to trigger spawning and artificially induce oocyte maturation were investigated, live phytoplankton at 1 x 10⁵ cell ml⁻¹ was the most successful technique; moreover, among a handful of chemicals tested, only Dithiothreitol (DTT) at 10⁻¹ M induced significantly more oocytes to ovulate than the control (seawater), although eggs remained unfertilizable. These experiments led to the discovery of embryonic fusion and the formation of chimaeras (individuals composed of genetically distinct types of cells). Fusion occurred only among hatched blastulae and occurred in a maximum of 9% of the propagule population, generating individuals up to 5 times larger than singletons. Finally, development and behaviour of juveniles assessed from settlement to 21 months of age revealed that newly-settled juveniles had low tolerance to light and water flow, fed on deposited material, and preferred rocky substrates and black or red backgrounds. With age, juveniles grew ramified tentacles, shifted to suspension feeding, developed greater tolerance to light and water flow, and showed a preference for coralline algae and red backgrounds. The findings presented here provide important advances to optimize gonad development and egg quality in captive broodstock of C. frondosa, to induce or enhance spawning and fertilization, as well as to elucidate the optimal conditions for embryos and juveniles. This work presents a pilot-scale assessment of commercial production in C. frondosa, with potential applicability to similar cold-water suspension-feeding species