The Christian fish symbolizes Icythys
Until The Day I Die (Story of The Year)
In a narrative, a lot that you learn about the plot and the characters (more importantly the main character) is through dialogue. If dialogue isn't effective in a narrative, your reader may not capture the situation that the characters are facing nor the personalities and of these characters.
Isolation is one thing, but interplanetary isolation is a whole different ball game. Just ask Mark Watney. In The Martian, we watch as this brave botanist is stranded on Mars, separated from everyone and everything he holds dear. It's a life filled with danger, disaster, and panic, yet the thing that stings the most are his feelings of loneliness. Sometimes they make him feel a little crazy. Sometimes they just make him feel hopeless. At others, they make him wish he had a volleyball for a best friend. As we watch him adapt and fight back against these dark feelings, however, we learn a lot about the powerful effects isolation can have on even the strongest minds.