The impact of human activities and social industrialization on the marine environment and aquatic life cannot be underestimated. By utilizing information transmission intermediates such as underwater wearable sensors, it is possible to promptly and precisely assess the state of the marine environment, as well as the behavior of biological populations, thereby ensuring accurate protection of the marine ecology. Flexible electronic tags maintain accurate monitoring performance while addressing the biocompatibility of sensors. When the tag is attached to an organism's surface or implanted in the body, it can perform real-time monitoring, providing valuable insights into their biology and behavior. At the same time, allow them to attach to the animal without causing injury or disruption to their inherent behavior. In this paper, implantable electronic tags and wearable flexible sensing systems are examined while exploring their potential applications in this field. The review discusses four aspects of these systems: physical information monitoring in the marine environments, chemical information monitoring in the marine environments, physiological information monitoring in animals, and biochemical information monitoring in animals. Finally, the article explores upcoming challenges and trends in the development of implantable electronic tags and wearable, flexible sensors for aquatic animals. Flexible electronic tags that accompany animals have the ability to detect a wider area of the ocean, maintaining sensing performance while being more biocompatible. The functions and main structures of wearable flexible tags and implantable devices for marine animals are reviewed. The challenges and possible strategies for the development of flexible electronic tags are discussed. image