The potential for aquaculture of Cherax destructor (the yabbie).

Abstract

63 THE POTENTIAL FOR AQUACULTURE OF CHERAX destructor (THE YABBIE). PETER N. CARROLL2 SUMMARY . The current increased `public interest in freshwater crayfish was The Cherax genus was discussed in terms of its taxonomy . 'highlighted. and geographic .distribution and the required characteristics of a cultured organism considered in relation to Cherax destructor. Aquacul'ture facilities available at 'Hawkesbury Agricultural College were The marketability of Cherax destructor was considered and described. Results of investigations of the . compared with marine crustaceans. sensory characteristics and yield of different portions of Cherax The yield of edible meat and crustacean ' destructor were presented. .;flavour of Cherax destructor were found to be less than in prawns. The resistance of crayfish to pollution and disease was consider'It was noted that Cherax destructor is relatively.free of. disease. . ed. It is adapted to a wide range of habitats but does not tolerate many The ease of breeding and rearing of. the crayfish types of pollutants. and a number of experiment& conducted at larvae was discussed These indicated the Hawkesbury Agricultural College considereg. above 20 C for controlled breeding importance of water temperatures during the winter months and suggested the need for daylength control as well. . A trial .investigating the nutritional value of four formulated feeds was described which resulted in an average increase in individual weight (on a meat meal based diet) of 17.4 g over a 15 week period. Other experiments investigating the effect of the type of bottom substrate and the presence ,or absence of shelters on the The use of :survivability of juvenile crayfish were described. shelters and a sand bottom were advocated. . .I A summary of several investigations on growth. rate was given indicating that, growth was optimal above 20�C and a feed conversion efficiency of 2.8 : 1 or better, could be expected for animals on `pelleted feed. Recommendations were made for lighting, temperature, bottom substrate, filtration system, shelters, water quality, stocking densit.y, mating ratio, selection methods, nutrition annd control of predation. It was conc1ude.d that there were a number of problems that needed to be resolved before' the farming 'potential of Cherax destructor could be fully realised. . sz Animal Production Centre, Hawkesbury Agricultural College, Richmond, N.S.W. 2753. 64 1. INTRODUCTION 'It appears probable `that as the population of Australia increases, the freshwater crayfish might assume as much importance as an article of food as the lobster in America and England. It would probably be practical to farm these animals artificial,ly in ponds. Much work would have to be done upon the habits, food, rate of growth etc, before the undertaking could be placed upon a practical footing, but the enquiry would be well worth undertaking? (Smith 1911). Inspite of this' early observation on the farming potential .of freshwater crayfish, very little progress has in fact 'been made. Presently the crayfish is experiencing.a marked revival of interest by many members of the community. Hawkesbury Agricultural College has some 500 names and addresses of people who have made enquiries about crayfish and 170 people have attended the 2 weekend schools on Freshwater crayfish conducted at the College in 1979 and 1980. One must ask the question 'is this interest misplaced or do crayfish in fact have a potential for farming.'' The answer to this .question 'depends upon several factors including the characteristics of the crayfish being considered. All crayfish belong to theClass CRUSTACEA Order DECAPODA and There are three fre'shwater crayfish to the Super Family ASTACOIDEA. families, two of which occur in the northern hemisphere (Cambaridae and Astacidae) and one which occurs in Australia and other areas of #the southern hemisphere (Parastacidae) (Riek 1969). It is members of the former two families which are eaten with great relish. by Europeans (particularly the Scandinavians) and by Americans and about which most of the available information is published. Australia .and America have the greatest diversity of freshwater crayfish, while the tropics from 10 degrees north latitude to 10 degrees south, are devoid of freshwater crayfish, as is the African continent. There are,, according'to Riek (1969), nine ,different genera in Australia containing 97 different species, though many. biologists .argue that some of these species are. variants' within the one species. . The distribution of these.species is indicated in table 1. Some of the Australian' freshwater crayfish reaching lengths of 4O.cm or more and liveweights .Astacopsis gouldi, is the largest in kilograms. which will probably ensure its extinction as it is who are ignorant of its' very slow growth rate environmental requirements. are very large, of two to three the world, a fact hunted by gourmets and very specific . The genus Euastacus also contains some ,large specimens of which .Euastacus armatus (the 'Murray river lobster') is probably the best Members of this genus are very spiny and in the main prefer known. Although a 'large. animal with excellent flavour, cool r,unning water.. .t;he .the edib'le portions (tail and' chelae) are sma'LL in proportion to overall size and meat yield is low. 66, described 27 different species in this genus but the two of greatest importance are Cherax tenuimanus. and Cherax destructor. The former,' commonly known as the Marron, only occurs in the south-western portion of Western Australia. It is the third largest .crayfish in Australia reaching 38cm in length and attaining weights of, 2 - 2.5kg. Cherax destructor has the ,widest distribution of all species of' Australian crayfish indicating its ability to adapt to a wide range of ,environ-mental conditions and habitats. It is found in South Australia, New South Wales, Western Queensland and the Northern Victoria, Territory where it not only occurs in natural streams and ponds, but is a frequent inhabitant of farm dams, 'bore-drains and irrigation canals. * The genus with the widest distribution and hence whose members are most commonly referred to as the 'yabbie' is Cherax. ,Riek (1969) MAP 1 Distribution of the genus Cherax in Australia according to Riek (1969) The distribution boundaries in the above map shou'ld only be Johnson (1978) indicated that the best . taken as a rough guide. natural crayffsheries in N.S.W. occurred in the Western districts of This crayfish Buronga, Menindee, Balranald, Bourke and Condobolin. has a smo,oth shell or' exoskeleton which may be one of a. variety of colours ranging from greenish black, brown, browny green, browny red 67 . to blue and almost white. It is this colour variation which frequentThe adult crayfish may' ly causes speculation of a different species. be. 16cm long dnd weigh up to 280 gms though a more common weight is 60 to100gm. There are a number of factors which must be considered when attempting to answer the question of the suitability of crayfish for 'farming. Bardach et al (1972) described the desirable characteristics of a cultured organism which may be summarised 'as follows:(i1 ('ii) (iii) (iv) (V > (vi> (vii) it must be marketable itmust be resistant to, pollution and disease it must breed easily in captivity its eggs and' ldrvae must be hardy and easy to culture it should be low on 'the food chain it must be adaptable to crowding it should have a rapid growth rate ., The rest of this pape.r will discuss each of these characteristics in turn as they relate to Cherax destructor, citing investigParticipants ations carried out at Hawkesbury Agricultural College. at this school should understand that thess investigations, normally of only one semester's duration, have in the main been conducted by undergraduate students while fulfilling their course requirements. (a) Aquaculture facilities Facilities available at Hawkesbury Agricultural these and other aquaculture projects include: College for . (i) A Fish laboratory which is air-conditioned to a mdximum 20�C and contains some 60' aquaria ranging from'5 - 900 .Power, water and compressed air lines litre.capacity. are available at all points. in the labor'atory.. There is ample bench space .for the use of the various pieces of equipment including a top-pan electronic balance, pH meters, Oxygen meter, thermistor thermometer, Hach Water Test Kits (spectrometer and smaller),, binocular micro. scope9 etc; (ii) Immediately outside the laboratory there are 15 x 10,OOOl` circular fish tanks which have access to air, water and . power supplies and which are in a bird proof enclosure. (iii) Other outside facilities include 2 crayfish .ponds of l~,OO.O Kl capacity and several farm dams which range in size from 55 - 90 Ml. These are scattered over the 1,400 ha property of the College. _ II. . Crustaceans expensive gourmet and is increasing which Australians October 1979:OBSERVATIONS AND DISCUSSION (a) Marketability in general supply som%e of the most sort after and The demand exceeds the, supply meats in the-world. This is- reflected in the high prices steadily. pay for such food e.g. N.S.W. Fish Market prices in 68 Some 77 percent of Australia's fish export earnings come from ithe ,export of crustaceans (chiefly lobsters and prawns) (Australian A total of 21,500 tonnes of prawns were Fisheries 38; 52. 1979). caught in Australia in 1978-9. Overseas prices for crustaceans are as For example in the *high or higher, even in. developing countries. 'Philippines the price of prawns was in the range of A$6 to A$10.20 per kilogram in 1979 (Carroll 1980). . The question 1% can freshwater crdyfi.sh enjoy a similar. demand At present the availability of freshwater f and price structure? crayfish is very limited, small quantities trickling in to the I :Melbourne and Sydney Fish M,arkets during the summer months. These are. . . iusually live, poorly packed and of very variable quality. They are supplied by a number of mainly part-time fisherman from a variety. of ' sources, and normally arrive by train packed in 20 to 30 kg lots in hes.sian bags. The small demand comes mostly from a handful of restauranteurs The great bulk.of the . '(chiefly french) and is easily saturated. Australian public have neither seen nor tasted freshwater crayfish and i certainly are not aware of their occasional availability at the Under these conditions the market price in Sydney has ranged 'markets. 'between.$4 and.$5/kg (Ruello, personal communication) and in -Melbourne tbetween $2.20 and $6.60/kg (Mortimer, ,persona'L communication) during ':1979-80. Mr A. F. D'Mello* of Hawkesbury Agricultural College carried out . taste testing programmes during both the 1979 and 1980 Freshwater The first programme compared banana .prawn meat with. 'Crayfish Schools. crayfish tail m e a t . No salt was used and cooking was standardised. They were asked to'rate the One hundred ,panelists ,were involved. intensity of crustacean flavour using .a 1 to.5 &ore where 5 indicated ,a very strong crustacean flavour and 1 an absence of such a flavour. TABLE II Crustacean flavour of prawn and freshwater crayfish meat (Cherax destructor) as rated by 100 panelists in a taste test pro*gramme conducted by Mr A. F. D'Mello at Hawkesbury . Agricultural College .' x Quite .clearly the freshwater crayfish used in this test were. Thelatter were also much. milder in flavour than salt water prawns. A subsequent taste testing prorated Xs having a firmer texture.. * Lecturer, School of Food Sciences, Hawkesbtiry Agricultural College, ' Richmond. the gramme comparing the tail meat of freshwater crayfish with meat from chelae (claw) indicated that the latter may be quite strong in crustacean flavour and differed significantly from the tail meat. . Another taste test during the 1980 Freshwater Crayfish School to establish a sensory profile for freshwater used 70 .panelists crayfish of the species Cherax destructor. ,TABLE III Sensory. profile of the cooked meat of cherax destructor as determined. by a taste testing programme conducted by Mr A. F:D'Mello at Hawkesbury Agricultural College The author recently carried out tests on the yield of marketable and edible portions of 54 specimens of Cherax destructor obtained live The r.esulting yields are indicated in from Bourke in western N.S.'W. Crayfish portions were cooked individually for a standard Table IV. time (10 minutes) in 2% saline* 70 . . The proporti.on of edible meat (average 20.4%) from the freshw a t e r crayfish Che.rax destructor compares with 28 - 37% from' the 'prawns. The freshl?rater zrayfish would appear to yield some 27 - 56% less e'dible portion ,than the prawn. While this evidence disadvantage compar,ed' to ,people who have eaten both ,flavour and texture of the . I .might a.ppear to put freshwater crayfish at a prawns and other' marine- crustaceans, inany under normal dining conditions, prefer the freshwater crayfish. The Europeans have indicated their appreciation of' freshwater crayfish by paying. as much as $1.7 to $25 ,per kilogram in Sweden and France (Karlsson .1977) and $10.50 per kilogram in the United Kingdom (Richards and Fuke '1977). Freshwater crayfish are farmed in Europe but Sweden needs to import 2000 tonnes ,per year from Rumania and '.'Turkey, to meet the demand. 1 By comparison, Australia's maximum recorded production to 197.9 'was approximately 300 tonnes caught from natural fisheries in 1973-4. Since that time 'there has been a steady decline' in production, most likely due to drought conditions which. have afflicted many* of the Very little, if any of this production has natural production areas. come from crayfish farms. It is very difficult to obtain reliable ,information on the number of farms attempting to produce crayfish in Australia. Crayfish . farming (Marron) 'was legalised in ,Western In .New South Wales there were 17 licenced warm Australia in 1976. water-fish-farms (including 5 nominally for crayfish) registered'with N.S.W. State .Fisheries in 1979. It should not be overlooked that crayfish are a valuable bait sought after by fishermen, and that the supply of bait could be an In Melbourne they are worth 15c each important part of the industry. as, bait (Mortimer, personal communication). The export of crayfish to European markets is another possibility, though the requirement for a very .high quality product, usually the intact animal, and the,cost of packaging and. transport will create difficulties in establishing and maintaining this market outlet. A whole The size. of crayfish required varies with the market. animal' weight. of approximately 45g is preferred by the Swedes wher.eas larger animals of 60 - IOOg or more 'are sought by Australian's and Americans. The conclusion that can be made is that though the present local market is very small and specialised, it could, with appropriate market development, be expanded to support a moderately large local Intending. crayfish.' farmers would have to support this Industry. This could market with 'a reliable supply of a .high ,quality product.. probably only be achieved by some form of cooperative development between intending producers, processors and marketeers. (b) Resistance to pollution and disease, .The Australian freshwater crayfish would seem to be relatively There 'have been no reports of the fungal disease free o'f disease. to the American Aphanomyces Astaci-schikora which is indigenous continent and which has. decimated the European crayfish to such an extent that areas are being repopulated with imported species from Ame,rica ( e . gOrconectes' limosus and Pacifastacus leniusculus) which . are re$istant to this disease (Karlsson 1977) 71 There have been reports of a microsporidian parasite'(Thelohania sp.) which parasitises' the tail musculature and may become a problem when high densities of crayfish occur (Australian Fisheries 1978). A careful watch will need to be. kept for this disease in any farming . operation. Infections with the common fuligus,Saprolegniasp,may occur if the It primarily iwater becomes highly. polluted with organic matter. iattacks sick or wounded animals, eggs & juvenile crayfish. There is a flat worm, a commensal parasite (Temnocephala sp.), :which 'is frequently found on crayfish caught in the wild. This -.parasite may cause mechanical interference with respiration when it This organism does not 'lays its eggs in'high densities on the gills. appear to -be a problem .under culture conditions when water quality is controlled. '. Freshwater crayfish are very susceptible to pollution of the lwater with chlorinated hydrocarbons (pesticides such as DDT 'or Dieldrin), oil and other petroleum products, creosote and'heavy metals : such as zinc and cadmium (South Australian Department of Agriculture land Fisheries, 1977). Adult specimens of Cherax estrw'tor would appear to be tolerant ,of very low levels of &ssoly,ed oxygen, frequently being found alive in water with a dissolved oxygen' content of 0.5 mg/l. However experience' \at Hawkesbury Agricultural College has indicated that this tolerance to iow oxygen level's is not shared by either' the eggs or young 'crayfish. High mortalities to both of these have occurred when diss' #olved oxygen has been allowed to fall to low levels, with no apparent There is a need for a proper study to be effect on adults present. In the made on the oxygen requirements. of crayfish eggs and young. :meantime it is recbmmen'ded that oxygen levels be maintained above '4mgll in the breeding and nursery ponds or tanks. (c) Ease of'breeding and rearing of larvae 1 The normal, breeding of Cherax destructor in the wild is seasonal, with .a peak in summ,er and no breeding in the winter months . when these animals appear to hibernate. There is considerable variation -between 'districts in the length of the growing and the breeding . The water temperature would appear to be the season (Johnson 1978) A number 'of experiments have critical factor controlling breeding. been conducted at Hawkesbury Ag,riculturdl College since 1976 which investigated the effect of temperature on the breeding of Cherax ' All the, experime3t.s were conducted in 320 1 glass aquaria destructor. The water was constantly filtered' with 'a. floor area of 0.74m . through a *bottom-sand-bed filter using air-lift pumps to move the When required, the ,wate,r was .heated using 2OOW, thermostaticwater; Stocking density was commenced at ally controlled, fish-tank heaters. A total of 102 female crayfish six' females and two males per tank. The treatments (in duplicate) have been used in six experiments. 0 were; water at room temperature, water a,t 25 C and water temperature varying between ,room temperature and 25�C. .!'Room temperature1V was never above 20�C but in the winter months fell to a minimum of ll..O�C. , For a ,summary of the results see Graph I. l ! 73 . When the water temperature was falling and below 17'C, there.was A no breeding activity. . rising temperature and warmer temperatures stimulated gonadal'development and general activity, see Table V. TABLE V Effect of water temperature on the gonadal development of Cherax destructor over a period af 9 weeks in late Autumn (April, May, June) Several weeks of treatment at elevated water temperatures were usually required before sexual activity (indicated by the occurrence of berried females i.e. females with eggs tier the tail) was observed However when when experiments were covenced in March or April. experiments commenced in July or August, berried.females were observed It is suggested that this was due primarily to the within' a few days. effect of rising water' temperatures, but that daylength patterns probably effect the rate .of response to these changes to water temperAn experiment using controlled daylength patterns is currently ature. ..* being conducted to investigate th$s effect. . Tempez&x+c mrked1y effects the rate of development of the eggs after fertilization, the size of the youw at hatching, their subsequent ,growth rate, and the interval between egg production: An example of.these effects is'shown in Table VI. TABLE VI Effect of Water temperature on the period of 'berryingJ1, the number of young produced and the weight of the young at the free swimming stage. . 'berried females, and a reduction in the incubation period by at least , The .apparent smaller number of young .produced per batch at 50%. higher temperatures, was due .to some problems with fungal attack on The actual number of eggs ,produced per female incubating eggs i averaged 450 but this varied considerably with the size of the female. The larger the female the greater the number of eggs she is, likely to Females have become berried in their firstyear of life, at carry. The number of eggs at weights of, as little as 18g (length 7.5cm). this weight is small (30 to 100). Temperature also appears to have a m.arked effect on the abreast? interval between berryings and on the number of times an individual female becomes berried in a given period. This is indicated by the data described in Table VII. In an earlier experiment in a constant water tempe,rature of 25'C, the average interval between berryings was 60 days. Eighty, eight percent of the females were berried at least once during the-8 month period (March to November), 25%.were berried three. times 'and '12% One female became berried again only 25 days . were berried four times. after the release of her former batch. There is considerable evidence that elevating the water temperature in the winter months, results in out-of-season breeding .of Cherax Experiments need to be conducted on the effect of. destructor. . eye-stalk ablation on reproduction, as is commonly practised with the Development of controlled ' breeding of marine prawns in captivity. breeding programmes will be of great benefit to intensive crayfishfarming operations. (d) Nutrition :Freshwater crayfish are essentially detritus ,feeders (Morrissy 1979) though they can be fed a wide range of material including grass, . vegetables ,' gr'ain, animal feed pellets, animal manure and fresh meat, There is very little published work on the nutrition of freshwater crayfish and there is a great need for studies in this area (Maguire 1980). In 1978 an experiment was conducted- at Hawkesbury Agricultural College comparing formulated feeds made up' 'with different sources'. of Five treatments were run in triplicate over a 26 week period protein. The treatments were allotted at random in betwe,en May and October. Stocking density was seven smallponds located- outside the building. The five diets were:per s.quare me,tre., . Natural feed Ewos trout pellets Soybean.meal based diet I Fishmeal based diet Meatmeal based diet '' 75 diets except Watural fe.ed' had' 4 crude protein content of The formulae of the d&s made up at the College approximately 36%. Prawnhead meal was included to act as an are shown in Table VIII. attractant. . All 'crayfish ' TABLE VIII Formulae of ' Agricultural College. dfets tested at Hawkesbury '76 The diets were fed at two rates; 10% of bodyweight per week during the winter months when water temperatures were below 16'C, and ,20% of` body weight when the water 'temperatures had increased above 16'C. Very li.ttle.growth occurred,at water temperatures below 16oC so' that the effective duration of the experiment was only 15 weeks. .The' average .weight increase per animal in. each treatment .is shown in Table VIX. TABLE VIX Growth rate and feed. conversion ratio of crayfish fed five Initial weight approximately five grams. . dif'ferent .diets. The only significant differences in weight increase (at the 5% level) were between soybean meal and meatmeal and between natural feed and. the rest. The maximum growth exhibited by any single animal during the trial was 23.2g ,and by any single replicate was 17.4g average. (both on * meatmeal diet).. Some problems. were encountered with poor stability of A more the pellets, especially with the fishmeal and soybean diets. suitable binder than gelatine needs to be used. Formulated diets for aquatic organisms are very expensive e.g. It would b,e the above diets cost in the vicinity of $400 per tonne. imperative to develop efficient farming systems for Cherax destructor before the use of such high cost feeds would be economic. Alternative, cheaper feeding-systems need to be *de'veloped to enable this industry to become e,stablished. (e) Adaptability to crowding Cannibalism is a constant problem with freshwater crayfish and 'perhaps is' the greatest factor to be controlled before. successful farming of these animals can occur. Observat<ons at th.e College, indicate that. stocking density' and Expertemperature are not the .onIy factors affecting this problem. ience has shown that a stocking density for large animals. of 11 per However square metre is normally permissable in the glass aquaria. some tanks will 'contain 'rogue' crayfish which will continue to 'Other cannibalise their, fellows until they themselves are removed. tank populations, under identical conditions, will remain static for It would appear that it may be worthwhile to select the more months. docile .animals for breeding purposes. .An experiment investigating the type of substrate' and the presence or absence of shelters, indicated that maximum growth rates and survivability were obtained with shelters (beer cans) ,o 9 a sand bottom. . The survival rates .(at a stocking density of 175/m and an - average starting weight of 0.05g over a period of 11 weeks) tire shown in Table X. High turbidity in the tanks with a dirt bottom appeared to reduce the need for shelters but made it more difficult to monitor water quality., TABLE X Effect of substrate and shelteron the survivability, over a 11 week period', of s all Cherax destructor stocked in aquaria 9 at a density of 175/m . . * A resulted 77.7% in crayfish period. subsequent experiment using only sand as the bottom substrate in an average survival of 99.6% in tanks with shelter and The stocking rate was 133 juvenile tanks without. shelter. per square metre and the trial was conducted over a 7 week Water temperatures were 17OC. An experiment is currently being conducted to investigate the effects of muitiple-storey shelters, similar to thos,e used for crab farming in the Philippines, on surviv bility at high stocking densit9 The stocking densities are 54/m of animals weighing two to four ies. Results to date indicate that the animals are using all levels grams. of the multi-storey shelter. Morrissy (1979) achieved overall surv$val rates in -his ponds stocked with Cherax tenuimanus (up to, 15/m ) of 80.5%. over a four month period, using shelters of rope-fibre or lengths of PVC pipe. (f) Rapid growth rate The ,growth rate of Cherax destructor is particularly influenced by water' temperature and nutrition but also by other factors such as It is .difficult to bottom substrate, shelter. and stocking density. find definitive reports on the. growth rates of this animal and estimates of the time taken to grow an animal to a marketable size Clearly, if the animal. is to be . . vary between one and thre-e years. farmed successfully,the growth rate should be as rapid as possible. Results obtained at the ,College indicate that there is' very. . little growth of Cherax destructor 'at water temperatures below 16'C. '. Frost (1973) reported that this species begins to aestivate when Morrissy (1976)' reported temperatures fall below this temperature. 12'C as being the 'lower temperature limit for grbwth of Cherax It. would therefore be imperative to select a site for tenuimanus. farming these animals where' the water. temperature remains above 16OC . for'as much of the.year 'as possible. As reported earlier in section single animal over an effective 15 temperature above l6oC) .obtained at average for a gboup of animals was' (d) the maximum growth rate of a week growing period (i.e. water the College was 23.2gj and the 17.4 k 4.Og (initial weight 6.4& 78 and final weight 23.8 5 2.9g). Mwrissy (193) reported a of 45g in 12 months .and 120 g in two growthrate for Cherax tenuimanus This would appear to indicate that Cherax destructor has a years. similar rate of growth to Cherax tenuiraanus in the first year. 1..8g . Growth trials with Cherax dest-tor conducted at the College, were normally only a few weeks in length. The results of several trials conducted with different sizecd animls, fed o,n a variety of feeds, in water at various temperatures, are summarised in Table XI. These results suggest that crayfish growth rates are optimal'in water temperatures above 20�C when feed conversion efficiencies of the order of 2.8:1 or better, could be expected. A growth rate equivalent. to approximately 8% of the initial weight per week could be expected for crayfish with 'an initi,al weight between '10 - 30g. At smaller initial weights the growth rate is much faster and at larger initial weights it is slower. (g) Recommendation . Very little is really known about the habits and requirements of The current upsurge of public. interest in this Cherax 'destructor. animal makes it very easy for anyone with a little experience to It is with this thought in mind that become regarded as an expert. the following tentative recommendations and suggestions are made for . the breeding.& growi= of the g&y. (i) Lighting It may be desirable increasing daylength to months. The intensity of conditions at the bottom behaviour. (ii) Temperature Water temperatures should be above 20 C and rising to 25 C .in There is some evidence that a fluctuating the breeding tanks. 0 temperature between 20 - -25 C may be more effective in inducing reproduction than a constant tempesature of 25'C.. . ( i i i Bottom substrate . ) Sand would appear 'to be the most desirable substrate in tanks used for controlled breeding, facilitating easier water management and self cle,ansing of the tank. (iv) Filtration 0. 0 to expose breeding crayfish to a constant or ensure successful breeding in the winter the light should perhaps be dim to simulate of a -muddy pond and to reduce agonistic Water in the breeding tanks should be' circulated through the sand filtration-bed on the bottom of the tank, using air-lift pumps to .This aids in the removal of move .the water through the system. organic ,matter from, the environment of the crayfish, maintains oxygen levels and reduces the risk of fungal attack on eggs and juveniles. 80 (v) Shelters Cannibalism is markedly reduced by the ,provision of shelters in the form of aluminium drink cans or sections of PVC pipe. There should be at least one shelter for each .animal. Stacking of shelters may allow an increase in stocking density though this needs further . investigation. (vi) Water quality Maintenance of good water quality.is. essential, particularly in the breedin-g tanks. Oxygen levels should be maintained above 4mg/l and pH between 7.5 and 8.5. Crayfish require large amounts'of calcium and water levels of this element should be no less than 20mg/l CGreenway, personal communication) and preferably above lOOmg/l. (vii) Stocking, density . Various conditions ill determine the optimum stocking density, but a density of 10 - 15/m3 wou-ld seem to be reasonable. (viii) Mating ratio that the mating ratio, approximates trials at Hawkesbury Agricultural ratios 'of one male to 3 females, males in. the harem. The- recommend:a or multiples there of. In the wild it would appear 1 :l (Woodlands 1967). Breeding College have bee