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Chocolate / Red rusty shrimp

Macrobrachium dayanum

The aggressive Himalayan prawn: robust body in chocolate/rust color with developed claws. Native to the Himalayan region and southern India. Opportunistic omnivore/carnivore: hunts sleeping fish, snails and smaller shrimp. Territorial and aggressive — males fight. Nocturnal. NOT suitable for peaceful community tanks. Many hiding spots mandatory for molts. Freshwater breeding with large eggs and fully formed offspring.

Taxonomy
Class:Malacostraca
Order:Decapoda
Family:Palaemonidae
Genus:Macrobrachium
Species:Macrobrachium dayanum

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Water Temperature

20 - 30 °C

pH Value

7 - 8.5

Water type

Freshwater

Invertebrate type

Freshwater shrimp

Adult size

5 cm

Minimum group

>= 1

GH

6 - 18 dGH

KH

3 - 15 dKH

TDS

120 - 420 ppm

Ecological role

Scavenger

Copper sensitivity

High

Species description

Geographical Origin and Habitat: Endemic exclusively to the pristine, intensely cool, high-altitude mountain rivers and fast-flowing rocky streams of the Himalayan foothills across northern India and Nepal. Macrobrachium dayanum (universally known in the hobby as the Himalayan Chocolate Shrimp or Rusty Shrimp) natively colonizes the fiercely turbulent, highly oxygenated shallow rapids. These specific micro-habitats are completely characterized by extreme water currents, massive beds of smooth, water-worn river stones, and a substrate entirely devoid of fine silt or heavy aquatic vegetation.
Taxonomy: Scientifically classified within the Palaemonidae family, it is a spectacular, biologically robust, and highly active "long-arm" shrimp. Morphologically, fully mature adults reach a substantial maximum of roughly 6.0 to 8.0 centimeters (2.5-3.2 inches) in length, making them significantly larger than any standard dwarf shrimp. It possesses a deeply robust, heavily armored, slightly arched body structure. Its absolute defining, evolutionary signature anatomical features are its exceptionally long, heavily built front arms (chelipeds) ending in functional, distinct pincers.
Social Behavior: Unlike communal dwarf shrimp, Macrobrachium dayanum are highly intelligent, boldly active, and intensely territorial benthic invertebrates. They possess a strict hierarchical social structure and can be aggressive toward conspecifics (their own kind) if insufficient space is provided. In the aquarium, they possess a fascinating, highly dominant, and deliberate foraging lifestyle. They spend their day aggressively patrolling the substrate, confidently moving massive pieces of gravel with their strong arms, actively hunting small prey and aggressively defending their chosen rocky cave.
Coloration and Sexual Dimorphism: Sexual dimorphism is absolute and unmistakable when fully mature; mature males are significantly larger, possess vastly longer, massively overgrown, and heavily armored front arms (chelipeds), and possess a narrower abdomen compared to the females. The coloration of the Himalayan Chocolate Shrimp is striking, entirely natural, and designed for rocky camouflage. The entire body is deeply saturated with a highly opaque, glowing reddish-brown, copper, or deep "chocolate" hue. The shell is frequently accented by stark, distinct reddish or rusty-orange horizontal bands.

Care, breeding and tankmates

Tank Setup: The aquarium architecture MUST flawlessly accommodate their large size, aggressive territoriality, and high-current riverine nature. A minimum 80-liter (20-gallon) tank is absolutely mandatory for a small group (1 male, 2-3 females). The absolute most critical requirement is overwhelming rocky hardscape: massive piles of smooth river stones and specifically, numerous distinct PVC pipes or slate caves to provide individual territories and prevent lethal fighting during molting. A powerful powerhead or oversized canister filter is unconditionally mandatory to simulate high-velocity river currents.
Diet and Feeding: Unlike standard dwarf shrimp, Macrobrachium dayanum are highly active, aggressive omnivores and opportunistic macro-predators. In the aquarium, their diet MUST be heavily protein-based. While they will scavenge decaying plant matter, they strictly MUST be fed a high-quality meaty diet to prevent aggression. Daily offerings of sinking carnivorous pellets, frozen bloodworms, live blackworms, chopped earthworms, and specifically, raw shrimp or fish meat are unconditionally mandatory. They possess large claws and will actively hunt and consume any slow or weak tankmates.
Water Quality: Originating from pristine, high-altitude Himalayan rivers, they are incredibly robust but possess specific, uncompromising temperature requirements. They strictly demand highly oxygenated, intensely COOL water (18-24°C / 64-75°F); prolonged exposure to temperatures above 26°C will cause severe stress and drastically shorten their lifespan. They absolutely require moderately hard, heavily mineralized water (GH 8-15) and a neutral to alkaline pH (7.2 - 8.2) to maintain their massive, thick exoskeletons. Rigorous weekly water changes (30-40%) are unconditionally mandatory.
Compatibility and Tankmates: Compatibility is strictly limited by their large size, formidable pincers, and highly aggressive, predatory nature. They are the perfect centerpiece for a dedicated, high-flow river biotope. They MUST NEVER be housed with standard dwarf shrimp (Neocaridina), small peaceful bottom-dwellers (Corydoras), or slow-moving fish (Bettas), as the Macrobrachium will violently hunt, dismember, and consume them at night. They can only be housed with fast-moving, robust, upper-water-column river fish (like large Danios or Hillstream Loaches) that can evade their grasping claws.
Aquarium Breeding: Breeding is highly prolific and surprisingly straightforward in a dedicated, cool-water aquarium. Unlike many large shrimp, they are direct developers; they do NOT have a marine larval stage. Triggered by clean, highly oxygenated water and abundant meaty food, mature females will carry roughly 30-60 large, dark brown eggs under their abdomen for roughly 4-6 weeks. When they hatch, the babies emerge as fully formed, miniature replicas of the adults. The carnivorous babies are aggressively cannibalistic; massive amounts of rock rubble are absolutely mandatory for the babies to hide.
Risks and Diseases: The absolute greatest physical risk is rapid, lethal toxicity; they possess absolute zero tolerance for Copper, heavy metals, or chemical medications (especially fish Ich treatments). The second major risk is lethal conspecific aggression (cannibalism); keeping too many males in a small tank without hundreds of distinct rocky hiding spaces will inevitably result in violent deaths, especially during the vulnerable molting phase. Finally, maintaining them in standard tropical heat (above 26°C) will rapidly induce physiological collapse.

Geographic Origin and Distribution

Endemic exclusively to the pristine, intensely cool, high-altitude mountain rivers and fast-flowing rocky streams of the Himalayan foothills across northern India and Nepal. Macrobrachium dayanum (universally known in the hobby as the Himalayan Chocolate Shrimp or Rusty Shrimp) natively colonizes the fiercely turbulent, highly oxygenated shallow rapids. These specific micro-habitats are completely characterized by extreme water currents, massive beds of smooth, water-worn river stones, and a substrate entirely devoid of fine silt or heavy aquatic vegetation.

Origin

South and Southeast Asia

Invertebrate profile

Diet
Omnivore
The diet of Macrobrachium dayanum must be carefully managed to ensure robust health, vibrant coloration, and long-term survival in captivity. In its natural environment, it has specific foraging habits that should be replicated as closely as possible in the aquarium. Supplementing its diet with high-quality, targeted commercial foods or fresh preparations ensures it receives necessary vitamins and minerals. Care should be taken not to overfeed, as uneaten food will quickly degrade water quality and harm the animal.
Ecological role
Scavenger
Within its native ecosystem, Macrobrachium dayanum plays a vital biological role that contributes to the overall stability of the environment. Whether acting as a scavenger, filter feeder, predator, or prey, it helps to efficiently cycle nutrients through the food web. Its natural behaviors prevent the over-accumulation of organic waste or the unchecked growth of specific prey populations. Introducing this species to a home aquarium often replicates these beneficial ecological functions, promoting a cleaner and more balanced system.
Shock sensitivity
Medium
Aquarists must be aware that Macrobrachium dayanum is exceptionally sensitive to rapid fluctuations in its surrounding water parameters. Sudden shifts in temperature, specific gravity, pH, or dissolved organics can induce severe physiological shock, leading to rapid decline or death. A prolonged and careful drip acclimation process is highly recommended whenever moving this animal between systems. Maintaining pristine and unwavering water conditions is arguably the single most critical factor for its successful husbandry.
Calcium and minerals
Medium
Proper mineral balance is crucial for Macrobrachium dayanum, as it requires consistent access to dissolved calcium and related trace elements for physiological maintenance. Depending on its specific biology, calcium is utilized for building external shells, hardening exoskeletons after molting, or supporting skeletal growth. In enclosed aquarium systems, these essential minerals can be rapidly depleted and may require regular supplementation. Routine water testing is encouraged to ensure that general hardness or specific calcium levels remain within the optimal range.
Molting
Yes
For invertebrate species that undergo ecdysis, Macrobrachium dayanum requires a safe and stress-free environment to successfully shed its old exoskeleton. During and immediately following a molt, the animal's new shell is soft, leaving it extremely vulnerable to physical damage and predation. It is important to provide ample hiding spaces where it can retreat until its body fully hardens. If applicable, the discarded exoskeleton should be left in the tank, as the animal will often consume it to reclaim vital minerals.
Reproduction
Oviparous
The reproductive strategies of Macrobrachium dayanum are varied and often highly adapted to its natural environmental conditions. Breeding efforts in a captive aquarium setting can range from straightforward to exceedingly difficult, often depending on specific larval requirements. Successful rearing of young frequently involves managing microscopic planktonic stages and specialized diets away from the main display tank. Nevertheless, captive propagation remains a rewarding endeavor that helps reduce the reliance on wild-caught specimens.
Compatibility & tankmates
Aggressive
Careful consideration of tank mates is required to ensure the safety and wellbeing of Macrobrachium dayanum in a community setup. It should generally be housed with peaceful species that will not relentlessly harass it, nip at its appendages, or view it as a food source. Conversely, its own predatory or territorial instincts must be evaluated to ensure it does not harm smaller or slower-moving tank inhabitants. Observation during the initial introduction period is vital to confirm a harmonious balance within the aquarium.

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Last updated: 06/30/2026
Chocolate / Red rusty shrimp (Macrobrachium dayanum) Care Guide & Tank Setup | Atlarium