This means to feel nauseous or seasick.
It means the person looks sick. Usually they are pale and green in the face.
An idiom that means prone to nausea might be "green at the gills." This refers to the fact that your face pales when you feel nauseated. Some people thought that color was a pale green, and this started the phrase. You might also hear "an upset stomach." This can mean any sort of discomfort in the abdominal area, from nausea to diarrhea.
It is a trade mark registration symbol so no one can copy it in the country it was registered
Not neccessarily. Some Bettas do have very dark gills.
Do you mean frogs? If you do Frogs don't have gills there a cold blooded reptile and frogs are purely air breathers so they don't need gills.
If you go fishing or even just go to the fish market, look down into a fish's mouth. You will see the gills on both sides and just after the gills in the oral cavity you will see the opening of the gullet. If you have a particularly well-fed fish, the gullet may show unswallowed food because the stomach is too full to hold more so, it is waiting to be swallowed. Humans don't have gills but the analogy can be appropriate when you feel you have swallowed more than your stomach can hold.
Gills are an organ that fish have, that enables them to obtain oxygen from the water that they are in; it is what fish use instead of lungs.
gills are like "lungs" to a fish.
gills is the answer
Total? do you mean turtle? If so turtle have lungs.
it means they are having trouble breathing
The only animal that has true lungs and gills is the lungfish. Animals like frogs often have gills for a portion of their lives and then later develop lungs.