Review of the family Rivulidae (Cyprinodontiformes, Aplocheiloidei) and a molecular and morphological phylogeny of the annual fish genus Austrolebias Costa 1998

The family Rivulidae is the fourth most diverse clade of Neotropical fishes. Together with some genera of the related African family Nothobranchiidae, many rivulids exhibit a characteristic annual life cycle, with diapausing eggs and delayed embryonic development, which allows them to survive in the challenging seasonal ponds that they inhabit. Rivulidae also includes two species known as the only the self-fertilizing vertebrates and some species with internal fertilization. The first goal of this article is to review the systematics of the family considering phylogenetic relationships and synapomorphies of subfamilial clades, thus unifying information that is dispersed throughout the literature. From this revision, it is clear that phylogenetic relationships within Rivulidae are poorly resolved, especially in one of the large clades that compose it, the subfamily Rivulinae, where conflicting hypotheses of relationships of non-annual and annual genera are evident. The second goal of this work is to present an updated phylogenetic hypothesis (based on mitochondrial, nuclear, and morphological information) for one of the most speciose genus of Rivulidae, Austrolebias. Our results confirm the monophyly of the genus and of some subgeneric clades already diagnosed, but propose new relationships among them and their species composition, particularly in the subgenus Acrolebias.La familia Rivulidae es el cuarto clado más diverso dentro de los peces Neotropicales. Junto con algunos géneros de la familia Nothobranchiidae, muchos rivulidos presentan un característico ciclo de vida anual, con huevos resistentes a la desecación y embriones con diapausas que les permiten sobrevivir en los ambientes estacionales donde habitan. Los Rivulidae presentan también dos especies consideradas como los únicos vertebrados hermafroditas suficientes y algunas especies con inseminación interna. El primer objetivo de este artículo es actualizar la sistemática de la familia considerando las relaciones filogenéticas y las sinapomorfías de los clados que la componen, reuniendo información que se encuentra dispersa en la literatura. De esta revisión surge que las relaciones filogenéticas dentro de Rivulidae están todavía sin resolver, especialmente en uno de los grandes clados que la componen, la subfamilia Rivulinae, donde relaciones conflictivas entre géneros anuales y no anuales son evidentes. El segundo objetivo de este trabajo es presentar una hipótesis filogenética, basada en datos morfológicos, mitocondriales y nucleares, de uno de los géneros más diversos de la familia, el género Austrolebias. Nuestros resultados confirman la monofilia del género y de algunos clados subgenéricos previamente definidos, y propone nuevas relaciones entre ellos, particularmente de las especies del subgénero Acrolebias

Effect of temperature on growth of the threatened annual fish Austrolebias nigrofasciatus Costa & Cheffe 2001

This study evaluated the effect of temperature on growth of Austrolebias nigrofasciatus, an endemic and threatened annual killifish species of the Patos-Mirim lagoon system in Southern Brazil. In order to verify the effect of temperature on initial growth of A. nigrofasciatus, eggs stored in the laboratory were hatched and juveniles reared for eight weeks at 16 and 22 ºC. The standard length of newly hatched fishes was 4.67 ± 0.25 mm and after eight weeks they reached 23.68 ± 3.73 and 22.68 ± 5.36 mm, respectively at 16 and 22 ºC. However, initial growth of fish reared at 22 ºC was faster and they reached sexual dimorphism at an earlier age compared to those reared at 16 ºC. Final length of females reared at 22 ºC was 23.00 ± 2.83 mm, they were significantly larger than those reared at 16 ºC (17.91 ± 2.47 mm). Males were significantly larger than the females at 16 ºC, but there was no difference for growth between sexes of fish reared at 22 ºC. The sex ratios were 1:0.6 and 1:1.1 (M:F) at 16 ºC and 22 ºC, respectively, suggesting temperature determination of phenotypic sex. Considering the results, it appears that juveniles to be developed in captivity should be kept at 22 ºC during the first six weeks of life, thus ensuring a higher growth rate until puberty

Growth of Critically Endangered annual fish Austrolebias wolterstorffi (Cyprinodontiformes: Rivulidae) at different temperatures

Given the importance of knowledge of the biology of endangered species for the planning of conservation and management efforts, the aim of this study was to investigate the influence of temperature on the growth of Austrolebias wolterstorffi (Ahl, 1924). To clarify the thermal influence on the growth of the species, temperatures of 16, 20, 24 , and 28°C were tested in triplicate. The present study showed that a water temperature of 28°C is detrimental to the growth of the species. Among the other tested temperatures, it was found that the optimum temperature for growth decreases as an individual ages and is slightly lower for females. It was demonstrated here that males reach a higher weight and length, and grow faster than females, reaching sexual maturity earlier. To optimize the growth of this species in captivity, the ideal temperature of the water during the initial life period is 24°C, until after puberty when the temperature should decrease to about 21°C.Devido à importância do conhecimento da biologia das espécies ameaçadas de extinção para o planejamento de ações de conservação e manejo, o objetivo deste estudo foi investigar a influência da temperatura sobre o crescimento de Austrolebias wolterstorffi (Ahl, 1924). Para verificar a influência da temperatura no crescimento da espécie, as temperaturas de 16, 20, 24 e 28° C foram testadas em triplicata. O presente estudo mostrou que a temperatura da água de 28° C é prejudicial para o crescimento da espécie. Entre as outras temperaturas testadas, verificou-se que a temperatura ótima para o crescimento diminui ao longo da vida e é ligeiramente menor para as fêmeas. Foi demonstrado aqui que os machos alcançam um maior peso e comprimento e crescem mais rápido do que as fêmeas, atingindo a maturidade sexual anteriormente. Para otimizar o crescimento da espécie em cativeiro, a temperatura ideal da água durante o período inicial de vida é de 24° C, já após a puberdade, a temperatura deverá diminuir para cerca de 21°C