Asians has very old origins in tattooing. This grants them good traditions but some stagnation. This all is ok, nowadays these tattoos are becoming more and more popular not only because the meaning of them but because they look very nice and are customizable with ease. OK, koi fish isn't an animal, it's a fish. Koi fish has a special meaning for Asians - sexual orientation or perseverance and achievement. Pick the one you like! No doubt, that the sexual background of the koi fish is because of its eating habits, it doesn't eats like a shark, grasping all in sight, it gently sucks the food in. And besides that the fish is very beautiful and rare.
For express yourself, these were the words my first tattoo master said to me, when I asked him what tattoo would be good for me. And I did so. The all black koi fish tattoos are very popular in Asian culture. Basically all of the koi fish are very popular and important for Asians.
If your choice fell for all black koi fish, I suggest making tattoo with it, because the symbolism behind this tattoo is certain. You can't get wrong with koi! But before you make tattoo make sure that the placement is suitable for a tattoo like this. And the size of tattoo depends on the power of it (by legends), tattoo in a size or a frog won't be as powerful as an tattoo in size of furious dog! Keep all this in mind and you should be just OK with your tattoo!