Since it's talking about a fish, I would use "small fry."\

On the other hand, one could look at a published translation of the story in English and write "half-pint" and "little one":

Hearing her neighbor's voice, the mother came out of the house and said, "What's the world coming to! Now children even want to teach their mothers something!"
How so? "asked the neighbor."
Listen to the places this half-pint wants to go!" replied the mother. "Saying over and over again I want to go see what's happening in the world. What pretentious talk!"
"Little one," said the neighbor, "let's see. Since when have you become a scholar and philosopher and not told us?"
"Madam," answered the little fish, ...
http://www.iranchamber.com/literature/sbehrangi/works/the_li...