I have 3-4 kg size fish in my non-frost-free deep freezer. They always stick very hard to the base of the freezer and it takes me hours to get the fish out. I have to keep the freezer turned off, which affects other fish or food items. Is there a way that I can get the fish out in a much shorter amount of time, so that I can thaw it outside of the freezer? 
For the already-stuck fish: no, there is no way. Don't try to chisel them out, I've known somebody who damaged their freezer that way. For any fish you will be placing there in the future: find a packaging material which will not stick to the freezer. Plastic bags are the most common way of doing it. You also have to ensure that your freezer's bottom is dry. It is OK if it gathers a bit of loose frost over time, but there shouldn't be a big lake of frozen liquid on the bottom. If that has happened already (for example because you held in items which leaked, or because you defrosted it and didn't dry it before it froze again), you have to defrost the fridge until the complete lake is melted, then remove all the liquid, then let it freeze empty, without any food in it. Then package the food in liquid-proof packaging, and re-arrange it in the freezer. 