Fish breeding is a mechanic added by Mariculture. It is used to acquire fish breeds that cannot be acquired in the wild through fishing. Different fish produce different products or do different special things for the player. To get started with fish breeding the player will need:
In order to start breeding the player will need to build a Fish Tank by using the Fish Feeder and some hard blocks. There are three different sizes of tanks, but the default medium size will suffice for most Fish. Some of the more advanced species will require larger tanks. (See the Fish Tank page for a guide on how to setup/build the Fish Tank.) Once the tank has been set up, place the male and female Fish into the Fish Feeder that is in the center of the tank and provide them with Fish Food. They will only reside in the tank if it is 100% suitable to them. (See the Fish page for more information).
While residing in the tank the Fish will produce droplets and possibly another type of product. When the female dies she will produce a Fish Egg and a raw version of her main breed, while the male will just produce a raw version of himself. The raw Fish can be eaten, used in recipes, melted down into Fish Oil, etc. The Fish Egg should be placed inside of an Incubator. While in an Incubator, the egg will periodically make an attempt to hatch; this is cumulative and the egg is not consumed upon birth of any fish spawn. Once the egg has reached the end of its life, it will check how many males or females it has generated. If it has generated neither one, it will spawn a male and female Fish before it expires; in other words, an egg is guaranteed to spawn 1 Fish of both sexes.
After mastering the basics the player should try crossbreeding different breeds of fish. Typically hybrids of the parent breeds will be born though there is a chance for each Fish to mutate into a whole new breed that gives new products for the player.