Stickletrout are aquatic fish critters that live in the small pond at the bottom right corner of the Norn Terrarium. They eat insect critters such as Dragonfly nymphs, but they are often subject to extinction from over-hunting by the Kingfisher or not having enough to eat. This can be easily solved by putting some Balloon Bugs or the Fish Food agent in the pond with them, or by installing the NWFP. The Steam release of Docking Station also includes a fix that stops their main prey item, the dragonfly, from going extinct prematurely.
The stickletrout can change sex if it is required for the species' survival. If there are no females left, a male will change into a female, and vice versa. (This is a phenomena seen in many real-life fish.)