Delta Tail Guppy
Poecilia reticulata
About this strain
The Delta Tail is a tail-shape standard rather than a color strain: the caudal fin fans out in a wide, equilateral triangle with a straight top edge, straight bottom edge, and a flat rear margin — ideally forming a 45-degree angle from spine to each corner. A well-formed Delta should show no drooping or uneven lobes and should represent roughly the same width as body length. Delta is the dominant tail shape in competitive guppy showing and serves as the base form for many color strains. When buying fancy guppies, Delta is the benchmark for tail quality even if not explicitly named.
Origin
The Delta tail standard was formalized through North American show associations — principally the IFGA — during the mid-to-late 20th century as the defining competitive tail shape for Poecilia reticulata.