Improved method for shipping Tridacna gigas seed

Aquacufrure, IO2 ( 1992) 193- 199 Elsevier Science Publishers B.V., Amsterdam

193

Technical Paper

Improved method for shipping Tridacna gigas seed R.D. Braley Giant Clam Project. Zoology Department. James Cook University, Townsville, Qld. 481 I, Australia (Accepted 26 May 199 I )

ABSTRACT Braley, R-D., 1992. Improved method for shipping Tridacna gigas seed. Aquaculture, 102: 193-l 99. Four-month-old juvenile Tridacna gigas were placed in plastic bags and exposed to pure oxygen in combination with four treatments: seawater, seawater+antibiotic, wet paper toweling (below clams), wet paper toweling (ahove ana below clams j. The only treatment which had high survival (98.5%) after 30 h application was seawater+antibiotic (streptomycin sulphate, 25 ppm). Desiccation as a clause of death was apparent, especially in smaller size classes in other treatments. A shipment of 5000 5.5-month T. gigas juveniles was scentto Fiji Fisheries. Despite a 40-h period from packing to reimmersing clams, survival was 64% after 4 days of reimmersion in the quarantme system in Fiji.

INTRODUCTION

Advances in the production of giant clam seed (Heslinga et al., 1984; Ccawford et al., 1986; Braley et al., 1988) have helped to secure the survival of the most heavily poached species, Tridacna gigas and T. derasa, and to move one step further toward commercial farming (Heslinga and Pitt, 1987; Braley, 1989). There are giant clam hatcheries and ocean nursery projects operating or under ccnstruction in several islands of Micronesia (CM. Crawford, pers. commun., 1990 ), in Piji, Tonga and Cook Islands ( ACIAR Giant Clam Project) and in the Solomon Islands (ICLARM Coastal Aquaculture Centre). The ability of these regional hatcheries to successfully ship seed clams for cultivation will be vital to their operations. The effect of desiccation and improvement in survival with pure oxygen for 8omonthlold Tridacna derasa seed clams has been documented (Lopez and Heslinga, 1985; Solis and Heslinga, 1989). Desiccation was more stressful on smaller clams ( < 20 mm ) at 24-28 “C, but more stressful on larger clams ( > 20 mm) at 11“C (Lopez and Heslinga, 1985). Use of oxygen al0044-8486/92/$05.00

0 ! 992 Elsevier Science Ptiblishers B.V. All rights reserved.

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R.D. BRALEY

lowed an exposure period of 48 h with acceptable levels of survival (Solis and Heslinga, 1989), thus assuring that shipments by air to even remote areas in the Pacific could be accomplished with a degree of success. If very small juvenile clams coul e treated by a method which results in high survival, then overall costs would be reduced. A substantial amount of the giant clam nursery phase is spent in tanks at the hatchery ( > 8 months), so that if this time could be reduced by almost half it would represent a significant savings in running costs. This experiment tested different treatments in addition to the use of yufe ti;rxy&non survival of very small T. gigas seed. Results of this and of an actual shipment of 5000 T. gigas seed to Fiji using the most successful experimental treatment are discussed. METHODS

Experiments Juvenile Tridacna gigas spawned 1 November 1989 at Orpheus Island Re-

search Station (OIRS ) , Queensland, Australia, were collected at 4 months of age from the settlement tank bottom. One hundred clams were chosen randomly for each of two replicates used in four treatments. The treatments were: seawater at about 1 ml/clam, using a 25 ppm concentration of streptomycin sulphate (Sigma Chem. Co. ); seawater only at about 1 ml/clam; seawater wetted paper toweling below the clams with about 0.3 ml seawater/clam soaked into the paper toweling; seawater wetted paper toweling above and below the clams with about 0.5 ml seawater/clam soaked into the paper toweling. The clams in all treatments were placed in 20-l clear plastic bags and the bags laid flat in a dark room after inflation with oxygen gas. The mean temperature was 28 OC (26-30°C range). This simulated shipment ran for 30 h. There was an additional experiment that tested seawater wetted paper toweling below the clams, with two replicates which ran for 20 h exposure. At the end of the exposure period, clams were removed from the plastic bags and each group placed into a 1O-lcrystallite aquarium with flow-through of 60-l/h seawater in moderate light. In the 30-h exposure trials, clams were checked for mortalities 35-85 h from the start of the experiment, and in the 20-h exposure trial, clams were similarly checked for mortality and measured at 20-X h. Dead or moribund clams (regressed mantle, no response to touch over adductor muscle region) were removed and shell length recorded. Finally, all remaining live clams were measured to record shell lengths. Fiji shipment

At 5.5 months of age, 5000 7’.gigas from the same batch were packed in seawater+ antibiotic (2s described.above), placing about 1250 clams per 201clear plastic bag at slightly less than 1 ml/clam. The clams were packed at OIRS (Great Barrier Reef) using polystyrene fish boxes to hold the plastic

IMPROVED METHOD FOR SHIPPING TRIDACNA GlCiASSEED

195

bags and clams. If the shipment had gone smoothly the clams would have been at their destination in about 24 h from packing. However, an error with the air freight shipment in Australia resulted in there being 40 h before clams were opened from their packages. They were set into aquaria for 9 h, then repacked and shipped another 10 h before finally settled into the flow-through quarantine system at Makogai Island, Fiji. RESULTS

Experiments The combined results of replicates of all the treatments are shown in the series of graphs in Figs. 1 and 2. There was much superior survival in the seawater + antibiotic treatment over all the other treatments. A one-way ANOVA was used to compare the survival of clams in the four treatments. There was a significant difference between treatments (P=O.O12) with 89% of the variation being between the groups. Even the smallest clams in the seawater+antibiotic treatment were very active upon reimmersion and moved up the walls of the aquaria. No signs of desiccation or stress were apparent. The clams in seawater only looked well upon reimmersion at 30 h. They were not desiccated, but stress was evident since fewer clams were as active as in the seawater+antibiotic treatment. Here, mortalities began at 35 h and peaked at 45 h (Fig. 1). Contrary to the seawater treatments, desiccation in the paper toweling treatments was a serious problem. The highest mortality occurred during the oxygen exposure and upon opening for reimmersion for the paper toweling below clams (Fig. 2). The mortalities were initially heavier in the sinall size classes but had more effect upon medium to larger size classes after 35 h. Initially, survival was high in the paper toweling above and below clams (Fig. 1). Here, mortalities peaked by 45 h. Finally, less devastating mortality is apparent in the 20 h oxygen exposure, paper toweling below clams (Fig. 2). Here, small to medium size clams died and most mortality had occurred before 30 h. A two-way ANOVA was used to test the survival of clams in the four 30-h treatments and within four pooled groups of size classes. There was a significant difference (PC 0.0 1) between treatments and between size classes (PC 0.05), but there was no significant interaction. Fiji shipment The survival of juveniles at the final settlement in the quarantine tanks at Makogai Island, Fiji, was 80.4%. After 4 days in the quarantine system the survival was down to 64%. The smaller size classes suffered the highest mortality in this shipment. Mortalities continued for several weeks at a decreasing rate.

R.D. BRALEY

196

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Fig. I. Threetreatments used in the 30-h exposure experiment. Percent survival over time from start of experimenton left and total number of live and dead clams in each size class on right. TWOreplicateshave been combined in these graphs; each replicate, n= 100.

IMPROVED METHOD FOR SHIPPING TRUhKNA GlGASSEED

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DISCUSSION

The most striking result was the nearly total survival of clams of all size classes in the seawater + antibiotic treatment. The explanation would appear to be that waste products from the clam released into the small amount of seawater contribute to rapid increases in bacterial numbers from bacteria introduced with and on the clams. The seawater+antibiotic curbs this bacterial population increase so that there is no delayed detrimental effect after reimmersion. It is not known whether these clam mortalities result from pathogenic bacteria or from a general ,ovcrload of bacteria in the system. Lewis et al. ( 1986) have shown that in oyster larval cultures there is a sign of something wrong in the culture when general bacterial levels become higher than 1 O5 cells/m.1 Work in this area needs t’obe further quantified to better understand the cause of the mortalities.

i98

R.D. BRALEY

Clams subjected to the paper towehng treatments were probably dying at least initially from desiccation. Thei-c was a direct relationship between the initial survival at the end of the 30-h treatment and the amount of protective wet paper toweling, but no difference by the end of 85 h. Some of the latter mortalities may also be related to bacterial population increases. Desiccation was considered to be the cause of death for larger T. derasa used by Lopez and Heslinga ( 1985 ) and Solis and Heslinga ( i 989 ). After a 32-h oxygen exposure time the mean survival of 8-month-old ( 1O-30 mm) T. derasa at 56 h from the start of the experiment was 93.8% (Solis and Heslinga, 1989). Although older seed clams are more tolerant of desiccation, there may also be a different in tolerance between T. derasa and 7’.gigas. The survival of the 4-month-old T. gigas from the seawater +antibiotic treatment is welcome news for hatcheries which will ship seed to quarantine facilities in other countries The shorter rearing time is of economic benefit to the hatchery of origin. Likewise, if clam seed are shipped at a younger age, there is less chance of juvenile clams becoming infected with a potential parasite, such as Perkinsusspp. (Goggin and Lester, 1987; Humphrey, 1988 ). The shipment to Fiji resulted in good survival of juveniles (64%) to 4 days after arrival, despite air freight difficulties which caused the clams to be stressed for an additional 29 h longer than the experimental animals. If these difftculties can be overcome then very good survival could be expected for large shipments. ACKNOWLEDGMENTS

I thank S.R. Lindsay, J. Whitford, J. Kennedy, P. Lee, Dr. J.S. Lucas and volunteers who assisted in the experiment. I also thank the Fiji Fisheries for making transport available to me for collection of the clam seed, especially to E. Ledua, A. Batibasanga, M, Bai, and M. Tavisa. I thank the OIRS manager, G. Charles for use of oxygen and assistance with transport off OIRS. This study is part of the ACIAR-funded Giant Clam Project (Project No. 8733). REFERENCES Braiey, R.D., 1989. Farming the giant clam. World Aquacult., 20: 6- 17. Braley, R.D., Nash, W.J., Lucas, J.S. and Crawford, C.M., 1988. Comparison of different hatchery and nursery culture methods for the giant clam Tridacna gigas. In: J.W. Copland and J.S. Lucas (Editors), Giant Clams in Asia and the Pacific. ACJAR Monograph no. 9, Australian Centre for International Agricultural Researcir, Canberra, pp. 1IO- 114. Crawford, C.M., Nash, W.J. and Lucas, J.S., 1986. Spawning induction, and larval and juvenile rearing of the giant clam, Tridacna gigas. Aquaculture, 58: 28 l-295. Goggin, C.L. and Lester, R.J.G., 1987. Occurrence of Perkinsus species (Protozoa, Apicomplexa) in bivalves from the Great Barrier Reef. Dis. Aquat. Org., 3: 113- 117. Heslinga, G.A. and Fitt, W.K., 1987. The domestication of reef-dwelling clams. Bioscience, 37 (5): 332-339.

Heslinga, G.A., Perron, F.E. and Orak, O., 1984. Mass culture of giant clams (F. Tridacnidae) in Palau. Aquaculture, 39: 197-2 15. Humphrey, J.D., 1988. Disease risks associated with translocation of shellfish, with special reference to the giant clam Tridacna gigas. In: J.W. Copland and J.S. Lucas (Editors), Giant Claims in Asia and the Pacific. ACIAR Monograph no. 9, Australian Centre for Intemational Agricultural Research, Canberra, pp. 24 l-244. Lewis, T.E., Garland, C.D. and McMeekin, T.A., 1986. Manual of Hygiene for Shellfish Hatcheri:zs. University of Tasmania Printing Department, 45 pp. Lopez, M.D.G. and Heslinga, G.A., 1985. Effect of desiccation on Triducnn de-ma seed: implications for long distance transport. Aquaculture, 49: 363-367. Solis, E.P. and Heslinga, G.A., 1989. Effect of desiccation on Tridacna derusa seed: pure oxygen improves survival during transport. Aquaculture, 76: 169- 172. NOTE ADDED IN PRESS

Survival of seed shipments to the Philippines and Tcmga/Fiji in 199 1 using the antibiotic treatment described in this paper; Tg= Tridacna gigas, Hh = Hippopus hippopus Country Philippines Tonga

No. of seed

Age

Survival after

(weeks)

2 weeks (%.b )

11 OOOTg 11 OOOTg 20 000 Hh

11.5

99.0

19.2 12.0

97.1 99.8

20 000 Hh

12.0

99.0

Fiji (via

Tonga)