Can you tuna fish?

No.  But I know a guy who can tune a piano.

Sure, as long as you have the right kind of fork.

There a fish knives too, but they a useless for tuning.

Dunno if this will be understood in the US but it should go OK in the UK...

A shark met his buddy the squid in the English Channel and said, "Whazzup with you?"
"I'm not feeling so well, Sharky," he said. 
"You need to swim down to the Med and get some warm water."
"I'd never make it in this condition."
"Climb on my back," said the shark. "I'll take you down." 
So squid climbs aboard and shark heads down the coast and into the med where he swims right up to a big tuna and sayd, "Hey, Tuna! Here's that sick squid I owe you." 

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Don't blame me. Max Bygraves told it first.

I can can it!

I still like walleye. Tuna is some nasty creature that gets caught in the net by mistake.