Abalone mariculture in China.

ABSTRACT Remarkable progress has been made in recent years in abalone cultivation in China. Beginning in the early 1980s, commercial scale mariculture of abalone has involved 2 species: Pacific abalone, Haliotis discus hannai Ino and the small tropical abalone, H. diversicolor Reeve. Intensive culture of H. d. hannai is distributed mainly in the northern China region, Liaoning and Shandong Provinces with an annual production increasing from about 47 mt (1992) to 4500 mt (2003). The small tropical abalone is the dominant species with a total production of H. diversicolor reaching 3878 mt produced in 2001 in Fujian, Guangdong and Hainan Provinces. Seeds for cultivation are exclusively produced from hatcheries with well-developed technology. Cultivation practices may vary widely among different sea types. Three major forms of grow-out are used in abalone cultivation, land-based tanks, suspended longline cages and intertidal ponds. Abnormal mortality has threatened sustainable development of the abalone industry from its inception. During 1992 to 1996, many facilities in the north ran at a loss due to mass mortality occurring in juveniles and seeds. Mortality usually occurred in the postsettlement nursery phase when spat remain on settlement plates, characterized by cease of dietary intake and falling from the substratum. The cause of this large-scale mortality remains as yet unknown. The same situation occurred in Fujian from 1996, after 2 y of large-scale farming, and has already spread to all other provinces of abalone mariculture. Genetic improvement of abalone has drawn much attention. Hybridization between different populations from Japan and China has been achieved to obtain significant heterosis with growth and survival. Preliminary results on H. d. hannai have shown that survival of selective strains is significantly higher than normal controls.

KEY WORDS: Abalone, Haliotis discus hannai Ino, H. diversicolor Reeve, mariculture, seed production, grow-out, disease, abnormal mortality, hybridization, heterosis, selection breeding, marketing, China

INTRODUCTION

Six species of abalones are naturally distributed along the coast of China, Haliotis discus hannai Ino, H. diversicolor Reeve, H. asinina Linnaeus, H. ovina Gmelin, H. planata Sowery, H. varia Linnaeus, and H. clathrata Reeve (Nie 1992). Abalone aquaculture has been dominated by H. discus hannai and H. diversicolor, whereas culture of H. asinina has drawn considerable attention in recent years.

Experimental production of abalone seed in Pacific abalone was conducted in 1977 (Chen et al. 1977) in China, and commercial seed production was accomplished in 1987 in Dalian, Liaoning. From 1987 to 1992, abalone aquaculture in China grew steadily with most research focused on the development of hatchery seed production techniques and grow-out modes. A series of key techniques involving spawning, larval rearing, and juvenile and seed nursing were established. Grow-out systems including culture in suspended longline cages, land-based tanks, intertidal ponds, and tanks were also established.

From 1992 to 1996, however, abalone aquaculture suffered severely from disease in the northern provinces of China. Abnormal mortality of cultured abalone seed, H. d. hannai, was first observed in 1992. The mortality problem became evident after 1994, when most abalone hatcheries suffered severe loss of abalone seed, either larvae or juveniles. From 80% to 90% mortality has been reported. During this period, approximately 20% to 30% of 1-3-y-old cultured abalone suffered abnormal death. Meanwhile, wild abalone stocks also suffered mass mortality. Therefore, output of abalone in northern China decreased considerably during 1996 to 1998.

From 1997 aquaculture of H. d. hannai in northern China rejuvenated and entered a stage of rapid and stable development. Success of abalone industry, in north China, resulted from improvement of seed production techniques and implementation of sanitary measures.

During the 1990s, commercial cultivation of the southern abalone, H. diversicolor emerged and then expanded rapidly in Southern China. The first trial of hatchery seed production was conducted in Shenzhen in 1992, following the procedure for H. discus hannai in the north. This trial, however, came to an unsuccessful end. A package of cultivation techniques was well developed in Taiwan province and popularized in southern provinces of China from 1994. Subsequently, seed production of H. diversicolor on a commercial scale expanded until 1998 and saw the rapid development of abalone farming in southern China. Mass mortality occurred initially in January 1999 in Dongshan, Fujian, and then in Shantou, Guangdong. Some companies lost all their abalone. The problem has now spread to Hainan and Guangxi. Most of the abalone hatcheries on the southern Chinese coast are now running limited operations or considering closing.

To summarize, intensive culture of H. discus hannai is mainly distributed in north China, with the majority of the production in Liaoning and Shandong. H. diversicolor is the dominant cultured species in south China. Abalone culture has become one of the most important components of molluscan mariculture in China. Abalone holds the top position in terms of commercial value among farmed molluscan products. Mariculture production of abalone increased steadily during the 1990s. Despite production of H. diversicolor undergoing a decline since 2000, total output of marketable abalone has continued to grow from 1997 onward. This growth is mainly attributable to the rapid increase in production volume of H. d. hannai.

In this study, development of large-scale cultivation of abalone, in association with technology, as well as marketing of abalone is reviewed. Meanwhile, problems arising from abalone mariculture and possible countermeasures are discussed herein.

SEED HATCHERY PRODUCTION

Sufficient seed supply is crucial to the development of abalone mariculture. All abalone seeds are hatchery produced with sophisticated technology. For H. discus hannai, seed production typically begins in early spring with broodstock conditioning at gradually elevated temperatures and stabilization at 20[degrees]C. The most widely used and effective method for abalone to ripen is by effective accumulative temperature (EAT) control. Experiments with Pacific abalone demonstrate that the required EAT is 800[degrees]C.day for males and 1000[degrees]C.day for females. Meanwhile, plenty of algal food, Laminaria japanica, Undaria pinnatifida, and Ulva pertusa should be provided with this conditioning method. However, conditioning at elevated temperatures is not effective for H. diversicolor. Alternately, conditioning is conducted for tropical abalone by lowering culture density to 10-15 individual/cage and adding supplements of fresh macroalgae.

To induce spawning, well-developed abalones are exposed to air for desiccation and then subjected to ultra-violet-irradiated seawater. Adult spawning is usually induced by combined thermal shock and UV-treated seawater exposure. Few hatcheries use hydrogen peroxide to induce spawning for H. diversicolor. Males usually are induced 1 h later than females because the former are more sensitive to inducement than the later. Fertilized eggs are incubated at 21[degrees]C to 22[degrees]C and 22[degrees]C to 30[degrees]C for the northern and southern types, respectively. Approximately 60 h postfertilization, H. d. hannai larvae are ready for settlement. Eyed larvae are set on the collecting plates made of transparent corrugated plastic with diatom-precoated for H. d. hannai. In southern China, plastic films (usually polythene with 0.2-0.3 mm thickness), which are precoated with diatoms, are widely used for H. diversicolor larval collection. Using plastic film has achieved satisfactory settlement percentage and postsettlement survival. However, this stage is critical and survival after settlement is the biggest challenge for abalone seed production. The diatoms must be supplied in sufficient quantities as well as in good quality to ensure the growth and survival of postlarvae. Water quality and light level should be carefully controlled during this critical period.

Juveniles are manually moved from settlement plates to nursery culture plates at approximate size of 3-7 mm. For H. discus hannai, spat are usually transferred to large punctured plastic plates with dark color. For H. diversicolor, however, spat are reared in concrete nursery tanks. Square cement plates, with feet on the four corners, are placed on the bottom of the tanks. During early juvenile stages, an artificial diet is exclusively used as food supply. Several commercial diets, from various diet producers, are available to aquaculturists. The major ingredient of artificial diets is dried kelp powder and fish meat powder. Fresh kelp is the principal food for older juveniles. The quality of artificial diet plays an important role in postsettlement survival.

GROW-OUT SYSTEMS

There are at least 3 major grow-out methods being used widely for abalone culture. First, grow-out in land-based tanks is a popular system, and the most intensive and sophisticated. The method is applicable to both the cultured species. In southern China, this method had developed in Taiwan before 1994. It has become the predominant culture method for the abalone culture industries in South China. The major husbandry measures include adequate feeding, control of water flow, periodic elimination of abalone waste, and adjustment of the culture density. Usually this grow-out system has a high running cost, including cost for water pumping, heating, and aeration. For northern China, this grow-out system is applied less than in southern areas. One of the most successful facilities running this grow-out system is Xinda Products Co. located in Dalian, Liaoning, retaining stable full production for many years.

The second cultivation form is in cages or barrels on suspended longlines. This system was initially tried in north China in the late 1980s. For the southern coast, the first trial was conducted in Shenzhen, Guangdong, in 1992. Relatively fast growth at lower costs could be obtained with this abalone grow-out system. Therefore, this method has been widely adopted along the coast of China. Feeding with macro-algae is usually conducted weekly. The grow-out usually lasts for 8-13 mo for H. diversicolor on the south China coast.

The third form is culture in intertidal ponds. The seed of H. diversicolor is put into a cement tank, diameter 120 cm and height 60 cm, wall thickness 5 cm, with a cover and a rack for the abalone settlement. There are several poles in the cover, bottom, and wall for the water change between the inner and outer parts of tank; 500 to 700 seeds of 2 cm shell length can be placed in each tank. Tanks are set in the low intertidal or upper subtidal zone and fed with fresh algae once per week or more according to the weather, and the amount is 20% to 30% of the total weight of abalone in the tank. The grow-out of abalone usually takes an average of 7 mo, varying from 5 to 11 too. This is a closed system and has first applied in Zhanjiang, Guangdong in 1993. From the unprecedented success of this culture mode in 1997, an upsurge in popularity occurred during 1998 to 2000. Since 2002, however, the practice has declined sharply due to abnormal mortality from early seed to adult. One reason is that rapid development of abalone farming has resulted in environmental disruption in coastal water and epidemic pathogens.

In northern China, intertidal farming emerged in 1998 when hybrid seeds were successfully produced and the over-wintering problem solved. Some cement ponds have been built in the low intertidal zone with an area 0.5-1.0 hectare, with stones placed in the pond for the settlement of abalone. Ponds are about 1-2 m(s) depth depending on the position and the system of water exchange. There is a net along the pond wall to prevent abalone escape. No tank was used in the north. The seed size is 2.0-2.5 cm shell length and 15-20 individual/[m.sup.2]. The grow-out needs 16-20 mo to reach the size for market in Qingdao. Generally, there is an opening system for abalone grow-out, which has been developing quickly off the coast of Qingdao, Shandong. The ratio of marketable abalone produced from this grow-out system has steadily increased in recent years. In 2003, production of marketable abalone reached 2615 mt in the Qingdao area, accounting for over 58% of the total yearly output in Shandong. Grow-out management includes periodic feeding on macro-algae and removal of dead bodies. One disadvantage of this opening system in the intertidal zone is that it impedes natural beach scenery.

In addition to the above mentioned grow-out modes, abalone can also enhanced on the bottom of the subtidal zone. This has been used in a couple of coastal area, such as the Changhai County in Dalian, Liaoning.

During the grow-out period, abalone are fed primarily on the macroalgae, Laminaria japonica, Undaria pinnatifida or Ulva pertusa for H. d. hannai and Gracilaria sp. for H. diversicolor. Additionally, Laminaria and other macroalgae are used partially for H. diversicolor. During summer, following the completion of the kelp harvest, kelp supply could be in short supply for 2-3 mo. Salted or cold-stored Laminaria substitutes for fresh kelp as the abalone food supply during supply problems of fresh food. Both salted and cold-stored Laminaria should be processed before use.

MARKETING OF MARICULTURE PRODUCTS

Aquaculture products of abalone are primarily sold fresh in domestic markets of China. Tinned products are available at some abalone farms. Most canned products were sold in the overseas market.

CHALLENGES TO ABALONE MARICULTURE

Mortality frequently occurs during the first month of the juvenile phase, following the movement of juveniles from settlement plates to the nursery culture plates, especially when the juveniles are taken-off the diatom plates at <5 mm shell length. It is generally believed that the change of feeding habits is the major cause of this high mortality. Survival in this critical nursery period has dropped to lower than 5% at the lowest level during the early 1990s. Survival of early juveniles has been much improved by hybridization breeding, declining juvenile density in the collecting plate, and extension of diatom feeding, therefore, allowing for removing the juveniles, at a larger size than normal, to the nursery culture plates (Zhao & Zhang 2000). In particular, hybridization was made between Japan and China's broodstock to produce hybrid seeds. When all diatoms on the settlement plate are consumed, juvenile abalone (approximately 2-3 mm) are transferred to another batch of transparent corrugated plastic plates on which diatoms are well covered. Therefore, size of juvenile abalone reached 5-7 mm when transferred to the nursery culture plate, enhancing the adaptive ability of juveniles to artificial diets. The practice of transferring juvenile abalone is now becoming part of routine hatchery procedure. With the application of hybridization and plate-transfer techniques, production of H. d. hannai remains stable in the northern Chinese coast areas.

This problem, however, was not solved completely due to incomplete understanding of the physiologic variation associated with the change of feeding habits, following larval metamorphosis. In addition, a lack of quality control, with respect to broodstock, often leads to failure of utilization of heterosis. Hybrid abalone seeds have now been widely adopted throughout the northern coasts. Nevertheless, breeding of high quality lines of abalone will be the best solution in terms of genetic modification.

Availability of adequate commercially formulated diets is another problem for the abalone aquaculture industry in China. Abalone is a slow feeder, therefore, reducing leaching of water-soluble ingredients from artificial diets would be key to good diets. Furthermore, dietary essentials should be balanced to meet the nutrient requirement of abalone. As yet, however, nutritional requirements of the cultured species have not been fully demonstrated.

RECENT ADVANCE AND PROSPECTS

With the development of abalone aquaculture, the demand for abalone lines that are genetically improved has become a common concern. To meet this urgent demand, the Ministry of Science and Technology of China has provided funding for genetic improvement and breeding of mass culture species (e.g., H. d. hannai). Heterosis has been used extensively in Pacific abalone farming. Most seeds used for mariculture are hybrids of the Japanese and Chinese populations, all showing a significant heterosis in growth and survival with 17.98% in shell length, width 22.07%, total weight 61.93%, and survival 180% compared with the control. Heterosis is the foundation of a modern abalone breeding program. The selective strain study has made significant progress with a selective line obtained. This abalone has the characteristics of uniform size, fast-growth, and high survival in all developmental phases. The selection pressure in the first generation was conducted at 0.2%. Selection was undertaken for 2 successive generations and F3 offspring have been obtained. This abalone line is a high-quality candidate for aquaculture and has the potential for promotion of the abalone culture industry in China.

To facilitate abalone breeding, marker assistance selection (MAS) based on molecular markers has been conducted in cultured abalone species. For example, the random amplified polymorphic DNA (RAPD) technique has been used to investigate genetic differences of the abalone, H. d. hannai in 4 progeny families from different geographical populations in China and Japan, as well as genetic variation between parent abalone (from Japan and China, respectively) and their hybrid offspring (Wan et al. 2001, Zhang et al. 2002). The construction of full length cDNA library of H. d. hannai Ino from [F.sub.1] offspring of [J.sub.1][R.sub.h] family had been fulfilled (Liu et al. 2004) and EST sequencing of the "Chinese Red" line of abalone (Liu et al. 2003) and genetic linkage mapping for high quality family in growth and survival are ongoing.

Chromosome manipulation has been conducted in both H. d. hannai (Wang & Zhang 1990) and H. diversicolor (Rong & Weng 1990). Triploids were induced with various methods including cold shock, treatment of cytochalasin B, or of 6-dimethylaminopurine (6-DAMP) in the abalone, H. d. hannai (Sun et al. 1993, Zhang et al. 1998). Unfortunately, no successful application of triploid abalone in mariculture has been reported until now.

High mortality occurring during abalone culture, either nursery or grow-out stage is another crucial issue for both abalone aqua-culturists and researchers. Epidemiology investigation and pathogen identification are ongoing and progress has been made. Two major diseases have been reported in China. First, a fester disease has been reported in juvenile abalone. The pathogenic bacteria of the fester disease was verified as Pseudomonas fluoresce and some antibiotics, including Kanamycin,

Oxolinic, and Furaxone have been found to be effective in curing this disease (Ye et al. 1997). An Elisa method for detecting the pathogenic bacteria of the fester disease in cultured juvenile abalone was reported (Ye et al. 1998). Second, a serious pustule disease was also found, usually in grown-out abalone, caused by Vibrio fluvialis (Liu et al. 1995). Various antifibrosis vaccines for cultured abalone H. d. hannai were examined. There is still a long way to go before mortality can be effectively controlled. The occurrence of inexplicable mortality will complicate abalone aquaculture for the near future.

ACKNOWLEDGMENT

The authors thank Dr. Huang Bo, Dr. Ke Caihuang, and Miss Lin Zhishu for providing valuable first-hand information on abalone mariculture of various provinces; and Miss Kirsty for her review in English. This study was financially supported by National High Tech R & D Plan (863 Plan), grant number 2001 AA621070 and 2003AA603023.

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GUOFAN ZHANG, (1) * HUAYONG QUE, (1) XIAO LIU, (1) AND HUASEN XU (2)

(1) Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, People's Republic of China; (2) Zhanjiang Marine and Fishery Bureau, Zhanjiang 524074, People's Republic of China

* Corresponding author. E-mail: [e-mail]