Whenever you want to keep fish with tank mates in an aquarium, compatibility is a major consideration. However, in most cases, we never consider whether or not the tank mates will feed on each other’s eggs.
For example, if you keep fish with mystery snails, it might be important to determine whether the snails will eat the fish’s eggs and vice versa.
Mystery snails can eat fish eggs when they’re starved and their preferred food sources, such as algae, biofilm, and decaying plant matter, are not available in the aquarium. While the snails are not a threat to fish eggs, they may eat them if given the opportunity.
Keeping snails with tank mates is a great way to diversify your aquarium. Snails play a major role in cleaning the aquarium as they eat algae and decaying plant material. However, that does not mean you shouldn’t feed your snails because they need nutritional supplementation to remain healthy.
Why do snails eat fish eggs?
If you have spawning fish in your aquarium, you want to put measures in place to protect the eggs of your fish. Typically, mystery snails feed on algae and rotting plant material. As a good pet parent, we recommend you feed them algae wafers, kale, and spinach to keep them healthy and prevent them from feeding on the eggs of their tank mates.
In case they do, the reasons could be any of the following:
Snails require a balanced and nutritious diet to meet their nutritional needs. If you recently cleaned your tank and removed most of the biofilm, algae, and decaying plant matter, your mystery snails may feel hungry due to a lack of food in the tank.
Starved snails become desperate for food and consume anything available in the aquarium, including fish eggs.
According to Nalini Mohan of the Columbia State University, some snails will even eat eggs and juveniles of other snails when desperate for food.
In fact, mystery snails are known to overeat. They’ll eat almost anything in the aquarium if they don’t get enough food, which is why you should feed them adequately if you have fish that lay eggs in the same tank.
Mystery snails are prolific breeders; within a short time, you can easily have a population outbreak in the tank. We recommend stocking 1-2 mystery snails per 5 gallons of water in the tank. If you have more snails as well as other tank mates, you’ll likely have increased instances of the snails eating fish eggs.
An overpopulated tank also means increased competition for food. The snails will likely food on just about anything in the tank that’s edible to them.
Snails require a lot of calcium to build and maintain their shells. If your snails aren’t getting enough calcium, they’ll eat fish eggs or other aquarium inhabitants’ eggs to obtain the required calcium.
Eggs are a good source of calcium, and snails will eat them to quench their calcium cravings.
Can snails eat their own eggs
Some types of snails are known to eat their eggs. This behavior is called egg cannibalism. Baur, B. in the journal of Functional Ecology states that in some snails, “Egg cannibalism occurs exclusively during the hatchling stage, i.e. in snails younger than 16 days.” 
In Arianta arbostrorum snails, egg cannibalism occurs among hatchlings feeding on unhatched eggs in the same clutch for nutrition. This behavior is called hatching asynchrony and is an adaptation to population control in these snails.
How to Protect Fish Eggs from Snails
We recommend cory cats, otocinclus catfish, guppies, killifish, and shrimp as compatible tank mates for mystery snails. Even betta fish can live with the snails if some important conditions are met. However, despite feeding your snails well, take precautions to protect fish eggs from being eaten by mystery snails.
1. Feed your mystery snails regularly
Feed your snails a balanced diet to prevent them from eating fish eggs. Although mystery snails feed on algae and decaying plant material in the tank, you still want to provide adequate food to satisfy them.
I recommend feeding your snails on a regular basis. Here are some foods to try:
- Algae wafers
- Fish pellets
Ensure you blanch the vegetables to make them soft for the snails to eat.
2. Provide calcium supplements
Calcium is vital in the diet of snails. It keeps their shells healthy and tough enough to offer protection against predators and unfavorable environmental conditions. Calcium deficiency is a known reason mystery snails lose their shell through breakage, weakening, and peeling.
A rule of thumb is to supplement for calcium by adding crushed eggshells or putting cuttlebone in the aquarium with snails.
The vegetables I’ve recommended above are also a great source of calcium for snails.
3. Use a breeding net
The idea is to provide a safe place for fish to lay their eggs. A breeding net is ideal for this.
A breeding net is a mesh container that can be attached to the side of the aquarium or hung from above. This allows the fish to lay their eggs inside the container, which prevents the snails from reaching them.
4. Move the snails to a separate tank until after the eggs hatch
If you have an extra tank, moving the snails would be wise. This way, you will be guaranteed no snail will eat the fish eggs. You can return the snails to the parent tank after the fish eggs have hatched.
Carnivorous snails should not be put back because they will eat the fry.
- Baur, B. “Possible Benefits of Egg Cannibalism in the Land Snail Arianta Arbustorum (L.).” Functional Ecology, vol. 4, no. 5, 1990, pp. 679–84. JSTOR, https://doi.org/10.2307/2389736. Accessed 11 Mar. 2023.
- Baur B, Baur A. Proximate factors influencing egg cannibalism in the land snail Arianta arbustorum (Pulmonata, Helicidae). Oecologia. 1986 Sep;70(2):283-287. doi: 10.1007/BF00379252. PMID: 28311670.