So:
Available by fishing (* means they''re available on land as well):
Cascadet* - early-mid
Trillogill - early
Slowpoke* - early
Staryu - late-mid
Qwilfish - mid
Corsola - late-mid
Reefrain - late-mid
Goldrake - late
Remoraid - early
Octillery (perhaps) - late-mid
Corphish - mid
Crawdaunt (Victory Road) - late