Capricorn
The Sea-Goat
The Astronomica ascribed to Hyginus gives two reasons for the fish's tail. Pan pelted the Titans with murex shells, after Eratosthenes, or leapt into a river to escape Typhon, after Egyptian priests.
Hyginus (attributed), De Astronomia II.28 (Capricornus), Latin text at The Latin Library
Tenth sign of the zodiac, the Sea-Goat, a fish-tailed goat: in astrology cardinal earth ruled by Saturn.
More context
In modern astrology Capricorn, ruled by Saturn, climbs the highest mountains through discipline and time. It is read as the architect of society: responsibility, ambition and legacy. Astrologers take the Sea-Goat to symbolise deep emotional wisdom joined to practical earthly achievement.
Light
Discipline, mastery, pragmatism, enduring ambition, and profound wisdom born of experience.
Shadow
Pessimism, rigidity, coldness, ruthlessness in ambition, and being overly burdened by duty.