River Shrimp Macrobrachium Care: Long Arm Freshwater Shrimp

Long-arm river shrimp look like ornamental dwarf shrimp scaled up by 400 percent, and many beginners buy them assuming they will behave the same way. They will not. This river shrimp macrobrachium care guide from Gensou Aquascaping at 5 Everton Park covers the diverse Macrobrachium genus — predatory freshwater shrimp ranging from 5cm peaceful species to 30cm fish-killers, several with brackish larval stages. Identifying the exact species before purchase decides everything.

Quick Facts

• Genus: Macrobrachium, over 240 described species
• Adult size: 5 to 30cm depending on species
• Minimum tank: 60 litres for small species, 200 litres for giants
• Temperature: 24 to 28°C — Singapore ambient is suitable
• Water: pH 7.0 to 8.0, GH 8 to 15, KH 4 to 8
• Behaviour: predatory, territorial, almost all eat small fish and dwarf shrimp
• Many species require brackish water for larval development

Identifying What You Actually Bought

Most “river shrimp” sold loose in Singapore aquarium shops are imported wild-caught from Malaysia, Indonesia or Thailand and arrive without species ID. Common visitors include Macrobrachium lanchesteri (small, peaceful, fully freshwater), M. rosenbergii juveniles (sold cheap, will reach 30cm), M. lar, and various unidentified Sulawesi or Borneo species. A 6cm pet-shop shrimp could grow to 25cm or stop at 8cm — the difference matters enormously.

Key identification points: claw length relative to body, presence of spines on the rostrum, and colour pattern of the second pereiopods. If a shop cannot give you a species name, assume it grows large and predatory.

Tank Setup

Minimum 60-litre tank with sand substrate, dense hardscape and many hiding places. Driftwood pieces, slate caves and PVC sections all work. Plants are largely safe — unlike crayfish, Macrobrachium generally do not chop vegetation, though they will dislodge unanchored stems. A tight lid is essential as adults climb filter intakes and CO2 lines to escape.

Filtration should be moderate — a sponge or hang-on filter rated 4x turnover suits most species. Strong current is not appreciated by lowland species; species from hill streams (M. trompii, some Sulawesi) prefer more flow.

Water Parameters and Brackish Stages

Adults of nearly all hobby Macrobrachium live in fresh or very slightly brackish water and adapt well to Singapore PUB tap remineralised to GH 8 and KH 4. The complication is breeding: many species, including M. rosenbergii, release zoea larvae that must develop in brackish water (SG 1.005 to 1.015) for two to four weeks before metamorphosing and returning to freshwater. M. lanchesteri and a handful of others bypass this stage with direct development. Always research the species before attempting to breed.

Feeding

Carnivorous omnivores. They take sinking pellets, frozen bloodworm, frozen brine, mussel, prawn, snails, and any small fish or shrimp slow enough to catch. Vegetable matter — blanched courgette, algae wafer — is accepted but not preferred. Two small feeds per day suit growing juveniles; a single feed every other day works for adults.

Predation and Tank Mates

This is the section most beginners ignore. A 10cm Macrobrachium will catch and eat ember tetras, chili rasboras, sleeping bettas and every Neocaridina shrimp in the tank. Even small species like M. lanchesteri will pick off newborn fish. Suitable companions are limited to fast mid-water schools larger than the shrimp’s claw reach: zebra danios, larger rasboras, hatchetfish. Bottom dwellers, slow fish and any shrimp under 4cm are food.

Aggression Within the Species

Long-arm shrimp are territorial and males will fight for cave space, sometimes fatally. A pair or trio in a small tank will reduce to one within a week. Either keep them solitary or provide enough caves and visual breaks for each animal to claim a corner. Females after a moult are particularly vulnerable.

Moulting

Like all decapods, Macrobrachium moult to grow — every three to six weeks in juveniles, every two to three months in adults. Calcium availability matters. Keep crushed coral in the filter or cuttlebone in the tank. Leave the cast exoskeleton for re-ingestion. The 24 hours after moulting are the most dangerous; cohabitants will eat a soft shrimp without hesitation.

Singapore Context

River shrimp turn up regularly in Singapore wet markets and several Pasir Ris and Lim Chu Kang farms keep them as food and ornamentals. AVS rules apply: do not release any non-native specimen into local waterways. M. rosenbergii in particular is a known invasive risk. If your shrimp outgrows your tank, rehome through hobby groups, donate to a research institution, or freeze humanely.

Common Problems

The two most common failures are buying a “small” shrimp that turns into a fish-eating monster, and losing breeding attempts because the keeper did not know the larvae need brackish water. Health issues such as missing antennae, white fungal growth at joints, or failed moults usually trace to soft water, poor diet or aggression from tank mates. Solid identification at purchase prevents most disappointments.

Related Reading

• Wood Shrimp Fan Shrimp Care Guide
• Bamboo Shrimp Care Guide
• Vampire Shrimp Care Guide
• Amano Shrimp Breeding Guide
• CPO Dwarf Crayfish Care Guide