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Summary | |
The Green Tiger Prawn (Penaeus semisulcatus, de Haan 1844) is a crustacean that lives in tropical, sand-muddy habitats. P. semisulcatus have an omnivorous diet feeding on a variety of material including seagrass, algae and invertebrates while cleaning the seafloor from 2-300 metres by eating decaying matter. The iconic brown-green colouration in combination with the brown striation pattern on the exoskeleton of the Green Tiger Prawn has evolved to provide camouflage while the hard exoskeleton protects the crustacean from predators such as other crustaceans, fish and squid. Being the most commercially important ocean prawn for most of South East Asia and the Middle East, the Green Tiger Prawn's main threat is over-fishing by commercial fisherman in these areas. In an attempt to reduce the load on the wild populations, aquaculture farms have been established in these regions.
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Physical Description |
Appearance | |
Penaeus semisulcatus has a hard exoskeleton which it's colour can depend upon diet and the turbidity of the water with the most common colours being a pale brown-green which is banded with dark brown and pale-yellow transverse stripes on the abdomen. The antennae of the Green Tiger Prawn is also banded with reddish-brown and white transverse stripes. These stripes are defining feature of this species of tiger prawns with the bands caused by a genetic change in shell pigments which improve camouflage with the sand-mud substrates. The Green Tiger Prawn also has protection by a smooth carapace and straight rostrum with 5-8 dorsal and 2-4 ventral teeth (Food and Agriculture Organisation of the United Nations (FAO), 2018; Sea Life Base, 2018; Wild Fact Sheet, 2015).
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Size | |
The adult green tiger prawn can grow up to 130 grams with males growing up to 180mm in length while the females can reach up to 228mm (FAO, 2018).
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Ecology | |
Penaeus semisulcatus live on sand-mud substrates from depths of 2-300m. Predominantly nocturnal and buried in the substrate during the day, green tiger prawn’s settle on seagrass beds and with an omnivorous diet, feed upon seagrass, algae, bivalves, gastropods, ophiuroids, polychaetes, other crustaceans as well as decaying matter. Eating the decaying matter is an important ecological process by reducing the decomposition process which can cause damaging damage to the ecosystem. The burrowing and nocturnal behaviour is to reduce the chance of interactions with predators such as other crustaceans, fish and birds (Fortes, 1995; Heales, Vance, & Loneragan, 1996; Wassenberg, & Hill, 1987).
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Life History and Behaviour |
Life Cycle | |
P. semisulcatus spend the majority of its life in the ocean however will spend its post-larvae stage of development in shallow, estuarine systems (Figure 3).
When finding a mate, the Green Tiger Prawn will perform precopulatory courtship routines using olfactory and tactile cues to attract a mate (FAO, 2018). Once a mate is achieved, the male will insert a spermatophore (sperm capsule) through the soft shell of the female into her reproductive system. Inside the female reproductive system, the eggs are fertilised and then released (Department of Primary Industries and Regional Development (WA), 2013). Within the following 24 hours, the eggs will hatch offshore and float to the hypersaline shore in which the post-larvae prawn will continue developing (Department of Primary Industries and Regional Development (WA), 2013; Ronquillo et al., 2006). Once the prawn reaches juvenile stage of development they will sink to the seafloor taking shelter amongst seagrass meadows (FAO, 2018; Ronquillo et al., 2006). 6-8 months post fertilisation, the green tiger prawn will move offshore to spawn as an adult (Department of Primary Industries and Regional Development (WA), 2013; Niamaimandi et al., 2008; Ronquillo et al., 2006).
A female adult prawn can spawn multiple times a year during autumn and the main spawning event in late winter/early spring. Living for 2-3 years, the green tiger prawn can lay hundreds of thousands of eggs in a single event and up to half a million eggs in its lifetime (Department of Primary Industries and Regional Development (WA), 2013). However, most of these eggs will be eaten before reaching maturity by predators such as squid and fish or the adults will be caught for human consumption (Oceana, 2018).
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| Figure 3 |
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Anatomy and Physiology |
External | |
A Green Tiger Prawn is a crustacean which has a exoskeleton (shell) that protects the internal organs. The exoskeleton is made of chitin, calcium carbonate as well as a protein that combine to create the hardness of the shell. The exoskeleton cannot grow with the organisms thus the organism must moult which begins by retracting the chitin out of the shell, making it soft. The soft shell makes the prawn vulnerable however as the shell hardens the prawn grow into the shell until they outgrow the new shell (Roberts, 2018).
The shell is made up of sections that overlap and spread allowing the prawn to move. The exoskeleton is the combination of the head, abdomen and tail. The exoskeleton of the head is made of the rostrum and the carapace (Figure 2). The rostrum is the teethed section of shell that is used to attack organisms out of protection or in a show of dominance over other prawns. The carapace protects the important internal organs including the heart, brain and stomach. The abdomen section includes the abdominal segments which overlap and stretch to allow locomotion through the swift movement of its abdomen. The tail section incorporates the telson which provides protection from the rear and the uropods are used to direct and provide power in the locomotion action of the prawn (Figure 5) (Pink Gold Rush, 2018; Roberts, 2018).
At the head, the antenna and eyes provide sensory input that allows the prawn to identify predators, prey and their surroundings. Located on the underside of the head, the mandible and molar teeth aids in the physical breakdown of food while the maxillipeds direct water flow into the mouth and gills of the prawn which allows feeding and breathing to occur due to the movement of these specialised appendages (Figure 6). Other specialised appendages that allow feeding to occur is the pereopods which allow the prawn to remove and capture prey from the substrate. As the sediment is soft, the pleopods allow the burrowing of the prawn for protection as well as additional locomotion in combination with the uropods (Fathi, 2013).
Overall, the external structures purpose is to provide locomotion, protection of internal organs or direction of water flow into the internal structures.
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Internal | |
The main internal organs of P. semisulcatus are located under the carapace in the head section (Figure 7). These organs make up the nervous, cardiovascular, digestive and reproductive systems.
Nervous System
The nervous system is made up of the brain, compound eyes and antennae. Visual and chemical stimuli are received by the eyes and antennae respectively and is interpreted by the brain which is located under the rostrum. The brain interprets these signals and relays responses to nerves that are located throughout the body and coordinates the physical or chemical response required (Fathi, 2013; Vandana, 2018). During the mating process, the prawn will receive chemical and physical cues which prompt the release of the respective gametes (Department of Primary Industries and Regional Development (WA), 2013).
Reproductive system
The reproductive system is made up of the gonads. In order to mate, the male and female prawn hook together using their pereopods as the male inserts a sac of sperm called a spermatophore into the female and fertilisers her eggs which are released and hatch within 24 hours (Department of Primary Industries and Regional Development (WA), 2013; Fathi, 2013).
Cardiovascular system
Consisting of the heart and gills, the cardiovascular system of a green tiger prawn is a closed system that uses a triangular heart to transport oxygen, waste and chemicals around the organism. Oxygen is absorbed from the water at the gills which uses a counter-current system which ensures maximum oxygen absorption. From the gills, the oxygen is transported around the body via the closed circulatory system (Fathi, 2013; Vandana, 2018). The heart is located in the posterior of the head while the gills are proximal to the mouth.
Digestive system
Including the mouth, stomach, hepatopancreas and hindgut, the digestive is responsible for the breakdown and absorption of nutrients. The mouth consists of the molar teeth, mandible and maxillipeds which provide a funnel effect and physical breakdown of prey which allows the digestive chemicals from the hepatopancreas to effective breakdown the food (Vandana, 2018). Most of the digestion of nutrients occurs in the stomach through the digestive chemicals secreted from the heptopancreas which acts similar to a pancreas and liver in vertebrates (Fathi, 2013). After the stomach, the material moves through the hindgut to the anus near the tail where it is released and removed from the body.
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| Figure 7 |
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Biogeographic Distribution | |
Penaeus semisulcatus favours tropical environments with water temperatures above 27ºC, with sand-mud substrates and seagrass meadows. As seen in Figure 8, Green Tiger Prawns are found on the coastlines of the Eastern Mediterranean, Red Sea, East Africa, India, South East Asia, Korea, Japan and Northern Australia (FAO, 2018; Sea Life Base, 2018).
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| Figure 8 |
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Evolution and Systematics | |
Penaeus semisulcatus is iconic for the banded pattern along its shell and antenna. The banded shell has evolved to provide camouflage in the seagrass meadows and sand-mud substrates. The brown-yellow striations match the sand-mud substrates almost perfectly making it virtually impossible for predators to identify the prawn when buried in the soft sediment (FAO, 2018).
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Conservation and Threats | |
The main threat to P. semisulcatus is human inference through overfishing and habitat destruction. The green tiger prawn is the most abundant and commercially important marine prawn in the Indo-West Pacific region (Ronquillo et al., 2006). Thus, the green tiger prawn is caught in large numbers using a method called bottom trawling which uses a net to scrape the soft sediment and collect the prawns. This method removes the sea grass and destroys the habitat of the prawns (Oceana, 2018). To reduce the impact to the environment as well as pressure on the wild population, aquaculture farms have been established around the world in countries such as Thailand and India (FAO, 2018).
A variety of diseases also plague the green tiger prawns populations including a viral pathogen, white spot virus (Figure 9). This virus is highly contagious and has recently been infecting populations in South East Asia and Australia. White spot virus does not have an effect to human health however can have huge implications to the Prawn Farming Industry (Department of Agriculture and Fisheries (QLD), 2018).
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| Figure 9 |
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References | |
Cindy (2018) Green gooey stuff when removing head from rawshrimp. Seasoned Advice. Retrieved from https://cooking.stackexchange.com/questions/56749/green-gooey-stuff-when-removing-head-from-raw-shrimp
Department of Agriculture and Fisheries (Qld) (2018) Whitespot disease overview. Queensland Government. Retrieved from https://www.daf.qld.gov.au/business-priorities/animal-industries/animal-health-and-diseases/a-z-list/white-spot-disease/overview
Department of Primary Industries and Regional Development(WA) (2018) Prawn. Fisheries. Government of Western Australia. Retrieved from http://www.fish.wa.gov.au/Species/Prawn/Pages/default.aspx
Fathi, S. (2013) Zoology notes – Prawn (Penaeus) –Morphology and anatomy. Biology learnspot. Retrieved from http://biolearnspot.blogspot.com/2013/12/prawn-penaeus-morphology-and-anatomy.html
Food and Agriculture Organisation of the United Nations(FAO) (2018) Penaeus semisulcatus. Species Fact Sheet. Retrieved from http://www.fao.org/fishery/species/3408/en
Fortes, M. D. (1995) Seagrasses of east Asia: Environmental and management perspectives. RCU/EAS Technical Reports Services, 6: 1-79.
Heales, D. S., Vance, D. J. & Loneragan, N. R. (1996) Field observations of moult cycle, feeding behaviour, and diet of small juvenile tiger prawns Penaeus semisulcatus in the Embley River, Australia. Marine Ecology Progress Series, 145:43-51.
Niamaimandi, N., Aziz, A., Khalijah, D. S., Roos, S. C.,& KIabi, B. (2008) Reproductive biology of the green tiger prawn (Penaeus semisulcatus) in coastal water of Bushehr, Persian Gulf. Journal of Marine Science, 65(9): 1593-1599.
Oceana (2018) Tiger Prawns. Cephalopods, Crustaceans and other Shellfish. Retrieved from http://oceana.org/marine-life/cephalopods-crustaceans-other-shellfish/tiger-prawn
Roberts, M. D. (2018) Body Systems. Weebly. Retrieved from https://sciencemardi.weebly.com/prawn-skeletal-system.html
Ronquillo, J. D., Saisho, T., & McKinley, R. S. (2006) Early developmental stages of the green tiger prawn, Peneus semisulcatus deHann (Crustacea, Decapoda, Penaeidae). Hydrobiologia, 560(1). DOI: 10.1007/s10750-005-1448-y
Sea Life Base (2018) Penaeus semisulcatus de Haan,1844. Sea Life Base. Retrieved from http://sealifebase.org/summary/Penaeus-semisulcatus.html
Vandana, S. (2018) Dissection of prawn. Biology discussion. Retrieved from http://www.biologydiscussion.com/zoology/prawn/dissection-of-prawn-zoology/60750
Wassenberg, T. J. & Hill, B. J. (1987) Natural diet of the tiger prawns Penaeus esculentus and P. semisulcatus. Australian Journal of Marine and Freshwater Research 38(1): 169-182.
Wild Fact Sheets (2015) Penaeid prawns. Wild Fact Sheet. Retrieved from http://www.wildsingapore.com/wildfacts/crustacea/othercrust/shrimp/penaeidae.htm
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