New occurrences of the endangered Notholebias minimus (Cyprinodontiformes: Rivulidae) in coastal plains of the State of Rio de Janeiro, Brazil: populations features and conservation

Notholebias minimus is an endangered annual killifish endemic to the coastal plains of the State of Rio de Janeiro, Brazil. This study aimed to present new occurrences in the Atlantic Forest biome, provide unprecedented population features (body and egg size, fecundity, sexual ratio, and length-weight relationship - LWR), and compare changes in land use and coverage between 1985 and 2021 in biotopes located inside and outside protected areas. Three new occurrence localities were found in shallow temporary wetlands with acidic pH (6.4 ± 0.2) and low concentrations of dissolved oxygen (2.0 ± 0.9 mg/L). Males and females total length ranged from 11.1 to 31 mm and 11 to 26 mm, respectively. Batch fecundity ranged from 18 to 40 oocytes (24.8 ± 8.8), corresponding to oocytes with sizes between 800-1,006 µm (905 ± 56). Males were significantly larger than females (W = 2193.5, p = 0.0067), but both sexes occurred in similar proportions (p = 0.472). LWR showed positive allometry (b = 3.18). Biotopes located within protected areas exhibited higher conservation. Our discoveries expand the knowledge about habitat and population features of N. minimus and reinforce the importance of establishing protected areas for the conservation of annual fish biotopes.

Notholebias minimus é um peixe anual ameaçado de extinção, endêmico das planícies costeiras do Estado do Rio de Janeiro, Brasil. Neste estudo, objetivamos apresentar novas ocorrências no bioma Mata Atlântica, fornecer características populacionais inéditas (tamanho do corpo e dos ovos, fecundidade, proporção sexual e relação peso-comprimento), e comparar mudanças no uso e cobertura do solo entre 1985 e 2021 em biótopos localizados dentro e fora de unidades de conservação. Registramos três novos locais em áreas úmidas temporárias rasas com pH ácido (6,4 ± 0,2) e baixas concentrações de oxigênio dissolvido (2,0 ± 0,9 mg/L). O comprimento total de machos e fêmeas variou de 11,1 a 31 mm e de 11 a 26 mm, respectivamente. A fecundidade do lote variou entre 18-40 oócitos (24,8 ± 8,8), correspondendo a diâmetros entre 800-1.006 µm (905 ± 56). Os machos foram significativamente maiores que as fêmeas (W = 2193,5; p = 0,0067), mas ocorreram em proporções similares (p = 0,472). A relação peso-comprimento detectou alometria positiva (b = 3,18). Biótopos localizados dentro de áreas protegidas exibiram maior preservação ambiental. Nossas descobertas ampliam o conhecimento sobre as características do habitat e da população de N. minimus e reforçam a importância do estabelecimento de áreas protegidas para a conservação dos biótopos dos peixes anuais.

The recapture of Leptopanchax opalescens (Aplocheiloidei: Rivulidae), a critically endangered seasonal killifish: habitat and aspects of population structure

Leptopanchax opalescens (Myers, 1942) is a small seasonal killifish endemic to coastal drainages in the state of Rio de Janeiro, Brazil. Leptopanchax opalescens was recaptured in temporary open vegetation pools (22°42.35S, 43°41.59W) in the hydrographic basin of the Guandu River, state of Rio de Janeiro, Brazil, after eight years without records. Information on habitat and population parameters (Capture per unit area (CPUA), size, sex ratio and length-weight relationship (LWR)) are given to provide subsidies for the conservation of this species. Specimens were captured during the rainy season (January-April 2020) in shallow pools (mean depth = 21 ± 12 s.d. cm), with relatively acidic pH (5.2 ± 0.8) and low concentrations of dissolved oxygen (3.5 ± 1 mg/L). The estimated CPUA of the population was 0.89 fish/m2. The total length (TL) of males ranged from 21.1 to 28.8 cm, and females ranged from 17.0 to 31.2 mm. Males were significantly larger (t-test = 2.04, p 0.05) than females, which were in greater proportion (2.83Female: 1Male, p 0.001). A positive allometric coefficient (b = 3.19) was found through length-weight relationship curve, indicating that individuals of the species gain proportionally more increment in weight than in length. Leptopanchax opalescens is a critically endangered species, and the results of this study contribute to the knowledge of the distribution, population structure and conservation of the species and its natural habitats.

The recapture of Leptopanchax opalescens (Aplocheiloidei: Rivulidae), a critically endangered seasonal killifish: habitat and aspects of population structure

Leptopanchax opalescens (Myers, 1942) is a small seasonal killifish endemic to coastal drainages in the state of Rio de Janeiro, Brazil. Leptopanchax opalescens was recaptured in temporary open vegetation pools (22°42.35S, 43°41.59W) in the hydrographic basin of the Guandu River, state of Rio de Janeiro, Brazil, after eight years without records. Information on habitat and population parameters (Capture per unit area (CPUA), size, sex ratio and length-weight relationship (LWR)) are given to provide subsidies for the conservation of this species. Specimens were captured during the rainy season (January-April 2020) in shallow pools (mean depth = 21 ± 12 s.d. cm), with relatively acidic pH (5.2 ± 0.8) and low concentrations of dissolved oxygen (3.5 ± 1 mg/L). The estimated CPUA of the population was 0.89 fish/m2. The total length (TL) of males ranged from 21.1 to 28.8 cm, and females ranged from 17.0 to 31.2 mm. Males were significantly larger (t-test = 2.04, p 0.05) than females, which were in greater proportion (2.83Female: 1Male, p 0.001). A positive allometric coefficient (b = 3.19) was found through length-weight relationship curve, indicating that individuals of the species gain proportionally more increment in weight than in length. Leptopanchax opalescens is a critically endangered species, and the results of this study contribute to the knowledge of the distribution, population structure and conservation of the species and its natural habitats.(AU)

Discovery of endangered annual killifish Austrolebias cheradophilus (Aplocheiloidei: Rivulidae) in Brazil, with comments on habitat, population structure and conservation status

Austrolebias genus comprises about 40 small annual killifishes endemic to South America and their highest diversity occurs in southern Brazil and Uruguay, especially in drainages of Patos-Mirim system. Austrolebias species are severely threatened with extinction because their life cycle and restricted ranges. Low dispersal ability and the extensive loss and fragmentation of freshwater wetlands contribute to this threat. Accurate information on the geographic distribution and ecology of the species, vital to plan conservation and management strategies, are scarce. In order to provide basic knowledge for annual fish conservation this paper reports the presence of Austrolebias cheradophilus and present data about its population structure (CPUA, size, sex ratio, length-weight relationships and condition factor) and conservation status in southern Brazil. The estimated CPUA of populations was 0.86 fish/m2. Standard length (SL) of males ranged between 32.14 and 49.17 mm and for females between 25.11 and 41.6 mm. There were no differences in SL between the sexes (t-test = - 1.678; P = 0.105), and Chi-squared test demonstrated marginal differences in proportions of sexes (2.25:1; χ2 = 3.846; P = 0.07). Allometric coefficient of the LWR was slightly hyperallometric (b = 3.08) and K of the specimens ranged from 1.84 to 2.42 (mean ± S.E. = 2.12 ± 0.04). Populations have low density and their biotopes are under critical threat, mainly due to suppression by agriculture, pastures for livestock and increase housing. The species is considered "Critically Endangered" in Brazil, furthermore is strongly recommended its inclusion on lists of endangered fauna and ensures the protection of their remaining habitats. O gênero Austrolebias compreende cerca de 40 espécies de peixes anuais endêmicos da América do Sul, cuja maior diversidade está concentrada no sul do Brasil e Uruguai, especialmente nas drenagens do sistema hidrográfico Patos-Mirim. A combinação de seu ciclo de vida peculiar com suas restritas distribuições, baixa capacidade de dispersão e ampla fragmentação das áreas úmidas fazem com que suas espécies sejam consideradas ameaçadas de extinção. Entretanto, informações sobre sua distribuição e ecologia são escassas. Visando fornecer informações básicas para a conservação, este estudo registra a presença de Austrolebias cheradophilus no sul do Brasil e apresenta dados sobre sua estrutura populacional (CPUA, tamanho, razão sexual, relação peso-comprimento e fator de condição) e estado de conservação. O CPUA total das populações foi de 0,86 peixe/m2. Não foram encontradas diferenças no tamanho padrão entre os sexos (t-test = - 1,678; P = 0,105) e o teste do Qui-quadrado apresentou um valor marginalmente significativo para a proporção dos sexos (2,25:1; χ2 = 3.846; P = 0.07). O coeficiente de "b" calculado com base na relação peso-comprimento indica um padrão de crescimento levemente alométrico positivo (b = 3,08). O fator de condição dos indivíduos variou entre 1,84 e 2,42 (média ± S.E. = 2,12 ± 0,04). As populações identificadas têm baixa densidade e estão sob ameaça crítica, principalmente devido à supressão do habitat pela agricultura, pecuária e aumento da urbanização. A espécie foi considerada "Criticamente Ameaçada", portanto recomenda-se sua inclusão em listas de fauna ameaçada e a urgente proteção dos seus habitats.(AU)

Discovery of endangered annual killifish Austrolebias cheradophilus (Aplocheiloidei: Rivulidae) in Brazil, with comments on habitat, population structure and conservation status

Austrolebias genus comprises about 40 small annual killifishes endemic to South America and their highest diversity occurs in southern Brazil and Uruguay, especially in drainages of Patos-Mirim system. Austrolebias species are severely threatened with extinction because their life cycle and restricted ranges. Low dispersal ability and the extensive loss and fragmentation of freshwater wetlands contribute to this threat. Accurate information on the geographic distribution and ecology of the species, vital to plan conservation and management strategies, are scarce. In order to provide basic knowledge for annual fish conservation this paper reports the presence of Austrolebias cheradophilus and present data about its population structure (CPUA, size, sex ratio, length-weight relationships and condition factor) and conservation status in southern Brazil. The estimated CPUA of populations was 0.86 fish/m2. Standard length (SL) of males ranged between 32.14 and 49.17 mm and for females between 25.11 and 41.6 mm. There were no differences in SL between the sexes (t-test = - 1.678; P = 0.105), and Chi-squared test demonstrated marginal differences in proportions of sexes (2.25:1; χ2 = 3.846; P = 0.07). Allometric coefficient of the LWR was slightly hyperallometric (b = 3.08) and K of the specimens ranged from 1.84 to 2.42 (mean ± S.E. = 2.12 ± 0.04). Populations have low density and their biotopes are under critical threat, mainly due to suppression by agriculture, pastures for livestock and increase housing. The species is considered "Critically Endangered" in Brazil, furthermore is strongly recommended its inclusion on lists of endangered fauna and ensures the protection of their remaining habitats. O gênero Austrolebias compreende cerca de 40 espécies de peixes anuais endêmicos da América do Sul, cuja maior diversidade está concentrada no sul do Brasil e Uruguai, especialmente nas drenagens do sistema hidrográfico Patos-Mirim. A combinação de seu ciclo de vida peculiar com suas restritas distribuições, baixa capacidade de dispersão e ampla fragmentação das áreas úmidas fazem com que suas espécies sejam consideradas ameaçadas de extinção. Entretanto, informações sobre sua distribuição e ecologia são escassas. Visando fornecer informações básicas para a conservação, este estudo registra a presença de Austrolebias cheradophilus no sul do Brasil e apresenta dados sobre sua estrutura populacional (CPUA, tamanho, razão sexual, relação peso-comprimento e fator de condição) e estado de conservação. O CPUA total das populações foi de 0,86 peixe/m2. Não foram encontradas diferenças no tamanho padrão entre os sexos (t-test = - 1,678; P = 0,105) e o teste do Qui-quadrado apresentou um valor marginalmente significativo para a proporção dos sexos (2,25:1; χ2 = 3.846; P = 0.07). O coeficiente de "b" calculado com base na relação peso-comprimento indica um padrão de crescimento levemente alométrico positivo (b = 3,08). O fator de condição dos indivíduos variou entre 1,84 e 2,42 (média ± S.E. = 2,12 ± 0,04). As populações identificadas têm baixa densidade e estão sob ameaça crítica, principalmente devido à supressão do habitat pela agricultura, pecuária e aumento da urbanização. A espécie foi considerada "Criticamente Ameaçada", portanto recomenda-se sua inclusão em listas de fauna ameaçada e a urgente proteção dos seus habitats.