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Leptopanchax opalescens is a critically endangered small annual fish. Reproductive traits of this species were studied to improve our understanding of the strategies that facilitate the occupation of temporary wetlands. We compiled egg diameter and maximum total length (TLmax) data from 132 neotropical freshwater fish (83 genera, 43 families) to establish comparisons with this species. We used the egg diameter / TLmax ratio to test the hypothesis that annual fish in temporary wetlands have relatively larger eggs than non-annual species from perennial habitats (lakes, rivers). Fish were collected from Guandu River drainages (Brazil). DNA barcoding was employed to confirm the species identity. The phases of gonadal development and spawn type were described using histological techniques. Egg size and fecundity were determined with microscopic analysis. Females with batch spawning and males with continuous spawning were detected. The bath fecundity ranged from 22–32 vitellogenic oocytes (mean 27 ± 7 SD). Annual species presented greater relative egg size than perennial species (p L. opalescens and other annual fish in temporary wetlands.

A new approach for visual fish survey in reservoirs using underwater drones (remotely operated vehicle- ROV) is presented. The ROV was applied to identify abiotic gradients and to compare fish assemblages on the steep slopes in a tropical reservoir. The tested hypothesis is that fish are concentrated in the littoral zone due to the better physicochemical and habitat conditions, compared to deep and hypoxic layers. Twelve species were recorded (seven native, five exotic), with all species occurring in the littoral zone, seven species in the transition, and four in the profundal zone. A greater fish abundance and richness was found in the littoral zone corroborating the main hypothesis. The littoral zone was dominated by exotic cichlids (Cichla spp., Coptodon rendalli), while native catfish (Loricariichthys castaneus, Pimelodella lateristriga) occupied deeper areas. The fish distribution seems to be driven by local factors, such as oxygen availability and habitat structure. The preference for the littoral zone by alien cichlids may have led to the extirpation/decrease of native characids and induced catfishes to occupy deep habitats. Underwater drones can be a valuable tool for the simultaneous collection of abiotic/biotic data, especially in deep reservoirs with complex habitats, resulting in advances in the environmental monitoring. Supplementary Information The online version contains supplementary material available at 10.1007/s10750-021-04790-9.

The reproductive strategy of the non-native predator cichlid Cichla kelberi was determined to explain its success after more than 60 years of being introduced into an isolated reservoir in southeastern Brazil. This was one of the first known translocations of the genus Cichla out of its natural range. Macro and microscopy characteristics of the gonadal development stages and the maturation phases were described, along with the reproductive features (size at first maturation size, gonadosomatic index and sex ratio). We hypothesized that the stable conditions of the reservoir, with low connectivity, weakly defined spatial gradient, and slight seasonal changes in environmental variables favour the equilibrium strategy that enable predators to have high offspring survivorship because of great parental investment in individual progeny. Sex ratio was well balanced with males and females reaching first maturity between 30.0 and 28.6 cm total length (LT ), respectively. The stages of oocytes (primary and secondary growth, vitellogenic and atresia) and spermatocytes (spermatogonia, spermatocytes, spermatids and spermatozoa) development were identified. Five phases of gonadal development (immature, developing, spawning capable, regressing and regenerating) were described for both sexes. A long reproductive season was found, with spawning peaks in August/September and, to a lesser extent, in April/May. Parental care and spawns in parcels (batch spawns) corroborated the raised equilibrium strategy that was effective in this isolated reservoir. This species developed reproductive mechanisms that fit to different environmental conditions, with multiple spawning being associated with lentic environments and asynchronous development of oocytes, which are released over long periods. The reproductive plasticity in reservoirs may be one of the main factors inherent to the successful of colonization and establishment of the peacock bass in the environments in which they were introduced. This article is protected by copyright. All rights reserved.

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°42.35’S, 43°41.59’W) 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.

Fragmentation and interconnection of water bodies cause severe changes in the natural flow regime of continental water systems. However, assessments of these impacts on the freshwater fish distribution are still scarce. We investigated whether an artificial flow regime generated by discharges from an aqueduct would promote a longitudinal environmental gradient in an off-river reservoir. We tested the hypothesis that the incoming water from aqueduct discharges promotes environmental gradient between lotic and lentic conditions. We expect that environmental changes and the artificial flow regime promote the structuring of fish assemblage and that the lotic-lentic transition areas present the highest fish species richness. A longitudinal gradient in environmental characteristics with differing fish assemblage structure was found. Temporal changes in the fish assemblages occurred only in areas near the discharge of the aqueduct. The highest fish richness and diversity were recorded in the transition zone during the wet season, associated with the greater environmental heterogeneity of this ecotone, whereas the lowest was found in the lotic zone, probably associated with the altered flow regime. The greatest abundance was recorded in the upper lentic zone in the wet season, whereas the lowest was found in the lower lentic zone in both seasons. Our results corroborate the hypothesis that the artificial flow regime, modulated by the seasonality of discharges and the influence of environmental variables, promotes longitudinal gradients in reservoirs when rivers are not present. The findings are relevant in a scenario where ever more interconnections of aquatic bodies have been diffused around the world.

O Parque Natural Municipal Bosque da Barra é uma Unidade de Conservação de Proteção Integral criada em 2003 e uma das mais visitadas do Município do Rio de Janeiro. Estudos prévios indicam que a lagoa da UC é artificial e o parque abrange ambientes de brejos, originais da restinga da Mata Atlântica. Suas águas são provenientes da chuva e do complexo lagunar de Jacarepaguá, onde ocorrem diversas espécies de peixes que colonizaram a lagoa do Bosque. Levantamentos realizados no início do ano 2000 revelaram a ocorrência de 12 espécies de peixes de água doce, pertencentes a 11 gêneros e 7 famílias: jeju (Hoplerythrinus unitaeniatus), traíra (Hoplias cf. malabaricus), tamboatá (Callichthys callichthys), barrigudinhos (Phalloptychus januarius e Poecilia vivipara), mussum (Synbranchus marmoratus), acará (Geophagus brasiliensis), tilápiado-Nilo (Oreochromis niloticus), tilápia-do-Congo (Coptodon rendalli) e peixe-dasnuvens (Notholebias minimus). Em 2015 uma importante estiagem afetou diversas regiões do Brasil e culminou na completa seca da lagoa do Bosque da Barra. Neste projeto temos como objetivo realizar um novo levantamento das espécies de peixes dessa área, com a finalidade de determinar que espécies ocorrem como consequência da recolonização a partir do mesmo estoque inicial de espécies disponíveis na Lagoa de Jacarepaguá. Estão previstas duas campanhas de amostragem, uma no período seco e outra no período chuvoso. A primeira campanha (seca) foi realizada em 4 de agosto de 2022. A área amostral foi subdividida em 4 sítios de amostragem, sendo eles: (1) porção do fundo da lagoa próxima da manilha que conecta a lagoa de Jacarepaguá, (2) a zona inundada presente na lateral da lagoa, (3) na porção da lagoa artificialmente escavada e (4) nos brejos dentro da floresta. Fizemos registros dos parâmetros físico e químicos, por meio de sondas multiparâmetro, para medição de: Temperatura, pH, OD, Condutividade, Salinidade e Sólidos dissolvidos. A amostragem de peixes utilizou 4 redes de espera, espalhadas em pontos equidistantes por 1 hora, 1 rede de arrastinho com esforço concentrado próximo às macrófitas aquáticas emersas e 5 puçás com esforços de 1 hora nas margens. Foi registrada a ocorrência de 5 espécies, pertencentes a 4 gêneros e 3 famílias: Acará (Geophagus brasiliensis), traíra (Hoplias malabaricus), barrigudinhos (Poecilia vivípara, Phalloptychus januarius), tilápia-do-Nilo (Oreochromis niloticus). Os resultados desse levantamento deverão auxiliar na avaliação do estado dos estoques originais nas Lagoas de Jacarepaguá e sua importância no processo de recolonização das lagoas do Bosque.

Several species of marine fish use different coastal systems especially during their early development. However, these habitats are jeopardized by anthropogenic influences threatening the success of fish populations, and urgent measures are needed to priorize areas to protect their sustainability. We applied taxonomic (Δ+) and functional (X+) distinctiveness indices that represent taxonomic composition and functional roles to assess biodiversity of three different costal systems: bays, coastal lagoons and oceanic beaches. We hypothesized that difference in habitat characteristics, especially in the more dynamism and habitat homogeneity of oceanic beaches compared with more habitat diversity and sheltered conditions of bays and coastal lagoons results in differences in fish richness and taxonomic and functional diversity. The main premise is that communities phylogenetically and functionally more distinct have more interest in conservation policies. Significant differences (P < 0.004) were found in the species richness, Δ+ and X+ among the three systems according to PERMANOVA. Fish richness was higher in bays compared with the coastal lagoons and oceanic beaches. Higher Δ+ was found for the coastal lagoons compared with the bays and oceanic beaches, with the bays having some values below the confidence limit. Similar patterns were found for X+, although all values were within the confidence limits for the bays, suggesting that the absence of some taxa does not interfere in functional diversity. The hypothesis that taxonomic and functional structure of fish assemblages differ among the three systems was accepted and we suggest that coastal lagoons should be priorized in conservation programs because they support more taxonomic and functional distinctiveness.