Adaptation of the eyes of grass puffer (Takifugu niphobles) to the riverine and marine environments

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 both 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 phylogeny and population genetics of riverine and marine grass puffers indicated that riverine and marine grass puffers are from the same population. 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 adaption of 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. These genes showed higher expression in riverine grass puffer than in other marine and river pufferfish species, suggesting that the grass puffer individuals adapt to the environmental difference when they migrate to the river by increasing the expression levels of heat shock protein and related genes.