Meanings

the fish rots from the head

whale

dried fish

yuxiang (Chinese seasoning mixture)

fish tail

low-grade fish

Pacific saury is only good if it's from Meguro

to miss a big chance

enormous fish

the biggest fish is always the one that got away

landlocked fish

mandarin fish (Siniperca chuatsi)

fish farmer

background character (in a manga, anime, etc.)

human torpedo

ayu

ayu

fishfinder

dried fish skin (oft. used as bait for fishing)

oolite