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Rhythms play an important role in the precise spatiotemporal regulation of biological processes during development and patterning of embryos. We here investigate the rhythmic contractions of the yolk during early development of the goldfishCarassius auratus. We quantify these contractions and record robust and persistent rhythmic yolk movements that are not seen in closely-related species (carp and zebrafish). We report that yolk contractions are an intrinsic emergent property of the egg, i.e. goldfish eggs are independently irritable / excitable. These contractions do not require sperm entry / fertilization nor cell division, and they notably emerge at a precise time — suggesting that goldfish eggs are able to measure elapsed time from what we infer to be egg activation. As the yolk itself is known to confer critical cues for early dorsoventral (DV) patterning of teleost embryos, we hypothesize that its contractions in goldfish may influence the patterning process of this species. Indeed, we find that embryos in conditions that result in ventralized phenotypes (i.e. goldfish embryos acutely treated with microtubule-depolymerizing drug nocodazole and embryos of the twin-tail goldfish strainOranda) display altered yolk contraction dynamics (i.e. faster and/or stronger contractions). We aim to uncover whether the yolk contractions happening during early development of domesticated goldfish are the licensing process which explain the variety of novel DV patterning phenotypes naturally-observed in this species (e.g. twin-tail and dorsal-finless strains) and which are instead not found among closely-related species (e.g. carp) whose yolks do not contract.

This manuscript is here published as a living communication (as described in Gnaiger (2021)). The authors intend to share findings when they are available, encourage feedback and discussion, and invite knowledge exchange and collaboration.