Industries have been producing nanomaterials (NMs) for years and using them in various commercial applications. The toxicological effects of nanoparticles (NPs) provide an uncontrolled introduction to the environment and inspire concerns regarding their affecting the aquatic animals. We reviewed the literature on the toxicity of NMs and NPs to aquatic animals from the perspective of relevance and reliability in a regulatory framework. In this chapter, we summarise the data on the effect of NMs on aquatic animals and provide a holistic overview of the effects of penetration and accumulation of NPs in the body of aquatic animals and their toxic effect, biotransformation, and migration along food webs are considered. Understanding the unique properties of nanoscale materials has proven to be an essential aspect of their toxicity. We critically examine the progress of applying wide-ranging organisms to understand the holistic pathways involved in the mechanisms that may be affected by exposure to NMs. It is demonstrated that the behaviour of nanomaterials in the environment and their effect on living organisms have been studied insufficiently and require close attention because their release into the environment will increase very soon.