The perception of a shrimp is often that of a small, curled crustacean, but the diversity within this group of aquatic animals is vast. There are over 2,000 known species, inhabiting every corner of the world’s oceans and freshwater systems. This extensive array of life includes species that stand out as the largest of their kind, challenging the common understanding of their size. Our focus is to identify the true record holder for size among this fascinating group.
Setting the Biological Boundaries
Determining the largest specimen requires first establishing a clear definition of what constitutes a “true shrimp.” Scientifically, true shrimp are classified into the infraorder Caridea based on physical structure, not size. This distinction is necessary because many large crustaceans called “prawns” or “shrimp” in the seafood industry belong to a separate suborder, Dendrobranchiata. The primary difference between the groups lies in their anatomy, particularly their gills and the way they carry their young.
True shrimp (Caridea) possess plate-like gills and exhibit a distinct body curvature where the second abdominal segment overlaps the segments both in front and behind it. Females in this group also brood their fertilized eggs, attaching them to their swimmerets until they hatch. Conversely, the Dendrobranchiata group has branching gills and releases their eggs directly into the water column.
Identifying the Largest Species
The title of the world’s largest true shrimp belongs to the Giant Freshwater Prawn, Macrobrachium rosenbergii. Although its common name includes “prawn,” its classification within the Caridea infraorder confirms it as the record holder. This species is capable of reaching impressive dimensions that dwarf most other shrimp.
Males of this giant species are typically much larger than the females. They have been recorded reaching a maximum total length of up to 33 centimeters (about 13 inches) and weighing over 500 grams (1.1 pounds). Much of this size is attributed to the male’s disproportionately long second pair of walking legs, which can sometimes exceed the length of the body itself.
The Giant Freshwater Prawn is the largest species in its genus, Macrobrachium. Its immense size is a result of years of growth, as the largest specimens are often the oldest individuals in the population.
Habitat and Unique Characteristics
Macrobrachium rosenbergii is native to the tropical and subtropical zones of the Indo-Pacific region, ranging from India through Southeast Asia and into Northern Australia. It is an amphidromous species, meaning it regularly migrates between freshwater and saltwater habitats during its life cycle. Adults live primarily in freshwater, but their larval stage requires brackish water to develop successfully.
The species exhibits a nocturnal, bottom-dwelling lifestyle, preferring muddy or sandy substrates. They are omnivorous, consuming a wide variety of food sources, including insects, aquatic worms, mollusks, algae, and plant detritus. This adaptability contributes to their robust size and successful cultivation in aquaculture worldwide.
A striking feature is the male’s second pair of walking legs (pereiopods), which are extremely long and armed with prominent, spiny claws. These “great claws” are used in territorial defense and aggressive encounters with other males, establishing a dominance hierarchy. The blue or orange color of these long appendages makes the largest males visually distinctive.