ABSTRACT
Annual fish live exclusively in temporary wetlands and are among the shortest-lived vertebrates in the world. These fish persist in these habitats due to drought-resistant eggs, that which, through diapauses are able to detect stimuli from the environment to start the development processes. They are also able to direct their embryonic development in different trajectories with different development times. Our objective in this paper was to describe the different stages of embryonic development of Austrolebias wolterstorffi, a critically endangered annual fish. A total of 27 stages of embryonic development were identified for the two observed developmental pathways (direct and diapause 2). Of these 27 developmental stages observed, 24 were identical between the two types of trajectories and three different. A total of 90% of the embryos that completed their development proceeded normally, without pauses. One embryo had a different development from the others, entering diapause 2, with a pause in development for 48 h. Although the embryonic development of A. wolterstorffi is similar to that of other Neotropical annual fish species, the diapause 2 occurs when the embryo has a large body size and a well-developed brain, indicating that the lack of embryonic information of the genus Austrolebias may hide characteristics still undescribed or even different survival strategies than what has been observed for other annual fish.
Subject(s)
Cyprinodontiformes , Diapause , Animals , Embryonic DevelopmentABSTRACT
To analyse the survival, pathway and time of embryo development in the annual fish Austrolebias nigrofasciatus eggs were monitored in four liquid media and two damp media under experimental conditions for 130 days until their development was complete. Eggs kept in the same breeding water from oviposition remained in diapause I (DI) during all experiments. In constrast, up to the stage prior to entering diapause II (DII), the other media had no influence on development. Embryos at this stage (DII), however, show longer development time when treated in medium with water and powdered coconut shell so that about 80% of embryos remained in DII at 100 days. In contrast, all other treatments had a significantly lower proportion of embryos remaining in DII. When treated with Yamamoto's solution in humid media, embryos showed the fastest development. The first fully developed embryos (DIII) were seen at 27 days after oviposition. It took an average of 46-58 days for 50% of eggs in each treatment to reach DIII. Compared with other studies, survival in all incubation media was high at between 70 and 98%. Taken together, it can be concluded that all incubation media were found to be viable for maintaining embryos. Altering developmental trajectories through the manipulation of diapauses in different media makes this species a potential model organism for laboratory studies.
