Cryopreservation of marine species is a key tool for biodiversity conservation, population management, and the advance of aquaculture and biological research. Currently exist significant progress in the cryopreservation of gametes, embryos, larvae and even juveniles of several genus of marine invertebrates. However, cnidarians, and particularly jellyfish, remain largely underexplored. In this study, we report on the first successful cryopreservation of Aurelia aurita ephyrae, the first larval stage of this jellyfish species. This species is characterized by extremely high-water content (96.3 %), which represents a unique challenge in the method of cryopreservation. In this study we done toxicity tests using different concentrations ranging from 0.5 to 6 M of dimethyl sulfoxide (Me2SO). On the other hand, we designed two cocktails of cryoprotectants and evaluated the efficiency in a protocol of cryopreservation. The first one is based on 1 M Me2SO + 0.5 M dimethylformamide (DMF) and the second used 1.5 M Me2SO with 0.04 M trehalose (TRE) and 1 % BSA as a post-thaw supplement. The first protocol achieved 100 % survival immediately after thawing and 33 % survival at 48 h, while the second maintained a consistent 33 % survival across both time points. The damage and viability of the larvae was assessed using live/dead fluorescence dye and allowed confirming the integrity of surviving individuals. These results mark the first demonstration of successful cryopreservation protocol for jellyfish larvae and represent a significant advance for the ex-situ conservation of gelatinous zooplankton. This work lays the foundation for further research into cryopreservation protocols for marine species, understand most better water flow for organisms with high water content and opens new possibilities for marine biodiversity conservation and cnidarian model systems.
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