Fish farmers are Germans.

Reasoning process:

First, let's position ourselves. From left to right, 12345 is arranged according to the location of the house.

The Norwegian lives in room 1, on the far left. Because the British live in the red house and the Norwegians live next to the blue house, the colors of Norwegian houses can only be green, yellow and white, so the green house is on the left of the white house and the Norwegians live next to the blue house, so the Norwegians can only live in the yellow house and smoke Dunhill cigarettes. Because the second room is blue, the owner of the horse lives next door to the smokers on Dunhill Road, so the owner of the second house keeps horses. So the green house is on the left of the white house, so the green house can only be in the third or fourth room. If the green house is in the third room (that is, the middle room), then the people living in the middle house drink milk, so the owner of the green house drinks milk, which contradicts the conditions for the owner of the green house to drink coffee. So the assumption is wrong. The green house is in the fourth room, and its owner drinks coffee. Further on, the third room is a red house, where the British live and drink milk. The fifth house is a white house. Because Danes drink tea, green house owners drink coffee, British people drink milk, and people who smoke blue houses drink beer, so Norwegians can only drink water. So people who smoke mixed cigarettes have a neighbor who drinks water, so people who smoke mixed cigarettes can only live in a second house.

Now let's tidy it up again. 1 The room is a yellow house, where Norwegians live, smoke Dunhill cigarettes, drink water and keep cats. The second house is a blue house. The owner keeps horses and smokes mixed cigarettes. The third room is a red house, where English people live, drink milk, smoke Pall Mall cigarettes and keep birds. The fourth house is a green house, living in Germany, smoking prince cigarettes and drinking coffee. The fifth is the white house, where the owner smokes blue master and drinks beer. Because Swedes have dogs, and because the owners of rooms 1, 2 and 3 don't have dogs, and the owner of the fourth house is German, the fifth house lives in Sweden and has dogs. 1, 3, 4 and 5 The owners of the houses are Norwegian, British, German and Swedish respectively. The owner of the second family is Danish and is drinking tea.

Finally, draw a conclusion:

1 The room is a yellow house, where Norwegians live, smoke Dunhill cigarettes, drink water and keep cats.

The second house is a blue house, living in Denmark, smoking mixed cigarettes, drinking tea and raising horses;

The third room is a red house, where English people live, smoke Pall Mall cigarettes, drink milk and raise birds.

The fourth house is a green house. Germans live in it, smoking prince cigarettes, drinking coffee and raising fish.

The fifth house is a white house, living in Sweden, smoking blue, drinking beer and raising dogs.

Conclusion: Fish farmers are German.