Lauantaina nousi siikaa tolkuttomasti is not the point of this strip (the character who says that could have said just about anything in that panel) but just to decode the meaning of that phrase:
Lauantaina
On Saturday
nousi siikaa
whitefish [used here as an uncountable mass noun] rose up (surfaced)
tolkuttomasti,
absurdly (absurd amounts),
etenkin...
especially...
Or in better English: “We got absurd amounts of whitefish on Saturday, especially...” (and the story would have gone on if there hadn’t been that interruption)
X:ää nousi (vedestä), where ‘X’ is a species of fish is a sort of fisherman’s slang for expressing that a particular type of fish was eager to hit the lures, or was abundant in the (fish/drag)net or other type of trap.
