Here is the full list of all 7 Fishermurs achievements.
Complete the training level.
Kill a player with a sticky mine to sink one more by explosion.
Kill a player with a mine that your hook dragged in.
Kill two or more players at a time with the help of the octopus.
Sink another player with a mine blown by a shot or a paddle.
Win the battle. Award - delicious fish!
Kill the enemy with a paddle.