probally fresh because no salt in mouth or eyes
addition:
it is easier to float/swim in seawater since seawater is denser than fresh water.
It is easier to float, in any case, because salt water has a greater density.
Because there is salt in sea water and salt makes you float better so is easier to swim.
You are more buoyant in salt water than in fresh water, so it takes less energy just to stay afloat, making it easier to swim.
Salt water is denser that fresh water, so a swimmer (and ships) float higher in saltwater.
if they are naturally used to fresh water
Salt water has a slightly higher density, so it will be a little quicker to swim in fresh water.
Yes it is easier to swim in seawater because it contains salt which has a lesser density than water
It is easier to swim in salt water. Fresh water of 10 degrees Celsius has a density of 999.728 kilograms per cubic meter. Seawater of 10 degrees Celsius and of 3.5 % salinity has a density of 1026.978 kilograms per cubic meter. It is easier to floatin salt water because it has a higher density. Your strokes will create more force against the higher density, but the higher density will also cause more resistance to your body's forward movement. Without doing a scientific study, I would imagine this would allow you to swim faster and with less effort in fresh water. You would probably move faster through a liquid that was less dense, but if it is too ?undense? your movement would be down, not forward!
salt water
Catfish do not swim in the ocean, they are found in rivers, creeks, and fresh water ponds.
Swim
hmm.. swim?