Why the Olive Nerite Snail Won't Breed in Freshwater (Neritina natalensis)

The Olive Nerite (Neritina natalensis var. olive) lays egg capsules in freshwater, but its larvae need brackish or salt water to develop, so it cannot reproduce in a freshwater tank.

Overview

The olive nerite is a smooth olive-green colour variant of Neritina natalensis, a Neritidae snail from the coastal plain of East Africa. Like the zebra form it is a strong algae grazer that favours hard, alkaline water. It shares the same amphidromous biology, returning to brackish water to reproduce, so it can complete its life cycle only in brackish or salt water and not in an ordinary freshwater aquarium.

Sexing

Olive nerites, like all nerites, have separate sexes and are not hermaphroditic, so one snail alone cannot reproduce. The sexes cannot be told apart externally with any reliability, which is why keepers usually maintain a small group to ensure both sexes are present.

Conditioning

A diet of algae plus adequate minerals in hard, alkaline water keeps adults healthy and able to lay egg capsules. As with all nerites, conditioning the adults does not enable reproduction, because the larvae still require brackish or marine salinity to develop.

Breeding Setup

Completing the cycle means providing brackish or saltwater for the larval stage. Aquarists either acclimate adults to brackish water for laying or move egg-bearing surfaces into a brackish or saltwater rearing tank, because the veliger larvae need that salinity and specific gravity to grow into juveniles.

Why It Won't Breed in Freshwater

In freshwater the female lays hard, white egg capsules on surfaces, each holding many eggs, but they do not hatch into viable snails. The larvae cannot develop without brackish or marine water, so the snail population stays the same in a freshwater tank despite visible egg capsules.

Common Challenges

The white egg capsules are hard, adherent and hard to remove from decor and glass, and many keepers find them unsightly. Even with a brackish rearing setup, the tiny larvae are extremely difficult to feed, so successful captive breeding is uncommon.