Blue Mary Shrimp (Neocaridina davidi)

Choose Blue Mary Shrimp for a stable aquarium

The Blue Mary Shrimp is a blue aquarium form of Neocaridina davidi, a freshwater shrimp in the family Atyidae. It is native to Taiwan, east of China, the Korean Peninsula and Vietnam and reaches approximately 4 cm. It suits intermediate keepers prepared to provide mature biological filtration, measured water and gradual changes.

Wikipedia describes Neocaridina davidi as an omnivorous freshwater shrimp from lakes, ponds, rivers and streams. Wild-type animals are mottled brown, while selective breeding has produced numerous aquarium colours, including blue. These details explain the shrimp’s grazing behaviour, but aquarium conditions should be planned from measured care values rather than copied from a wild locality.

The current WoRMS entry for Neocaridina davidi places the species in the freshwater-shrimp family Atyidae and the order Decapoda. Blue Mary is the colour-line name used for this animal; it remains the same species as other selectively bred colour forms of cherry shrimp.

Decide whether the care pattern suits you

Our store care assessment is intermediate. The shrimp is peaceful and small, but successful care depends on mature biological filtration, measured water, gradual changes, protected equipment and careful use of treatments. A new or untested aquarium is therefore a poor shortcut even when its temperature and pH appear to fall inside the planning range.

Understand the animal and dispatch size

One purchase supplies one Blue Mary Shrimp. The dispatch size is 1–1.5 cm. Dispatch size describes the animal sent, not its final size: plan the aquarium around the approximately 4 cm adult length recorded for Neocaridina davidi.

Sex is guaranteed only when the selected option explicitly states male or female. This Blue Mary Shrimp listing has no sex-guaranteed option.

The gallery images are representative of this type of animal rather than photographs of the exact animal supplied, so colours can look slightly different from the live animal.

Start with the decisive planning figures

The OATA freshwater shrimp and snail sheet gives 17–27°C, pH 6.5–8.0, 4–18°dH general hardness and 3–15°dKH carbonate hardness for the group; these are not a species-specific optimum. It also advises at least five for social shrimp and at least 10 litres for a group of small shrimp. Tropical Fish Co uses a mature, filtered 20-litre aquarium as a more cautious starting policy for a small group because the extra volume gives more headroom for feeding, equipment and change. Neither volume is a permanent shrimp-per-litre formula.

• Temperature: plan within 17–27°C and prioritise stability.
• pH: use 6.5–8.0 as the initial screening range.
• General hardness: screen against 4–18°dH.
• Starting space: begin planning at 20 litres, then increase space for companions and possible population growth.
• Water quality: ammonia and nitrite must each measure zero mg per litre.

Use our complete Cherry Shrimp Care Guide for the wider care method, or browse the cherry shrimp collection when comparing colour forms. Packing, dispatch days and guarantee terms remain on the delivery and Live Arrival Guarantee policy.

Build a mature, filtered home

Prepare the aquarium before choosing an arrival date. A mature aquarium is one whose biological filter can process the planned livestock load while ammonia and nitrite remain at zero; it is not an aquarium that has merely stood for a fixed number of weeks. The RSPCA’s filtration guidance explains that beneficial bacteria convert toxic ammonia to nitrite and then to the safer nitrate. Shrimp still depend on that process even though the guidance describes aquarium welfare generally.

Our cautious starting policy is 20 litres for a small Blue Mary group. Use the real water volume after allowing for substrate, wood, rock and equipment, then account for every other animal. A larger aquarium may be needed when fish share the system or when juvenile survival could increase the population.

Give the shrimp safe surfaces and shelter

Use aquarium gravel or sand and provide live plants where practical. Aquarium-safe wood, rock, plants and suitable ornaments create sheltered surfaces on which shrimp can graze. Keep enough open access to inspect equipment and remove waste. A secure cover can reduce escape risk without obstructing ventilation or cables.

Fit a fine guard or suitable sponge over any filter inlet capable of drawing in a small shrimp. The important decision is inlet protection, not a promise that one filter design is always best. Flow, filter capacity and maintenance access must all suit the aquarium’s real volume and livestock load.

If this is your first system, follow our guide to preparing and maturing a shrimp aquarium before livestock arrives. Do not use clear-looking water as a substitute for water tests.

Choose water by measurement, not guesswork

Measure the aquarium rather than assuming that local tap water has a particular chemistry. Use 17–27°C, pH 6.5–8.0 and 4–18°dH as the initial water screen, then compare the aquarium with the holding water used for the batch. Keep any necessary change gradual because a value inside the range does not make an abrupt transfer safe.

Decide whether heating is necessary

Do not add a heater simply because the aquarium is in the UK. First measure the room and aquarium through the periods when they are coolest and warmest. Use a correctly sized, guarded and thermostatically controlled heater if the aquarium cannot remain inside the chosen stable range without one. A warm room needs an overheating plan rather than extra heating.

Compare values before changing them

Use our water-chemistry guide to understand temperature, pH, general hardness, carbonate hardness and nitrogen-waste readings. The water matcher can then organise the comparison between measured aquarium water and the planning range.

When a reading needs adjustment, change one controlled factor at a time and retest. Review the substrate, rocks, top-up water, conditioners and maintenance routine before altering chemistry. This makes the cause of any movement easier to identify and reduces the risk of replacing one problem with a sudden swing.

Feed the group without fouling the water

Neocaridina davidi is omnivorous in nature, while aquarium shrimp spend much of their time grazing algae and biofilm. Treat that grazing as part of the feeding environment, not as a complete diet or a promise that the shrimp will control a named algae. Provide an appropriate complete sinking shrimp food so nutrition does not depend on whatever growth happens to be present.

OATA advises feeding freshwater shrimp two or three times a week. Leave pellets or wafers for at least 30 minutes so slower animals can reach them, then remove recurring excess before it breaks down. Portion size depends on the number of shrimp, the amount of established grazing area, competition from companions and whether juveniles are present.

Use observation to set the portion

• If every shrimp cannot reach the food: spread the portion across more than one sheltered feeding point rather than immediately increasing the total.
• If food repeatedly remains: remove the excess and reduce the next portion.
• If ammonia, nitrite or nitrate trends worsen after feeding: review both the portion and filter capacity before adding variety.
• If fast companions take the food: change the placement or feeding arrangement so the shrimp have access.
• If the group grows: reassess access and water-test trends instead of applying a fixed food-per-shrimp formula.

Established surfaces give the group opportunities to graze between prepared feeds. Plants, wood, rock and suitable decor increase that usable area, but visible algae alone does not show that the diet is complete. Likewise, calling shrimp a clean-up crew must never become a reason to withhold food or tolerate accumulating waste.

Overfeeding adds organic waste and can overwhelm the system’s biological capacity. The safest adjustment is small and measurable: remove recurring leftovers, reduce the next portion, retain the established schedule and watch the next set of water readings. Avoid making simultaneous changes to food, filtration and water chemistry, because several changes at once make the response difficult to interpret.

Maintain water with a repeatable routine

Carry out a 25% partial water change at least once each week. Treat replacement tap water with a suitable conditioner to remove chlorine or chloramine before it enters the aquarium, and avoid a sudden temperature or chemistry difference. A siphon can remove solid waste from accessible areas of gravel without stripping every established grazing surface at once.

Test before problems become visible

Test at least weekly for ammonia and nitrite, which should remain at zero mg per litre. OATA advises that nitrate should not exceed 20 mg per litre above the normal tap-water level. Record results so a gradual change is visible; one isolated reading is less useful than a consistent sequence taken around the same maintenance routine.

If filter media needs cleaning, rinse it lightly in aquarium water removed during the partial change. Do not run it under the tap because chlorine or chloramine may damage the beneficial bacteria. Clean only what is needed to restore operation rather than making the filter and aquarium sterile-looking on the same day.

When ammonia or nitrite rises above zero, pause further stocking and feeding increases, check the filter’s operation and look for decaying food or other waste. Correct the cause while keeping changes controlled. A larger-than-usual intervention may be necessary for animal welfare, but it should be guided by measured conditions rather than used as a routine substitute for weekly maintenance.

Make introduction condition-led

Prepare the aquarium, tests and transfer equipment before the delivery arrives. Confirm that ammonia and nitrite in the destination aquarium are zero, note its temperature, pH and hardness, and keep any change gradual.

The OATA freshwater aquarium setup guidance supports gradual acclimation and gradual stocking. Increase livestock slowly because the beneficial-bacteria population must adapt as waste and feeding increase. Adding several animals or increasing food quickly can leave the filter unable to process ammonia and nitrite.

Follow the arrival procedure in order

1. Be present to receive the parcel because live animals cannot be left unattended.
2. Start filming before opening the parcel, showing it still sealed with the outer box visible.
3. Open the parcel in one continuous take and show the shrimp still inside the sealed bag.
4. Float the bag for 20–30 minutes before releasing the shrimp.
5. Never pour the bag water into the aquarium.

Use dedicated wet equipment for separation where practical, and avoid moving nets, containers or water between systems without cleaning them appropriately. A separate observation system can reduce the chance of carrying a problem into an established aquarium, but its filter and water must be ready for livestock; an uncycled container is not protective simply because it is separate.

During the first week, prioritise stable readings and access to shelter over cosmetic rearrangement. If several animals are being added to a community, stage the stocking so filtration and feeding can be reassessed between additions. Record any maintenance, new decor, plants or treatments because that timeline becomes useful if behaviour changes.

Respond to health changes with measurements

Learn the group’s normal activity, colour, feeding and use of cover so a change is noticeable. Warning signs include increased inactivity, restlessness, unusual swimming, darker or paler colour, increased hiding, altered breathing effort, white spots, lesions, abnormal growths, damage to the exoskeleton, lost appendages, abnormal swelling, weight change or reduced interest in food.

Check the environment before reaching for treatment

1. Measure temperature, ammonia and nitrite immediately.
2. Review nitrate, pH and hardness against recent readings.
3. Check filtration, inlet protection, aeration and heating equipment.
4. List recent water changes, foods, plants, animals, decor, aerosols and treatments.
5. Compare the affected shrimp with the rest of the group.
6. Record clear photographs and the timing of each change.

An empty exoskeleton can resemble a dead shrimp, and hiding may occur around moulting. Neither observation identifies a disease by itself. Inspect carefully before removing a shell or beginning treatment, and use the complete pattern of behaviour, appearance and measured water to decide the next step.

Freshwater shrimp are very sensitive to copper and will die if exposed even to low levels. Read the exact current label and every invertebrate warning before adding any medicine, plant treatment or other chemical. Do not calculate a supposedly safe dose from advice for a different animal or product. When suitability is unclear, obtain suitably qualified aquatic or veterinary advice before treating the occupied aquarium.

If severe signs appear or a change persists after immediate environmental checks, seek prompt help and provide the recorded water values, timeline and photographs. Keep the rest of the system stable while advice is obtained. Avoid changing food, water chemistry, filtration and medication simultaneously unless an urgent welfare response requires it, because uncontrolled changes add stress and make the underlying problem harder to identify.

Plan growth and reproduction without promises

Blue Mary Shrimp should be planned as a social group. Start with at least five under OATA’s freshwater-shrimp group guidance, then use the aquarium’s mature filtration, grazing area and real volume to decide whether additional animals are appropriate. Do not multiply litres by a permanent shrimp ratio: adult companions, feeding competition, equipment, maintenance and juvenile survival all change capacity.

Plan for an adult length of approximately 4 cm. This is distinct from the 1–1.5 cm dispatch size and should guide equipment protection, companion screening and long-term space decisions.

Neocaridina davidi does not have the prolonged saline planktonic larval stage associated with Amano Shrimp. A female carries eggs externally beneath her abdomen, and young hatch as bottom-dwelling juveniles. This lifecycle can allow juveniles to remain in a freshwater aquarium, but it does not promise that a mixed unsexed group will breed or that offspring will survive.

Prepare for juveniles before they appear

• Protect filter inlets that could trap newly hatched shrimp.
• Keep established grazing surfaces accessible within dense cover.
• Use an appropriate complete shrimp food and monitor whether juveniles can reach it.
• Leave filtration and water-volume headroom for population change.
• Review fish predation risk before treating a display aquarium as a breeding system.
• Keep a separation plan for crowding, aggression or equipment problems.

A shrimp-only aquarium removes fish predation from the plan, but it does not remove risks from water quality, food, filtration, equipment or population growth. Continue weekly tests and maintenance as the group changes, and adjust prepared food from observation rather than assuming that more shrimp automatically require a large increase.

If preserving the Blue Mary colour line matters, use a single-line aquarium and avoid promising that mixed colour forms will breed true. Appearance cannot establish sex, lineage or future colour outcome, and the unsexed purchase unit cannot guarantee the mix needed for reproduction. Judge success by animal welfare and stable water rather than a promised egg count, hatching date or monthly colony-growth target.

Screen every companion before mixing

Blue Mary Shrimp is peaceful, but peaceful behaviour does not protect it from predation. Avoid fish able to fit the shrimp in their mouth and species known to be predatory. Newly hatched shrimp are much smaller than adults, so a fish that appears to coexist with adults may still hunt juveniles.

Assess the complete adult community

• Mouth size: judge the companion at its adult size, not only its dispatch size.
• Hunting behaviour: include stalking, pecking and searching among plants or hardscape.
• Territorial behaviour: consider whether shrimp can be driven away from shelter or food.
• Feeding competition: check whether every shrimp can reach suitable food.
• Water overlap: use one stable temperature and chemistry plan that works for all animals.
• Cover: ensure shelter remains useful after plants are trimmed and during maintenance.
• Moulting risk: allow protected spaces for temporarily vulnerable shrimp.
• Separation: have a workable response if behaviour changes.

No fish is guaranteed safe with shrimplets. When maximum juvenile survival is the goal, a shrimp-only aquarium removes fish predation from the decision. When the goal is a mixed display, accept that close observation and dense cover reduce uncertainty but cannot turn an untested pairing into a guarantee.

For a stocking assessment, send our team the aquarium volume, measured temperature, pH and hardness, every intended companion at adult size, the amount of cover and whether juvenile survival matters. Those details support a conditional assessment; a species name by itself is not enough.

Design the community around shrimp access

Compatibility includes access to resources as well as direct predation. A companion can share the water range yet still take every sinking food item, occupy the only sheltered area or disturb shrimp immediately after moulting. Watch what happens at feeding time and inside cover rather than judging the aquarium only from open-water behaviour.

Use cover as usable space

Plants, wood, rock and suitable ornaments should create several sheltered grazing areas rather than one crowded refuge. Keep those areas connected to food and away from exposed filter inlets. Recheck the layout after trimming plants, moving decor or cleaning, because maintenance can remove the very cover on which the compatibility plan depends.

Another invertebrate is not an automatic match. Compare adult size, feeding method, behaviour, water requirements and treatment sensitivity for every proposed animal. Introduce livestock gradually so filtration and feeding can be reassessed, and do not rely on a label such as community animal as a substitute for observation.

Mixing different Neocaridina davidi colour lines may meet basic species-care requirements, but it does not promise predictable offspring colour. Keep a single named line when preserving Blue Mary appearance is part of the goal. If display coexistence matters more than colour inheritance, continue to plan around filtration, grazing area, population growth and the welfare of every animal.

Answer Blue Mary Shrimp questions

How big does a Blue Mary Shrimp get?

It reaches approximately 4 cm at maturity. Plan equipment, companions and long-term space around that adult length rather than the smaller dispatch size.

What size aquarium does Blue Mary Shrimp need?

Tropical Fish Co uses a mature, filtered 20-litre aquarium as a cautious starting policy for a small group. Increase the space for fish, other livestock and possible population growth rather than applying a permanent shrimp-per-litre formula.

How many Blue Mary Shrimp should I keep together?

OATA’s freshwater-shrimp group guidance advises at least five social shrimp. Base any larger group on mature filtration, real water volume, grazing area, feeding access and the needs of every companion.

Does Blue Mary Shrimp suit beginners?

It has an intermediate store care assessment because it needs mature biological filtration, zero measured ammonia and nitrite, gradual water changes, a protected filter inlet and careful treatment selection.

What does Blue Mary Shrimp eat?

It is naturally omnivorous and grazes biofilm and algae. Provide an appropriate complete sinking shrimp food, feed two or three times a week, allow at least 30 minutes for access and remove recurring excess.

What temperature and pH does it need?

OATA’s freshwater-invertebrate group guidance gives 17–27°C, pH 6.5–8.0 and 4–18°dH for aquarium planning. Keep ammonia and nitrite at zero mg per litre, measure the aquarium and make changes gradually.

Is this shrimp aggressive or likely to nip fins?

This shrimp is peaceful. Compatibility risk comes from companions hunting it, swallowing it, taking its food or preventing access to cover rather than from fin-nipping behaviour by the shrimp.

Which animals can live with it?

Avoid fish able to fit the shrimp in their mouth and species known to be predatory. Screen every proposed companion for adult mouth size, hunting and territorial behaviour, feeding competition, shared water values, cover and the importance of juvenile survival.

How does it arrive alive in the UK?

Start filming every delivery while the parcel is still sealed, then open it in one continuous take with the animal still inside the sealed bag. Someone must be present to receive it; float the bag for 20–30 minutes before release and never pour the bag water into the aquarium.

Consult the care references

• World Register of Marine Species: Neocaridina davidi — accepted scientific identity, family and order.
• Neocaridina davidi species account — natural distribution, habitats, feeding mode, colour forms and adult length.
• OATA: How to look after freshwater shrimp and snails — UK group guidance for water, social keeping, aquarium setup, feeding, maintenance and compatibility.
• RSPCA aquarium environment guidance — biological filtration and nitrogen-waste processing.
• OATA freshwater aquarium setup guidance — cycling, testing, gradual acclimation and gradual stocking.