Some fish have a density slightly less than that of water and must exert a force (swim) to stay submerged. what force (in n) must a 53.0 kg grouper exert to stay submerged in salt water if its body density is 1013 kg/m3?

The buoyancy force exerted by water must be equal to the weight of the fish to float, therefore:

F = w

Where weight is the product of mass and gravitational acceleration:

w = m g

Substituting:

F = m g

Therefore the force required is:

F = 53 kg * (9.81 m / s^2)

F = 519.93 N = 520 N