It is generally not recommended to touch a fish's gills. The gills are delicate organs that are used for respiration, and handling them can cause damage or stress to the fish. In addition, some fish have sensitive skin and can be easily distressed by being handled. If it is necessary to handle a fish, it is generally best to gently hold it by the body or base of the tail, rather than by the gills. This will minimize the risk of damaging the gills or causing stress to the fish. If you need to examine a fish's gills, it is generally best to do so in a controlled environment, such as in a tank or pond, rather than attempting to handle the fish directly. This will allow you to observe the gills without causing any harm to the fish.