Here is my version of the lyrics my grandfather used to sing. The current ones posted don't really fit in with the tempo/tune/melody of the song, but these fit in perfectly. So either my lyrics are wrong or my melody is wrong :p

On the swaying limb of a rubber tree, ten thousand miles away
On the banks of the Hula river in far off Uruguay
There sits a nervous monkey, his eyes in fear and gleam
His tail is hanging gently into a lipid stream

And every 90 minutes, he flips it through the air
With a South American whizfish dangling helpless there
But the bite of the angry whizfish is hard on the tender tail
and as he sits there fishing you can hear this monkey wail:

"Oh shades of Isaak Walton is that another bite?
If I didn't feel so hungry, I'd quit this job tonight
But I love those roasted whizfish, though it's bite drives me insane
and I do so wish to catch that fish that I manage to stand the pain"

Now one fine day a jummafish with a jaw 6 feet by 9
Chanced to paddle nearby; take hold of the monkeys line
He started down the river, quite unconcernedly
Until the monkey screamed and chattered and clung to that rubber tree

The tree stretched like a garter, a dozen miles or so
Until the fish let go and the monkey flew like an arrow from a bow
Now they say he's still a-flyin and if you care to try
You can hear him softly sobbing as he whistles through the sky:

"Oh shades of Isaak Walton is that another bite?
If I didn't feel so hungry, I'd quit this job tonight
But I love those roasted whizfish, though it's bite drives me insane
and I do so wish to catch that fish that I manage to stand the pain"