Consecutive Fishing is the simpler and earlier available of the two Shiny-catching methods. It works on a similar premise: when fishing, if you keep encountering the same species, one after another after another, you'll raise the chances of finding a Shiny Pokémon!
Obviously, that would imply the use of the Old Rod, since you usually only can find one Pokémon species (Magikarp or Luvdisc) by using it. Then again, you might prefer to actually have a Shiny Starmie, wouldn't you?
Anyways, that's the premise. To fish, face any body of water you could normally Surf on and use the Rod. Wait for some "!" or "!!" to appear and quickly press the A Button to start a battle. Then repeat as needed.
Again, Consecutive Fishing relies on a chain similar to the PokéRadar. To break the chain, the following can occur:
- Encountering a different Pokémon species.
- Not getting a bite on the line and having to recast it.
- Moving from that spot whatsoever.
- Pressing the A Button too early or too late.
- Switching rods? This is theorized, but untested - it usually changes the species anyways, per the first thing listed here.
After a while, we did manage to hook a Shiny Gyarados on Route 3 after about forty previous ones hooked. Ah, nostalgia...