Water is a really good conductor of sound so I would have to say that it would be to send the message underwater because a more dense medium produces a louder sound
M = mass of the larger fish =5kg <span>V = velocity of the larger fish =10m/s</span> <span>m = mass of the smaller fish =2kg</span> <span>v = velocity of the smaller fish =10m/s </span>formula= <span>MV = mv 5kg*10m/s=2kg*10m/s biggern mass fish has more momentum hope this helps