Marine molluscs are hugely diverse and most make excellent inhabitants. Some perform an excellent ‘cleaner’ role in the aquarium and others will exhibit interesting behaviours. Octopus and cuttlefish also fall into this group, however as their care needs are very specialised, they will not be covered in this care sheet. Ask your OATA retailer for advice if you are planning to keep these animals. As molluscs are so diverse, they have many different needs. Always consult your OATA retailer before purchasing any marine mollusc to ensure they will mix with current tank mates.
Thanks to TMC for the use of this photo
Water requirements
Molluscs are usually undemanding of water chemistry and their suggested parameters are shown below. These parameters are a general guide for this group of invertebrates, so it is important to check with your OATA retailer for any species-specific requirements before purchasing. Please also note that if keeping these invertebrates in a reef aquarium, some parameters will need to be altered to accommodate more sensitive species.
- Salinity: Between 1.023-1.026
- Temperature: Between 24-26°C
- pH: 7.9-8.3
- Ammonia: Zero mg per litre
- Nitrite: Zero mg per litre
- Nitrate: Not to exceed 50 mg per litre
- Carbonate hardness: Hard (8-12°dkH)
- Calcium: Between 380-450 ppm
- Magnesium: Between 1250-1350 ppm
Biology
Molluscs are invertebrates that all share the common feature of a mantle. This is a type of tissue that sits on top of the body and, in some species like snails, is used to make the shell. The mantle is more obvious in some species than in others. For example, clams have a very exposed mantle, whereas it is unlikely to be seen in snails. Marine molluscs vary in size: some species of snail (Collonista species) will only grow to 6mm whereas giant clams (Tridacna species) can grow up to 45cm in aquariums (but larger in the wild). Some molluscs such as turbo snails (Turbo species) or sea hares (Dolabella auricularia) perform a grazing function in the aquarium and will readily consume algae. Other species such as berghia nudibranch (Berghia stephanieae) will consume unwanted pest Aiptasia anemones that appear in marine aquariums. Species such as flame scallops (Ctenoides species), many nudibranchs and giant clams are kept for their vivid colours.
Some nudibranch species contain toxins which are excreted if stressed or on death. These should be mixed with extreme caution and only bought if they can be cared for long term. For more information on how to manage these animals, please see our Hazardous Aquatic Animals guidance.
Some species, particularly smaller snails are unlikely to live longer than two years, but other species can live for many years in a well-matured set-up with good water quality. Marine molluscs can be kept in groups or alone as they are not territorial and do not require company. As marine molluscs are invertebrates, copper is toxic to them and so care should be taken when using treatments in the aquarium or introducing fish from retailers using copper in their systems.
Aquarium requirements
As a general rule, you should within reason, buy an aquarium as large as possible. It is recommended that an aquarium of at least 40 litres is used for smaller species such as snails or nudibranchs. The larger species will need a larger aquarium of approximately 200 litres. A larger aquarium will also provide more stability to environmental conditions, such as temperature and water quality. Whatever the size, a filter is essential. For marine set-ups this can be in the form of live rock with sufficient water flow, an internal or external filter, or a sump-based filter. A protein skimmer can also be beneficial for maintaining water quality as it will help to remove dissolved organic waste before it can break down into more harmful substances.
Marine molluscs are undemanding of décor and need very little. Live or artificial rock will provide opportunities for grazing, places to place immobile species and will provide cover for mobile ones. Some molluscs will require a deep sand bed in which to bury themselves, so the aquarium should have at least 4cm of coral sand on its base. There should be a moderate water flow to provide good surface movement and to ensure detritus doesn’t accumulate, but do not place filter feeding molluscs such as clams or scallops in areas with a high water flow.
A heater is required to maintain a suitable temperature all year round. To minimise fluctuations in water temperature, the aquarium should not be situated near any draughts or heat sources. It should also be out of direct sunlight and away from loud noises, vibrations and sudden movements. Overhead tank lighting is recommended to maintain a correct day-night cycle. This will not need to be particularly bright for most species, but any that photosynthesise (such as giant clams) will need sufficient light. Ask your OATA retailer for more advice.
Water testing kits are essential so that water quality can be checked on a regular basis (once a week) to ensure it does not slip below the water requirements stated earlier.
Introducing your mollusc
Before adding any invertebrate, seek advice from your OATA retailer to make sure that your aquarium is appropriate for the mollusc you would like to keep. Check that the water quality in your aquarium is suitable i.e. levels of ammonia and nitrite are zero. Only increase the number of livestock you have in your aquarium slowly, as the population of beneficial bacteria established when maturing your aquarium filter need to increase every time more livestock are added and feeding increases. Overstocking or stocking your aquarium too quickly can result in ‘new tank syndrome’. This occurs when there are not enough nitrifying bacteria to cope with the increased waste from the livestock, leading to unhealthy levels of ammonia and nitrite, which may cause invertebrates to become ill or die.
Your OATA retailer will usually sell your mollusc to you in a plastic bag, try not to keep them in this for too long. Once purchased, take your new invertebrate home as quickly as possible because they are easily stressed by bright lights, extreme temperatures, noise and movement.
Once home, your invertebrate will need to acclimatise to their new environment and a common method of doing this is known as the ‘floating bag’ method. Switch off the aquarium lights and take the bag containing your new invertebrate out of its outer wrappings carefully, avoiding exposure to bright light. Float the bag in the water of your tank to ensure the temperature in the bag is the same as the aquarium water. After 10 minutes, slowly introduce small amounts of aquarium water into the bag containing the invertebrate for up to an hour. Invertebrates will struggle with changes in water chemistry more than fish and so good care should be taken during the acclimation process. Once complete, carefully place the mollusc into the aquarium whilst introducing as little bag water into the aquarium as possible. After this, dispose of the bag and any excess water appropriately.
For very sensitive species, a better method might be the use of drip acclimation. This could be achieved by keeping the mollusc in the container in which it is sold and a small airline siphon started to drip water into the container, slowly changing the water parameters to that of the aquarium. Ensure that the temperature does not fall too low during this procedure. Once conditions match, carefully remove the invertebrate from the container and place it in the aquarium. Dispose of the water in the transport container appropriately.
Monitor your new invertebrate carefully for the first week, paying particular attention to water quality. If in doubt, contact your OATA retailer for advice.
If possible, quarantining new livestock in a separate aquarium for at least a week before they enter the main tank can help reduce any risk of disease spread from new inhabitants. Ask your OATA retailer for advice on this topic.
Maintenance
At least once every week, a partial water change of 25% is strongly recommended (a siphon device is useful to remove solid waste from the gravel). Filters should be well maintained, with regular checking and cleaning to prevent blockages. If the filter needs cleaning, do not run it under the tap because any chlorine or chloramine present may kill the beneficial bacterial population that has established in the media. Instead, it should be rinsed lightly in the tank water which is removed during a partial water change as this reduces the amount of bacteria which are lost. Protein skimmers should be regularly cleaned to maintain their performance.
Good husbandry is essential as molluscs can be stressed by even the smallest amounts of ammonia and nitrite which may then cause them to develop various diseases. Test the water to monitor the ammonia, nitrite and nitrate levels, together with pH and carbonate hardness every week, especially during initial set-up and after adding extra livestock. It is also important to regularly monitor salinity and use reverse osmosis water to replace any water lost through evaporation.
What to watch out for
All fish will have slight variations in their behaviour or appearance, but keeping an eye on any changes in the following will help to identify any potential problems before they become a real health issue:
- swimming behaviour – hanging at the surface, sitting on the bottom or erratic swimming
- colour – turning a darker or paler colour than normal
- temperament – changes in level of aggression or hiding more than normal
- breathing – gill covers moving at a slower or faster rate than normal
- appearance – development of white spots or fluffy growths, loss of fins or scales
- condition – increase or decrease in body weight and condition
- feeding – reduced intake or lack of interest in food
If you are concerned about the health of any of your livestock, then test your water quality and contact your OATA retailer for further guidance.
Feeding
Marine molluscs vary in their dietary requirements. Many species are herbivorous and will consume algae in the aquarium. If this runs out, it will need to be supplemented with nori algae sheets. Other species such as berghia nudibranchs will require live Aiptasia anemones that will need to be provided. Species such as clams and scallops will consume phytoplankton and zooplankton from the water column. This can be purchased or cultured at home. Some of these species will also photosynthesise and so sufficient light should be provided.
As many molluscs graze throughout the day, it is not possible to say how many times they should be fed. This will also depend on what natural food items are in your aquarium. When extra feeds are given, take care not to overfeed as this can lead to a build-up of uneaten food which breaks down releasing toxic waste into the water. If in doubt, ask your OATA retailer for advice on appropriate feeding levels.
Compatibility
Marine molluscs will generally mix with all fish considered ‘reef-safe’, but those that are not ‘reef-safe’ are likely to predate on them and they should not be kept together. Although marine mollusc species can generally be mixed, it is best to avoid mixing species that require the same food sources unless you are sure that you can provide for all of them.
Breeding
Some molluscs may spawn in the home aquarium and it is not uncommon to see snail eggs on the aquarium glass, but they are unlikely to survive being predated upon. If they do hatch, thousands of planktonic larvae will be produced. It is likely that they will get sucked into filters and pumps or eaten by other aquarium inhabitants. They also require specific live feeds and so a specialist set up is required to raise them to adulthood.
Checklist
Before purchase make sure:
- You have the appropriate equipment and position for the aquarium.
- You have researched all the species in which you are interested and your final choices are all compatible.
- You are familiar with how to transport and release your livestock.
- You are aware of the daily, weekly and monthly maintenance your aquarium will require.
- You are prepared to look after your livestock properly for the duration of their life.
Shopping list
- Glass or acrylic aquarium
- Filter*
- Heater
- Lighting (required for live plants)*
- Gravel or sand
- Tap water conditioner/dechlorinator
- Gravel cleaner/siphon cleaning device (recommended)
- Water testing kits (ideally ammonia, nitrite, nitrate, pH and water hardness)
- Aquarium salt and a hydrometer or refractometer
- Access to reverse osmosis water or a reverse osmosis unit
- Live or artificial rock
- Protein skimmer* (optional but recommended)
- Ultraviolet steriliser (optional but recommended)
- Aquarium decorations and/or live plants
- Bucket for water changes
*may be included in branded aquarium sets but can be purchased separately.
Before purchase make sure:
- The aquarium is of a suitable size that ideally can accommodate the livestock once they are fully grown.
- Water parameters are as advised in this leaflet.
- Aquarium is cycled and ready to receive livestock.
Top tips
Always buy…
test kits and regularly check the water for ammonia, nitrite, nitrate and pH. This will allow you to make sure the water in your aquarium is not causing welfare problems for your livestock.
Establish a routine…
for testing the water in your aquarium. Record your results to enable you to identify fluctuations quickly. Also check the temperature of the water.
Maintain…
the water in the aquarium within the accepted parameters highlighted above. You may need to do regular water changes to achieve this.
Always wash your hands…
making sure to rinse off all soap residues, before putting them into your aquarium, or use long sleeved rubber gloves. Wash your hands again afterwards and certainly before eating, drinking or smoking.
Never siphon by mouth…
A fish tank can harbour bacteria which can be harmful if swallowed. Buy a specially designed aquarium gravel cleaner which can be started or primed without the need to place the siphon in your mouth
Five Welfare Needs Checklist:
The Animal Welfare Act 2006 states that all pet owners have a legal duty of care to their pets. Anyone who is cruel to an animal or is found not to be providing the five animal welfare needs, as listed below, can be prosecuted.
- A suitable environment e.g. appropriately sized tank (with water heater if tropical set up) within a suitable location in your home.
- A suitable diet which meets the needs of your chosen fish.
- Behaviour – Fish are able to exhibit their normal behaviour e.g. hiding places for timid fish, enough room for fish to swim freely.
- Companionship – Ensure you know whether your chosen fish need to be kept with, or apart from, other fish.
- Health – Protected from pain, injury, suffering & disease e.g. you are aware of the daily, weekly and monthly maintenance that your aquarium will need.
Remember...
Water quality test kits are a necessity not an optional extra.
You must be prepared to look after your fish properly for the duration of their life and provide an aquarium which can accommodate your fish when fully grown.
Never release your aquarium animals or plants into the wild. It is illegal and for most fish species this will lead to an untimely and possibly lingering death. Any animals or plants that do survive might be harmful to our native countryside. Take care to properly dispose of any soiled substrate (e.g. sand or gravel) water or decorations so that non-native organisms do not enter natural watercourses.
