If you're looking for manga similar to The Larva Island Movie, you might like these titles.
Shintaro and his school of salmon have been living in a small lake for generations. Tired of being muscled out of food by the bigger fish, they decide to make a bold move and head for the “ocean” that they’ve heard about in stories where it is vastly large and food is beyond plentiful. As Shintaro leads his school of salmon out into the sea, they soon realize how protected they were in the lake and realize how dangerous it is.
Baku-chan, a little tapir from the planet Baku, immigrates to Earth and comes to live with Hana, a human girl who has come from Nagoya to live in Tokyo. Baku-chan comes into contact with new and different things in everyday life and encounters discrimination toward immigrants. However, he also gets support from Hana and other friendly Earthlings, and also from his immigrant friends, and lives a cheerful and robust life. Masumura's experiences as an immigrant in Canada are reflected in a story depicted through colorful and fantastically designed drawings. While heartwarming, the story also depicts immigrant situations and feelings that could come about in the real world, including thoughtless violence, pressure to conform, and the difficulty of adapting to a new land. It is an adventure that poses questions for society.