Reproductive Similarities

• Both fish and reptiles lay eggs, though the eggs of each animal are much different. Reptiles lay hard, leathery-shelled eggs on land while fish lay soft, gel-like eggs in water. Both eggs include a food source that nourishes the developing embryo. Both fish and reptiles breed in the early spring months and do not form lasting pair bonds. Neither fish nor most reptiles offer any parental care to their offspring.
  
  

Body Tempertaure Regulation

• Another commonality between fish and reptiles is the inability of the animals to create their own body heat. This is known as being cold-blooded or exothermic. Both fish and reptiles lack the structures that allow them to maintain a constant body temperature. Reptiles rely on solar energy to help them warm up while fish move into shallower or deeper water to help them maintain optimum temperature.
  
  

Outer Covering Similarities

• Both fish and reptiles' bodies are completely covered by scales instead of fur or skin. These scales help the animals protect themselves against territorial attacks as well as attacks by predators. A protective mucus layer covers the scales of fish while the scales of reptiles remain dry.
  
  

Skeletal Structure

• Both species have spinal cords and backbones. Because of this characteristic, both animals belong to the classification Chordata and are considered vertebrates. Fish and reptiles also have internal skeletal structures.
  
  

Differences

• Of course, along with their many similarities, there are many characteristics that set fish apart from reptiles. Fish breathe through gills instead of lungs like reptiles. The majority of fish live in water, while reptiles live on land. Fish are omnivorous animals, which means they eat meat and plant matter, while reptiles are carnivorous, feeding only on meat. However, both animals are opportunistic feeders as well as active hunters, meaning that they will feed on dead animal matter and hunt for fresh prey.