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Effect of desiccation on Tridacna derasa seed: Pure oxygen improves survival during transport
Aquaculture, 76 (1989) 169-172 Elsevier Science Publishers B.V., Amsterdam -
169
Printed in The Netherlands
Technical Paper
Effect of Desiccation on Triducna derasa Seed: Pure Oxygen Improves Survival During Transport E.P. SOLIS’ and G.A. HESLINGA’ ‘Silliman University Marine Laboratory, Dumaguete City 6200 (The Philippines) 2Micronesian Mariculture Demonstration Center, P.O. Box 359, KOFOT-, Repubtic of P&u 96940 (Caroline Islands) (Accepted 3 July 1988)
ABSTRACT Solis, E.P. and Heslinga, G.A., 1989. Effect of desiccation on Tridacna derasa seed: pure oxygen improves survival during transport. Aquaculture, 76: 169-172. A simple and inexpensive method is described for shipping Tridacna derasa seed in a pure oxygen environment. Under experimental conditions, survival of seed in pure oxygen was higher than that in ambient atmosphere at exposure times ranging from 16 to 48 h. The low cost of the treatment justifies its routine use for commercial shipments of T. derasa seed.
INTRODUCTION
The recent development of technology for hatchery culture of tridacnid clam offers the opportunity to re-establish populations of these commercially important molluscs where they have become rare or extinct, such as in parts of Micronesia and The Philippines (Munro and Heslinga, 1983; Heslinga et al., 1984,1986; Heslinga and Watson, 1985; Heslinga and Fitt, 1987; Heslinga, in press). In this context it is important to identify optimal conditions for longdistance transport of juvenile “seed” clams. Lopez and Heslinga (1985) reported that Triducna derasa seed exhibit good survival when shipped moist (but not submerged), with the byssal apparatus intact, and within a temperature range similar to that found in their natural habitat. In this article’we present data showing that pure oxygen is an effective tool for improving the survival rate and extending the potential transport time for T. derma seed.
0044-8486/89/$03.50
0 1989 Elsevier Science Publishers B.V.
170
METHODS
Eight-month-old T. derasa, lo-30 mm in shell length, were used to determine survival rate after various exposure periods in ambient atmosphere or pure oxygen. Each treatment had four replicates with 20 clams per replicate. Clams were packed moist in 25 x 50 cm polybags. After being filled with air or pure oxygen, the bags were sealed with rubber bands and placed in lidded styrofoam shipping boxes (dimensions: 55 x 40 x 40 cm) for periods of 8,16,24,32 and 48 h. Temperatures inside the boxes ranged from 27 to 32°C. After exposure, the clams were unpacked and placed in flowing-seawater raceways at 20 cm depth. Survivors in each replicate were counted following a reimmersion period of 24 h. RESULTS
The number of survivors per replicate in each exposure period, mean survival rate, and statistical significance levels for t-tests of the means are given in Table 1. The data are plotted in Fig. 1. After 8 h of exposure, clams in air and clams in pure oxygen showed 100% survival. At all exposure times beyond 8 h, clams in air showed increasingly lower survival than those in oxygen. The differences in survival rates were highly significant in the, 32, 40 and 48 h treatments. After 48 h of exposure, clams in oxygen showed surprisingly high survival (83.8% ) while those in air were virtually all dead (95% ) . Clams in both treatments typically began gaping after 3-4 h of exposure and, unless disturbed, remained in this condition until recovery or death. TABLE 1 Number of survivors per replicate (n=20) and mean survival rate (% ) of lo-30-mm !fridacna derasa seed after various exposure periods in ambient atmosphere and pure oxygen. Survival was assessed after 24 h of reimmersion Exposure time (h)
Ambient atmosphere
Pure oxygen
Survivors
%
8 16 24
20,20,20,20 19,20,20,20
100 98.8
11,11,19,17
72.5
21
18,20,20,20
97.5
5
32 40 48
11,7,8,7 9135 9, , , 0,2,1,1
41.3 22.5 5
9.5 17 4
19,20,19,17 19,18,18,17 19,15,17,16
93.8 90.0 83.8
17 4 9
S.D. 0 2.5
Survivors
%
S.D.
20,20,20,20 20,20,20,20
100
0
100
0
Significance level (t-test) n.s.
.. it.:. (PzO.057) P
171
<
70-
5 cr CO2
.
,50tt
mno-
30t
\T
’
0 0
’
’
’
8
16
B
’ 24
EXPOSURE
’
’ 32 TIME
’
’ 40
a
$ 48
(I?)
Fig. 1. Survival of T. derusa seed clams exposed to pure oxygen or ambient atmosphere (air) for various times. Each point represents the mean ( 3~1 S.E. ) of 4 replicates; n = 20 clams per replicate.
DISCUSSION
The relatively rapid gaping response shown by the seed clams in these experiments indicates that after brief periods of exposure, young T. derasa specimens rely primarily on aerial respiration. Their capacity for anaerobic metabolism seems relatively low, especially compared to some intertidal bivalve species that can survive in air for days without gaping. The hypertrophied mantle of young T. derasa offers a proportionately large surface area for gaseous exchange and is probably important in this function during periods of exposure. The significance of the mantle as a respiratory organ ought to decrease with clam body size; field experience with larger tridacnids seems to corroborate this. Most are prone to gaping and appear stressed after less than 8 h of aerial exposure. For purposes of transporting seed, it is clear that survival of T. derasa juveniles can be improved dramatically by maintaining a high oxygen tension in the shipping bags. For the treatment to be effective, however, temperature should be reasonably stable (24-28’ C appears ideal; Lopez and Heslinga, 1985). Further work is needed to determine the rate at which T. derasa seed clams consume oxygen under shipping conditions, and to clarify the relationship between packing density and survival rate of seed in the shipping bags. There is also a need to extend the work to other species and larger sizes of tridacnid clams. Even in the absence of additional information, however, the data shown here demonstrate that routine use of oxygen in commercial shipments of T.
172
derasa seed is biologically justifiable. The low cost and ready availability of compressed oxygen make it economically justifiable as well. ACKNOWLEDGEMENTS
This study was conducted at the MMDC, Palau, during the training of the first author under the Regional Giant Clam Project of the Pacific Fisheries Development Foundation, with a travel grant from the Australian Centre for International Agricultural Research. We thank Dr. T. Adams (Suva, Fiji) for suggesting the use of pure oxygen with Tridacna seed shipments.
REFERENCES Heslinga, G.A. in press. Biology and culture of the giant clam. In: J. Manzi and M. Castagna (Editors), Clam Mariculture in North America. Elsevier, Amsterdam. Heslinga, G.A. and Fitt, W.K., 1987. The domestication of reef-dwelling clams. Bioscience, 37 (5): 332-339. Heslinga, G.A. and Watson, T.C., 1985. Recent advances in giant clam mariculture. Proceedings of the 5th International Coral Reef Congress, Tahiti, 1985, Vol. 2, pp. 531-537. Heslinga, G.A., Perron, F.E. and Orak, O., 1984. Mass culture of giant clams (f. Tridacnidae) in Palau. Aquaculture, 39: 197-215. Heslinga, G-A., Watson, T.C. and Isamu, T., 1986. Cultivation of giant clams: beyond the hatchery. In: J.L. Maclean, L.B. Dizon and L.V. Hosillos (Editors), The First Asian Fisheries Forum. Asian Fisheries Society, Manila, The Philippines, pp. 53-57. Lopez, M. and Heslinga, G.A., 1985. Effect of desiccation on Tridacna derma seed: implications for long-distance transport. Aquaculture, 49: 363-367. Munro, J.L. and Heslinga, G.A., 1983. Prospects for the commercial cultivation of giant clams (Bivalvia: Tridacnidae ) . Proceedings of the Gulf and Carribean Fisheries Institute, Nassau, Bahamas, 35: 122-134.
169
Printed in The Netherlands
Technical Paper
Effect of Desiccation on Triducna derasa Seed: Pure Oxygen Improves Survival During Transport E.P. SOLIS’ and G.A. HESLINGA’ ‘Silliman University Marine Laboratory, Dumaguete City 6200 (The Philippines) 2Micronesian Mariculture Demonstration Center, P.O. Box 359, KOFOT-, Repubtic of P&u 96940 (Caroline Islands) (Accepted 3 July 1988)
ABSTRACT Solis, E.P. and Heslinga, G.A., 1989. Effect of desiccation on Tridacna derasa seed: pure oxygen improves survival during transport. Aquaculture, 76: 169-172. A simple and inexpensive method is described for shipping Tridacna derasa seed in a pure oxygen environment. Under experimental conditions, survival of seed in pure oxygen was higher than that in ambient atmosphere at exposure times ranging from 16 to 48 h. The low cost of the treatment justifies its routine use for commercial shipments of T. derasa seed.
INTRODUCTION
The recent development of technology for hatchery culture of tridacnid clam offers the opportunity to re-establish populations of these commercially important molluscs where they have become rare or extinct, such as in parts of Micronesia and The Philippines (Munro and Heslinga, 1983; Heslinga et al., 1984,1986; Heslinga and Watson, 1985; Heslinga and Fitt, 1987; Heslinga, in press). In this context it is important to identify optimal conditions for longdistance transport of juvenile “seed” clams. Lopez and Heslinga (1985) reported that Triducna derasa seed exhibit good survival when shipped moist (but not submerged), with the byssal apparatus intact, and within a temperature range similar to that found in their natural habitat. In this article’we present data showing that pure oxygen is an effective tool for improving the survival rate and extending the potential transport time for T. derma seed.
0044-8486/89/$03.50
0 1989 Elsevier Science Publishers B.V.
170
METHODS
Eight-month-old T. derasa, lo-30 mm in shell length, were used to determine survival rate after various exposure periods in ambient atmosphere or pure oxygen. Each treatment had four replicates with 20 clams per replicate. Clams were packed moist in 25 x 50 cm polybags. After being filled with air or pure oxygen, the bags were sealed with rubber bands and placed in lidded styrofoam shipping boxes (dimensions: 55 x 40 x 40 cm) for periods of 8,16,24,32 and 48 h. Temperatures inside the boxes ranged from 27 to 32°C. After exposure, the clams were unpacked and placed in flowing-seawater raceways at 20 cm depth. Survivors in each replicate were counted following a reimmersion period of 24 h. RESULTS
The number of survivors per replicate in each exposure period, mean survival rate, and statistical significance levels for t-tests of the means are given in Table 1. The data are plotted in Fig. 1. After 8 h of exposure, clams in air and clams in pure oxygen showed 100% survival. At all exposure times beyond 8 h, clams in air showed increasingly lower survival than those in oxygen. The differences in survival rates were highly significant in the, 32, 40 and 48 h treatments. After 48 h of exposure, clams in oxygen showed surprisingly high survival (83.8% ) while those in air were virtually all dead (95% ) . Clams in both treatments typically began gaping after 3-4 h of exposure and, unless disturbed, remained in this condition until recovery or death. TABLE 1 Number of survivors per replicate (n=20) and mean survival rate (% ) of lo-30-mm !fridacna derasa seed after various exposure periods in ambient atmosphere and pure oxygen. Survival was assessed after 24 h of reimmersion Exposure time (h)
Ambient atmosphere
Pure oxygen
Survivors
%
8 16 24
20,20,20,20 19,20,20,20
100 98.8
11,11,19,17
72.5
21
18,20,20,20
97.5
5
32 40 48
11,7,8,7 9135 9, , , 0,2,1,1
41.3 22.5 5
9.5 17 4
19,20,19,17 19,18,18,17 19,15,17,16
93.8 90.0 83.8
17 4 9
S.D. 0 2.5
Survivors
%
S.D.
20,20,20,20 20,20,20,20
100
0
100
0
Significance level (t-test) n.s.
.. it.:. (PzO.057) P
171
<
70-
5 cr CO2
.
,50tt
mno-
30t
\T
’
0 0
’
’
’
8
16
B
’ 24
EXPOSURE
’
’ 32 TIME
’
’ 40
a
$ 48
(I?)
Fig. 1. Survival of T. derusa seed clams exposed to pure oxygen or ambient atmosphere (air) for various times. Each point represents the mean ( 3~1 S.E. ) of 4 replicates; n = 20 clams per replicate.
DISCUSSION
The relatively rapid gaping response shown by the seed clams in these experiments indicates that after brief periods of exposure, young T. derasa specimens rely primarily on aerial respiration. Their capacity for anaerobic metabolism seems relatively low, especially compared to some intertidal bivalve species that can survive in air for days without gaping. The hypertrophied mantle of young T. derasa offers a proportionately large surface area for gaseous exchange and is probably important in this function during periods of exposure. The significance of the mantle as a respiratory organ ought to decrease with clam body size; field experience with larger tridacnids seems to corroborate this. Most are prone to gaping and appear stressed after less than 8 h of aerial exposure. For purposes of transporting seed, it is clear that survival of T. derasa juveniles can be improved dramatically by maintaining a high oxygen tension in the shipping bags. For the treatment to be effective, however, temperature should be reasonably stable (24-28’ C appears ideal; Lopez and Heslinga, 1985). Further work is needed to determine the rate at which T. derasa seed clams consume oxygen under shipping conditions, and to clarify the relationship between packing density and survival rate of seed in the shipping bags. There is also a need to extend the work to other species and larger sizes of tridacnid clams. Even in the absence of additional information, however, the data shown here demonstrate that routine use of oxygen in commercial shipments of T.
172
derasa seed is biologically justifiable. The low cost and ready availability of compressed oxygen make it economically justifiable as well. ACKNOWLEDGEMENTS
This study was conducted at the MMDC, Palau, during the training of the first author under the Regional Giant Clam Project of the Pacific Fisheries Development Foundation, with a travel grant from the Australian Centre for International Agricultural Research. We thank Dr. T. Adams (Suva, Fiji) for suggesting the use of pure oxygen with Tridacna seed shipments.
REFERENCES Heslinga, G.A. in press. Biology and culture of the giant clam. In: J. Manzi and M. Castagna (Editors), Clam Mariculture in North America. Elsevier, Amsterdam. Heslinga, G.A. and Fitt, W.K., 1987. The domestication of reef-dwelling clams. Bioscience, 37 (5): 332-339. Heslinga, G.A. and Watson, T.C., 1985. Recent advances in giant clam mariculture. Proceedings of the 5th International Coral Reef Congress, Tahiti, 1985, Vol. 2, pp. 531-537. Heslinga, G.A., Perron, F.E. and Orak, O., 1984. Mass culture of giant clams (f. Tridacnidae) in Palau. Aquaculture, 39: 197-215. Heslinga, G-A., Watson, T.C. and Isamu, T., 1986. Cultivation of giant clams: beyond the hatchery. In: J.L. Maclean, L.B. Dizon and L.V. Hosillos (Editors), The First Asian Fisheries Forum. Asian Fisheries Society, Manila, The Philippines, pp. 53-57. Lopez, M. and Heslinga, G.A., 1985. Effect of desiccation on Tridacna derma seed: implications for long-distance transport. Aquaculture, 49: 363-367. Munro, J.L. and Heslinga, G.A., 1983. Prospects for the commercial cultivation of giant clams (Bivalvia: Tridacnidae ) . Proceedings of the Gulf and Carribean Fisheries Institute, Nassau, Bahamas, 35: 122-134.