Embryonic development of the grass pufferfish (Takifugu niphobles): From egg to larvae
Introduction
The grass pufferfish (T. niphobles) is a teleost fish with a wide distribution in the Northwest Pacific Ocean. This species is one of around twenty four pufferfish species in the genus Takifugu, and there are some reasons that justify its study: i) it is placed on the IUCN Red List due to the reduced knowledge about the stage of its current populations, making it a possible endangered species [1]; ii) the closely related species (like Takifugu rubripes) is widely-kept by scientists as a model organism for genomics [2], [3]; and iii) some species of this genus are considered a popular food in Japan.
The genome of the congeneric species T. rubripes (Fugu) has been sequenced and assembled recently, the second vertebrate genome to be sequenced and the shortest known genome of any vertebrate species [4]. In this respect, the pocket-sized genome of Fugu should help to resolve contentious estimates of human gene number, where the genome of Fugu has directly contributed to the annotation of protein-coding genes on 11 human chromosomes and has also helped unearth nearly 1000 new human genes [5], [6]. In this regard, closely related species such as T. niphobles could be similarly applied in this purpose due to its small and similar genome. One advantage of T. niphobles over the other pufferfish species currently used for genomic studies is the potential for the study of essential steps in development: staging series based on morphological traits will provide in-depth knowledge of the developmental processes governing teleost fish [7], [8].
Staging by morphological criteria is an useful tool for generating developmental comparisons between different species and, in this sense, to determine the underlying mechanisms of evolutionary changes among them [9]. For Fugu (T. rubripes), a developmental stage series has been published [10], but a standard and cost-effective laboratory breeding protocol is not available. In contrast, T. niphobles, with a high fertility rate during a wide spawning period (offering the availability of thousands of eggs [11]), can be kept and maturated in laboratory conditions [12]. As a result, both species have remained virtual models, mostly confined to genome sequence analyses. In this study, we have set out to promote T. niphobles as a laboratory model for functional and comparative genomic and developmental projects. We report the embryonic development of T. niphobles, raised under laboratory conditions, describing the series of embryonic stages and provide fundamental data to facilitate its use for future developmental studies.
Section snippets
Fish handling
Takifugu niphobles shows a singular spawning behavior at Arai Beach near Misaki Marine Biological Station (MMBS, Japan). Large schools of fish (200–1000 [13]) arrive to the beach around the new or full moon at spring tide during the spawning season, which occurs between May and July. Spawning takes place repeatedly from 2 h before the sunset and includes a beach-spawning behavior, where the fish are routinely found out of the water on the beach until the next wave. During this time, males and
Zygote period
The zygote period started from in vitro fertilization until the onset of cleavage period, when the embryonic polar cell mass transitioned from the 1-cell stage to the 2-cell stage (Fig. 1A–B). Zygote period spanned 0–1.7 hpf for reaching the cleavage.
Cleavage period
During the cleavage period of Takifugu niphobles embryonic development, a single cell (1st blastomere), formed at the animal pole by separation of cytoplasm from the yolk, was divided (cleaved) into an increasing number of smaller cells, decreasing
Discussion
In this study, we report the developmental stages of T. niphobles based on morphological characteristics. This information is anticipated to allow the use of pufferfish as a model for developmental studies [19], uncovering the morphological diversification of this group of highly derived teleost fishes. Regarding the different embryonic stages during the egg development, cell division cycle from the 2-cell to the 1k-cell stage lasted approximately 12 h in T. niphobles. These intervals were
Acknowledgements
Funded by the Spanish Ministry of Economy and Competitiveness (MINECO; AGL2010-16009). VG had a predoctoral grant (MINECO; BES-2009-020310) and had been granted by a fellowship (EEBB-I-12-05858) of the MINECO's Spanish Personnel Research Training Programme to carry out this research in the Misaki Marine Biological Station (Miura, Japan). This research was also supported by the Great Britain Sasakawa Foundation (grant to GJF). The authors would like to thank to L. Clement for her help in the
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2017, Animal Reproduction ScienceCitation Excerpt :The staging of embryonic development of target species is essential for studies on developmental mechanisms. Embryonic development has been defined in detail for several fishes, such as zebrafish, Danio rerio (Kimmel et al., 1995), Nile tilapia Oreochromis niloticus (Morrison et al., 2001), medaka, Oryzias latipes (Iwamatsu, 2004), Anabarilius grahami (Ma et al., 2008), goldfish, Carassius auratus (Tsai et al., 2013), barramundi, Lates calcarifer (Thépot and Jerry, 2015), and grass pufferfish, Takifugu niphobles (Gallego et al., 2017). However, the developmental stages in C. trutta need to be detailed to facilitate its use for future developmental studies and domestication for this species.
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