Some stuff may be outdated or incomplete because it's based on an old HellMOO version.
Difficulty is a combination of several subjective factors I pulled out of my arse.
One of the bigger factors is how many fish are left on the tile. Less fish on tile, worse chances per heartbeat.
'Baby Acid Gar' and 'Gravelash Jellyfish' will attack all types of fish. 'Miniature Ross Seal' will eat 'Silverfish'. For the rest it doesn't matter.
'Carbon Fishing Rod' is approximately twice as effective as other fishing rods. This used to be true, but according to Father it might not be anymore.
'Worms' are/were not correctly classified as generic bait fish and thus are worse than 'Anchovies' or 'Silverfish', but according to Father this might be updated on SamsaraMOO.