Gill transcriptome of the yellow peacock bass (Cichla ocellaris monoculus) exposed to contrasting physicochemical conditions

Freshwater habitats of the Neotropics exhibit a gradient from relatively neutral, ion-rich whitewater to acidic, ion-poor blackwater. Closely related species often show complementary distributions among regions with divergent water quality, suggesting that distinct osmoregulatory environments may be a major constraint to fish distribution and an important driver of Neotropical fish diversity. To provide a foundation for further investigation, we reconstructed the gill filament transcriptome of Cichla ocellaris monoculus , a highly exploited Neotropical cichlid that inhabits a broad range of habitats, in experimental conditions meant to mimic opposing endpoints of the whitewater-blackwater gradient. The optimal combined transcriptome contained 185,480 transcripts (> 200 bp) and contained 281.9 Mbp (N50 2,648 bp), from which 17,379 putatively orthologous protein-coding loci were annotated. We observed evidence of utilization of peptide hormone signaling that may have activated signaling cascades to moderate the permeability of the gills in response to these physicochemical challenges. Expression of genes related to paracellular tight junctions and transcellular ion transport indicated responses broadly similar to euryhaline fishes in fresh versus seawater. These results provide a useful foundation for investigating the axes of acclimation or constraint for Neotropical fishes facing increasing habitat modification due to anthropogenic forces, and more broadly the proximate and ultimate modes of diversification in the hyperdiverse Amazon fish fauna.