Symbolism, Imagery, Allegory
The devilfish is one of the Karana's great adversaries in the book, even though she doesn't beat him in the way that she wanted to. The devilfish supposedly have the sweetest meat in the ocean, but Karana never gets to taste the giant devilfish, no matter how hard she tries at first.
What does she learn from her interaction with the creature? Let's take a look:
Rontu had a gash on his nose from the giant's beak, and I had many cuts and bruises. I saw two more giant devilfish along the reef that summer, but I did not try to spear them. (19.39)
Karana's pursuit of the giant devilfish hits a dead end: she kills the fish, but then she can't carry his body from the shore. She and Rontu are left wounded. This shows that big game hunting is probably not the best thing to do with your time and can be harmful.