Drawings: Kasia Jackowska
Habitat and development
Like other farmed shrimp species, the Pacific whiteleg shrimp belongs to the Penaeides family within the order of Decapoda. Its origins are in the Eastern Pacific between Mexico and the North of Peru, but mainly in Central American waters. As a tropical species it appreciates year-round water temperatures of about 25 °C, not bearing below 12 or beyond 34 °C. It lives in seawater but adapts to brackish water as well.
Adults live and spawn in the open sea. The post-larvae migrate to the shore where they develop in lagoons, estuaries and mangrove belts.
An adult Whiteleg shrimp is the result of a complex development in three larval stages with numerous sub-stages and moults. First, a nauplius hatches from the egg feeding entirely from its yolk sac. After one and a half days, having reached a length of hardly half a millimetre, it turns into a protozoea and begins to search for food. After reaching 2 millimetres, it enters the mysis stage, the late larval stage of Penaeides in which they begin to resemble the adult animal.
By the age of about two weeks (ca 0.1 g and ca 16 mm) the animal develops into a post-larvae, beginning to form its sexual organs. At 9 to 10 weeks (ca 2 g and ca 72 mm) it differentiates its gonads by sex.
Reproduction and way of life
Males start reaching maturity at a weight of 20 g, while females who usually grow faster and bigger reach this stage from 28 g on and by the age of 6-7 months. The male chases the receptive female, palpates her genitals from behind by means of the antennae, finally transferring the sperm to her. About 12 hours later the fertilised eggs are released into the water column.
Whiteleg shrimps are omnivorous. In the stomach of juveniles considerable amounts of mud and detritus are to be found, suggesting they graze on the seabed. With increasing body size, the proportion of small aquatic animals in their diet increases. At the beginning and end of a moulting cycle they suspend ingestion partially or completely.
Shrimps groom themselves extensively in order to rid their body of debris.
The antennae are supposedly the most important sensory organ for shrimps by which they distinguish their environment, conspecifics and the opposite sex and by which they apparently communicate. To what extent this applies to L. vannamei is still to be determined.
Probably the second most important sensory organ are the two stalked eyes whose structure fully develops already at the larval stage (from ca 10 mm body length on). Light is important for the development of the juveniles, even more important than darkness. There is however evidence for nocturnal activity of Whiteleg shrimps that search for darkness during the day in order to rest.
Whiteleg shrimps dive down to depth of 20 m, and juveniles can swim at a speed of five times their body length in a second. In nature they live far away from each other, requiring at a minimum 3 square metres each except in the spring when up to 5 juveniles per square metre can be found in lagoons.
Some shrimp species form groups or live in pairs. To what extent this applies also to L. vannamei is still to be determined.
The development of the farming
The first successful propagation of L. vannamei in captivity was in 1973 in Florida with nauplii gained from a wild-caught female from Panama. In 1976, in Panama, eyestalk ablation was identified as a method for boosting oogenesis. That is how intensive farming of this species developed, spreading in the early 80s to Hawaii, mainland USA as well as to big parts of Central and South America where it increased rapidly. This growth was interrupted, however, by outbreaks of diseases affecting big stocks. Nevertheless Latin America alone produced already 270,000 tons in 2004.
Even faster grew the farming of Whiteleg shrimps in Asia, surprisingly reaching more than a million tons in 2004. The Asian production is concentrated mainly in China, Taiwan and Thailand, whereas other countries limit the farming of L. vannamei for fear of introducing exotic diseases. In Thailand and Indonesia farming is free in fact, but only certain broodstocks may be imported. Most Latin American countries regulate broodstock import as well.
Shrimp farming is based on thorough division of labour. Hatcheries (e.g. in Florida, Hawaii, Singapore) provide the eggs to nauplii breeders, who in turn deliver to farms where the shrimps are grown to post-larvae, and then they end up in growout farms.
Major problems of farming
L. vannamei is by far the most frequently farmed shrimp species. It is all the more astonishing that the ethology (behavioural biology) of this species has hardly been explored so far. How can farming be designed to respond to species-appropriateness when we know so little about the species? Should not reservation be required then?
Pain and welfare: For big crayfish in the Decapoda order, namely lobsters, spiny lobsters and other big crabs, pain perception has been proven. A scientific committee commissioned by the European Food Safety Authority (EFSA) cited as early as 2005 evidence for pain perception in decapods, not excluding shrimps.
FishEthoBase is based on an understanding of fish welfare that not only aims at pain avoidance but at respecting the integrity and the dignity of the animal. Even if Whiteleg shrimps should prove unable to experience pain, their welfare has to be assured – and we do not simply mean their physical welfare in which interest is taken because of the animal’s growth…
Artificial habitat: In extensive farms, up to 10 juveniles are kept per square metre, in semi-intensive ones up to 30, in intensive ones up to 300 and in super-intensive farms up to 450 per square metre. Hence, farmed Whiteleg shrimps have to live up to 1350 times as dense as in their natural habitat, and usually at a depth of only about 1.5 metres. When the population density increases there is a growing risk of disease outbreaks and of injuries, for example of the antennae.
Artificial reproduction: As a routine, one or both eyestalks of females are ablated in order to boost their fecundity. In males the same routine leads to enhanced fertility. This is a massive intrusion in the animal’s integrity and dignity as it impedes the vision or even renders it impossible at all.
A somehow less direct intrusion in the life of the adult animals to stimulate their fertility would consist of manipulating the photoperiod, a method however for which a protocol has not yet been established.
There is a need for investigating farming conditions and business models in which neither the animals nor the photoperiod have to be manipulated.
Slaughter without stunning? In general, shrimps are netted out of basins and poured on ice or into ice-slurry. The convenient assumption is that quick cooling down renders the crustaceans unconscious painlessly, but this has to be proven for any species. Should this be true for L. vannamei, it must be followed by rapid and reliable killing.
Stunning and killing by electricity immediately afterward is a method that has been extensively used on large decapods. Research still needs to be done on how this method can be applied to shrimps as well.
Feeding wild caught fish: With increasing age, Whiteleg shrimps increasingly feed on other small aquatic animals. Farmers will have to decide whether or not to rear a carnivorous species that is fed wild fish. As more and more consumers become aware of overfishing being linked in part to the farming of carnivores, aquaculture of omnivorous or herbivorous species could prove to be the better choice in the very near future. This is even more so as feed derived from wild catch impairs the welfare of milliards* of fish that are industrially caught and processed exclusively for this purpose.
* Milliard in FishEthoBase = a thousand millions
Labels are not helpful for clients who care for the welfare of farmed shrimps. The guidelines of organic labels are the ones most inclined to grant animal welfare, yet they define no tangible instruction. All other labels address animal health at best, but do not acknowledge all-encompassing aspects of animal welfare. That is to say that even shrimps farmed under labels like organic, ASC, or Friend of the Sea, often live under the conditions of intensive animal husbandry.
If we want to change the disregard for animal welfare, we need more of two things: ethological research and pressure from concerned consumers who want to eat respectfully-farmed shrimps.
Billo Heinzpeter Studer, 22.10.2015 © fair-fish international
Sources: FishEthoBase, Findings and Recommendations, and FishBase.org
Reviewed by Jenny Volstorf. English proofreading by Tanya Slosberg.
Cite as: «Studer, Billo Heinzpeter, 2015. Pacific whiteleg shrimp (summary). In: FishEthoBase Research Group (editor), FishEthoBase. World Wide Web electronic publication. www.fishethobase.fair-fish.ch»