Introduction to Shrimp Fish

Crustaceans are seen to form a large and diverse taxon of arthropods. Crustaceans include animals like crabs, lobsters, shrimp fish, prawns, crayfish, woodlice and barnacles. A shrimp is a decapod crustacean. It has an elongated body. The primary mode of locomotion of shrimps is swimming. Shrimps are closely related to other crustacean animals like crabs, crayfish and lobsters. Caridea is the shrimp scientific name. Shrimps have covering stalk-eyes. They are swimming crustaceans. Due to similar characteristics, they are often compared with prawns. Shrimps have whiskers that act as antennae. The antennae of shrimps are long and whiplike. They have long narrow muscular tails which act as their abdomen. The legs of the shrimps are extremely slender. Shrimps are abundantly found in nature. Thousands of species of shrimps can be found in nature. They are adapted to a variety of habitats and regions. Shrimp in the ocean is very common. 


Definition of Shrimp

To explain what is shrimp, we can say that it is a small crustacean that swims freely. It has an elongated body. The appendages of shrimps are highly modified for them to swim. A shrimp is generally marine. A decapod crustacean like a shrimp fish has a body that can be divided into 20 body segments. These body segments can be divided into two groups which are the cephalothorax and the pleon which represent the abdomen. A shrimp animal body may possess one pair of appendages. These appendages may be missing in various groups or may be reduced. A shrimp animal has a flattened body that extends from side to side. The shrimp fish has a flexible abdomen that terminates with a fan-like tail. A shrimp can swim forward by the mode of paddling with the help of swimmerets that are present on the upper side of the abdomen. Small shrimp are found in both shallow and deep water. They are also found in freshwater, lakes and streams.


Characteristics of Shrimp

The head and thorax of the shrimp are fused to form the cephalothorax and a narrow abdomen. There is a shell present that protects the cephalothorax. The shell is hard and thick in nature. This hell is harder than any other shell present on the body of shrimp. This is called the carapace. The carapace of the shrimps are found to surround the gills. Water is pumped through the gills by the action of the mouthparts. The carapace gives rise to the rostrum, eyes and whiskers. The word rostrum comes from the Latin word  “rostrum” which means beak. The rostrum of the head of a shrimp looks like a beak. It is pointed and is present at the front of the shrimp's head. The shrimp uses the rostrum to attack for attack or defense. It is an extension that is rigid and placed forward of the carapace. It is also used by the shrimps to stabilise themselves and maintain balance while swimming.


Shrimps are found to have two eyes which are bulbous in nature. They sit on either side of the rostrum. These eyes provide panoramic vision. These eyes are compound by nature. The vision provided by these eyes are extremely helpful to detect movement. The head of the shrimps provides them with whiskers. Shrimps usually have two pairs of whiskers. One of the extremely interesting shrimp facts is that one of these pairs of whiskers can be twice the length of the entire body length of the shrimps. The other pair is kept short. Shrimps have sensors in their antennae. These sensors help them to feel the places they touch. These sensors on the antennae also help them to smell and taste things. The long antennae help the shrimps in orientation according to the environment. The shorter antennae help the shrimp to assess the prey.


In shrimps, eight pairs of appendages are found. These appendages arise from the cephalothorax. The appendages are further divided. The first three pairs of appendages are called the maxillipeds which is a Latin word for ”jaw feet”. These are in mouthparts. After the maxillipeds, five more pairs of appendages arise which are called pereiopods. Pereiopods form the ten decapod legs of the shrimps. In Crangon crangon, the first two pairs of the pereiopods are found to possess claws or chela. This chela is used for grasping food items by the shrimps and shrimps use this chela to bring the food to the mouth. Pereiopods can also be used for fighting and grooming. The remaining four legs of the shrimps are used for walking and perching by shrimps.


The muscular abdomen of shrimps has six segments. It has a thinner shell than the carapace of the shrimps. Each segment of the abdomen has a separate overlapping shell. This overlapping shell is transparent. The first five segments possess a pair of appendages on the underside. These appendages are shaped like paddles. They are used for swimming forward by the shrimps. These appendages are called pleopods or swimmerets. Swimmerets can also be used for other purposes. 


Shrimps can swim with their swimmerets and their escape response is quite different. Their escape response involves repeated flicks of their tails that tend to drive them backwards. Swimmerets are also used by some shrimps for brooding eggs. Other shrimp species have gills on the swimmerets and they can be used for breathing. The first two pairs are also used by males for insemination. The sixth segment usually terminates in the telson that arises from the two pairs of appendages. These are called uropods.


Shrimps have fragile legs, unlike other crabs and lobsters that are primarily used by them for perching. Shrimps have a wide diversity. This can be ascertained as they are found on most coats, near the seafloor. They are found near the estuaries. A shrimp animal can also be found in rivers and lakes. To avoid predators shrimps behave in an interesting way.  The species of the shrimps are found to flip off the seafloor to escape the predators and they dive into the sediment. The life span of shrimps are usually from one to seven years. The shrimp representative species of the crustaceans tend to live their life in solitary. During the spawning season, they form like groups.


Classification of Shrimps

There are different types of shrimp. Shrimps are crustaceans which are able to swim. Long narrow muscular abdomens and long antennae assist them in swimming. Well developed pleopods(swimmerets) and slender walking legs are present in shrimps, unlike lobsters and crabs. Shrimp are adapted more for swimming instead of walking. The primary taxonomic division into suborders Reptantia and Natantia was formed due to the distinction between walking and swimming. Members of Reptantia such as lobsters and crabs were adapted more for walking and crawling whereas those of Natantia (shrimp in a wider sense) were adapted for swimming. Other groups too have shrimp in their names. Small swimming crustaceans similar to a shrimp are called one.


Habitat

Shrimps occur in abundance. They are found in the seafloor of the majority of coastal areas, estuaries, lakes and rivers. Numerous species exist and also there is a species adapted to a particular habitat. Though very few are found in freshwaters, most shrimps are usually marine. The species which are marine appear upto the depth of 5000 metres(16,000 ft). Almost all shrimps are entirely fully aquatic, there is an exception to the two species of Merguia. They are semi-terrestrial and spend a major portion of their lives in mangroves.


Behaviour

There are a variety of shrimps that differ particularly because of their look and how they behave. The pistol shrimp caridean family are identified by their large asymmetrical claws. The larger claws produce a snapping loud sound. The family of pistol shrimp consists of 600 species distributed worldwide. Snapping shrimp colonies are the main cause of noise inside the ocean and also interferes with underwater communication and SONAR. 


The emperor shrimp, smaller in size, shares a symbiotic relationship with the sea cucumbers and the sea slugs and also keeps a check on ectoparasites. Mostly omnivores, but there are some which are specialised for particular feeding modes. There are some filter feeders which use their setose legs as a sieve and also some scrap algae from rocks. Parasites are ingested by Cleaner shrimps. They also feed on the necrotic tissue of the reef fish . They are sometimes also known to cannibalize others as well if sources of food are not available. Shrimps are in turn consumed by various animals particularly seabirds and fish. 


Conclusion

Shrimps are extremely important in the ecosystem of the earth. They are also an important food source for the larger animals They provide food to larger fish like whales. They are also consumed by human beings.


Excess bycatching of shrimps and water pollution have been affecting the pollution of shrimps. A lot of damage has been done to estuaries of shrimps by these ways. Every year the commercial shrimp species support almost 50 billion dollars. In the year of 2010, the total commercial production of shrimp was almost 7 million tonnes.


Did You Know?

  1. The ancient raised paved areas near the costa in Chapas of Mexico were used as platforms to dry shrimp in the sun. According to archaeologists, when there was no sun, the adjacent clay hearth were used to dry the shrimps. However the evidence is extremely circumstantial since the chitinous shells of shrimps are so thin that they degrade rapidly leaving no fossils behind.

  2. In the year of 1920, diesel engines were used to operate shrimp boats.Now only small crews were needed to rapidly lift heavy nets and empty them.As a result new fishing grounds could be explored and trawls could be deployed in deeper offshore waters.

FAQs (Frequently Asked Questions)

1. Write a Short Note on the Mating of Shrimp.

Ans. The mating behaviour of shrimps can be divided into 4 different phases-

  1. approach

  2.  crawling

  3. chasing

  4. mating.

The male mating and the transfer of spermatophore to the mature female takes place at the intermolt stage C4. It has been observed that the glutinous spermatophore of the males is transferred onto the open thelycum of female. It takes place in the ventralto-ventral position in mating. Females are capable of storing sperm from multiple shrimp male partners. Females thus can produce progeny from different paternities. The reproductive success of shrimps is found to be inversely related to their genetic relatedness with the female shrimps who act like their mother.

2. Which Shrimps are Used as Commercial Species?

Ans. There are several species of shrimps present in the world. However, only 20 shrimps are commercially significant for human beings. Following are the most extensively used 7 species of shrimps:

  1. Whiteled shrimp-This is the most extensively farmed species of the shrimp.

  2. Giant tiger prawn

  3. Akiami paste shrimp-This an intensively fished species of shrimp. This is a small shrimp. This group of shrimps have smalls and black eyes and red spots on the uropods.

  4. Southern rough shrimp

  5. Fleshy prawn

  6. Banana prawn- They are typically trawled in the wild and frozen places.

  7. Northern prawn- It has been fished since the early 1900s.

3. State the Differences Between Prawn and Shrimp.

Ans. Shrimps have lamellar gills and claws on two pairs of their legs. Prawns on the other hand have branching gills and claws on three pairs of their legs. Prawns lack any distinct bent in their bodies. This bend is seen in the bodies of shrimps. In prawns, each of the body segments is seen to overlap the one behind in succession whereas in shrimps the second segment overlaps with the first and the third segments. The sizes of the shrimps are much smaller than the prawns. In terms of farming and aquaculture shrimps are marine creatures whereas prawns tend to live in freshwaters.