What is the best fish for the pond?

Fish Ponds can be used for two purposes: multiplying fish or other water dwellers, and harvesting roe or other products.

These fish that seem to be particularly useful:

Carp

With a value of only 30g, carps are perfect to turn into sashimi for a quick refill of energy.

Sturgeon

Sturgeon roe becomes caviar when processed in a preserves jar, which sells for 500g each and benefits from the Artisan profession. Not bad for a constant, passive source of income.

Lava Eel

As the most expensive fish that can be placed in fish ponds, lava eels are an obvious choice for anyone just looking for additional money.

Eel

Regular eels can be cooked with hot peppers to make the spicy eel dish, which increases both luck and movement speed. Having an easy way to cook many of these is certainly useful, given how luck and movement speed affect almost every aspect of a farmer's life.

Lobster

When cooked with milk, lobsters can be turned into lobster bisque, which provides a huge +3 boost to the Fishing skill. Very useful when going after some of the trickier fish to catch.