There are four variant skin concepts for the mob. The idea was so broad I wasn't sure which one was the best fit for the concept.
The Fishing Spider
Drops: Spider Eye, String. Probably my favorite skin option, because it adds value to the "Bane of Arthropods" enchantment and is also the cutest li'l guy. Look at him! D'aww, he's so cute.
Drops: Prismarine Shard. Prismarine Crystal (very rare), Glowstone Powder (very rare). I liked the idea of an Anglerfish that drops glowing compounds.
Drops: Ink sacs? Honestly I don't have a lot of ideas for super-valuable things for this guy to drop. If you do, let me know.
Drops: Bucket of milk, enchanted boots [depth strider], kitten [auto-named Fisher]. This is a really weird idea.
In theory, all variations may also drop: boats, enchanted fishing rods, or leashes.