1 more thing
I have seen 90 % of fishermen releasing fish by putting their hands to the gill even they are fishing ethically
is it a safe practice to do so ?
NO! A fish should ALWAYS be tailed if you are going to release it, and it should be done so in 1-2 feet of water optimally. The fish shouldn't be removed from the water (unless a quick photo is desired), and then the fish should be held gently into the current to encourage water to flow through it's mouth and out it's gills.
Fish's gills are perhaps the most sensitive part of it's body, and unless you know EXACTLY what you are doing (and even then you're probably still likely to do some unecessary damage), sticking your hand in there could prove deadly to the fish - think of it's gills as it's lungs, but exposed. Would you want someone sticking their hand into your guts if there was a hole in your stomach?
Good question - now armed with this information, share it with others who may not know the proper way to release a fish.
Tex