Editorial: The physiological and molecular response of aquatic animals to environmental stresses

The aquatic organisms include approximately 20% of species on the Earth. Many of those aquatic species play essential roles in ecosystems and/or the economy. In the past two hundred years, the significantly increased anthropogenic activities and climate change generated much more pressure on the aquatic organisms. Many species demonstrated phenotypic and genotypic changes in response to environmental pressure. In this Research Topic, “The physiological and molecular responses of aquatic animals to various environmental stressors” were discussed. With the significant global climate change, the aquatic environment starts to become unstable. The most common concern is the temperature, which is directly caused by global warming in the past two centuries. The direct effect of increasing temperature in the aquatic environment on aquatic animals is the change of gene expression profiles upon the thermal stress. With the well-developed, low-cost next-generation sequencing techniques, alterations in transcriptomes under the pressure of high temperature have been identified in many aquatic organisms, including Pacific oyster (Crassostrea gigas) (Tan et al.), ark shells (Scapharca subcrenata) (Zou et al.), and Farrer’s scallop (Chlamys farreri) (Liu et al.). Long-term thermal stress on oysters even resulted in a global divergence in the genome (Tan et al.). Hypoxia has been long recognized as an environmental stressor that negatively impacts aquatic animals. Since oxygen is critical to oxidation and metabolic activities in animals, lack of oxygen in water showed a significant influence on the post-translational regulation in aquatic animals, such as protein phosphorylation (Sokolov et al.) and gluconeogenesis (Jiang et al.). These changes indicated the activation of alternative metabolic pathways with less oxygen consumption in the animals. The hypoxic stress also impacts the aquatic animals at the transcriptomic level leading to the upregulation of a classic molecular chaperone family, heat shock proteins (Sun et al.), which is similar to that of the animals under thermal stress. Interestingly, hypoxia also influences the brain function in teleost fish (Atlantic croaker, Micropogonias undulatus) by manipulating the activity of neuronal nitric oxide synthase (Rahman and Thomas), which explains the behavioral change of the fish associated with hypoxic stress