Laboratory mate choice experiments have confirmed species status for cichlid fish in the African Great Lakes that differ in colour and little else. Colour differences between allopatric populations of the South American cichlid genus Apistogramma are known for many species, yet the status of such populations has not been previously tested. Analysis of the genetic relationships and mate choice characteristics of populations previously described as Apistogramma caetei from eastern Amazonia indicates genetic differentiation into at least three allopatric lineages, which also show strong prezygotic isolation through female mate choice, confirming them as Biological species. If future studies confirm that this result is indicative of a general trend, the species richness of the South American cichlid fishes may presently be seriously underestimated.

Aim The aim was to analyze the incidence of microplastics in the diet of fish in the middle Uruguay River. Methods The present work analyzed the gastrointestinal content of two species: Astyanax lacustris and Iheringichthys labrosus. Results This study provides the first evidence of synthetic materials, such as fibres and plastics in the gastrointestinal tract of fish species in the Middle Uruguay River basin. A sample of sixty-one A. lacustris and twenty-nine I. labrosus were examined to highlight the ingestion of microplastics in the middle section of the Uruguay River in Brazil. In the A. lacustris, eleven fibres and two fragments were found in their gastrointestinal contents, corresponding to 18.1% of the specimens, while in the I. labrosus, twelve fibres and one fragment were found, corresponding to 34.5% of the specimens analyzed. Blue staining was also prevalent in the occurrence of microplastics. Conclusions These data are the first record of microplastics in this zone and represent a baseline for this contamination for future studies.

Length‐Weight relationship (LWRs) were estimated for four fish species occurring in the Ibicuí River drainage basin, southern Brazil. Samples were captured monthly during the spring and summer seasons (October 2018 to March 2019). The fish were caught with gillnets of different meshes (15, 20, 25, 30, 40 mm between adjacent nodes) and a trawl net (5 mm mesh between adjacent nodes) Eighteen excursions were realized in three sites, with a length of approximately 100 km, in third‐order flux, all distributed in sub‐basin Ibicuí River. The captured tools were installed at the end of the day (6 p.m.) and removed around 6 a.m. the next day. The present study provides the length‐weight relationship for four species (Astyanax dissensos, Galeocharax humeralis, Hypostomus roseopunctatus e Hypostomus uruguayensis).

Currently, there are several types and models of plankton nets available on the market. However, it is not known for sure how the differences in size and shape of these nets influence the capture of eggs and larvae. Therefore, the objective of this study was to investigate the influence of mouth size and collection cod-end type on the capture of ichthyoplankton organisms. Collections were carried out in October and November 2019 on the Ibicuí River (Rio Grande do Sul, Brazil) using four different plankton trawl nets: T1: Wide mouth pelagic net with closed collection cod-end; T2: Wide mouth pelagic net with opened collection cod-end; T3: Narrow mouth pelagic net with closed collection cod-end and T4: Narrow mouth pelagic net with opened collection cod-end. At the laboratory, the samples were screened and the larvae were classified in the Yolk-Sac, Pre-Flexion, Flexion and Post-Flexion stages. To evaluate the variation of eggs, total larvae and developmental stages in each of the trawl nets, a two-way Analysis of Variance (ANOVA) was used. When the ANOVA results were significant, Tukey's a posteriori test was performed to detect differences. There was no statistically significant difference (P>0.05) in the capture of eggs and total larvae in the different nets in October. However, November has registered the highest number of total larvae in the widest mouth nets. In both months of sampling, there was greater capture of the Flexion and Post-Flexion stages on the wide mouth and opened collection cod-ends nets. The efficiency of ichthyoplankton capture seems to be related to larval developmental stages, which demonstrates the importance of choosing a net that adapts to the objectives of each study.

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