Differential expression genes in the eye-transcriptomes of the riverine and marine grass puffer (Takifugu niphobles).

Many marine fish species migrate to rivers, but little is known about whether these species switch their vision when inhabiting rivers or adapt their vision to the environment of rivers and the sea. Grass puffer (Takifugu niphobles) is a marine fish species frequently migrating to rivers. In this study, we investigated grass puffers from riverine and marine populations and analyzed the gene expression in their eyes. The phylogenetic analysis did not separate riverine and marine grass puffers. Principal component analysis and ADMIXTURE based on genome-wide SNPs showed no population differentiation of these two populations. Gene expression levels by high-throughput RNA sequencing indicated no differences in the expression patterns of vision-related genes in marine and riverine grass puffers. This result indicates that the grass puffers adapt their visual system to both marine and riverine environments rather than switching the expression of vision-related genes. Additionally, riverine grass puffers increase the expression levels of heat shock proteins and related genes, suggesting that they adapt to the environmental differences when they migrate to the river by increasing the expression levels of these genes.