The number of non-native species in Brazil has exceeded 500 taxa, represented mainly by land animals (^{Coradin and Tortato, 2006}). The principal vectors of exotic species introductions in aquatic environments are activities such as aquaculture, sport fishing, and the aquarium trade (^{Vitule and Prodocimo, 2012}; ^{Gubiani et al., 2018}). These environments, especially lakes, lagoons, and reservoirs, are highly vulnerable to invasive species, mainly by crustaceans and fish (^{Karatayev et al., 2015}; ^{Gubiani et al., 2018}). Among the non-native species cultivated in Brazil is the crustacean Macrobrachium rosenbergii (De Man, 1879), which has been introduced into at least 40 countries (^{FAO-DIAS, 2020}).

Chimaera, represented by 52 species, are deep-sea animals, therefore difficult to access for study; moreover, they are vulnerable to fishing due to their k-strategic characteristics. Despite being vulnerable, there are few studies on its life history, which makes it difficult to understand the population status of the species. Life-history parameters are essential in population ecology to assess the status and trends of population. In this study, it was proposed to evaluate the publication trends on Chimaera and the gaps in knowledge, analyzing which subject and species are most frequently studied. For this, the scientometric method was used, based on search of articles using a group of words directed to Chimaera in databases of bibliographic references (Scopus® and Web of ScienceTM). The articles were classified by year of publication, authors' location (at the country level), focus species and subject matter. The number of articles per year showed an exponential growth trend, indicating that studies on chimaera have been increased. Among the authors’countries, such as the United States of America and the United Kingdom, are prominent. The most studied species were: Hydrolagus colliei, Callorhinchus milii and Chimaera monstrosa. The main themes of the articles were anatomy, morphology and physiology, followed by systematics and evolution. The most diminished research topics were fishing and growth, for almost all species. Therefore, even with the growth trend, more effort and reinforcement is still required in the research of these fish, mainly in the aspects on fishery, growth, and reproduction themes.

The prawnMacrobrachium amazonicumhas been considered a successful colonizing species of freshwater environments beyond its native range; however, information on the distribution of the species in rivers in northeastern Brazil is doubtful or incomplete. This study updates the presence of the Amazon River prawnMacrobrachium amazonicumin the São Francisco River (northeast Brazil) where eight areas were sampled downstream from the Xingó Hydroelectric Plant (Alagoas/Sergipe) up to the mouth of the river, between April 2014 and February 2016. The specimens were sampled using manual trawls and artisanal traps. Hydrological data were obtained using a multi-parameter probe. Only 258 specimens were found in Piranhas, Pão de Açúcar, and Belo Monte, which are regions far from the mouth of the river. They were found in shallow (3.96 ± 1.01 m), warm (26.15 ± 1.18 °C), and oxygenated fresh waters (5.70 ± 1.14 mg L^-1) with low turbidity (71.33 ± 6.43 mg L^-1) and slight alkalinity (7.26 ± 0.53), always associated with the aquatic vegetation. The presence ofM. amazonicumhas not yet been evaluated in relation to possible impacts on local native diversity. Therefore, studies addressing the interaction of this species with native species are necessary to understand whether or not it poses a risk to endemic species.

The biological invasions are considered the second biggest threat to global biodiversity (Wilson 1975; Williamson & Griffiths 1996; McNeely et al. 2001; Bellard et al. 2016). It is characterized as...