Earthquakes are generally caused by the sudden slipping of rock masses along a fracture or fault. The energy transmitted from the focus of an earthquake is transmitted in the form of waves. The waves, known as seismic waves spread out in all directions from the focus of the earthquake, similar to sound waves. There are 2 kinds of seismic waves, P Waves and S Waves. P Waves, or compressional waves travel at over 6 km/s (13,500 mph). When P Waves pass through a substance, they compress or push the atoms closer together. After the wave passes, the atoms respond elastically and return to their normal spacing. P Waves are similar to sound waves. It has been suggested that some animals here or detect P Waves. Humans generally feel a bump when the wave passes.

S Waves or Shear Waves can change the shape of materials, as such, they case the majority of the destruction attributed to earthquakes. S Waves travel up and down or from side to side. They only move through solids, S Waves do not travel through liquids.

At best, when an earthquake occurs, there might be a slight change in water pressure due to the P Waves. More than likely, the fish will detect the vibrations of the P Waves. The P Waves will propagate through the entire water body just like sound. However, it will not have a physical effect on the fish.

Some of you will be asking, "Well what about tsunamis?". Tsunamis are the result of the movement of the sea floor. The can be the result of an underwater landslide or seismic activity associated with oceanic crust. The resulting physical movement of the sea floor causes the propagation of waves within the water. The waves disperse from the point of disturbance. When the wave begins to reach shallow water, a "tidal" wave is formed, which ultimately crashes upon the land surface. Sure the fish will sense the movement of the water, they may even move with the current, but is has no physical effect on the fish.

Hope this answers the question.

PS - - - The PG in PG Flyfisher stands for Professional Geologist.