If one gallon of water weights 8.34 pounds would adding a 2 lb fish to the water change the weight of the water?

Answer 1

10.34

Answer 2

It depends on whether any water leaves the bucket when the fish goes in.

If the water is in a bucket and the fish is added to it, the contents of the bucket would then be 8.34 lbs + 2 lbs = 10.34 lbs. But the water would weigh the same: 8.34 pounds. No water would have been gained or lost because of the presence of the fish.

But the answer may be a bit tricky if the bucket had initially been filled to the brim. In that event, adding the fish obviously would cause the bucket to overflow. Thus the water would weigh 2 pounds less: 6.34 pounds.

But why precisely 2 lbs. less? Does the fish have a different density than water?

The answer to that is NO! The density of a two-pound fish is the same as the density of the water. Fish can swim and hover in the water because, using their internal air bladders, they control their buoyancy to be neutral. That's why they neither sink nor float. So they weigh the same as the water they displace, thus leaving the mass of the contents of the bucket unchanged in that special case.

AddendumDon't forget that the fish is composed of mostly water so really you are probably adding 1 to 1.5 pounds of water into the container by adding the fish.

The total volume of water in the bucket would increase, as would the weigh of the total water

Addendum #2

This sounds a lot like the old trick question: What weighs more, a ton of coal or a ton of feathers? Water is water, and a fish is fish. Humans, too, are mostly water. But, putting a man in a tank of water doesn't alter the amount of water, assuming there's no overflow caused. A pound of water is a pound of water, and a pound of fish is a pound of fish. Apples and Oranges. Of course, if you count the water content of whichever creature you drop in the bucked as water, that's different. For the sake of my meandering, any water contained within the skin of the fish, or the man, is considered fish or man respectively.

Addendum #3How would adding a fish (or an octopus, or a gold nugget, or an automobile) change the weight of the water? The water weighs what it weighs. The only way to change the weight is by changing the strength of the gravitational field.

But I'd guess that original questioner meant to ask something quite different than what he actually did.

Assuming that placing an object in the container would displace water, the answer has to do with the size (volume) of the inserted object (fish) - not its weight. Placing an object in water displaces an equal volume of water. Thus, the answer would depend on the weight of the volume of water displaced compared to the weight of the object inserted. If an object (fish) is added where the weight of the water displaced is more than the weight of the object inserted, the total weight of the container and contents would decrease. If the weight of the volume of water displaced was less than the weight of the inserted object, the total weight of the container and contents would increase.

Think of it this way: If a one-cm cube of gold (19.2g or 0.0423 lb) was inserted, it would displace one cubic cm of water (1 g or 0.0022 lb), but the weight of the displaced water would be less than the weight of the gold, thus the total weight of the container would increase.

Now if it were a goldfish...