Typically if your fish is surfacing, it's typically a water quality problem. You should test your water for ammonia, nitrites, and nitrates which should be 0, 0, and less than 10 respectively. In addition also check your PH to ensure that it has not crashed too low as this can also cause fish to surface quite often.
To keep your water at it's best, you should perform weekly water changes of at least 50%, and make sure that the water that you are adding back to the tank is the same temperature as the water you removed.
the fish tank
fish tank
You can tell if your fish tank has enough oxygen for your fish by observing their behavior. If they are swimming near the surface gasping for air, it may indicate low oxygen levels. Additionally, you can use a water test kit to measure oxygen levels in the tank.
its the scuba tank on the swimming guys back.
As long as the tank water is clean, and the fish are being fed properly, the catfish may just be entertaining itself by swimming that way.
A fish tank would hold about 6 liters.
Give it a deep tissue massage. It may just be tired from swimming all the time.
if your fish is going around the tank with its eyes cosed multiple times.
Some fish prefer swimming at the top of the tank while others the bottom or middle.
I hope your tank is large enough for the 7 or 8 inches of fish you have in there. (1 inch of fish needs 1 gallon of water). Shortage of oxygen will cause fish to go to the top/surface for air. However Guppies (Poecilia reticulata) are naturally surface feeding fish so that is where I would expect them to spend most of there time. Surface feeders are easy to recognise simply by looking at the construction and shape of the fishes mouth. Note that it tends to open in such a way as to skim the surface of the water.
Cause its dead
That depends on the weight of the fish as compared to the weight of the water their bodies displace. If it's a heavy, dense fish, then the tank with the fish would weigh more. If it's a light, less dense fish, then the tank with water only would weigh more. This assumes that the water displaced has been removed from the tank, right? If you are adding the fish to the water then I think it should increase the weight regardless of the density of your fish. The question then might be, does the fish weigh less when it is swimming than it would on a dry scale?