Emphasizing "pretty":
* Jolie petite poisson femelle: This is a direct translation, but it sounds a bit formal.
* Charmante petite poissonne: This uses a more endearing term for a female fish ("poissonne").
* Belle petite poissonne: This emphasizes beauty ("belle") and uses the endearing term for a female fish.
Emphasizing "little":
* Petite poissonne adorable: This uses the endearing term for a female fish and emphasizes cuteness ("adorable").
* Mignonne petite poissonne: This uses a term that evokes a small, delicate and charming creature.
Other options:
* Un joli petit poisson femelle: This is a more neutral translation.
* Une petite poissonne gracieuse: This emphasizes elegance and grace.
Ultimately, the best translation depends on the specific context and the desired tone.