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Responses of juvenile Penaeus monodon Fabricius to natural and artificial sea waters of low salinity
Aquaculke, 32 (1983) 165-1’74 Elsevier Scientific Publishing Company,
165 Amsterdam
- Printed
in The Netherlands
RESPOI~SES OF JUVENILE PAPAL US ~0~~~0~ FABRICIUS TO NATURAL AND ARTIFICIAL SEA WATERS OF LOW SALINITY
D.F. CAWTHORNE*,
T. BEARD **, J. DAVENPORT
*Natural Environment Research Council, Unit Science l,aboratories, Menai Bridge, Gwynedd **Ministry of Agriculture, Fisheries and Food, Experimtznt Station, Conwy. Gwynedd (Great ~ommu~~ications (Accepted
concerning
this paper should
* and J.F. WICKINS**
of Marine Invertebrate Biology, Marine (Great Erita~~~ Directorate of Fisheries Research, Fisheries Britain) be addressed
to J.F.W.
16 June 1982)
ABSTRACT Cawthor’ne, D.F., Beard, T., Davenport, J. and Wickins, J.F., 1983. Responses of juvenile Penaeus monodon Fabricius to natural and artificial sea waters of low salinity. Aquaculture, 32: 165-174. Juvenile Penaeus monodon from three regions (Thailand, Tahiti and South Africa) were acclimated from sea water (33.5°/00 salinity) to fresh water and waters of reduced salinity, ranging from 1.7’/,, to lo“&,, at different rates of salinity change. The changes were made over periods of up to 3 days and by direct transfer. Exposure to fresh water produced 100% mortality within 4 h. Young prawns (< 40 days post-metamorphosis) tolerated short acclimation periods of 6 h to 3 days and survived in low salinity water better than older animals. The exposure of prawns to dilute artificial media revealed a requirement for a complex medium containing more than one salt. An osmoregulation curve for 150-day-old laboratory reared prawns was also constructed.
Pemeus monodon is a large brackish water-marine prawn widely distributed throughout the tropical IndoPacific region. It has been fished for and cultured in many regions of the world (Wickins, 1976). In the U.K. it has attracted attention for aquaculture studies because of its high survival and good growth rate in marine controlled environment systems (Forster and Beard, 1974). A major obstacle to the commercial culture of a tropical prawn species in a temperate country such as the U.K. is the necessity for maintaining high rearing temperatures (Wilkins and Beard, 1978). The use of fresh water rather than saline water would allow a wider range of possible culture sites with access to waste heat (e.g. inland power stations). Successful acclimation and growth of young post-larvae of P. ~uno~~~ in a fresh water lake has recently been reported from the Philippines by Pantastico (1979). In i his paper we describe the survival and growth of P. monodon post-larvae acclimated to fresh and low salinity water in laboratory culture systems. 0044~8486/83/$03.00
0 1983 Elsevier
Science
Publishers
B.V.
166
MATERIALS
AND METHODS
Origin of post-larvae Three batches of post-larvae of Penaeus monodon were used in the study. The first batch was imported in March 1980 from Thailand. It consisted of hatchery reared post-larvae aged 15 days post-metamorphosis - the offspring of wild parents. The second group of post-larvae aged 19 days post-metamorphosis were obtained in April 1980 from Tahiti. These were reared from hatchery-raised parents. The final group of prawns aged 22 days post-metamorphosis was obtained from South Africa in October 1980, again from hatchery stock. All post-larvae were initially fed live Artemia nauplii and were weaned over a 2-week period onto a diet of fresh mussel (My tilus edulis) mantle tissue for acclimation trials, or mussels and frozen shrimp (Crangon crangon) for growth studies. Food was given daily throughout all trials. Post-larvae were maintained in a laboratory recirculation system at 26-30°C and 28-30°/oo salinity until used in experiments. Acclimation
studies
Two independent techniques were employed in an attempt to acclimate P. monodon post-larvae to fresh water, namely: linear reduction of salinity and a progressively decreasing rate of salinity change. In an initial series of experiments at the Marine Science Laboratories, Menai Bridge, the juvenile prawns were exposed to linear declines in salinity (see Cawthorne, 1979) from full salinity sea water (33.5’/,,) to fresh water over periods of 3 days, 24 h or 6 h using the apparatus described by Davenport et al. (1975). A direct transfer test was also conducted. All trials were performed at 26-30°C. In a second series of tests, salinities were reduced to 1.7°/oo (5% sea water) over the same time periods. Ten animals were used in each experiment, and mortalities were assessed 2 h after reaching the final salinity. Animals were also held continuously in sea water as controls. These experiments were repeated with animals from all three sources and at various stages in their development. The survival of Thailand prawns was studied in seven artificial media made up to be iso-osmotic with 5% sea water (1.7’/,,): (1) Sodium chloride in tap water (1.9 g NaCl 1-l) (2) Sodium chloride in distilled water (1.9 g NaCl 1-l) (3) Calcium chloride in distilled water (5.9 g CaCl, * 6H,O 1-l ) (4) Magnesium sulphate in distilled water (12.6 g MgSO, * 7H,O 1-l) (5) Sodium carbonate in distilled water (2.4 g NazC03 1-l) (6) Artificial sea salts in distilled water (Natura, Waterlife Research Ltd., Longford, Middlesex, U.K.) (7) Artificial sea water (Ayres and Wood, 1977) as used for the storage of live lobsters.
167
All osmolarities were determined on a Knauer semi-micro osmometer. Batches of 10 animals were placed in the salinity apparatus at 33.5°/,,0 and the salinity reduced to 1.7°j00 over a 6 h period. At this point they were transferred to small tanks containing the artificial medium. The survival of animal: in each medium was monitored. A series of animals was kept in diluted normal sea water of 1.7o/o,, for the duration of the experiment. At t’he Fisheries Experiment Station, Conwy, prawns were exposed to a progressively decreasing rate of salinity change over l-, 2- or 3-day periods with the slowest rate of change occurring between 8 and 2%, . The rate of salinity change with time in the experimental tanks is shown in Fig. 1. The tanks measured 76 X 42 X 9.5 cm water depth and were arranged as shown in Fig. 2. Warm fresh water and sea water, mixed to give a salinity of 2o/oo at a temperature of 28” C, was recycled between a 400 1 reservoir and an ele30
24
6
L 0
24
72
48
time
(hours)
Fig. 1. The pattern of salinity reduction in the at the Fisheries Experiment Station, Conwy.
experimental
tanks
used for acclimation
waste
Fig. 2. The arrangement of experimental Fisheries Experiment Station, Conwy.
tanks
used for acclimation
studies
at the
168
vated 60 1 tank to provide a constant head of water. A proportion of the water flowed by gravity to the experimental tanks via one, two or three pipes. The flow rate (30 ml min-’ ) for each pipe was selected so that each tank received a 99% water change in either 1, 2 or 3 days. Adequate mixing was ensured by aeration at four points in each tank, and satisfactory oxygen and ammonia levels (see Wickins, 1981) were maintained even at the lowest water exchange rate. Three replicate populations were exposed to each treatment. Three replicate control populations were also maintained in sea water at 30°/oo with 99% replacement of water over 3 days. At the start of each experiment each tank was filled with sea water at 3Oo/oo, 10 prawns added, and the flows started. Growth
trials
Growth and survival after acclimation were tested at the Fisheries Experiment Station, Conwy, where the prawns were grown for up to 4 weeks in octagonal tanks (approx. 2.13 m diameter, floor area 3.01 m2) at salinities of 2, 5 or lOo/oo and 28-30°C. In the first two experiments the prawns were selected from the survivors of previous acclimation experiments and thus contained individuals that had been exposed to different acclimation rates. In the third experiment all the prawns had been acclimated at the same rate over a 48-h period to the test salinities. During the growth trials each tank received flows of fresh water and sea water adjusted to give the required salinity at a combined flow rate of 16 1 min-’ . Control tanks also had an inflow of 16 1 min-’ , but of sea water (30-32°/oo) only. Temperature was maintained at 28--30°C. Tanks were lightly stocked (17-42 prawns/m2 ): the animals were counted, blotted dry and weighed as populations at the beginning and end of each experiment. Osmoregulation
tests
Specimens of 150--day-old Tahiti stock were acclimated over a 24-h period to a series of sea water concentrations, ranging from full sea water to 10% sea water (3.4’/,,, ) at 10% sea water intervals. Six animals were exposed to each concentration and these were acclimated to their respective media for 1 week prior to examination. At the end of this period a blood haemolymph sample of 50 d was taken from each animal, and its concentration measured using a semi-micro osmometer. RESULTS
Acclimation
and growth studies
For all combinations of stock, and rate of salinity change, exposure to fresh water produced 100% mortality within 4 h. In all three stocks young
169 TABLE I. Mortality of Penaeus ~~0~0~0~ juveniles at different ages during acclimation to iow salinity water (1 .Y/,,) (values are % mortality of 10 post-larvae per treatment) Initial age (days)
(a) Thailand 40 110 155
Period of transfer _--____ Direct
--
6h
24 h
3d
0 80 100
0 0 10
-
100
10
10
0 0
0 0
~.....
stock 20 100 100
0
(b) Tahifi stock 150
100
cc) South African 28 40
15 20
stock -
prawns. (< 40 days old} showed a much greater tolerance to reduced salinities than older animals (Table I). The younger prawns also survived rapid introduction to a reduced salinity level better than older prawns, for which at least 24 h was required for the salinity reduction. After direct transfer to 1.7°/00 some mortality (15%) was apparent even in the youngest animals tested (2%days old S. African post-larvae). However, in post-larvae up to 40 days old, no difference in survival could be detected between animals transferred over periods ranging from 6 h to 3 days. All !?ost-larvae exposed to dilute single salt solutions died within 60 h, while in both types of artifidial sea water, 20% mortality was evident after 48 h, but had not increased after a further 48 h when the experiment was terminated. (Table II). Prawns from Thailand and Tahiti showed similarly poor growth and survival rates in 2o/00when compared with ‘control’ prawns in normal sea water; survival was as low as 23.2% in 2°/00, compared with 97% survival in full salinity water (Tables III a,b). Table IV shows the effect upon growth and survival of acclimating postlarvae to 5 and 10°/OO.Even at these salinity levels growth and survival were extremely poor when compared with prawns in full sea water controls. Thus, in no experimental salinity other than full strength sea water was good growth or good 4 week survival achieved. Osmcregulation
Mei~uremen~ of haemolymph concentrations in 150-day-old Tahiti prawns held at different medium concentrations indicated that in media between 320
0 0 10
60 90 100
100 100
6 12 24
36 48 60
72 96
water)
100 100
70 100 100
0 0 20
NaCl
100 100
100 100 100
60 100 100
CaCl,
of (h)
Duration exposure
NaCl (in tap
of 40-day-old Penoeus monodon upon exposure stock). Values are % mortality of 10 post-larvae
II
Mortality (Thailand
TABLE
MgSo,
to dilute media per treatment
NaFo,
isomotic
20 20 20 20 20
20 20
0 20 20
(Ayres
10 20 20
0 0 0
‘Natura’
sea water
1.7’/,,,, sea water
Artificial
with
& Wood
1977)
0 0
0 0 0
0 0 0
~~_
Natural sea water (control)
171 TABLE
Il.1
Growth and survival of Penoelrs ~~~od~n in water of 2”/,, salinity and in natural sea water (3O-32o/,, ). (a) 27-day-old Thailand stock. (b) 66-day-old Tahiti stock. The prawns were weighed as populations -. ~(a)
2O100
control 30-32°/0, --.._
Mean wt. (start) (g) % survival (4 weeks) (%) Mean wt. (4 weeks) (g) ___----
0.062 51.7 0.33
0.074 98.8 1.12
(b)
2’/,, acclimated in 24 h
2’/,, acclimated in 48 h
control 30--32&,
0.25 23.2 0.33
0.26 34.4 0.43
0.29 97.0 0.64
_^___I Mean wt (start) (g) % survival (2 weeks) (%) Mean wt (2 weeks) (g)
._--_
-
-
TABLE IV Growth and survival of 86-day-old Penaeus monodon in water of 5 and lO’/v, salinity compared with prawns in recirculating and throughflow sea water at 30-32’/,, . (Tahiti stock). The prawns were weighed as populations ~5%0 ^_cMean wt,. (start) (g) Mean wt.. (2 weeks) (g) Survival (2 weeks) (%) Mean wt. (4 weeks) (g) Survival (4 weeks) (W)
0.47 0.96 44 1.47 6
lW,*
0.52 1.13 100 1.70 34
Controls
( 30-320/,,
)
Recirculating
Throughflow
0.44 1.43 94 2.07 92
0.57 1.84 96 3.17 94
and 870 mOsm the post-larvae exerted good osmoregulatory control (Fig. 3). In media below 320 mOsm the haemolymph became rapidly diluted and the haemolymph concentration curve ran parallel to the isomotic line. Clearly osmoregulation was comparatively inefficient in media below 320 mOsm. Post-larvae aged 150 days post-metamorphosis were isomotic at a medium concentration of around 790 mOsm: above this concentration the animals were slightly hypo-osmotic to their environment.
172
I 100 -
,I’ /’ #’
II
ml
200
300
ml
ml
environment
600
700
800
900
1 1000
mOsm
Fig. 3. The osmoregulation curve for 150-day-old Penaeus monodon post-larvae (Tahiti stock). Vertical lines indicate 2 x SE. and the dashed line represents the isosmotic line. DISCUSSION
The lower limit of salinity tolerance of Penaeus monodon in our studies was probably close to 1.7°/00. This resuit was found for prawns from all three geographical sources and agrees well with other quoted lower salinity limits for penaeid prawn species (Gunter et al., 1964). The data indicate that older prawns are less able to adapt to low salinity than young ones; similar results were found for Penaeus monodon by Pantastico (1979) for Philippine stock. This greater tolerance to reduced salinity in juvenile penaeid prawns has also been demonstrated for Penaeus setiferus and Penaeus stylirostris (Castille and Lawrence, 1981a). The poor survival in single salt dilute media indicates a requirement for a mixture of ions. Survival in both commercially available sea water salt, and in artificial sea water (made up according to the formula employed by Ayres and Wood (1977) was slightly inferior to that recorded in natural sea water, again indicating a requirement for a complex medium. We obtained poor growth at all salinities tested (2, 5 and 1Oo/0o)below full salinity sea water. This result is at variance with the data obtained by Pantastico (1979) who reported good growth and survival in fresh water. One possible explanation for this discrepancy may lie in the importance of substrate. Our growth experiments were conducted in bare floored tanks whereas Pantastico (1979) reared animals in open floored cages held on the bottom of an open lagoon, intermittently subject to sea water inflow. She stressed the importance of giving the prawns access to the lagoon bottom for optimum development. In such a situation the animals may well have had access to heightened salt concentration within, or very close to, the substrate even
173
though the overlying medium was fresh or of low salinity water (O.14-1.3o1,o; Anon. 11979). The possibility that Philippine stock differed physiologic~ly from those tested was not evaluated because of the loss of Philippine postlarvae curing shipment to Great Britain. The osmoregulation data presented here for 150-day-old animals agree well with Chen (1976) who quoted the normal salinity range of Penaeus monoclon in Taiwan as 15-30°/00. Over this salinity range the prawns are able to maintain a narro’w range of internal fluid concentrations. The isosmotic concentration obtained in our experiments corresponded to about 23-Z5°/oo region, which is similar to the value obtained in Castille and Lawrence (1981b) for several species of penaeid prawns in the U.S.A. We therefore conclude that whilst it may be possible to introduce Penaeus monodm to water of very low salinity under certain conditions, the species seems unlikely to be able to survive and grow well in fresh water and low salinity cultures in bare-floored tanks. ACKNOWLEDGEMENTS
It is a pleasure to thank the following scientists and their organisations for sending us shipments of post-larvae: Mr Kasemsant Ch~ayondeja, Department of Fisheries, Ministry of Agriculture and Cooperatives, Bangkok, Thailand; Dr A. hlichel, AQUACOP, Taravao, Tahiti; Dr H.F.B. Champion, Kwazulu Development Corporation, Gingindlovu, South Africa, and Dr F. Santiago, SEAFDEC, Binangonan, Philippines.
REFERENCES Anon., 1979. Ecology of Laguna lake. Asian Aquaculture, 2 (7): 6. Ayres, P.A. and Wood, P.C., 1977. The live storage of lobsters. Lab. Leafl., MAFF Direct. Fish. Res., Lowestoft, (New Series), No. 37, 9 pp. Castille, F.L., Jr. and Lawrence, A.L., 1981a. A comparison of the capabilities of juvenile and adult Penaeus setiferus and Fenaeus stylirostris to regulate the osmotic, sodium and chloride concentrations in the haemolymph. Comp. Biochem. Physiol., 68A: 677680. Castille, F.L. Jr. and Lawrence, A.L., 1981b. The effect of salinity on the osmotic, sodium and chloride concentrations in the haemolymph of euryhaline shrimp of the genus Penatus. Comp. Biochem. Physiol., 68A: 75-80. Cawthorne, D.F., 1979. A comparative study of the closure responses of some Cirripede species exposed to falling seawater concentration. J. Mar. Biot. Assoc. U.K., 59: 811817. Chen, T.P., 1976. Aquaculture Practices in Taiwan. Fishing News Books Ltd. Farnham, Surrey, 162 pp. Davenport, J., Gruffydd, L1.D. and Beaumont, A.R., 1975. An apparatus to supply water of fluctuating salinity and its use in a study of the salinity tolerance of larvae of the scallop Pecten maximus L. J. Mar. Biol. Assoc. U.K., 55: 391-409. Forster, J.R.M. and Beard, T.W., 1974. Experiments to assess the suitability of nine species of prawns for intensive cultivation. Aquaculture, 3: 355-368.
174
Gunter, G., Christmas, J.Y. and Killebrew, R., 1964. Some relations of salinity to population distribution of mobile organisms, with special reference to penaeid shrimp. Ecology, 45: 181-185. Pantastico, J.B., 1979. Research paper presented at the ‘Technical Consultation on Available Aquaculture Technology in the Philippines’. South-East Asian Fisheries Development Centre, Aquaculture Department, Tigbauan, Iloilo,Philippines. 8-10 February 1979. 5 pp. (mimeo). Wickins, J.F., 1976. Prawn biology and culture. Oceanogr. Mar. Biol. Ann. Rev., 14: 435-507. Wickins, J.F., 1981. Water quality requirements for intensive aquaculture: a review. In: K. Tiews (Editor), Aquaculture in Heated Effluents and Recirculation Systems. Vol. 1 Heenemann Verlagsgesellschaft, Berlin, pp. 17-37. Wickins, J.F. and Beard, T.W., 1978. Ministry of Agriculture, Fisheries and Food, Prawn culture research. Lab. Leafl., MAFF Direct. Fish.Res., Lowestoft, No.42, 41 pp.
165 Amsterdam
- Printed
in The Netherlands
RESPOI~SES OF JUVENILE PAPAL US ~0~~~0~ FABRICIUS TO NATURAL AND ARTIFICIAL SEA WATERS OF LOW SALINITY
D.F. CAWTHORNE*,
T. BEARD **, J. DAVENPORT
*Natural Environment Research Council, Unit Science l,aboratories, Menai Bridge, Gwynedd **Ministry of Agriculture, Fisheries and Food, Experimtznt Station, Conwy. Gwynedd (Great ~ommu~~ications (Accepted
concerning
this paper should
* and J.F. WICKINS**
of Marine Invertebrate Biology, Marine (Great Erita~~~ Directorate of Fisheries Research, Fisheries Britain) be addressed
to J.F.W.
16 June 1982)
ABSTRACT Cawthor’ne, D.F., Beard, T., Davenport, J. and Wickins, J.F., 1983. Responses of juvenile Penaeus monodon Fabricius to natural and artificial sea waters of low salinity. Aquaculture, 32: 165-174. Juvenile Penaeus monodon from three regions (Thailand, Tahiti and South Africa) were acclimated from sea water (33.5°/00 salinity) to fresh water and waters of reduced salinity, ranging from 1.7’/,, to lo“&,, at different rates of salinity change. The changes were made over periods of up to 3 days and by direct transfer. Exposure to fresh water produced 100% mortality within 4 h. Young prawns (< 40 days post-metamorphosis) tolerated short acclimation periods of 6 h to 3 days and survived in low salinity water better than older animals. The exposure of prawns to dilute artificial media revealed a requirement for a complex medium containing more than one salt. An osmoregulation curve for 150-day-old laboratory reared prawns was also constructed.
Pemeus monodon is a large brackish water-marine prawn widely distributed throughout the tropical IndoPacific region. It has been fished for and cultured in many regions of the world (Wickins, 1976). In the U.K. it has attracted attention for aquaculture studies because of its high survival and good growth rate in marine controlled environment systems (Forster and Beard, 1974). A major obstacle to the commercial culture of a tropical prawn species in a temperate country such as the U.K. is the necessity for maintaining high rearing temperatures (Wilkins and Beard, 1978). The use of fresh water rather than saline water would allow a wider range of possible culture sites with access to waste heat (e.g. inland power stations). Successful acclimation and growth of young post-larvae of P. ~uno~~~ in a fresh water lake has recently been reported from the Philippines by Pantastico (1979). In i his paper we describe the survival and growth of P. monodon post-larvae acclimated to fresh and low salinity water in laboratory culture systems. 0044~8486/83/$03.00
0 1983 Elsevier
Science
Publishers
B.V.
166
MATERIALS
AND METHODS
Origin of post-larvae Three batches of post-larvae of Penaeus monodon were used in the study. The first batch was imported in March 1980 from Thailand. It consisted of hatchery reared post-larvae aged 15 days post-metamorphosis - the offspring of wild parents. The second group of post-larvae aged 19 days post-metamorphosis were obtained in April 1980 from Tahiti. These were reared from hatchery-raised parents. The final group of prawns aged 22 days post-metamorphosis was obtained from South Africa in October 1980, again from hatchery stock. All post-larvae were initially fed live Artemia nauplii and were weaned over a 2-week period onto a diet of fresh mussel (My tilus edulis) mantle tissue for acclimation trials, or mussels and frozen shrimp (Crangon crangon) for growth studies. Food was given daily throughout all trials. Post-larvae were maintained in a laboratory recirculation system at 26-30°C and 28-30°/oo salinity until used in experiments. Acclimation
studies
Two independent techniques were employed in an attempt to acclimate P. monodon post-larvae to fresh water, namely: linear reduction of salinity and a progressively decreasing rate of salinity change. In an initial series of experiments at the Marine Science Laboratories, Menai Bridge, the juvenile prawns were exposed to linear declines in salinity (see Cawthorne, 1979) from full salinity sea water (33.5’/,,) to fresh water over periods of 3 days, 24 h or 6 h using the apparatus described by Davenport et al. (1975). A direct transfer test was also conducted. All trials were performed at 26-30°C. In a second series of tests, salinities were reduced to 1.7°/oo (5% sea water) over the same time periods. Ten animals were used in each experiment, and mortalities were assessed 2 h after reaching the final salinity. Animals were also held continuously in sea water as controls. These experiments were repeated with animals from all three sources and at various stages in their development. The survival of Thailand prawns was studied in seven artificial media made up to be iso-osmotic with 5% sea water (1.7’/,,): (1) Sodium chloride in tap water (1.9 g NaCl 1-l) (2) Sodium chloride in distilled water (1.9 g NaCl 1-l) (3) Calcium chloride in distilled water (5.9 g CaCl, * 6H,O 1-l ) (4) Magnesium sulphate in distilled water (12.6 g MgSO, * 7H,O 1-l) (5) Sodium carbonate in distilled water (2.4 g NazC03 1-l) (6) Artificial sea salts in distilled water (Natura, Waterlife Research Ltd., Longford, Middlesex, U.K.) (7) Artificial sea water (Ayres and Wood, 1977) as used for the storage of live lobsters.
167
All osmolarities were determined on a Knauer semi-micro osmometer. Batches of 10 animals were placed in the salinity apparatus at 33.5°/,,0 and the salinity reduced to 1.7°j00 over a 6 h period. At this point they were transferred to small tanks containing the artificial medium. The survival of animal: in each medium was monitored. A series of animals was kept in diluted normal sea water of 1.7o/o,, for the duration of the experiment. At t’he Fisheries Experiment Station, Conwy, prawns were exposed to a progressively decreasing rate of salinity change over l-, 2- or 3-day periods with the slowest rate of change occurring between 8 and 2%, . The rate of salinity change with time in the experimental tanks is shown in Fig. 1. The tanks measured 76 X 42 X 9.5 cm water depth and were arranged as shown in Fig. 2. Warm fresh water and sea water, mixed to give a salinity of 2o/oo at a temperature of 28” C, was recycled between a 400 1 reservoir and an ele30
24
6
L 0
24
72
48
time
(hours)
Fig. 1. The pattern of salinity reduction in the at the Fisheries Experiment Station, Conwy.
experimental
tanks
used for acclimation
waste
Fig. 2. The arrangement of experimental Fisheries Experiment Station, Conwy.
tanks
used for acclimation
studies
at the
168
vated 60 1 tank to provide a constant head of water. A proportion of the water flowed by gravity to the experimental tanks via one, two or three pipes. The flow rate (30 ml min-’ ) for each pipe was selected so that each tank received a 99% water change in either 1, 2 or 3 days. Adequate mixing was ensured by aeration at four points in each tank, and satisfactory oxygen and ammonia levels (see Wickins, 1981) were maintained even at the lowest water exchange rate. Three replicate populations were exposed to each treatment. Three replicate control populations were also maintained in sea water at 30°/oo with 99% replacement of water over 3 days. At the start of each experiment each tank was filled with sea water at 3Oo/oo, 10 prawns added, and the flows started. Growth
trials
Growth and survival after acclimation were tested at the Fisheries Experiment Station, Conwy, where the prawns were grown for up to 4 weeks in octagonal tanks (approx. 2.13 m diameter, floor area 3.01 m2) at salinities of 2, 5 or lOo/oo and 28-30°C. In the first two experiments the prawns were selected from the survivors of previous acclimation experiments and thus contained individuals that had been exposed to different acclimation rates. In the third experiment all the prawns had been acclimated at the same rate over a 48-h period to the test salinities. During the growth trials each tank received flows of fresh water and sea water adjusted to give the required salinity at a combined flow rate of 16 1 min-’ . Control tanks also had an inflow of 16 1 min-’ , but of sea water (30-32°/oo) only. Temperature was maintained at 28--30°C. Tanks were lightly stocked (17-42 prawns/m2 ): the animals were counted, blotted dry and weighed as populations at the beginning and end of each experiment. Osmoregulation
tests
Specimens of 150--day-old Tahiti stock were acclimated over a 24-h period to a series of sea water concentrations, ranging from full sea water to 10% sea water (3.4’/,,, ) at 10% sea water intervals. Six animals were exposed to each concentration and these were acclimated to their respective media for 1 week prior to examination. At the end of this period a blood haemolymph sample of 50 d was taken from each animal, and its concentration measured using a semi-micro osmometer. RESULTS
Acclimation
and growth studies
For all combinations of stock, and rate of salinity change, exposure to fresh water produced 100% mortality within 4 h. In all three stocks young
169 TABLE I. Mortality of Penaeus ~~0~0~0~ juveniles at different ages during acclimation to iow salinity water (1 .Y/,,) (values are % mortality of 10 post-larvae per treatment) Initial age (days)
(a) Thailand 40 110 155
Period of transfer _--____ Direct
--
6h
24 h
3d
0 80 100
0 0 10
-
100
10
10
0 0
0 0
~.....
stock 20 100 100
0
(b) Tahifi stock 150
100
cc) South African 28 40
15 20
stock -
prawns. (< 40 days old} showed a much greater tolerance to reduced salinities than older animals (Table I). The younger prawns also survived rapid introduction to a reduced salinity level better than older prawns, for which at least 24 h was required for the salinity reduction. After direct transfer to 1.7°/00 some mortality (15%) was apparent even in the youngest animals tested (2%days old S. African post-larvae). However, in post-larvae up to 40 days old, no difference in survival could be detected between animals transferred over periods ranging from 6 h to 3 days. All !?ost-larvae exposed to dilute single salt solutions died within 60 h, while in both types of artifidial sea water, 20% mortality was evident after 48 h, but had not increased after a further 48 h when the experiment was terminated. (Table II). Prawns from Thailand and Tahiti showed similarly poor growth and survival rates in 2o/00when compared with ‘control’ prawns in normal sea water; survival was as low as 23.2% in 2°/00, compared with 97% survival in full salinity water (Tables III a,b). Table IV shows the effect upon growth and survival of acclimating postlarvae to 5 and 10°/OO.Even at these salinity levels growth and survival were extremely poor when compared with prawns in full sea water controls. Thus, in no experimental salinity other than full strength sea water was good growth or good 4 week survival achieved. Osmcregulation
Mei~uremen~ of haemolymph concentrations in 150-day-old Tahiti prawns held at different medium concentrations indicated that in media between 320
0 0 10
60 90 100
100 100
6 12 24
36 48 60
72 96
water)
100 100
70 100 100
0 0 20
NaCl
100 100
100 100 100
60 100 100
CaCl,
of (h)
Duration exposure
NaCl (in tap
of 40-day-old Penoeus monodon upon exposure stock). Values are % mortality of 10 post-larvae
II
Mortality (Thailand
TABLE
MgSo,
to dilute media per treatment
NaFo,
isomotic
20 20 20 20 20
20 20
0 20 20
(Ayres
10 20 20
0 0 0
‘Natura’
sea water
1.7’/,,,, sea water
Artificial
with
& Wood
1977)
0 0
0 0 0
0 0 0
~~_
Natural sea water (control)
171 TABLE
Il.1
Growth and survival of Penoelrs ~~~od~n in water of 2”/,, salinity and in natural sea water (3O-32o/,, ). (a) 27-day-old Thailand stock. (b) 66-day-old Tahiti stock. The prawns were weighed as populations -. ~(a)
2O100
control 30-32°/0, --.._
Mean wt. (start) (g) % survival (4 weeks) (%) Mean wt. (4 weeks) (g) ___----
0.062 51.7 0.33
0.074 98.8 1.12
(b)
2’/,, acclimated in 24 h
2’/,, acclimated in 48 h
control 30--32&,
0.25 23.2 0.33
0.26 34.4 0.43
0.29 97.0 0.64
_^___I Mean wt (start) (g) % survival (2 weeks) (%) Mean wt (2 weeks) (g)
._--_
-
-
TABLE IV Growth and survival of 86-day-old Penaeus monodon in water of 5 and lO’/v, salinity compared with prawns in recirculating and throughflow sea water at 30-32’/,, . (Tahiti stock). The prawns were weighed as populations ~5%0 ^_cMean wt,. (start) (g) Mean wt.. (2 weeks) (g) Survival (2 weeks) (%) Mean wt. (4 weeks) (g) Survival (4 weeks) (W)
0.47 0.96 44 1.47 6
lW,*
0.52 1.13 100 1.70 34
Controls
( 30-320/,,
)
Recirculating
Throughflow
0.44 1.43 94 2.07 92
0.57 1.84 96 3.17 94
and 870 mOsm the post-larvae exerted good osmoregulatory control (Fig. 3). In media below 320 mOsm the haemolymph became rapidly diluted and the haemolymph concentration curve ran parallel to the isomotic line. Clearly osmoregulation was comparatively inefficient in media below 320 mOsm. Post-larvae aged 150 days post-metamorphosis were isomotic at a medium concentration of around 790 mOsm: above this concentration the animals were slightly hypo-osmotic to their environment.
172
I 100 -
,I’ /’ #’
II
ml
200
300
ml
ml
environment
600
700
800
900
1 1000
mOsm
Fig. 3. The osmoregulation curve for 150-day-old Penaeus monodon post-larvae (Tahiti stock). Vertical lines indicate 2 x SE. and the dashed line represents the isosmotic line. DISCUSSION
The lower limit of salinity tolerance of Penaeus monodon in our studies was probably close to 1.7°/00. This resuit was found for prawns from all three geographical sources and agrees well with other quoted lower salinity limits for penaeid prawn species (Gunter et al., 1964). The data indicate that older prawns are less able to adapt to low salinity than young ones; similar results were found for Penaeus monodon by Pantastico (1979) for Philippine stock. This greater tolerance to reduced salinity in juvenile penaeid prawns has also been demonstrated for Penaeus setiferus and Penaeus stylirostris (Castille and Lawrence, 1981a). The poor survival in single salt dilute media indicates a requirement for a mixture of ions. Survival in both commercially available sea water salt, and in artificial sea water (made up according to the formula employed by Ayres and Wood (1977) was slightly inferior to that recorded in natural sea water, again indicating a requirement for a complex medium. We obtained poor growth at all salinities tested (2, 5 and 1Oo/0o)below full salinity sea water. This result is at variance with the data obtained by Pantastico (1979) who reported good growth and survival in fresh water. One possible explanation for this discrepancy may lie in the importance of substrate. Our growth experiments were conducted in bare floored tanks whereas Pantastico (1979) reared animals in open floored cages held on the bottom of an open lagoon, intermittently subject to sea water inflow. She stressed the importance of giving the prawns access to the lagoon bottom for optimum development. In such a situation the animals may well have had access to heightened salt concentration within, or very close to, the substrate even
173
though the overlying medium was fresh or of low salinity water (O.14-1.3o1,o; Anon. 11979). The possibility that Philippine stock differed physiologic~ly from those tested was not evaluated because of the loss of Philippine postlarvae curing shipment to Great Britain. The osmoregulation data presented here for 150-day-old animals agree well with Chen (1976) who quoted the normal salinity range of Penaeus monoclon in Taiwan as 15-30°/00. Over this salinity range the prawns are able to maintain a narro’w range of internal fluid concentrations. The isosmotic concentration obtained in our experiments corresponded to about 23-Z5°/oo region, which is similar to the value obtained in Castille and Lawrence (1981b) for several species of penaeid prawns in the U.S.A. We therefore conclude that whilst it may be possible to introduce Penaeus monodm to water of very low salinity under certain conditions, the species seems unlikely to be able to survive and grow well in fresh water and low salinity cultures in bare-floored tanks. ACKNOWLEDGEMENTS
It is a pleasure to thank the following scientists and their organisations for sending us shipments of post-larvae: Mr Kasemsant Ch~ayondeja, Department of Fisheries, Ministry of Agriculture and Cooperatives, Bangkok, Thailand; Dr A. hlichel, AQUACOP, Taravao, Tahiti; Dr H.F.B. Champion, Kwazulu Development Corporation, Gingindlovu, South Africa, and Dr F. Santiago, SEAFDEC, Binangonan, Philippines.
REFERENCES Anon., 1979. Ecology of Laguna lake. Asian Aquaculture, 2 (7): 6. Ayres, P.A. and Wood, P.C., 1977. The live storage of lobsters. Lab. Leafl., MAFF Direct. Fish. Res., Lowestoft, (New Series), No. 37, 9 pp. Castille, F.L., Jr. and Lawrence, A.L., 1981a. A comparison of the capabilities of juvenile and adult Penaeus setiferus and Fenaeus stylirostris to regulate the osmotic, sodium and chloride concentrations in the haemolymph. Comp. Biochem. Physiol., 68A: 677680. Castille, F.L. Jr. and Lawrence, A.L., 1981b. The effect of salinity on the osmotic, sodium and chloride concentrations in the haemolymph of euryhaline shrimp of the genus Penatus. Comp. Biochem. Physiol., 68A: 75-80. Cawthorne, D.F., 1979. A comparative study of the closure responses of some Cirripede species exposed to falling seawater concentration. J. Mar. Biot. Assoc. U.K., 59: 811817. Chen, T.P., 1976. Aquaculture Practices in Taiwan. Fishing News Books Ltd. Farnham, Surrey, 162 pp. Davenport, J., Gruffydd, L1.D. and Beaumont, A.R., 1975. An apparatus to supply water of fluctuating salinity and its use in a study of the salinity tolerance of larvae of the scallop Pecten maximus L. J. Mar. Biol. Assoc. U.K., 55: 391-409. Forster, J.R.M. and Beard, T.W., 1974. Experiments to assess the suitability of nine species of prawns for intensive cultivation. Aquaculture, 3: 355-368.
174
Gunter, G., Christmas, J.Y. and Killebrew, R., 1964. Some relations of salinity to population distribution of mobile organisms, with special reference to penaeid shrimp. Ecology, 45: 181-185. Pantastico, J.B., 1979. Research paper presented at the ‘Technical Consultation on Available Aquaculture Technology in the Philippines’. South-East Asian Fisheries Development Centre, Aquaculture Department, Tigbauan, Iloilo,Philippines. 8-10 February 1979. 5 pp. (mimeo). Wickins, J.F., 1976. Prawn biology and culture. Oceanogr. Mar. Biol. Ann. Rev., 14: 435-507. Wickins, J.F., 1981. Water quality requirements for intensive aquaculture: a review. In: K. Tiews (Editor), Aquaculture in Heated Effluents and Recirculation Systems. Vol. 1 Heenemann Verlagsgesellschaft, Berlin, pp. 17-37. Wickins, J.F. and Beard, T.W., 1978. Ministry of Agriculture, Fisheries and Food, Prawn culture research. Lab. Leafl., MAFF Direct. Fish.Res., Lowestoft, No.42, 41 pp.