Rods and stats

There are no rod tiers to buy. Every player has exactly one rod, named after them, %player%s Fishing Rod, given free on join, and upgraded in place for the rest of the game.

That is a good design call. There is no wrong rod to own and no dead-end purchase; every coin you put in stays with you.

The six stats

StatWhat it does
StrengthHeavier fish. Weight multiplies sell price, so this raises the value of everything you catch. See Fish weight.
BobbersHow many bobbers you cast at once: directly proportional to how many fish you land per reel-in
SpeedHow fast fish are lured to the bobber
LuckChance of rarer fish: up through Common, Rare, Epic, Legendary, Mythic and Ethereal
ShiftChance to mutate a fish. Affected by weather
CastCasting distance
Cast may be removed. it is currently the least useful of the six.

Which to upgrade first

The two that compound are Bobbers and Strength. Bobbers multiplies how many fish you get per cast; Strength multiplies what each one is worth. They stack with each other, and both apply to every single catch.

Luck matters most when you are chasing a specific fish or hunting the Ethereal one, rather than earning steadily.

Upgrading

Upgrades cost coins as you progress, and XP acts as the unlock gate for higher tiers. See Currencies.

Reels, lines and hooks

Planned, not built. Rusty will sell external parts at the Tacklebox that boost these same stats, a Sturdy Reel granting +5 Luck and +10% catch speed, that kind of thing, rolled rather than bought outright.

Awaiting data

Exact upgrade costs and how much each level gives.