This info is taken from the dev on the offical New Day discord server:
If you're unable to view the image for whatever reason, here's a transcript:
"If you throw a Fredollar around every 8 times you fish, he'll never show up
His percentage chance of showing up goes up by 1% every time you successfully fish
the game takes that and runs a random number
if the number is less than his number of showing up, he'll show up
if it's greater than, he won't
using the fredollar resets this % to 0"

Price: $10
Effect: -5% Rod Speed
Description: Forged specifically to attract fish that like to chew on substances that have the same texture as a pacifier. Doesn't actually catch anything more than basic fish.

Price: $20
Effect: -10% Rod Speed
Description: A letter from a previous island Fredrick had managed.

Price: $30
Effect: -15% Rod Speed
Description: It may, or may not have, been alive before being violently shoved onto a hook. The insides of this gummy bear is filled with cheese. So, is it a cheesy bear?

Price: $40
Effect: -20% Rod Speed
Description: Wanna find out if a light bulb can stay lit underwater? Probably not. Don't try this at home. Only in the ocean. And only on planets named XoronB.

Price: $50
Effect: -25% Rod Speed
Description: Sometimes you've just gotta cut a fish in order to catch it.

Price: $60
Effect: -30% Rod Speed
Description: Say you'll see me again even if it's just in your wildest dreams... ahh... ahh...

Price: $70
Effect: -35% Rod Speed
Description: A sentient mold of clay that looks like a basic islander. Fish on XoronB love to eat islanders due to their fantastically tasting clay bodies.

Price: $80
Effect: -40% Rod Speed
Description: Where did this chicken nugget even come from? No-one knows. It's a complete mystery to all residents on XoronB... maybe it came from XoronC?

Price: $90
Effect: -45% Rod Speed
Description: Some say if you give it a little taste, you'll start to taste colors.

Price: $100
Effect: -50% Rod Speed, Resets Fishdrick's spawn chance to 0%
Description: Fredrick's massive ego strikes again. A certain fish might rob you if you're not careful enough... use the Fredollar every once in a while to calm it down...

Rarity: NOOB
Minimum Bait: N/A
Sell Price: $5
Description: A boot that looks to have belonged to a fisherman. Hopefully he's okay, but knowing these oceans, that might not be likely.

Rarity: NOOB
Minimum Bait: N/A
Sell Price: $25
Description: Commonly known as the worst fish in the sea, the Potato fish is shaped -- and made -- out of a potato.You can broil it in the oven and in no time at all, you'll have a tasty snack!... it even comes pre-salted. I think.

Rarity: TERRIBLE
Minimum Bait: Hate Mail
Sell Price: $50
Description: The Popcorn fish is a deep sea predator that comes to the surface when it's searching for food. It holds out a small popcorn kernel to unsuspecting victims before it snatches them up into its belly. Yummers.

Rarity: VERY BAD
Minimum Bait: Gummy(?) Bear
Sell Price: $75
Description: The Woke fish is a multi-colored fish that swims fast but slays faster. Due to it being hidden at the bottom of the sea for centuries, it obtained a rainbow-like color pattern and now, glistens in the warm sun as it swims proudly at the surface of the water. Be free, Woke fish, be free.

Rarity: BAD
Minimum Bait: Lightbulb
Sell Price: $100
Description: The Tipsy Husband fish is what you expect. He goes out of the coral at night, swims all the way down to the local Surf'N'Turf and consumes many microplastics. When he wakes up in the morning, he'll complain about a pounding headache from the night before.

Rarity: MEDIOCRE
Minimum Bait: Razorblade
Sell Price: $125
Description: Pougil is the saddest fish in the ocean. No one knows why. It's often opening its eyes wide enough to look as innocent as possible so that the surrounding predators do not devour it. It usually never works.

Rarity: GOOD
Minimum Bait: Heart Lollipop
Sell Price: $175
Description: The Long Crescentfin is a descendant of the "Moon" fish, which are now extinct on Planet XoronB. Fortunately, the Long Crescentfin will eventually evolve back into its circle-like shape with due time.

Rarity: VERY GOOD
Minimum Bait: Islander-Shaped Sentient Clay
Sell Price: $225
Description: Squidjak is a rare occurrence on XoronB, as the species is currently going extinct. No one knows where it came from or how it got on the planet, as Fredrick didn't create it themself. It's just here.

Rarity: PRO
Minimum Bait: Suspicious Chicken Nugget
Sell Price: $275
Description: Lurks in the deepest part of the sea in a lagoon that generates a soda with a similar name. This fish is full of that carbonation goodness that'll quench your thirst.

Rarity: LEGENDARY
Minimum Bait: Out of this World Mushroom
Sell Price: $350
Description: A known traveler across XoronB. Fluffbee disguises itself as a fish and stings predators that gets too close. Their stinger contains a deadly poison that instantly incapacitates its victims.

Rarity: OP
Minimum Bait: Fredollar
Sell Price: $400
Description: One of Fredrick's many creations designed to look like them. Roams the oceans of XoronB and is an immortal bugger. Known for cowering away whenever a Frysh is scary, despite both fishes being siblings.