Fish & Marine Animals comparison

Krill vs Shrimp: Key Differences Explained

The short answer

Krill are not shrimp. Krill make up the order Euphausiacea, an exclusively marine group whose feathery gills hang outside the carapace and are visible from the side. Shrimp is a body-shape name applied across several decapod groups, and decapods keep their gills enclosed in a chamber beneath the carapace. Most krill graze plankton in open water using a thoracic feeding basket, while shrimp are far more varied: marine, brackish and freshwater, many of them bottom-dwelling scavengers carrying small pincers.

The main difference

Krill wear their gills on the outside of the carapace and filter plankton in open water; shrimp hide their gills in a chamber under the carapace and occupy far more habitats, including fresh water.

Krill are constantly described in documentaries as tiny shrimp, and the two really do share a translucent, segmented, many-legged outline, so readers need one anatomical rule that separates a euphausiid from a decapod without a microscope.

At a glance

Comparison of Krill and Shrimp across 7 dimensions, with an interpretation of each difference.
What differs	Krill	Shrimp	What it means
Order	Euphausiacea, with roughly 85 to 90 described species	Decapoda, spread across caridean and dendrobranchiate lineages	Krill form one compact order, while shrimp is a shape shared by several unrelated decapod branches.
Gills	Exposed and feathery, hanging visibly below the edge of the carapace	Enclosed in a branchial chamber beneath the carapace, hidden from view	This is the classic diagnostic feature and works on a preserved specimen or a clear photograph.
Water type	Marine only, in every ocean including polar seas	Marine, brackish and fresh water, from tropical streams to deep-sea vents	A shrimp-shaped crustacean in a river or aquarium is never a krill.
Feeding method	Mostly filter feeding on phytoplankton and small zooplankton using a thoracic feeding basket	Mostly grazing, scavenging and small-prey capture, often using pincered legs	Krill sit near the base of the food web; shrimp occupy many roles further along it.Some krill species also take zooplankton actively, and a few shrimp filter feed, so neither habit is absolute.
Claws	No enlarged pincers; the thoracic legs form a feeding basket instead	Many species carry small chelae on the first two or three leg pairs	Visible pincers on the front legs point away from krill.
Light organs	Photophores on the eyestalks and body in most species, producing blue-green light	Bioluminescence limited to certain deep-sea species rather than typical of the group	Widespread photophores are a euphausiid signature, likely involved in schooling and counter-illumination.
Aggregation	Dense open-water swarms that can extend for large distances and sustain whales and seabirds	Aggregations occur, but many species are solitary or loosely associated with the seabed	Swarming biomass is why krill dominate polar food webs in a way shrimp do not.

Order: KrillEuphausiacea, with roughly 85 to 90 described species
ShrimpDecapoda, spread across caridean and dendrobranchiate lineages
Krill form one compact order, while shrimp is a shape shared by several unrelated decapod branches.
Gills: KrillExposed and feathery, hanging visibly below the edge of the carapace
ShrimpEnclosed in a branchial chamber beneath the carapace, hidden from view
This is the classic diagnostic feature and works on a preserved specimen or a clear photograph.
Water type: KrillMarine only, in every ocean including polar seas
ShrimpMarine, brackish and fresh water, from tropical streams to deep-sea vents
A shrimp-shaped crustacean in a river or aquarium is never a krill.
Feeding method: KrillMostly filter feeding on phytoplankton and small zooplankton using a thoracic feeding basket
ShrimpMostly grazing, scavenging and small-prey capture, often using pincered legs
Krill sit near the base of the food web; shrimp occupy many roles further along it.Some krill species also take zooplankton actively, and a few shrimp filter feed, so neither habit is absolute.
Claws: KrillNo enlarged pincers; the thoracic legs form a feeding basket instead
ShrimpMany species carry small chelae on the first two or three leg pairs
Visible pincers on the front legs point away from krill.
Light organs: KrillPhotophores on the eyestalks and body in most species, producing blue-green light
ShrimpBioluminescence limited to certain deep-sea species rather than typical of the group
Widespread photophores are a euphausiid signature, likely involved in schooling and counter-illumination.
Aggregation: KrillDense open-water swarms that can extend for large distances and sustain whales and seabirds
ShrimpAggregations occur, but many species are solitary or loosely associated with the seabed
Swarming biomass is why krill dominate polar food webs in a way shrimp do not.

How they are related

Krill are the order Euphausiacea within the class Malacostraca, a compact group of roughly 85 to 90 described species. Shrimp is not a rank at all: it is a common name applied to slender, laterally compressed decapods drawn from the infraorder Caridea and the suborder Dendrobranchiata, which includes the prawns of commerce. Krill and shrimp are therefore relatives at the level of Malacostraca, but krill sit outside Decapoda entirely and are not a kind of shrimp.

A note on naming: Shrimp is a common name rather than a taxonomic rank, covering caridean and dendrobranchiate decapods that are not each other's closest relatives, and the words shrimp and prawn are applied inconsistently between regions and industries.

Telling them apart

The gills decide it. In a krill the gills are uncovered, projecting below the lower margin of the carapace as visible feathery tufts, and in a decapod shrimp they are sealed inside a branchial chamber. Beyond that, krill have large stalked eyes, a slender translucent body usually well under six centimetres, no enlarged pincers, and rows of small light organs. Many shrimp show pincers on the front legs and a more strongly flexed abdomen.

Open ocean, swarming, gills visible on the outside, no pincers, small light organs along the body: krill. Fresh water, a reef crevice, a market tray or a home aquarium, with gills tucked under the carapace and small claws on the front legs: shrimp. If the animal is described as a keystone food source for whales and penguins, the subject is almost certainly krill rather than any decapod.

Habitat and distribution

Krill are exclusively marine and mostly pelagic, occurring in every ocean, with Antarctic krill forming the enormous Southern Ocean swarms that support baleen whales, penguins, seals and seabirds. Shrimp occupy a far wider set of habitats: coral reefs, mangroves, estuaries, sandy shelves, mountain streams, caves and hydrothermal vents. Some shrimp species tolerate wide salinity swings, and freshwater shrimp are a substantial part of tropical stream faunas, which no krill ever is.

Diet and ecological role

Most krill graze phytoplankton, straining cells from the water with a basket formed by the thoracic legs, and many also take copepods and other small zooplankton. Antarctic krill additionally scrape algae from the underside of sea ice. Shrimp diets skew towards omnivory and scavenging, with species taking detritus, algae, worms, small crustaceans and carrion, and specialist relationships exist too, including cleaner shrimp that pick parasites from reef fish.

Behaviour

Krill swarm, sometimes in densities of thousands of animals per cubic metre, and many species undertake daily vertical migrations, rising towards the surface at night and descending by day. Krill also moult readily and can shrink between moults when food is scarce, an unusual response to starvation. Shrimp behaviour is more varied: burrowing, sheltering in crevices, forming pair bonds inside sponges, and in the case of snapping shrimp, living in eusocial colonies within a single host.

Senses and adaptations

Krill photophores emit blue-green light and can be rotated, which has been linked to counter-illumination against downwelling light and possibly to keeping swarms together in darkness. Their compound eyes are unusually large for the body size, matching a life spent in dim, deep water. Many shrimp instead invest in chemoreception through elaborate antennae, and snapping shrimp generate a cavitation bubble with a specialised claw whose collapse produces a loud acoustic pulse.

More on this topic: Animal senses and adaptations.

Lifespan and life stages

Antarctic krill are long-lived for such small animals, with published estimates commonly in the range of five to seven years and some individuals thought to live longer, while many warmer-water euphausiids complete their lives in one to two years. Shrimp lifespans vary far more with species and temperature, from under a year in many small tropical forms to several years in larger cold-water species. Captive and wild figures should not be pooled.

People and these animals

Shrimp support some of the largest fisheries and aquaculture industries in the world, and shrimp farming has been closely linked with mangrove clearance in several regions. Krill are harvested mainly for aquaculture feed and for krill oil supplements, with the Southern Ocean fishery managed under an international convention because so many predators depend on the same biomass. Both fisheries raise ongoing questions about bycatch, ecosystem effects and management limits.

Keeping them: what to understand first

Freshwater ornamental shrimp are widely kept in home aquaria, and krill are not kept at all outside research facilities, appearing instead as frozen aquarium food. Whether ornamental shrimp suit a particular household depends on stable water chemistry, tank maturity, local rules on species imports and a willingness to maintain conditions for the animals' whole lives. Health problems in an aquarium should be discussed with an aquatic veterinarian or an experienced fishkeeping professional.

What they have in common

Both are malacostracan crustaceans with segmented bodies, jointed legs and a moulted exoskeleton.
Both have stalked compound eyes and long sensory antennae.
Both swim using pleopods on the abdomen and can flick the tail to escape backwards.
Both are harvested commercially and both matter as food for fish, seabirds and marine mammals.

Key differences

Krill gills hang exposed outside the carapace; shrimp gills sit enclosed beneath it.
Krill are entirely marine, while shrimp also occupy brackish and fresh water.
Most krill filter feed with a thoracic basket, whereas most shrimp graze or scavenge.
Krill lack the enlarged pincers found on the front legs of many shrimp.
Photophores are widespread in krill but restricted to some deep-sea shrimp.

Where people go wrong

Describing krill as tiny shrimp when they sit outside the decapods altogether.
Calling freshwater amphipods or mysids krill because they look similar and are small.
Assuming market prawns and shrimp are the same taxonomic thing rather than overlapping trade names.
Expecting krill to have visible pincers like many shrimp do.

Frequently asked questions

Is krill just a small shrimp?

No. Krill belong to the order Euphausiacea and shrimp to the order Decapoda, so a krill is not a miniature version of a shrimp but a member of a different order that happens to share a slender crustacean outline. The clearest anatomical break is the gills: exposed and visible outside the carapace in krill, enclosed within a chamber in decapod shrimp.

Why are krill so important in the Southern Ocean?

Antarctic krill convert phytoplankton and ice algae into dense, predictable biomass that larger animals can harvest efficiently. Baleen whales, crabeater seals, penguins, flying seabirds and many fish feed heavily on the same swarms, so a large share of the regional food web funnels through one group. That concentration is also why the krill fishery is managed under an international convention with precautionary catch limits.

Can you find krill in fresh water?

No. Every described euphausiid is marine, which makes water type a useful shortcut. Shrimp-shaped crustaceans in rivers, lakes and home aquaria belong to freshwater decapod groups, and the small pale crustaceans people sometimes call freshwater krill are usually amphipods or mysids, both separate from Euphausiacea. If it lives in fresh water, it is not krill.

Do krill really shrink when food runs out?

Antarctic krill have been observed to moult into a smaller body size when food is scarce, most notably through the long polar winter, then grow again when phytoplankton returns. This makes size an unreliable proxy for age in the species and complicates population assessment. It is an unusual response among crustaceans and is one reason krill demography is harder to model than that of many shrimp.

What lights up on a krill?

Krill carry photophores, small light organs positioned on the eyestalks and along the underside of the body, which emit a blue-green glow. Some can be rotated, and researchers have linked them to counter-illumination that reduces an animal's silhouette from below, and possibly to keeping swarms coordinated in darkness. Bioluminescence exists in some deep-sea shrimp too, but it is not a general shrimp trait.

Read the full profiles

Sources and methodology

How this comparison is built: FaunaHub comparisons are assembled from the sourced animal profiles behind them rather than written as standalone claims. Figures such as size, mass, and lifespan are typical ranges that vary by subspecies, population, region, sex, age, and — where relevant — whether an animal lives in the wild or under human care, so they are presented as ranges rather than fixed values. Where a common name covers a group rather than a single species, the page says so instead of implying a species-to-species match. Conservation status changes over time and should be confirmed against the current IUCN Red List. Dimensions that could not be supported from the underlying profiles are omitted rather than filled in.

What this page does not do: it does not rank the two animals, predict the outcome of a confrontation, or present either one as stronger, smarter, or better. It is not veterinary, medical, first-aid, handling, capture, hunting, or pest-control guidance. For an animal in your care, or any situation involving injury, contact a qualified veterinarian, your local wildlife authority, or emergency services.

Sources and further reading

Authoritative references used for general educational context. External links open in a new tab. These sources do not endorse FaunaHub.

ReferenceWoRMS — World Register of Marine Species — Authoritative register of marine species names
GovernmentNOAA Fisheries — Marine Life — U.S. government science agency for marine species and habitats
Wildlife referenceIUCN Red List of Threatened Species — Authoritative source for current conservation status
UniversityAnimal Diversity Web — University of Michigan Museum of Zoology — Peer-edited reference accounts for animal species
ReferenceSmithsonian Ocean — National Museum of Natural History — Smithsonian Institution educational ocean-science resource

Last updated: 2026-08-04