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Associations between host genotype and host‐associated microbiomes have been shown in a variety of animal clades, but studies on teleosts mostly show weak associations. Our study aimed to explore these relationships in four sympatric Serrasalmidae (i.e., piranha) teleosts from an Amazonian lake, using data sets from the hosts genomes (single nucleotide polymorphisms from genotyping by sequencing), skin and gut microbiomes (16S rRNA gene metataxonomics) and diets (COI metabarcoding) from the same fish individuals. First, we investigated whether there were significant covariations of microbiome and fish genotypes at the inter‐ and intraspecific levels. We also assessed the extent of covariation between Serrasalmidae diet and microbiome, to isolate genotypic from dietary effects on community structure. We observed a significant covariation of skin microbiomes and host genotypes at interspecific (R2 = 24.4%) and intraspecific (R2 = 6.2%) levels, whereas gut microbiomes correlated poorly with host genotypes. Serrasalmidae diet composition was significantly correlated to fish genotype only at the interspecific level (R2 = 5.4%), but did not covary with gut microbiome composition (Mantel R = −.04). Second, we investigated whether the study of interspecific differentiation could benefit from considering host‐associated microbial communities in addition to host genotypes. By using a nonmetric multidimensional scaling (NMDS) ordination‐based approach, we observed that ordinations from skin‐ and gut species‐specific bacterial biomarkers identified through a random forest algorithm could significantly increase the average interspecific differentiation detected through host genotype data alone. Although future studies encompassing additional species and environments are needed, our results suggest Serrasalmidae microbiomes could constitute an insightful trait to be considered when studying the interspecific differences between members of this clade. [ABSTRACT FROM AUTHOR]

The world's richest freshwater fish community thrives in gradients of contrasting environments in Amazonia, ranging from ion‐poor acidic black waters, to ion‐rich circumneutral white waters. These hydrochemical gradients structure Amazonian fish assemblages via ecological speciation events. Fish bacterial communities contain an important genetic heritage essential for their hosts' survival and are also involved in adaptive divergence via niche adaptation processes, but the extent to which they evolve in response to hydrochemical gradients in Amazonia is unknown. Here we investigated bacterial communities (gut and skin mucus) of two ecologically and phylogenetically divergent host species (Mesonauta festivus and Serrasalmus rhombeus) distributed throughout these hydrochemical gradients. The goal was to characterize intra‐ and interspecific Amazonian fish microbiome variations across multiple scales. Using a 16S metabarcoding approach, we investigated the microbiota of 43 wild M. festivus, 32 S. rhombeus and seven water samples, collected at seven sampling sites encompassing both water colours. Taxonomical structures of bacterial communities from both host species were significantly correlated to the environmental continua of magnesium, sodium, dissolved organic carbon, calcium, dissolved O2, pH, potassium, hardness and chloride. Analysis of discriminating features in community structures across multiple scales demonstrated intra‐ and interspecific structural parallelisms in the response to the hydrochemical gradients. Together, these parallelisms suggest the action of selection on bacterial community structures along Amazonian hydrochemical gradients. Functional approaches along with reciprocal transplant experiments will provide further insights on the potential contribution of Amazonian fish microbiomes in host adaptation and ecological speciation events. [ABSTRACT FROM AUTHOR]

Lateral migrations are movements of fish schools to and from lentic and/or lotic environments, in order to feed, reproduce or seek favorable survival conditions. This study was conducted in the corixo Manoel Isaac, which connects Cuiabá River to Chacororé Lake in the Pantanal of Barão of Melgaço, State of Mato Grosso. Fish were collected in the period of April-December, that included the seasons of receding water, drought and flood aiming to analyze the lateral migration of fish. It was observed that 12 species used the systems during dry and flood seasons, to feed (time of "lufada") and to spawn (time of "spawning"), respectively. When the water level is higher, the fish migrate from the bay to the river. At the beginning of the ebb (April), the catch is high, extending up to July, and CPUEs decrease when the drought period begins (July) and there is a rise in the water level of the corixo at the end of September. A second elevation in the catch is verified; however, the direction of movement of the majority of the species is from the river to the bay, following water current. It was concluded that the lateral migration of fish between the Chacororé Bay and the Cuiabá River during the study presented greater catches during the months of April to June (ebb) with fish moving from the bay to the river and during the flood (October to December), the fish migrate in the opposite, from the river towards bay. [ABSTRACT FROM AUTHOR]

Several times throughout their radiation fish have evolved either lungs or swim bladders as gas-holding structures. Lungs and swim bladders have different ontogenetic origins and can be used either for buoyancy or as an accessory respiratory organ. Therefore, the presence of air-filled bladders or lungs in different groups of fishes is an example of convergent evolution. We propose that air breathing could not occur without the presence of a surfactant system and suggest that this system may have originated in epithelial cells lining the pharynx. Here we present new data on the surfactant system in swim bladders of three teleost fish (the air-breathing pirarucu Arapaima gigas and tarpon Megalops cyprinoides and the non-air-breathing New Zealand snapper Pagrus auratus). We determined the presence of surfactant using biochemical, biophysical, and morphological analyses and determined homology using immunohistochemical analysis of the surfactant proteins (SPs). We relate the presence and structure of the surfactant system to those previously described in the swim bladders of another teleost, the goldfish, and those of the air-breathing organs of the other members of the Osteichthyes, the more primitive air-breathing Actinopterygii and the Sarcopterygii. Snapper and tarpon swim bladders are lined with squamous and cuboidal epithelial cells, respectively, containing membrane-bound lamellar bodies. Phosphatidylcholine dominates the phospholipid (PL) profile of lavage material from all fish analyzed to date. The presence of the characteristic surfactant lipids in pirarucu and tarpon, lamellar bodies in tarpon and snapper, SP-B in tarpon and pirarucu lavage, and SPs (A, B, and D) in swim bladder tissue of the tarpon provide strong evidence that the surfactant system of teleosts is homologous with that of other fish and of tetrapods. This study is the first demonstration of the presence of SP-D in the air-breathing organs of nonmammalian species and SP-B in actinopterygian fishes. The extremely high cholesterol/disaturated PL and cholesterol/PL ra- tios of surfactant extracted from tarpon and pirarucu bladders and the poor surface activity of tarpon surfactant are characteristics of the surfactant system in other fishes. Despite the paraphyletic phylogeny of the Osteichthyes, their surfactant is uniform in composition and may represent the vertebrate protosurfactant. [ABSTRACT FROM AUTHOR]