Tiger pistol shrimp

The tiger pistol shrimp (Alpheus bellulus) belongs to the Alpheidae family, known commonly as snapping shrimp.

The Alpheidae family is incredibly diverse with over 500 unique species across the world. Alpheus bellulus shares a translocation and inversion event of trnE in its mitogenome with several other Alpheus species but there is not enough evidence to say this is a shared commonality among the entire genus. Phylogeny suggests Alpheus randalli and Alpheus bellulus belong to the same taxon within a monophyletic group. Amino acid composition of the cytochrome b protein in A. bellulus was also similar to those of A.randali and A. lobidens, two other species of snapping shrimp.

Description
The tiger pistol shrimp can grow to a size up to 4 to 5 cm, not including antennae. The body is stout and opaque. The background color of the body is yellowish white or plain yellow. The patterns drawn on the cephalothorax, abdomen and tail are irregular but symmetric, their coloration varies from light brown, brownish purple to brownish orange. The legs are banded with the same colors as the body and are covered with short bristles. The antennae are red. The chelipeds are also banded, with the right being bigger and modified into a powerful weapon. By closing at extreme speed, the cheliped expels an air bubble at more than 100 km/h towards the prey. This action is accompanied with a loud bang.

Alpheus bellulus uses their oversized claws to produce powerful bubbles of air that stun its prey. Pressure builds up when the claw opens, and water enters a small chamber in the claw’s bend. The claw quickly clamps down and a small plunger pushes water out with high pressure, releasing a high-speed bubble. This powerful sonic weapon creates a violent shock wave which can kill or knock out prey, which could be another shrimp or a small fish passing close to the tiger pistol shrimp. The sound emitted from the collapsing bubble can be up to 218 decibels, with a temperature of up to 4,800 degrees celsius, slightly cooler than the surface of the Sun.

Distribution
The tiger pistol shrimp can be found in tropical waters of the Indo-West Pacific area.

Habitat
The tiger pistol shrimp dwells in sandy, muddy and detrital substratum in shallow waters until 20m.

The structure of the burrows made by A. bellulus, studied through resin casting, show the three-dimensional shape, and provide insight on the construction habits of the species.

A.bellulus rely on burrows for shelter and protection. In the beginning stage of construction, there is rapid growth in size and dimensions of the burrow. During this phase, A. bellulus shows no interest in feeding or resting, placing total priority in burrow formation. This characteristic is similar throughout many alpheid shrimp species. A. bellulus is highly vulnerable to predation without a burrow, especially during the initial stages of burrow development, due to their limited vision and dependence on tactile cues from partner gobiid fish.

Burrows are reinforced with small pieces of shell and coral along the sides, preventing collapse. Sediment is constantly removed by A. bellulus to keep the internal burrow clean of settled deposits. Burrow production is also crucial to sediment cycling throughout the marine ecosystem, combining nutrients and debris along the seafloor.

Feeding
The tiger pistol shrimp is a carnivore, preying primarily on small invertebrates. It may also eat detritus and macroalgae, and will scavenge carcasses near its burrow. If it has formed a symbiotic relationship with a goby, the goby may bring it food. In aquaria, it is sometimes blamed for the death of fish, but it is very unlikely that it possesses the strength or willingness to attack fish for food. It can be fed many common foods given to aquarium shrimps, such as flakes, pellets, and most frozen foods, and will generally take prepared foods with no training required.

Behaviour
The tiger pistol shrimp lives in burrows in symbiosis with certain goby species such as Cryptocentrus cinctus, Amblyeleotris guttata or Stonogobiops yasha. The shrimp digs and maintains the burrows which are the dens for both animals, while the goby acts as a watchman, warning of danger the shrimp cannot see due to poor eyesight. Proven from a study, in an environment where goby fish and the tiger pistol shrimp are kept together, specifically in a tank, if there is no food source for the shrimp, the shrimp maintains its diet by consuming the feces of the goby fish from its burrow to survive. Hence, another example of their partnership.

The symbiotic relationship between snapping shrimp Alpheus bellulus, typically found off the coast of Japan, and the gobiid fish Amblyeleotris japonica begin from early stages of development, leading to the common existence of adult pairs. A. bellulus is not found in areas where this partner fish is absent and refrains from exiting the burrow while the partner fish is not near the entrance. A. bellulus stays in contact with the partner gobiid fish through its antennae and retreats into its burrow after noticeable movement from the fish. The gobiid fish, in return, use the burrows as a sheltering and nesting site. Given that both species are consistently found in tandem, neither species existing in high numbers without the other, it strongly suggests that their relationship is indispensable for the survival of both species.

Some burrows of A. bellulus were also found to be shared by a specific species of porcelain crab Enosteoides lobatus. In these observed burrows, E. lobatus stayed near the burrows entrance and followed warning signs from the gobiid fish, similar to the behavior of ''A. bellulus. E. lobatus'' are filter feeders, benefiting from abundant food sources outside the burrows due to higher rates of detritus flow through water movement. However, seeking refuge within the burrows offers them greater protection from predators.

In aquaria
The tiger pistol shrimp is one of the most popular pistol shrimp in the marine aquarium hobby as it has a peaceful temperament, is inexpensive and does not require complicated care.

Original publication
Miya, Y. & S. Miyake, 1969. Description of Alpheus bellulus sp. nov. associated with gobies from Japan (Crustacea, Decapoda, Alpheidae).— Publications from the Seto Marine Biological Laboratory 16: 307–314.