do I need to seperate predator fish to do 'pellet train'?

[Crono]

Neighbor brought a new predator fish... he didn't plan. the fish was too big for his tank (and jump out) before gave it to me.
sadly it's not pellet trained

I could pellet train like how I pellet train my other predator fish, but would it attack the tankmates?
if the same size, I no need to worry. but this one is huge than all fish I have in that tank. (aka. the newcomer is the biggest)
when it enters 'desperate hunger', will it attack & eat tankmate? or eat anything besides tankmate?

it's gar

 

[Trouser Cough]

When you starve with a tiger, the tiger starves last.

 

[Crono]

When you starve with a tiger, the tiger starves last.

...I don't get your words.
'starve last' you mean, after eat other before initiate another starve?

 

[Iwhoopedbatman]

What are the tank mates and how big is everyone? I've never had a gar go ham on tankmates, but I'm certain it can happen.

 

[Crono]

What are the tank mates and how big is everyone? I've never had a gar go ham on tankmates, but I'm certain it can happen.

bichir, another gar, big adult rainbow shark

all average 10-11cm. newcomer, 14cm (lenght)

 

[Trouser Cough]

...I don't get your words.
'starve last' you mean, after eat other before initiate another starve?

My apologies, Crono. Stated less cryptically my comment means the following:

When you change predators to pellets they get extremely hungry.

If you have a big predator that's really hungry amongst smaller fish, the big predator will eat them before he eats a pellet.

 

[Iwhoopedbatman]

bichir, another gar, big adult rainbow shark

all average 10-11cm. newcomer, 14cm (lenght)

I doubt he can catch the shark. Also doubt he'd try eating the gar or bichir unless he's truly starving. You could always use a divider until he's eating if you want to take more precautions.