REVIEW

Conservation breeding of the tadpole shrimpTriops cancriformis in BritainIan HughesDudley and West Midlands Zoological Society Ltd, 2 The Broadway, Dudley, WestMidlands, DY1 4QB, UK

Triops cancriformis (Bosc 1801), a branchiopod crustacean, is restricted to a single knownsite in the British Isles. The reasons for its rarity and decline in Britain are not fullyunderstood. A captive population has been established and a Triops Conservation Groupformed to co-ordinate the conservation of T. cancriformis and to research the reasons forits decline. Particular attention is given to reproductive biology, ecology and in-situconservation as these are important factors in both aquarium husbandry and ex-situconservation. The factors governing the hatchability of eggs are varied and complex butonce established in captivity, husbandry appears to present few problems. The objectivesof the conservation project are outlined.

KEYWORDS: Branchiopod, crustacean, Notostraca, tadpole shrimp, Triops

INTRODUCTION

Triops cancriformis (Bosc 1801), the tadpole shrimp (previously known as Apus),has been recorded from a number of sites in Britain in the last three centuries. Inthe 20th century however, it was recorded from just two sites. The first site inKirkcudbrightshire, Scotland, where it was recorded by Balfour-Browne in 1907and 1948 (Balfour-Browne, 1948), is thought to have been lost to the sea (Galliford,1967). The second site in the south of England is well documented and is anephemeral, temporary pool. Triops cancriformis has been known to exist at thesouthern site since 1934 (Fox, 1949) though it was not observed in the wild from1949 to 1971 (Khalaf, 1978). For security reasons the location of the site isexcluded from this paper.

In Britain T. cancriformis is listed under Schedule 5 of the Wildlife andCountryside Act (1981) and is classed as Endangered. The only known site whereit exists is a Site of Specific Scientific Interest (SSSI) and the site is covered byother protective legislation.

In 1993, English Nature (the Nature Conservancy Council for England)approached the Federation of Zoos to request that a captive population ofnative T. cancriformis be established. To co-ordinate the project, a TriopsConservation Group was created which included members from English Nature,The Wildlife Trusts, The Forestry Commission, Chester, Dudley and London Zoos,The Fish Conservation Centre in Stirling, the Universities of Buckingham and

Aquarium Sciences and Conservation, 1, 5–18 (1997)

1357–5325 # 1997 Chapman & Hall

Nottingham, Pond Action, and Patrick Wisniewski of the Wildfowl and WetlandsTrust (WWT) at Martin Mere. Whilst husbandry trials were in progress, EnglishNature asked the group to produce a ‘Species Action Plan’. This document, partof a ‘Species Recovery Programme’, would lay down a protocol for theconservation of T. cancriformis in Britain. The project has received financialsupport from English Nature, the Association of British Wild Animal Keepers andSt Andrews Orienteering Club, Glasgow.

THE EXISTING T. CANCRIFORMIS SITE

The existing T. cancriformis site is a seasonal pool which is often dry fromMay to September. It has a maximum depth of approximatley 30 cm and adiameter of roughly 30 m. The site is heavily trodden and grazed by a variety offarm animals which both disturb and enrich the water and mud. When wet, thepool’s plant life is dominated by the water starwort (Callitriche spp.) Being shallowand unshaded, the pool is able to warm relatively quickly, providing goodconditions for T. cancriformis eggs to hatch. Such an ephemeral habitat isunsuitable for most species of aquatic life, especially fishes which would prey onT. cancriformis.

The site is susceptible to various forms of human disturbance. The pool isclose to a busy road and is thus vulnerable to all types of road pollution,accidents and vandalism. Agricultural chemicals such as pesticides and fertilizersalmost certainly pose a threat. Ivermectin, a drug used to eradicate lung wormand external parasites, is suspected to be the most likely threat to T. cancriformis(Key, pers. comm.) as it will find its way into pools through the faecal matter offarm livestock which frequent the pool. Any changes in grazing or landmanagement or the arrival of alien species of animals or plants are likely tocause the extinction of T. cancriformis at the present site. Natural predatorsinclude insect larvae, fish (if present) and birds. Balfour-Browne (1948) recordedthat gulls almost completely eradicated the adults of the Kirkcudbrightshirepopulation in 1907. Triops cancriformis also suffers predation from othercrustaceans, including ostracods which will prey on both adults and immatureforms.

NATURAL HISTORY

Measuring up to 100 mm in total length, T. cancriformis is one of Britain’s largestfreshwater invertebrates (Fig. 1). It is normally pale olive-green with darker olive-green mottling on the carapace. Individuals often have areas of red or orangecolouration, depending upon the availability of oxygen and thus haemoglobinlevels. Triops cancriformis is able to generate haemoglobin quickly and thussurvive in poorly oxygenated water and in deep mud. Its haemoglobinconcentration equals that of many birds and mammals (Alygkrinskaya andDolgova, 1982).

The order Notostraca, collectively known as tadpole shrimps, comprises asingle family, Triopsidae, divided into two genera, Lepidurus and Triops, whichshare a similar cosmopolitan range. Lepidurus consists of five species, all of

6 I. Hughes

which are easily distinguished from Triops by the presence of a supra-anal plateclearly visible between the two caudal furcae. The genus Triops consists of fourspecies: T. australiensis is recorded from Australia and Madagascar and is dividedinto two subspecies; T. granarius is found throughout most of Africa through theMiddle East and India to China but absent from Europe; T. longicaudatus is foundin North and South America, West Indies, Galapagos, Hawaii and Japan and isdivided into two sub-species; T. cancriformis is an Old World species that occursin Western Europe from Spain north to Sweden, west to Britain and east toRussia, and its range also spans North Africa, through Asia Minor and the MiddleEast to India. There are no authenticated records of T. cancriformis from EasternAsia and it is not found north of 608 N. Triops cancriformis is divided into threesub-species: T. cancriformis cancriformis, the sub-species that occurs in Britain, isfound throughout the range of the species with the exception of areas occupiedby the two other sub-species and is the only member of its genus to be found inNorth Western Europe; T. cancriformis simplex is restricted to North Africa fromCeuta to Egypt; T. cancriformis mauretanicus is found in Morocco and Tangier,southern Spain and Minorca in the Balearics (all the above classification anddistribution is based on Longhurst, 1955a).

There are many reports of T. cancriformis being a pest to rice paddies byuprooting seedlings and young plants (Fox, 1949) but Scott and Grigarick (1978),

Fig. 1. The tadpole shrimp Triops cancriformis Bosc. 1801

Breeding T. cancriformis in Britain 7

working with T. longicaudatus, indicate that tadpole shrimps could be valuablepredators against aquatic pests on rice plants and seeds.

Triops cancriformis spends most of the time actively ploughing through thesubstrate, filtering out food particles which are derived mainly from the dung oflivestock. Larger prey, such as Daphnia spp. and the fairy shrimp Chirocephalusdiaphanus (Prevost, 1803) are grasped in the mandibles. Food items are passedalong the central canal between the appendages and broken down or filtered forconsumption. Longevity ranges from 12 days in the wild to 3.5 months inlaboratory conditions (Hempel-Zawitkowska, 1967). The author has recordedcaptive specimens living up to 106 days from the time of hatching. In the wildhowever, longevity tends to be less, with individuals reaching maturity morequickly than those in captivity.

REPRODUCTIVE BIOLOGY

Triops cancriformis has unusual environmental requirements and reproductivebiology which are outlined in Fig. 2. Sexual maturity can be reached as early as 12days from the time of hatching and this is common in the case of wild specimens(Hempel-Zawitkowska, 1967). In captivity, sexual maturity may be reached in 12 to75 days from the time of wetting the eggs (Hempel-Zawitkowska, 1967).Oviposition may begin at a carapace length of 14 to 15.9 mm. (Hempel-Zawitkowska, 1967). The author observed egg production at a carapace lengthof 12 mm but it is not yet known whether the eggs were viable or if ovipositionhad begun at the time of observation.

Longhurst (1955b) showed that the many follicular ducts that extend from theoviduct constitute ovo-testis and thus confirmed that the sub-species T.cancriformis cancriformis exists in populations of self-fertilizing hermaphroditeswith truly sexual individuals being completely unknown in many populations. It isthought that this asexual strain represents a highly successful adaptation whichenables the population to spread rapidly during inter-glacial periods whereaspopulations of the sexual strain have remained relatively static in their

Fig. 2. Life-cycle of T. cancriformis. (measurements and development information taken mainly fromGalliford (1967) and personal observations. Not to scale. (a) Eggs in dry mud. They are able tosurvive long periods of desiccation, exposure to various salts and high levels of ultraviolet light. (b) Anegg with section of shell removed (diameter 0.25 mm approx.). Eggs hatch when immersed in waterwith a low osmotic pressure, other varied stimuli encourage hatching but eggs may go through anumber of wettings before hatching. The egg has a thick, protective, alveolar layer which splits opento reveal the larva or metanauplius still enclosed in a protective membrane which itself splits a fewminutes later. (c) The first instar metanauplius (length 0.6 mm approx.) (d) A more advanced stage ofthe metanauplius at the 2nd or 3rd instar (length 0.7 mm approx.) (e) Intermediate stage (4th or 5thinstar) resembling a miniature adult (length 1–3 mm approx.). Propulsion is still achieved using strokesof the second antennae (the long appendages). With each moult more body segments, appendages andpigment appear. (f) Adult stage with eggs (carapace length 12–21 mm approx.). The antennae are nowhidden beneath the carapace and the first pair of trunk limbs can now be seen as the characteristic‘feelers’. (g) The eggs require 6 days in water after laying in order to reach gastrulation and thus beable to survive desiccation

8 I. Hughes

Breeding T. cancriformis in Britain 9

distribution (Longhurst, 1955a; Clarke, pers. comm.). The asexual adaptationoffers the potential for pools to be populated from a single egg. In terms ofgeographical distribution, sexual populations of T. cancriformis cancriformis havebeen recorded from the south of its range, whilst in central Europe males occuronly sporadically (Longhurst, 1955a).

The eggs are approximately 0.25 mm in diameter and are reddish-brown incolour due to their yolky contents (Fryer, 1988) which are rich in haemoglobin(Hempel-Zawitkowska, 1967). The eggs, which are hard and adhesive, areprotected by an outer cortex and a thick alveolar layer (Fryer, 1988) thechambers of which are filled with air when the eggs are in the dry state (Hempel-Zawitkowska, 1967). They are able to survive prolonged desiccation, possibly forperiods of up to 15 years (Tasch, 1963). They are also resistant to ultra-violetradiation, high concentrations of various salts and temperatures ranging fromfreezing up to within 18 of boiling point (Carlisle, 1968). Beneath the tough outerlayers the embryo is protected by a thin translucent membrane. After being laid,the eggs are carried in pouches on the 11th pair of trunk limbs which may beseen through the carapace as two light patches (Fig. 3). The shrimp mustphysically position the brood pouches in such a way that they catch the eggs asthey emerge, but the author knows of no observations of this behaviour. The

Fig. 3. Lateral view of T. cancriformis. The eggs in the brood pouch can be seen through the carapaceon the lower edge close to the posterior margin

10 I. Hughes

eggs remain in the brood pouches for approximately 24 h (Fox, 1949). The broodpouches help ensure that the eggs remain wet and comparatively safe andthereby perform a partially uterine function. Up to 462 eggs have been foundwithin a single pouch (Hempel-Zawitkowska, 1967).

Triops cancriformis excavates shallow chambers in the substrate in which itdeposits large batches of eggs. Eggs will also drop freely from the brood pouchesas the animal moves about. The adhesive film that coats the eggs allows them tobe attached to surfaces or to become coated with particles of substrate. Thesubstrate coating makes them invisible and may increase their protection againstadverse environmental conditions. This conclusion is drawn from the fact thatexposed ‘uncoated’ eggs seldom hatch successfully. This apparent infertility hasbeen noted by Hempel-Zawitkowska (1967), Khalaf (1978), Bell (pers. comm. 1995)and in personal observations.

According to Klekowski and Hempel-Zawitkowska (1968), after being releasedfrom the egg pouches the eggs must remain in water (or in air with 100% relativehumidity) for approximately 6 days in order to reach gastrulation, in which casedevelopment continues until the pre-hatching stage. The eggs will only hatch ifsubmerged in water. Embryonic development, which begins in the brood sacimmediately after fertilization and before the formation of the egg shell (Hempel-Zawitkowska, 1967), lasts from 9 to 40 days (Klekowski and Hempel-Zawitkowska,1968). Hatching is stimulated by, but not necessarily dependent upon, ultra-violetlight (Hempel-Zawitkowska, 1970) and a short exposure to certain salts:magnesium sulphate, potassium sulphate, magnesium chloride and potassiumchloride (Hempel-Zawitkowska, 1969). Other environmental factors may alsoinfluence hatching, such as gradual wetting of the mud, agitation of the mud byrain drops, a rise in temperature and/or a specific period of desiccation.Probably the most critical factor is that eggs require a low osmotic pressure tohatch (Longhurst, 1955b) which makes hatching in a newly flooded pond muchmore likely than in a mature, eutrophic pond. The eggs hatch in spring or earlysummer as the water warms, with the pool normally disappearing in mid-summer. A second hatching may then take place in the autumn when the poolfills again. Soon after immersion in water the horny outer shell of the egg breaksopen and the metanauplius emerges still enclosed in the transparent innermembrane which splits open after 20 min or more, possibly through absorptionof water (Galliford, 1967; Hempel-Zawitkowska, 1967). It appears that most eggsrequire a period of drying, though a high humidity during the diapause isreported to be beneficial (Hempel-Zawitkowska, 1967). Under laboratory condi-tions, eggs hatching without a period of desiccation is rare, but has beenrecorded on occasions by other workers (Hempel-Zawitkowska, 1967; J. Bell andP. Wisniewski Pers. comms.). There is some evidence to suggest that exposingthe eggs to a change of water may provide a trigger for hatching in the absenceof desiccation.

The shrimps hatch as metanauplii which propel themselves with strokes of theanterior appendages. After a couple of moults the neonate stage is reached whenthe animal is a miniature, translucent version of the adult, and propulsion is nowachieved with all the limbs working together in the characteristic series ofmetachronal waves.

Breeding T. cancriformis in Britain 11

CONSERVATION OF T. CANCRIFORMIS

In Britain, T. cancriformis is at the northern limit of its range, and reports ofpopulations are few, although it enjoys a wide global distribution and lives in awide range of habitats: desert, heathland, rice paddies, and even in brackish water(Lanfranco et al., 1991). It is probable that increasingly intensive agriculturalpractices have gradually reduced its range through habitat loss, changes ingrazing, and pollution. Climatic change may also be responsible (Maitland et al.,1995).

Three sub-species of T. cancriformis have been recognized (Longhurst, 1955a)and Fryer (1988) has observed that small differences between populations withinthe Notostraca, previously thought to be racial, have a functional significancewhich suggests that the taxonomy of the order is over-simplified. Thus, theBritish population which is an isolated, island population, may be of internationalsignificance (Bratton, 1991).

Conservation objectives

The Triops Conservation Project has two primary purposes:

1. To maintain a captive population of native T. cancriformis as an ‘insurance’against their extinction in the wild.

2. To produce a ‘Species Action Plan’ (SAP) for English Nature as a protocolfor the future in-situ and ex-situ conservation of T. cancriformis in Britain.

In-situ conservation

In addition to giving maximum protection to the pond where T. cancriformisoccurs, in-situ objectives include a study of the shrimp’s biology at the pond inrelation to the physicochemical and other conditions of this habitat together witha study of the genetic characteristics of the pond stock in relation to that ofmaterial collected from former British sites and from elsewhere within itsgeographic range.

An awareness programme is also invaluable to the conservation of T.cancriformis. Zoos and other natural history visitor centres will play an importantpart in promoting opportunities among the public for the appreciation andconservation of temporary ponds and their important flora and fauna. Thisinitiative should extend to land owners, managers, advisory bodies andgovernment agencies throughout the entire geographical range of T. cancriformisin order to assess its international status (Maitland et al., 1995).

CAPTIVE BREEDING

On 8 December 1994, the author visited the English T. cancriformis site with DavidHughes of Glasgow Zoo and collected five samples of mud (under licence) fromvarious areas of the pool which was filled to its maximum depth, 300 mm. Themud, which included samples of pond plants (mainly Callitriche sp.), was collectedin plastic buckets using a trowel to dig up the substrate through the water. Mud

12 I. Hughes

samples were distributed to Chester Zoo, Dudley Zoo and WWT Martin Mere onthe following day. Chester Zoo later distributed dried mud to London Zoo and theFish Conservation Centre. Husbandry trials continue, but to date (June 1996), onlytwo mud samples have yielded T. cancriformis at two separate institutions, namelyDudley Zoo and WWT Martin Mere, with the latter producing only Chirocephalusdiaphanus in the first wetting but several T. cancriformis after the mud was re-dried and subjected to a second wetting.

There are reports of stringent procedures to hatch the eggs of T. cancriformishaving failed (Khalaf, 1978; Bell, pers. comm.) whilst others hatch them ad hoc.Numerous colleagues report T. cancriformis being hatched from mud samplesheld within greenhouses or on windowsills or even on top of television sets. Ithas been found at Nottingham University that eggs of T. longicaudatus will nothatch in water in which an adult has died (Robinson, pers. comm.). However,some eggs of T. cancriformis will remain unhatched after exposure to two ormore wettings before eventually producing metanauplii. The processes behindthis postponsed hatching are unknown. As previously stated, eggs of Notostracaare known to have been kept in the dry state for up to 15 years and Khalaf(1978) suggests that the population of T. cancriformis at the known British sitewent through a diapause of nearly 22 years since it was not observed in the wildfrom 1949 until 1971.

Wetting of the mud was conducted following the instructions of Clive Chatters(The Wildlife Trusts), Dr Roger Key (English Nature) and a reference to T.cancriformis by Burton and Burton (1978), one of the few pieces of literaturesourced at the time. The procedure was a gradual wetting of the mud from thedry state in full daylight. Several authors refer to the importance of light,suggesting that it is a stimulus to hatching, with some evidence to support thistheory produced by Hempel-Zawitkowska (1970). It may be significant that, in thepresent study, all initial hatchings from the original mud took place under brightlight.

Husbandry techniques vary greatly, but eggs are usually hatched in glass orplastic aquaria, or similar watertight containers measuring 100 mm by 200 mm ormore. It is important to wet comparatively small amounts of mud as the waterwill otherwise become polluted before the eggs can hatch if the quantity of mudis too great. The stickiness of the eggs often causes them to be coated withsubstrate so they cannot be seen until the mud sample is flooded when theybreak free and float to the surface.

Initial hatchings were achieved by providing artificial light in a south-facingwindow and by heating the water to 218 C. Wisniewski (pers. comm.) hatchedeggs from mud samples in a greenhouse allowing mud to dry naturally over along period of time. With the exception of feeding, these animals were left tofend for themselves under conditions as natural as could be achieved.Subsequent generations have been hatched in tanks on west- and south-facingwindowsills. In contrast, co-workers at Chester and London Zoo and at the FishConservation Centre, using a wide variety of techniques and environments, hadno success in raising T. cancriformis from the mud samples although C. diaphanushatched in large numbers, as did ostracods. At Dudley Zoo, three wetted mudsamples weighing 3 g, 16 g and 16 g yielded two, three and two T. cancriformis

Breeding T. cancriformis in Britain 13

respectively. These animals were managed intensively with a procedure of waterand mud changes.

The small size of T. cancriformis together with its requirement for mud to digthrough, makes water filtration difficult. Additionally, the eggs are very small andcould be trapped in filter media, making manual water and mud changes morepractical than any attempts at filtration. Fortunately, T. cancriformis is suited tothis type of husbandry as it lives in pools that are continually disturbed bylivestock which pollute/eutrophy the water which is likely to be murky and mayhave very low oxygen levels. For this reason the shrimp is reared in smallpolythene, plastic and glass containers (approximately 200 mm long, 100 mmwide and 50 mm deep), at a density of one or two per container once they arepast the neonate stage.

The water used for the initial hatchings at Dudley Zoo was tap water whichhad been boiled, cooled and left to stand. However, after discussions withvarious co-workers (Key, Chatters and Bell, pers. comms), water was addeddirectly from the tap with no observable changes in the shrimp’s health orlongevity. In the wild in Britain T. cancriformis lives in water with a pH of 5.9 to6.8 (Khalaf and MacDonald, 1975). Dudley Zoo tap water has a pH of 7.8 anddiffers greatly in many other physicochemical conditions, suggesting that a rangeof water parameters are suitable for aquarium management of the shrimp.

Normally, eggs are buried in clutches or randomly in the substrate or are stuckto solid objects (rocks, glass, silicon sealant) or shed in the brood pouches withexuviae. The viability of the eggs may be poor if they are not coated withsubstrate. Triops cancriformis will eat its own eggs (Khalaf, 1978) – specimenswith full egg pouches have been moved to containers with no substrate, andlater the pouches have been found to be empty with no eggs present in thecontainer. Egg survival can therefore be increased by providing more space andsubstrate in the container or if the substrate is changed regularly.

Triops cancriformis appears to consume any organic material that it isphysically capable of dealing with. Fryer (1988) reports that the first instar doesnot feed. Later instars take a variety of micro-organisms including bacteria,protozoa, algae, diatoms and fungi (Hempel-Zawitkowska, 1967; Scott andGrigarick, 1978). Proprietary processed tropical fish flakes and goldfish flakes(various brands) appear to provide all the nutrients required, these beingcrushed to form a powder. Adults are also fed Daphnia spp. and dried Tubifexspp. Substrate from an African land snail terrarium was initially used by theauthor but this has since been abandoned because it appears to be of negligibleimportance as a food source. The author observed one T. cancriformis catch andeat a specimen of C. diaphanus that had hatched from the same mud. The shrimphas also been observed to feed on bacon scraps (Chatters, pers. comm.),crushed woodlice (Key, pers. comm.) and liver, beef, chicken and frozenbloodworm (Wisniewski, pers. comm.). After removing them from the substratein which they hatched, the author reared a number of specimens to maturitywith no substrate present and on a diet of processed fish flakes alone; growthappeared to be slower in these individuals.

To date, at least nine T. cancriformis have been hatched from the mudcollected in December 1994. At Dudley Zoo, mud collected from aquaria housing

14 I. Hughes

the first two specimens was kept separately and dried, yielding 45 and more than70 metanauplii, respectively, at the first wetting with one mud sample producinga further 88 animals with a second wetting (further wettings are planned).

Many of the shrimps reared at Dudley Zoo were dispersed to Chester Zoo,London Zoo, The Fish Conservation Centre, WWT Martin Mere, NottinghamUniversity, Marwell Zoo and Bristol Zoo. These institutions are keeping thedescendants of the founders as separate lines, though it is not known if anygenetic diversity exists within the pool from which the founding stock werecollected. Chester Zoo have successfully raised a third generation (Bell, pers.comm.).

The primary objective of the Triops Conservation Group – to establish acaptive population – has now been achieved. The shrimp generally proves to beextremely hardy in captivity but premature deaths (i.e. prior to egg production)are recorded and the reasons for this and for poor hatching in the mud samplesremain unclear and warrant further research.

RELEASE PROJECTS

There are no plans to release T. cancriformis to new sites at present. The existingwild population in the UK is considered to be healthy and shows no sign of declinein numbers. Chatters (pers. comm., 1995) reports a marked increase in the wildpopulation which he correlates with a recent reduction in sheep grazing and anexpansion of grazing by cattle and ponies in the vicinity of the pool.

As part of the in-situ work of the Triops Conservation Group, attempts arebeing made to discover any other populations that may exist, paying specialattention to all previously recorded sites and their surrounding areas. Triopscancriformis is seasonal and can be difficult to find even when known to bepresent (Chatters, pers. comm.). If none are found and the reason for theshrimp’s decline can be ascertained, a procedure to restore the species,following IUCN (World Conservation Union) guidelines, to at least ten suitablesites within its former range in the UK as a series of self-sustaining populations,would be carefully considered where appropriate. Captive bred stock would beused for re-introductions which would be monitored on a long-term basis.

Unofficial attempts have been made to introduce T. cancriformis to seeminglysuitable pools in the past. Little information is available and none of theseattempts are known to have succeeded (pers. comms. to Chatters and Reid).

DISCUSSION

Much is still to be learnt about T. cancriformis in Britain and its conservationrequirements. It appears hardy in captivity, though unpredictable, with earlyhusbandry trials suggesting some physicochemical or land management factorbeing the cause of the species’ decline and rarity in Britain. Hopefully additionalnatural sites will be discovered or the species will be given some stability with theestablishment of new sites, should this prove to be a suitable and successfulcourse of action. The ex-situ programme will be invaluable to the future in-situconservation work.

Breeding T. cancriformis in Britain 15

Conservation protocol

Dr Peter Maitland, in collaboration with the Triops Conservation Group, prepareda Species Action Plan for English Nature in 1995/96 which is under considerationat the time of writing. The Action Plan, which will be reviewed annually byinvertebrate specialists at English Nature and Scottish Natural Heritage, lays downthe following objectives and targets for ex-situ conservation:

To establish breeding populations of T. cancriformis in captivity which canthen be used as sources of stock for research and reintroductions, if appropriate.

To investigate environmental factors affecting egg production, developmentand survival leading to recruitment in order to achieve a better understanding ofthe shrimp’s reproductive strategy in relation to environmental variables.

To promote research into selected aspects of the autecology of T. cancriformis,including relevant physiology, to help refine habitat and site management andcaptive breeding requirements.

To promote research on wild and captive-bred populations to determine theirgenetic structure and suitability as founders for introductions.

To develop detailed protocols for captive breeding of T. cancriformis, includingartificial foodstuffs and suitable substrates within which the eggs may subse-quently be dried.

To research the effects of Ivermectin on captive bred populations of T.cancriformis.

To ensure the maintenance and expansion of the captive breeding programmeuntil the British populations are considered to be beyond threat.

Although a great deal has been written about T. cancriformis and otherNotostracans, the project, so far, yields more questions than answers, forexample:

1. Why is T. cancriformis now restricted to a single pool in the British Isles?2. In the wild, what special environmental conditions are required for T.

cancriformis to survive and what land management practices are required?3. What factors influence initiation and suppression of egg hatching?4. If agricultural chemicals are responsible for the decline of T. cancriformis,

which chemicals are a threat, how and at what life stages?5. How many wettings without hatching (‘false starts’) can eggs survive?

It is evident from this project that zoos, public aquaria and individual aquarists,working together, can play a valuable role in the conservation management of thetadpole shrimp.

Acknowledgements

I thank the following for personal (including verbal) communications: J. Bell,North of England Zoological Society, Chester; D. Bird, Poole Aquarium, Dorset;C. Chatters, Hampshire & Isle of Wight Wildlife Trust; Professor B. Clarke,Department of Genetics, University of Nottingham; Dr R. Key, English Nature,Peterborough; Dr Peter Maitland, The Fish Conservation Centre, Stirling;

16 I. Hughes

Dr G. Reid, North of England Zoological Society, Chester; T. Robinson,Department of Genetics, University of Nottingham; P. Wakefield, c/o MarwellZoological Park, Hampshire; P. Wisniewski, Wildfowl and Wetlands Trust, MartinMere, Lancashire.

The Triops Conservation Group is a sub-group of the Fish and AquaticInvertebrate Taxon Advisory Group of The Federation of Zoological Gardens ofGreat Britain and Ireland, Zoological Gardens, Regent’s Park, London NW1 4RY.Tel: 0171 586 0230 Fax: 0171 722 4427 Email cmlees@gn.apc.org.

Special thanks are extended to all those who provided personal communica-tions and contributed greatly to the project, to David Hughes of Glasgow Zoowho has provided much of the motivation behind the project and to Dr GordonReid who kindly took responsibility for the Triops Conservation Group byagreeing to become Chairman and, with his staff (J. Whitear and L. Wilkinson),gathered together most of the literature that is cited in this paper. Caroline Leesof the Zoo Federation kindly conducted the first literature search. DavidHampton, Kerry Hughes, Patrick Wisniewski, David Hughes, Justin Bell and JoyceNorman kindly read through the text.

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Balfour-Browne, F. (1948) Re-discovery of Apus cancriformis. Nature 162, 116.Bratton, J. H. (1991) British Red Data Books (3) Invertebrates Other than Insects, 1st edn.

Peterborough: Joint Nature Conservation Committee, pp. 108–110.Burton, M. and Burton, R. (1978) Apus. Purnell’s Illustrated Encyclopaedia of Animal Life,

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