Answer:
The same speed 20[m/s]
Step-by-step explanation:
We have to analyze the problem by means of relative velocities, the velocity of the small fish is zero since it is at rest. The large fish is directed towards the small fish with a velocity of 20 [m/s], therefore for an observer who sees the movement of both from a distant point, he will see:
Vbf = Velocity of the big fish = 20 [m/s]
Vsf = Velocity of the small fish = 0
Vob = 20 -0 =20 [m/s]