Final answer:
The similar body shapes of dolphins and fish are an analogous trait due to convergent evolution in aquatic environments, despite their separate evolutionary histories as mammals and fish, respectively.
Step-by-step explanation:
The question asks whether the similar body shapes of dolphins and fish are indicative of a homologous trait, deriving from a common ancestor, or an analogous trait, a result of convergent evolution. Dolphins are mammals, and unlike fish, they do not lay eggs, are warm-blooded, breathe air, and have different reproductive and biological systems.
The similarity in body shapes between dolphins and fish is, therefore, an analogous trait because it evolved independently in response to the need to move efficiently through water, despite their separate evolutionary paths.
On the other hand, since dolphins and fish are both vertebrates, they do share some degree of an evolutionary history, but this does not extend to the specific streamlined body shape which is an adaptation to aquatic life. Thus, it is the aquatic environment that has shaped both the dolphin and fish to have similar body structures, a concept known as convergent evolution.