Zebra Nerite Snail

Species: Neritina natalensis, the striped form.

Size: about 2.5 cm across the shell.

Water: 22–26 °C, pH 7.2–8.2, moderately hard to hard.

Eats: algae, biofilm and dead leaves; leaves healthy plants alone.

Breeding: lays eggs, but they cannot hatch in fresh water.

The zebra nerite is a rounded, thick-shelled snail marked with bold black and gold stripes that run in a spiral across the shell. It comes from rivers and estuaries along the east coast of Africa, from Kenya down to South Africa, where it lives on rocks in flowing water. In the aquarium it does one job well: it grazes algae. It works over glass, wood, rocks and the broad leaves of tougher plants, and it is one of the few animals that will clear green spot algae, the hard, flat dots that build up on glass and slow-growing leaves. It eats only algae, biofilm (the thin living film of bacteria and microscopic life that coats every surface underwater) and dead or dying leaves, so healthy plants are not touched.

One thing to know before you buy: females lay small, hard white eggs, each about the size of a sesame seed, on wood and rock. In fresh water those eggs never develop, because the larvae need salt water to grow, so the population cannot get out of hand. The eggs themselves are stubborn and take some scraping to remove. Nerites live around one to two years.

Water: 22–26 °C and a pH of 7.2–8.2, in moderately hard to hard water (about 10–25 dH, a measure of dissolved calcium and magnesium). Calcium is what the shell is built from, so very soft water leads to pitted, thinning shells over time.

Tank: a mature tank with some algae already growing gives it something to eat from day one. Nerites climb, and they will wander above the waterline and out of an open tank, so a lid with no gaps is needed.

Feeding: in a clean tank with little algae, offer an algae wafer or a slice of blanched vegetable such as zucchini or cucumber a couple of times a week, and remove what is left after a day.