I do for specific fish, if they're unique and/or have their own quirky personality. The rest of them... not so much (oh the joys of being overrun by platy fry)
My original parent platys: Daisy (female, orange mickey mouse), Kali (female, tuxedo), Jared (male, White Wagtail), Misty (female, blue mickey mouse, recently passed from dropsy...she was my favorite π)
Some of their offspring are named too: Mini-Misty(looks just like her mom), Sierra(Misty but with black fins, female), Dakota (Misty but with a bright orange top fin, female), Naranga (deep orange female, no markings and really stunning), Amber (gold mickey mouse, female), Luna (white mickey mouse, my prized female)
Sadly all of Kali's offspring kinda look the same so they're not named π³ those strong tuxedo genes!
In my community tank, I added an angelfish that I originally named Oreo (but has since morphed into Oiyo), and a neon blue dwarf gourami named Mordenkainen... Kai for short (MtG reference, my husband named him LOL)
Also my betta is named Vazidas, Vazi for short (my husband named him too)
Can you tell I get emotionally attached π I love my wet pets!