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Egg development and lifecycle timing in the noble crayfish (Astacus astacus)
Aquaculture, 64 (1987) 77-82 Elsevier Science Publishers B.V., Amsterdam
77 -
Printed
in The Netherlands
Egg Development and Lifecycle Timing in the Noble Crayfish (Astacus tzstacus) DAG 0. HESSEN,
TROND TAUGBBL,
EIRIK FJELD and JOSTEIN
SKURDAL
Department of Biology, University of Oslo, P.O. Box 1050, Blindern, 0316 Oslo 3 (Norway) (Accepted
17 December
1986)
ABSTRACT Hessen, D.O., Taugbel, T., Fjeld, E. and Skurdal, J., 1987. Egg development in the noble crayfish (Astacus astacus). Aquaculture, 64: 77-82.
and lifecycle timing
Egg development time in Astacus astacus was strongly influenced by temperature. Five batches of eggs were subjected to different temperature regimes after approximately 600 degree days and, by increasing the temperature, the total number of degree days to hatching was reduced from 1900 to 1300. There were no systematic differences in hatching success or juvenile survival due to different temperature treatments. Females molted and rematured ( 50-100% ) 4-8 weeks after hatching.
INTRODUCTION
Following the extensive development of aquaculture in Norway, the potential for crayfish cultivation has attracted considerable interest. The noble crayfish (Astacus astacus) has its obvious advantages in high market price, high demand, and is established as a delicacy far outside Scandinavia. As demands by far exceed capture from native populations, the most obvious prerequisites for noble crayfish as an aquaculture organism should be fulfilled. Its disadvantages are low fecundity and low growth rates in nature, as well as its cannibalistic nature, common to most of the crayfish and lobster species. Among the more important parameters to know and control are egg development time and the possibility of timed hatching. The importance of temperature to the overall life cycle of crayfish is well documented (Huner and Lindqvist, 1985; Westin and Gydemo, 1986). In the present paper, we present data on egg tolerance to fluctuating temperature as well as shortened and delayed hatching in crayfish eggs under different incubation temperatures. In Norway, the interest has so far been concentrated mainly on rearing in intensive, indoor conditions due to the cold climate, and the following account relates to this.
0044-8486/87/$03.50
0 1987 Elsevier Science Publishers
B.V.
78 TABLE 1 Date of hatching, occurrence of two-stage juveniles and malting of the adult females (percentage of females molting and percentage of these mating are given) Batch
1 2 3 4 5
N
6 9 6 16 2
Maturing ( % of molted)
Molting
Date Hatching
Two-stage juveniles
Date
10 March 14 April 9 April 6 May 13 June
18 March 25 April 20 April 15 May 20 June
28 April -12 14 May -24 No data” 16 May -31 30 June -17
% May June
100 44
100 100
July July
56 100
67 100
“All died due to accidental stop in water flow. MATERIALS AND METHODS
The crayfish for the present experiment were sampled from Lake Harestuvann, south-eastern Norway by SCUBA diving in September 1985. After acclimatization to aquaria conditions for 2 weeks, females ready for mating (yellow glands under the tail) were put together with males in a sex ratio of 3:l. All females became mated within 1-14 days. When mated, females were placed in single chambers prior to spawning, which occurred within l-7 days at a water temperature of 9-10°C (mid-October). The crayfish were kept individually in a raceway system, separated by movable walls. Each cell was 10x 12 cm, and each raceway consisted of 15-20 separate cells. Water was heated by passing it through a supercoiled tube in a thermostat-regulated water bath. Prior to heating, the water passed through a two-layer filter of activated charcoal and shellsand. To prevent supersaturation with air during heating, the water was aerated with an air pump in front of the raceways. Water flow varied between 0.2-0.4 1-l mini raceway-’ and dissolved oxygen was close to saturation (80-100% ) . An obvious improvement would be to incubate eggs apart from the females. This would require less space and allow a further preparation of females to a second mating. To test the survival of such eggs, half of the eggs were stripped from four individuals (corresponding to 30-50 eggs/individual) after 600 CTU, and placed in two different Artemia flasks with constant water flow, following the “Cukerzis-principle” (Cukerzis et al., 1979). In the experiment for testing egg development time, the conditions were identical for all individuals, with a gradual decrease in temperature from about 9 to 4 ’ C during October-January. From the middle of January and throughout April, different batches of two to 16 individuals (cf. Table 1) were exposed to different temperature regimes (Fig. 1) . Adaptation to temperature increase was short within all batches, and batch 2 was put directly from 5 to 16’ C. The stripped eggs were incubated at water temperatures identical to batches 1 and
79
20
’
N
5
0
J
‘F
M
A
M
’
J
J
J
J
I
A
2000 : 1800
-
600
-
400
-
200 -
0
N
0
J
F
M
A
Fig. 1. Weekly mean temperature Temperature
Units (CTU)
M
A
( ‘C) based on daily observations, and accumulated to hatching for the five different batches of crayfish egs.
Celsius
3. The crayfish were fed weekly with half-cooked potatoes and boiled pieces of prawn. Surplus food was removed the following day. Feeding was stopped 1 week before expected hatching, based on egg examination. Embryonic development was checked weekly from 600 CTU (Celsius Temperature Units = degrees Celsius x days) in batch 1, less frequently in the others, by stripping off one egg per female, measuring the diameter and examining the embryonic growth in a binocular microscope. RESULTS
Egg development time and hatching Large differences were recorded in the required CTU for hatching. Batch 1, which was offered temperatures between 15 and 18°C from 16 January (560
80
CTU), only required a total of approximately 1300 CTU to hatch. Batch 2, though kept for a longer period in cold water, required fewer CTU than batch 3, which was incubated at a slightly lower temperature (11-16’ C ) . By far the highest total CTU was required by batch 5, in whiich hatching took place after approximately 1900 CTU in mid-June, more than 3 months later than batch 1. No difference was found in required CTU for stripped or attached eggs at corresponding temperatures. Almost 100% hatched in all experiments (i.e., number of eggs giving viable juveniles). Egg losses varied between specimens, but no increase in egg loss was found with increased temperature or prolonged incubation in captivity. Only a few eggs were lost due to fungus, and no difference was found in fungus infection due to temperature. The incubation temperature influenced neither early growth nor survival of juveniles. The second molt was reached within 7-11 days for all batches, with mortality rates less than 20%. Embryonic development
The eggs remained dark brown with black or dark granules and a diameter of 24-27 mm until about 600 CTU, when a pale area could be distinguished at or near the base of the string. At approximately 650 CTU a lighter ring surrounded by a dark area appeared within the pale area, and at 700 CTU (end of January) a branched image of the thoraxial appendages appeared in connection with the first, central nerve ring. At 900-950 CTU the total number of appendages became visible, folded along the body axes, as the head area and eye anlage became visible, all within an opaque area. At this stage the embryo occupied 20-30% of the egg diameter. At 950-1000 CTU the light “half moon” with the embryo increasing to 40-50% of the egg diameter and the heart beats as well as the full shape of the juvenile crayfish could be seen. The eyes became pigmented after 1100 CTU, and during the last weeks there was a rapid absorption of yolk mass. The juveniles are, however, born with a considerable amount of yolk mass. During the last week, both the antennae as well as the red pigments alongside them are easily visible. Egg diameter increased slightly up to 20-30 mm until 2 weeks prior to hatching, but expanded to 32-35 mm-during the last week. Adult post-hatching development After removal of the offspring, the adults were again fed and the progress of molting and maturation was followed ( see Table 1) . Females in batch 1 molted 7-8 weeks after hatching, or 5.5-7 weeks after the offspring had left their
81
mother. All females became mature and generally this rematuration was visible 1-2 weeks after molting. Within the other batches, time between hatching and malting/maturation was less, but often a smaller proportion of individuals molted. In batch 4, several individuals molted while the offspring were still in stage 1 and attached, thus indicating a severe disturbance of the synchronization. DISCUSSION
The noble crayfish obviously have a great flexibility in required CTU, where higher temperatures have the effect of lowering the required amount of heat to fulfil embryonic development. In Norway, the effects of different temperature regimes within natural populations are relatively small, as temperature seldom exceeds 5 “C until early May, and hatching normally occurs in early July ( Skurdal and Qvenild, 1986). Literature data are scarce, but 1500 CTU is estimated as the requirement for hatching in nature (Cukerzis, 1973). Hofman (1979) states that 1340-1380 CTU are needed for embryonic development in Pacifastacus Zeniusculus, while Mason (1977) induced hatching at only 906 CTU. As CTU requirements are high compared both to other crayfish species, and especially to fish (three to four times CTU required by brown trout Salmo trutta and salmon Salmo salur) , the advantages of reducing this under rearing conditions are obvious for several reasons. First, the possibility of obtaining two reproductive cycles yearly could reduce the size of the broodstock population by 50%, thus giving more space for juvenile raising. Second, by manipulating the temperature the time of hatching may easily be shortened (or prolonged) to the most favourable for outdoor stocking of juveniles. In our experiment the incubation period was reduced from 8 to 5 months by elevating the temperature. The lower limit of CTU will depend first on the data at which the temperature can be raised, without increasing the mortality rate of the eggs; second it will depend on how fast, and at which level the temperature can be raised. Our data suggest that even a sudden increase in temperature will be harmless after approximately 600 CTU, but normally crayfish eggs are more susceptible to manipulations in the earlier stages. Mason (1977) states 650 CTU as the critical development time for stripping the eggs of Pucifastucus Zeniusculus. In the earlier stages, survival of stripped eggs was found to be strongly temperature dependent, with increased survival at the lower temperatures. The tolerance of stripped eggs cannot, however, be directly compared to attached eggs, and the lower tolerance limit to manipulation should be persued in later studies. By increasing the temperature, Westin and Gydemo (1986) were able to shorten egg development in Astucus astacus from the natural 9 months to 4 months. In their experiment, temperature was increased after approximately 3 months (October-January), although no CTU values were given. Cukerzis and Shestokas (1977) raised the temperature after only 15 days cold-water
82
diapause, thereby inducing hatching after only 45 days (temperature 18-20” C) , without recording reduced growth or survival of juveniles. The embryonic development during the low temperature period is arrested, thus acting as a “timing” control, well known from other arthropods. The extent to which this resting period is essential to the embryonic development is as yet unknown, although obviously it can be greatly reduced. There is, however, severe confusion concerning the required length of coldwater diapause with arrested egg development, and at which time and to what level temperature can be elevated in order to shorten the egg development. The present paper indicates the plasticity in total required CTU needed to fulfil embryonic development. As knowledge of effects of temperature manipulation serve as the most powerful measure for the control and change of seasonal timing, efforts should be made to elucidate this for all crayfish species of interest in aquaculture. In the present experiment rematuration occurred after molting in all batches without lowering the temperature. No attempt was made to mate the mature females, as males were not adapted to the same temperatures. Westin and Gydemo (1986) succeeded in inducing two matings during two subsequent years; however, the post-reproductive molting success in the second year was reduced, indicating increased stress following the shortened cycle.
REFERENCES Cukerzis, J., 1973. Biologische Grundlagen der Metode der kunstlichen Aufzucht der Brut des Astacus astacus L. Freshwater Crayfish. I. Austria, 1972, pp. 187-202. Cukerzis, J. and Shestokas, J.A., 1977. Embryonic diapause in Astacus astacus L. Zh. Obshch. Biol., 38: 929-933 (in Russian with English Abstract). Cukerzis, J., Sheshtokas, J.A. and Terentyev, A.L., 1979. Method for accelerated breeding of crayfish juveniles. Freshwater Crayfish. IV. France, 1978, pp. 451-458. Hofman, J., 1979. Die Flusskrebse, Biologie, Haltung und wirtschaftlige Bedeutung. 2. Auflage. Verlag Paul Parey, Hamburg, 109 pp. Huner, J.V. and Lindqvist, O.V., 1985. Effects of temperature and photoperiod on mating and spawning activities of wild-caught noble crayfish Astacus astacus Linne (Astacidae, Decapoda). Presented at World Mariculture Society Meeting, Orlando, FL, 1985. Mason, M.C., 1977. Artificial incubation of crayfish eggs [Pacifastacus leniusculus (Dana)]. Freshwater Crayfish, III. Finland, 1976, pp. 119-132. Skurdal, J. and Qvenild, T., 1986. Growth, maturity and fecundity of Astacus astacus in Lake Steinsfjorden, S.E. Norway. Freshwater Crayfish, VI. Sweden, 1984, pp. 182-186. Westin, L. and Gydemo, R., 1986. Influence of light and temperature on reproduction and molting frequency of the crayfish, Astacus astacus L. Aquaculture, 52: 43-50.
77 -
Printed
in The Netherlands
Egg Development and Lifecycle Timing in the Noble Crayfish (Astacus tzstacus) DAG 0. HESSEN,
TROND TAUGBBL,
EIRIK FJELD and JOSTEIN
SKURDAL
Department of Biology, University of Oslo, P.O. Box 1050, Blindern, 0316 Oslo 3 (Norway) (Accepted
17 December
1986)
ABSTRACT Hessen, D.O., Taugbel, T., Fjeld, E. and Skurdal, J., 1987. Egg development in the noble crayfish (Astacus astacus). Aquaculture, 64: 77-82.
and lifecycle timing
Egg development time in Astacus astacus was strongly influenced by temperature. Five batches of eggs were subjected to different temperature regimes after approximately 600 degree days and, by increasing the temperature, the total number of degree days to hatching was reduced from 1900 to 1300. There were no systematic differences in hatching success or juvenile survival due to different temperature treatments. Females molted and rematured ( 50-100% ) 4-8 weeks after hatching.
INTRODUCTION
Following the extensive development of aquaculture in Norway, the potential for crayfish cultivation has attracted considerable interest. The noble crayfish (Astacus astacus) has its obvious advantages in high market price, high demand, and is established as a delicacy far outside Scandinavia. As demands by far exceed capture from native populations, the most obvious prerequisites for noble crayfish as an aquaculture organism should be fulfilled. Its disadvantages are low fecundity and low growth rates in nature, as well as its cannibalistic nature, common to most of the crayfish and lobster species. Among the more important parameters to know and control are egg development time and the possibility of timed hatching. The importance of temperature to the overall life cycle of crayfish is well documented (Huner and Lindqvist, 1985; Westin and Gydemo, 1986). In the present paper, we present data on egg tolerance to fluctuating temperature as well as shortened and delayed hatching in crayfish eggs under different incubation temperatures. In Norway, the interest has so far been concentrated mainly on rearing in intensive, indoor conditions due to the cold climate, and the following account relates to this.
0044-8486/87/$03.50
0 1987 Elsevier Science Publishers
B.V.
78 TABLE 1 Date of hatching, occurrence of two-stage juveniles and malting of the adult females (percentage of females molting and percentage of these mating are given) Batch
1 2 3 4 5
N
6 9 6 16 2
Maturing ( % of molted)
Molting
Date Hatching
Two-stage juveniles
Date
10 March 14 April 9 April 6 May 13 June
18 March 25 April 20 April 15 May 20 June
28 April -12 14 May -24 No data” 16 May -31 30 June -17
% May June
100 44
100 100
July July
56 100
67 100
“All died due to accidental stop in water flow. MATERIALS AND METHODS
The crayfish for the present experiment were sampled from Lake Harestuvann, south-eastern Norway by SCUBA diving in September 1985. After acclimatization to aquaria conditions for 2 weeks, females ready for mating (yellow glands under the tail) were put together with males in a sex ratio of 3:l. All females became mated within 1-14 days. When mated, females were placed in single chambers prior to spawning, which occurred within l-7 days at a water temperature of 9-10°C (mid-October). The crayfish were kept individually in a raceway system, separated by movable walls. Each cell was 10x 12 cm, and each raceway consisted of 15-20 separate cells. Water was heated by passing it through a supercoiled tube in a thermostat-regulated water bath. Prior to heating, the water passed through a two-layer filter of activated charcoal and shellsand. To prevent supersaturation with air during heating, the water was aerated with an air pump in front of the raceways. Water flow varied between 0.2-0.4 1-l mini raceway-’ and dissolved oxygen was close to saturation (80-100% ) . An obvious improvement would be to incubate eggs apart from the females. This would require less space and allow a further preparation of females to a second mating. To test the survival of such eggs, half of the eggs were stripped from four individuals (corresponding to 30-50 eggs/individual) after 600 CTU, and placed in two different Artemia flasks with constant water flow, following the “Cukerzis-principle” (Cukerzis et al., 1979). In the experiment for testing egg development time, the conditions were identical for all individuals, with a gradual decrease in temperature from about 9 to 4 ’ C during October-January. From the middle of January and throughout April, different batches of two to 16 individuals (cf. Table 1) were exposed to different temperature regimes (Fig. 1) . Adaptation to temperature increase was short within all batches, and batch 2 was put directly from 5 to 16’ C. The stripped eggs were incubated at water temperatures identical to batches 1 and
79
20
’
N
5
0
J
‘F
M
A
M
’
J
J
J
J
I
A
2000 : 1800
-
600
-
400
-
200 -
0
N
0
J
F
M
A
Fig. 1. Weekly mean temperature Temperature
Units (CTU)
M
A
( ‘C) based on daily observations, and accumulated to hatching for the five different batches of crayfish egs.
Celsius
3. The crayfish were fed weekly with half-cooked potatoes and boiled pieces of prawn. Surplus food was removed the following day. Feeding was stopped 1 week before expected hatching, based on egg examination. Embryonic development was checked weekly from 600 CTU (Celsius Temperature Units = degrees Celsius x days) in batch 1, less frequently in the others, by stripping off one egg per female, measuring the diameter and examining the embryonic growth in a binocular microscope. RESULTS
Egg development time and hatching Large differences were recorded in the required CTU for hatching. Batch 1, which was offered temperatures between 15 and 18°C from 16 January (560
80
CTU), only required a total of approximately 1300 CTU to hatch. Batch 2, though kept for a longer period in cold water, required fewer CTU than batch 3, which was incubated at a slightly lower temperature (11-16’ C ) . By far the highest total CTU was required by batch 5, in whiich hatching took place after approximately 1900 CTU in mid-June, more than 3 months later than batch 1. No difference was found in required CTU for stripped or attached eggs at corresponding temperatures. Almost 100% hatched in all experiments (i.e., number of eggs giving viable juveniles). Egg losses varied between specimens, but no increase in egg loss was found with increased temperature or prolonged incubation in captivity. Only a few eggs were lost due to fungus, and no difference was found in fungus infection due to temperature. The incubation temperature influenced neither early growth nor survival of juveniles. The second molt was reached within 7-11 days for all batches, with mortality rates less than 20%. Embryonic development
The eggs remained dark brown with black or dark granules and a diameter of 24-27 mm until about 600 CTU, when a pale area could be distinguished at or near the base of the string. At approximately 650 CTU a lighter ring surrounded by a dark area appeared within the pale area, and at 700 CTU (end of January) a branched image of the thoraxial appendages appeared in connection with the first, central nerve ring. At 900-950 CTU the total number of appendages became visible, folded along the body axes, as the head area and eye anlage became visible, all within an opaque area. At this stage the embryo occupied 20-30% of the egg diameter. At 950-1000 CTU the light “half moon” with the embryo increasing to 40-50% of the egg diameter and the heart beats as well as the full shape of the juvenile crayfish could be seen. The eyes became pigmented after 1100 CTU, and during the last weeks there was a rapid absorption of yolk mass. The juveniles are, however, born with a considerable amount of yolk mass. During the last week, both the antennae as well as the red pigments alongside them are easily visible. Egg diameter increased slightly up to 20-30 mm until 2 weeks prior to hatching, but expanded to 32-35 mm-during the last week. Adult post-hatching development After removal of the offspring, the adults were again fed and the progress of molting and maturation was followed ( see Table 1) . Females in batch 1 molted 7-8 weeks after hatching, or 5.5-7 weeks after the offspring had left their
81
mother. All females became mature and generally this rematuration was visible 1-2 weeks after molting. Within the other batches, time between hatching and malting/maturation was less, but often a smaller proportion of individuals molted. In batch 4, several individuals molted while the offspring were still in stage 1 and attached, thus indicating a severe disturbance of the synchronization. DISCUSSION
The noble crayfish obviously have a great flexibility in required CTU, where higher temperatures have the effect of lowering the required amount of heat to fulfil embryonic development. In Norway, the effects of different temperature regimes within natural populations are relatively small, as temperature seldom exceeds 5 “C until early May, and hatching normally occurs in early July ( Skurdal and Qvenild, 1986). Literature data are scarce, but 1500 CTU is estimated as the requirement for hatching in nature (Cukerzis, 1973). Hofman (1979) states that 1340-1380 CTU are needed for embryonic development in Pacifastacus Zeniusculus, while Mason (1977) induced hatching at only 906 CTU. As CTU requirements are high compared both to other crayfish species, and especially to fish (three to four times CTU required by brown trout Salmo trutta and salmon Salmo salur) , the advantages of reducing this under rearing conditions are obvious for several reasons. First, the possibility of obtaining two reproductive cycles yearly could reduce the size of the broodstock population by 50%, thus giving more space for juvenile raising. Second, by manipulating the temperature the time of hatching may easily be shortened (or prolonged) to the most favourable for outdoor stocking of juveniles. In our experiment the incubation period was reduced from 8 to 5 months by elevating the temperature. The lower limit of CTU will depend first on the data at which the temperature can be raised, without increasing the mortality rate of the eggs; second it will depend on how fast, and at which level the temperature can be raised. Our data suggest that even a sudden increase in temperature will be harmless after approximately 600 CTU, but normally crayfish eggs are more susceptible to manipulations in the earlier stages. Mason (1977) states 650 CTU as the critical development time for stripping the eggs of Pucifastucus Zeniusculus. In the earlier stages, survival of stripped eggs was found to be strongly temperature dependent, with increased survival at the lower temperatures. The tolerance of stripped eggs cannot, however, be directly compared to attached eggs, and the lower tolerance limit to manipulation should be persued in later studies. By increasing the temperature, Westin and Gydemo (1986) were able to shorten egg development in Astucus astacus from the natural 9 months to 4 months. In their experiment, temperature was increased after approximately 3 months (October-January), although no CTU values were given. Cukerzis and Shestokas (1977) raised the temperature after only 15 days cold-water
82
diapause, thereby inducing hatching after only 45 days (temperature 18-20” C) , without recording reduced growth or survival of juveniles. The embryonic development during the low temperature period is arrested, thus acting as a “timing” control, well known from other arthropods. The extent to which this resting period is essential to the embryonic development is as yet unknown, although obviously it can be greatly reduced. There is, however, severe confusion concerning the required length of coldwater diapause with arrested egg development, and at which time and to what level temperature can be elevated in order to shorten the egg development. The present paper indicates the plasticity in total required CTU needed to fulfil embryonic development. As knowledge of effects of temperature manipulation serve as the most powerful measure for the control and change of seasonal timing, efforts should be made to elucidate this for all crayfish species of interest in aquaculture. In the present experiment rematuration occurred after molting in all batches without lowering the temperature. No attempt was made to mate the mature females, as males were not adapted to the same temperatures. Westin and Gydemo (1986) succeeded in inducing two matings during two subsequent years; however, the post-reproductive molting success in the second year was reduced, indicating increased stress following the shortened cycle.
REFERENCES Cukerzis, J., 1973. Biologische Grundlagen der Metode der kunstlichen Aufzucht der Brut des Astacus astacus L. Freshwater Crayfish. I. Austria, 1972, pp. 187-202. Cukerzis, J. and Shestokas, J.A., 1977. Embryonic diapause in Astacus astacus L. Zh. Obshch. Biol., 38: 929-933 (in Russian with English Abstract). Cukerzis, J., Sheshtokas, J.A. and Terentyev, A.L., 1979. Method for accelerated breeding of crayfish juveniles. Freshwater Crayfish. IV. France, 1978, pp. 451-458. Hofman, J., 1979. Die Flusskrebse, Biologie, Haltung und wirtschaftlige Bedeutung. 2. Auflage. Verlag Paul Parey, Hamburg, 109 pp. Huner, J.V. and Lindqvist, O.V., 1985. Effects of temperature and photoperiod on mating and spawning activities of wild-caught noble crayfish Astacus astacus Linne (Astacidae, Decapoda). Presented at World Mariculture Society Meeting, Orlando, FL, 1985. Mason, M.C., 1977. Artificial incubation of crayfish eggs [Pacifastacus leniusculus (Dana)]. Freshwater Crayfish, III. Finland, 1976, pp. 119-132. Skurdal, J. and Qvenild, T., 1986. Growth, maturity and fecundity of Astacus astacus in Lake Steinsfjorden, S.E. Norway. Freshwater Crayfish, VI. Sweden, 1984, pp. 182-186. Westin, L. and Gydemo, R., 1986. Influence of light and temperature on reproduction and molting frequency of the crayfish, Astacus astacus L. Aquaculture, 52: 43-50.