Shrimp are a highly diverse group of crustaceans inhabiting nearly every aquatic environment, from freshwater streams to the deepest parts of the ocean. Their feeding habits are equally varied, making the simple question of whether they eat fish surprisingly complex. While many assume these small creatures are strictly peaceful scavengers, the reality involves a spectrum of behaviors ranging from generalized grazing to highly specialized hunting. Understanding this topic requires distinguishing between the typical diets of common species, the true predatory exceptions, and opportunistic scavenging.
Primary Diets of Common Shrimp Species
The vast majority of shrimp species, particularly those encountered in the aquarium trade, are not active hunters of live, healthy fish. Common varieties, such as Amano shrimp (Caridina multidentata) and Cherry shrimp (Neocaridina davidi), function primarily as detritivores and herbivores. Their daily lives involve continuous grazing on surfaces, consuming microscopic organisms and decaying material.
A primary component of their diet is biofilm, a complex layer of microorganisms and organic matter that coats submerged surfaces, along with various forms of algae. By constantly scraping and sifting, they fulfill a crucial role as nature’s clean-up crew. For example, the Amano shrimp is prized for its appetite for nuisance algae in planted tanks.
Another popular species, the Ghost shrimp (often Palaemonetes species), displays a slightly more omnivorous tendency, consuming detritus, plant matter, and small particulates filtered from the water. While these peaceful species do not typically attack adult fish, they will consume fish eggs or newly hatched fry if encountered. The baseline for most shrimp is grazing and scavenging, not direct predation.
True Predation: When Shrimp Hunt Live Fish
A few specialized shrimp species have evolved into formidable predators that actively hunt and kill live fish, demonstrating a clear exception to the general rule. The most notorious hunters are the Mantis shrimp (Stomatopoda) and certain larger Pistol shrimp (Alpheidae). These creatures possess unique, powerful appendages that function as sophisticated weapons, allowing them to subdue prey larger than themselves.
Mantis shrimp are categorized into two hunting groups: the “spearers” and the “smashers.” Spearer species utilize sharp, barbed forelimbs to impale soft-bodied prey like fish after waiting in ambush. Smasher species, such as the Peacock Mantis shrimp, use a club-like appendage to deliver a blow with an acceleration speed comparable to a .22 caliber bullet.
This strike is so rapid that it causes a phenomenon called cavitation, where the water pressure drops low enough that vapor bubbles spontaneously form. When these bubbles collapse, they create a secondary shockwave that stuns or kills the prey. Similarly, the Pistol shrimp uses its oversized claw to rapidly snap shut, forcing out a jet of water that creates a high-speed cavitation bubble.
The collapse of this bubble produces a loud, snapping sound that can reach over 200 decibels, along with a brief flash of light and temperatures approaching that of the sun’s surface. This intense shockwave is enough to stun or kill small fish and invertebrates, allowing the Pistol shrimp to feed on its catch. These aggressive hunters are the only shrimp definitively described as true predators of live fish.
Opportunistic Scavenging of Fish Remains
The distinction between active predation and opportunistic scavenging is important when considering the feeding habits of most shrimp. While common Amano or Cherry shrimp will not pursue and kill a healthy fish, nearly all shrimp are opportunistic feeders that consume fish protein if readily available. This behavior is a natural extension of their role as detritivores, helping recycle organic matter in the environment.
If a fish dies from illness, injury, or old age, any shrimp nearby will quickly consume the carcass. Observing this in an aquarium can mistakenly lead an owner to believe the shrimp killed the fish, when in reality, they are simply cleaning up the remains. This scavenging instinct ensures they utilize any available nutrient source.
Therefore, shrimp will eat fish, but typically only if the fish is already deceased, severely injured, or incapable of escape. This cleanup function is beneficial for the ecosystem, preventing the buildup of decaying matter. The vast majority of shrimp are peaceful grazers whose diet only includes fish when it is a convenient meal.