Which animal serves as an intermediate host for Diphyllobothrium latum?

Diphyllobothrium latum, commonly known as the fish tapeworm, is a cestode that requires aquatic hosts to complete its life cycle. The primary lifecycle involves multiple stages, and specific animals act as intermediate hosts where the larvae develop. Fish, particularly freshwater fish, are crucial in this process. They ingest the eggs or proglottids of the tapeworm from contaminated water or sediments, allowing the larval form to develop within them. Humans typically become infected by consuming raw or undercooked fish that harbor the infectious larvae.

In contrast, pigs, cows, and goats are not part of the life cycle of Diphyllobothrium latum, as they do not facilitate the necessary larval stages for the tapeworm to propagate effectively. Therefore, fish are directly implicated in the transmission and lifecycle of this particular parasite, making them the correct answer.