From Creatures Wiki
The Zander fish is a species of small, blue-and-purple fish that appears in various forms across Creatures 2 and Creatures 3/Docking Station.
Zander fish are one of the two fish species included with Creatures 2 (alongside the Goldfish). Unlike the Goldfish, the Zander fish is edible, and thus a viable food source for Creatures. As well, it forms the diet of the sea monster Borland. They school and mate on the fourth day of summer, lay eggs on the first day of autumn, and the eggs will hatch on the third day of autumn (See Creatures 2 in-game miscellany). Should their species be significantly lacking, one can create more zander fish eggs with an egg launcher initially located underneath the dark ocean.
Two seperate versions of Zander fish exist for Creatures 3 and Docking Station.
One variant was made by Edash, and functions similarly to their Creatures 2 counterparts. They differ in that they can eat bugs to lengthen their lifespans (there are specially made Zander mites for this purpose), but cannot breed on their own and thus require their included egg launcher for reproduction. They are available from Edash's Creatures (old site).
The other variant was made by Grendel Man as part of the Past Seas metaroom. Here, they are roughly analogous to the Shrimp of Aquatilis Caverna, the adults reproducing by laying three eggs whenever their population gets low. In addition to being a fine snack for creatures, they form the natural diet of the orthocone, and tube anemones require zander fish for seed production.