Hi Ruth,
It was as far back in the bible regarding blood in the meat to when Noah came out of the ark. That is what I take the term "strangled" to refer to. The animal must be killed and drained of blood. However, as far as I know, the standard practices for processing animals in many countries involve draining the animal of blood. Strangling an animal to death is not common practice for obtaining meat as it makes it harder to get the blood out (also is very stressful to the animal), to my understanding, and I've heard the practice being banned in places.
Genesis 9:3 Every moving thing that liveth shall be meat for you; even as the green herb have I given you all things.
4 But flesh with the life thereof, which is the blood thereof, shall ye not eat.Paul made it clear to us that we don't need to be worried about buying meat in the markets. If it is available to purchase, Paul is saying that it is fine to eat.
1 Corinthians 10:25 Whatsoever is sold in the shambles, that eat, asking no question for conscience sake:26 For the earth is the Lord's, and the fulness thereof.If you are catching your own fish to eat, you probably wouldn't let it suffocate to death. You'd put it in water until time to prepare it and make a quick go of it so the animal doesn't suffer.
I hope that helps.
If anyone sees anything wrong with my reasoning, please let me know.