Common elements: Capricorn come from cold areas, and live most of their time underwater. Because of this, they relate better to the elements Water, Earth and Ice. In rare ocassions they can also learn Acid as a second affinity.
Hereditary magic: Capricorns obtain their affinities as they grow up and learn about themselves, and they dont heredate it from their parents.
Fire, Poison: Capricorns are extremely weak to these two elements. Fire will dry and burn their skin, and poison may intoxicate them, killing the coral on their horns. A Capricorn without horns is considered a Shameful, careless creature for their culture.
Others: Capricorns can be weak to many elements if they're used correctly. Because they're docile most of the times, they're not fit for combat or trained their affinities enough to defend themselves.
Common locations: Capricorns generally enjoy cold waters, so they're not a common sight in tropical areas. some of them move to cities with the help of aquariums and other people, to work for companies, cleaning the tanks and making sure the water is clean for other creatures to live in.
Climate preferences: They prefer cold areas over tropical ones. depending on the breed, they may also go to tropical places for reproduction.
Level of intelligence: About 75% Capricorns are capable of higher-level thinking, such as the ability to plan ahead, to reason, rationalize, and to understand abstract concepts and principles. Feral Capricorns can plan ahead and reason, but only based on their necessities at that moment.
Language: Most rational Capricorns speak Common. Feral Capricorns are unable to speak.
Trivia: Capricorns can reproduce with almost any aquatic creature of a decent size. because of this, one can see Capricorns who can only live underwater, while others cannot breathe underwater. those blessed with the genes of some mollusks or amphibians are capable of living and breathing in both envriorements.
They are not very good at socializing, specially at early ages. most of them are silent when they work in cities, except when they are with other capricorns, specially if they are in love.
Capricorns have a social hierarchy, where those with the hardest, most beautiful coral horns domain their society. Royal Capricorns in particular have extremely hard horns, despite how fragile they might look. they're considered the purest of all breeds.
Capricorns are fairly territorial and warn foreigners about their frontiers. they're loyal to their leaders and prefer to submit to them even if they are corrupt.
I do hope this becomes an official species one day!