Red Carp
Golden Carp, Red Koi, Golden Koi
noun
A scarlet colored carp is called a red carp and sometimes a golden carp because sometimes people don't understand colors.
ひごい
The reading is a combination of on'yomi and kun'yomi. That being said, both readings for both kanji are the readings you learned with the kanji so you should be able to read this.
ニシキゴイは緋鯉をもとに改良されたものです。
The colored carp was an improvement on the red and golden carp.