Fish are cold-blooded aquatic vertebrates that have gills, fins, and typically a streamlined body, enabling them to live and breathe underwater. Articles are a unique way for readers to learn about the world around them. In addition to building reading comprehension skills and increasing vocabulary, articles can be used for writing and research. Animals are broken into 6 single-page sections: What Is, Characteristics, Types, Why Important, Fun Facts, and Words to Know.