Final answer:
The aquatic, fish-shaped larva of a frog or toad is known as a tadpole, which undergoes metamorphosis to develop into an adult frog.
Step-by-step explanation:
The aquatic, fish-shaped larva of a frog or toad is called a tadpole. At the tadpole larval stage, these amphibians resemble fish, having no legs and possessing a long tail used for swimming, as well as gills to absorb oxygen from the water. As the tadpole undergoes metamorphosis, it experiences significant transformation including the growth of legs, loss of the tail, and development of lungs to prepare for terrestrial life.