I have to say I was quite relieved at the end. I approved of his choice to never go fishing alone at night again. However, at the start, I was subconsciously thinking 'No! fishing by yourself at night is a horrible idea!' I see now that in the start, there was some foreshadowing, the protagonist noting where the sparks from the cigarette go, just like him noting where the twin points from the sea devil are. Cigarettes are bad for you, as is netting a sea devil. As for the theme, I think that "Never get too cocky and think that nothing can go wrong," is pretty close.