Half black male guppy

 Half-Black Red Guppy (often referred to simply as a HB Red Guppy).

Here is a quick breakdown of what gives it away in your photos:

• The Half-Black Body: The entire back half of its torso (from just behind the dorsal fin to the base of the tail) features a dark, solid black or deep midnight-blue "tuxedo" pattern.

• The Vibrant Caudal Fin: It sports a bright, fan-shaped orange-red tail that contrasts sharply with the dark body.

• The Platinum/Silver Head: The front half of the fish has a lighter, iridescent silver or platinum sheen, sometimes showing a slight blue or violet catch in the light right near the dorsal fin.

A Fun Bonus

In the second and fourth photos, you can see its tankmates hanging around!

• The one right next to it with the dark blue/purple iridescent body and matching dark tail looks like a Half-Black Blue (or Purple) guppy.

• The smaller, slender one swimming below them with the intricate, speckled patterning on its tail and a distinct black spot near its pectoral fin is an Endler’s Livebearer hybrid (likely a Tiger or Snakeskin variant).

They make a fantastic, high-energy contrast against your bright substrate!