Aquatic organisms are increasingly exposed to lowering of environmental pH due to anthropogenic pressure (e.g. acid rain, acid mine drainages). Such acute variations trigger imbalance of fish-associated microbiota, which in turn favour opportunistic diseases. We used the tambaqui (Colossoma macropomum), an Amazonian fish tolerant to significant pH variation in its natural environment, to assess the response of fish endogenous microbiota to acute short-term acid stress. We exposed 36 specimens of tambaquis to acidic water (pH 4.0) over 2 consecutive weeks and sampled cutaneous mucus, feces and water at 0, 7 & 14 days. The 16S RNA hypervariable region V4 was sequenced on Illumina MiSeq. After two weeks of acidic exposure, fecal and skin microbiota taxonomic structures exhibited different patterns: skin microbiota was still exhibiting a significantly disturbed composition whereas fecal microbiota recovered a similar composition to control group, thus suggesting a stronger resilience capacity of the intestinal microbiota than cutaneous microbiota.

This study aims to evaluate the transcriptome alterations, through cDNA libraries, associated with the combined effects of two PAHs, benzo[a]pyrene (0.5 µg/L) and phenanthrene (50 µg/L), present in crude oil, on specimens of Symphysodon aequifasciatus (discus fish) after 48 h of exposure. The cDNA libraries were constructed according to the SOLiD™ SAGE™ protocol for sequencing in the SOLiD v.3 Plus sequencer. The results were analyzed by bioinformatics and differentially expressed genes were categorized using the gene ontology program. The functional categories (terms) found in the gene ontology and the gene network generated using STRING software were used to predict the adverse effects of benzo[a]pyrene and phenanthrene in the liver. In the present study, 27,127 genes (compared to Danio rerio database) were identified. Considering only those genes with a p-value less than or equal to 0.05 and greater than or equal to two-fold change in expression across libraries, we found 804 genes, 438 down-regulated (54%) and 366 up-regulated (46%), in the experimental group compared to the control. Out of this total, 327 genes were successfully categorized, 174 down-regulated and 153 up-regulated, using gene ontology. Using String, the gene network was composed by 199 nodes, 124 of them resulting in 274 interactions. The results showed that even an acute exposure of 48 h caused metabolic change in response to environmental contaminants, resulting in changes of cell integrity, in oxidation-reduction processes, in the immune response and disturbances of intracellular signaling of discus fish. Also the gene network has showed no central interplay cluster, exhibiting instead interconnected clusters interactions and connected sub-networks. These findings highlight that even an acute sublethal exposure of PAHs can cause metabolism changes that may affect survival of discus. Our findings using SOLiD coupled with SAGE-method resulted in a powerful and reliable means for gene expression analysis in discus, a non-model Amazonian fish.

The Arapaima gigas is an endemic fish to the Amazon basin and with great potential for aquaculture, although its reproduction in captivity is limited by the absence of sexual dimorphism. The demand increase for pirarucu in the Northern region of Brazil, has led to new studies on the reproduction of the species. Thus, we aimed to investigate patterns of sex-biased genes in brain and gonad tissues of A. gigas. A total of of 451,490,808 short sequencing reads were produced using the SOLiD v4 plus sequencing platform. An average of ~30% of sequencing reads were mapped to Asian arowana reference cDNAs, species that belong to the same group of bony-tongue fishes. Gene expression analysis identified 305 sex-biased genes for the brain, with 297 genes up-regulated in females and only eight genes up-regulated in males. The analysis of the gonads identified 120 sex-biased genes, with 110 genes up-regulated in females and only ten genes up-regulated in males. Gene ontology analysis found more than 50 terms enriched for the sex-biased genes in a wide range of pathways suggesting that multiple functions and processes differ between the sexes. Thus, the following areas of interest were approached: sex steroids/hormones, organism development process and macromolecule biosynthetic process, which exhibited sex-biased gene expression; these areas are known to influence sexual development in other species. Lastly, the information obtained in this study concerning the sex-biased genes in the A. gigas species is a contribution to further studies approaching the processes of gonadal development, and downstream molecular mechanisms in species.