The status of abalone culture in China.

ABSTRACT Since 1990 abalone culture has spread widely from north to south on China's coast. Estimated total yield for the year 2001 was around 4,500 tonnes (excluding Taiwan). There are several hundreds of abalone farms along the coast. Some of the bigger farms produce more than 100 t of live abalone each year. The main cultured species are Haliotis diversicolor aquatilis Reeve in the south and H. discus hannai Ino in the north. Additionally H. discus discuss Reeve has been introduced from Japan and hybridized with H. discuss hannai. Crossbreeding has been applied in production. Tank culture and floating raft methods are important in the south and north respectively. At present, epidemic virus diseases and Vibrio are the gravest threat. Farms have suffered heavy economic losses as a result of these.

KEY WORDS: abalone, culture, China

INTRODUCTION

Since the previous review of abalone culture in China, written for the 1989 First International Symposium on Abalone Biology, Fisheries and Culture (Nie 1992) there has been dramatic change. Abalone culture in a mass scale in China began in the mid 1980s. It developed rapidly in the 1990s spreading along the coasts from north to south. Estimated abalone output was about 4,500 tonnes (excluding Taiwan) in 2001, 99% produced by cultivation. Haliotis diversicolor aquatilis (i.e., H. diversicolor supertexta) was around 65% of the total yield. The cultured species are varied. The technique of crossbreeding has been used widely (Nie et al. 1995a, Nie & Wang 2000). Triploid breeding has already started in production situations (Wang et al. 1990, Sun et al. 1993, Sun et al. 1998, Zhang et al. 1998). Because the abalone industry has developed rapidly sales prices have declined sharply. This has been especially so for the price of small abalone. For example H. diversicolor aquatilis sales price has been sometimes less than the cost of production. Epidemic diseases have occurred frequently since 1993 (Liu et al. 1995, Nie et al. 1995a, Ma et al. 1996). In particular a virus disease has appeared successively during late winter in the south since 1999 (Huang et al. 1999). Farms have suffered heavy losses and the virus is a serious threat for abalone culture at present.

Cultured Species and Distribution

There are eight species of abalone along China's coasts. Geographically H. discus hannai Ino is the only species in Liaoning and Shandong Provinces in northern China. The other seven species are distributed in Fujian, Taiwan, Guandong, and Hainan, the southern provinces. These species are H. diversicolor diversicolor Reeve, H. diversicolor aquatilis Reeve, H. varia Linnaeus, H. planata Sowerby, H. ovina Gmelin, H. clathrata Reeve, and H. asinina Linnaeus (Lu 1978, Dai & Wu 1989). Because H. diversicolor diversicolor grows slowly, H. diversicolor aquatilis becomes very important. This species was introduced from Taiwan to the southern continental coasts in 1989 and is now raised widely there. Additionally H. discus discus Reeve was introduced from Japan in 1986, H. discus hannai Ino from Dalian in 1990 and their hybridized generation are raised in the mid and northern Fujian (Nie et al. 1995b). There are now several hundreds of abalone farms in China. The largest produce more than 100 tonnes of live abalone per year.

Culture Methods

The culture methods used in China are quite varied. Because of the coastal and climatic conditions they are different in the north and south. Long line raft is an important method in the north. A length of 60-80 m of rope ties together plastic floating globes to support cages. There are two sorts of cage currently in use. A special cage for abalone culture consists of 6-12 tiers of 60-cm diameter plastic dishes. The entire assembly is covered with a net sealed with a zipper. The second type used is a scallop cage, of 8-12 tiers of 33-cm diameter. Most rafts are mixed culture with abalone and algal food, Laminaria or Undaria. Rafts are also used in some bays in the south where the wind and waves are weak. In these instances a plastic basket, the same as indoor tank culture baskets, is used instead of the other cages.

Tank culture on land is the main type in the south. Because of frequent typhoons the culture had to develop on land. Concrete tanks are used of around 30-50 cubic meters. A dark PVC basket of 40 cm x 30 cm x 13 cm is in common use, usually in a stack of 8-12 tiers arranged in rows in a tank. The baskets occupy 40-70% of the tank capacity (Nie & Wang 2000).

In the western Guangdong and Hainan Province, in recent years, small abalone are cultured in the intertidal zone. A type of cylindrical concrete case, 110 cm x 80-120 cm (h) with an iron rack and net inside, is set on a low intertidal zone (Cai & Huang 2000).

Rocky intertidal zones in the north are also used. Here growers build frames and cover with net as well as other types of cages (Zhang et al. 1994).

Breeding Techniques and Present Problems

There are some differences in breeding techniques. The methods in the north are similar to Japanese methods in many ways, and in the south the methods approximate those of Taiwan.

All hatcheries in the north maintain parent stock with elevated temperature (20[degrees]C) in winter and induce spawning in spring. This allows sufficient warm weather for growing larger seed (to >15 mm) before the coming winter. In contrast the small abalone can induce spawning naturally from May to December (main season is September to November) in the south. Nonetheless some farms in the south also maintain parent animals with elevated temperature in winter and induce spawning from April to June.

The substrate for larval settlement in the north is a corrugated plastic plate (40 cm x 31 cm) held in racks. Variations appear in the southern farms. Most farms prefer a transparent plastic sleet (60 cm x 40 cm) frequently set up so that many plastic sheets are hung under a wooden bar. Other types of membrane (rather than racked) corrugated plates are also used (Nie & Wang 2000).

A method of spawning induction with UV light and water temperature alteration (3[degrees]C to 5[degrees]C) is current. In the north, the fertilized eggs are maintained to the post veliger stage and then put into a tank for settlement. In the south it is more common to place fertilized eggs directly in a settling tank, with no water exchange until larval settlement. From the viewpoint of mass production the latter is quite feasible because it saves a lot of labor, time, and facilities.

The young juveniles are removed from the transparent plate/ membrane at 2-4 mm, a much smaller size than during the early years of abalone culture in China. Commonly, in the north, the juveniles are then transferred in a box net with a dark plate on the net bottom. In the south they are raised directly on the bottom of another settling tank, on a substrate of square bricks with short legs that are arranged across the bottom of the settling tanks. The density of rearing is around 3,000-5,000 juveniles per square meter. A survival rate of about 40% to 60% is obtained and measured from the removal phase (2-4 mm) up to the end of nursery rearing (20 mm), in the south. A full cycle of nursery rearing takes about 6-8 mo with a mean production rate in all settling tanks of 2,000-3,000 seed.[m.sup.-2].

Present Problems

In recent years the nursery rearing has not been as easy as in the earlier years of abalone culture in China. On one hand large quantities of postlarvae after settlement (<20 days) tall off the substrate and die. On the other hand lots of young juveniles die when they are removed from substrate to horizontal rearing--usually within 15 days or so. These problems occur in the north and south, resulting in a requirement for more frequent spawning. Since 1995, in the north, a crossbreeding of local H. discuss hannai with the same species introduced from Japan has generated improvements in this phase of culture. Unfortunately the improvements were not sustained for any longer than 2-3 y (Wang Q., pers. com. 2001) and for this reason some have believed that the species has degenerated by inbreeding after a long term of artificial culture.

Grow-out, Density, Cycle, Output and Market Size

In the north, a special cage for abalone culture is used with 400-600 seed (at >15 mm) per tier at the start of the grow out cycle. These animals are then scattered into other cages to reduce stocking density four times in the 2-3 y of the culture cycle. When they reach size classes of >55 mm and 75 mm they are sold to domestic and overseas markets respectively. For this phase the rafts used hang 25-30 stacks and a stack of 12 tiers crops 25-30 kg of market size abalone (Wang Q., pers. 2001).

In the south, a plastic basket is used in tank culture for 30-35 individual animals of 20-mm shell length. They are then grown in this basket to market size. Some farms raise 50 individuals in this basket at the start and then scatter them to give 30 individuals when they reach 30-mm shell length. A cycle from 20 mm to >50 mm takes about 6-8 mo. At present the small abalone are consumed at 90 individuals per kg (about 47 mm shell length) in the southern markets. A basket crops 400 g in this 6-8 mo. Per cubic meter of water capacity there are 24-30 baskets, cropping 9-12 kg. Mean survival is about 75% (Nie & Wang 2000, Nie & Wang 2001).

The concrete cases used in the south for intertidal culture raise 500-700 juveniles at 10-20 mm shell length and harvest 6-7.5 kg in around 9-12 mo. The survival rate is about 50% to 60% (Qiu C.W., pers. comm. 2001).

Food

China is a country in which abundant culture, of algae such as Laminaria japonica and Undaria pinnatifida occurs. Natural resources of Gracilaria tenuistipitata abound in the south. The brown and red algae are favorites of H. discus hannai and H. diversicolour aquatilis respectively. The feeding habit of the latter is wideranging. Its growth rate when fed on dry or salted Laminaria is faster than when fed on the fresh Gracilaria (Nie et al. 2000). Additionally Eucheuma gelatinae, raised in Hainan, is also supplied for abalone food.

Artificial feeds for the nursery stage are very popular in China. There are powders and different sizes of granules. A few farms have fed on flat feed for the nursery stage. The growth rates of abalone, fed on artificial diets, are faster than the growth rates of those fed on algae (Nieet al. 1986, Nie et al. 2000).

Disease

Main Diseases and Enemies

Bacteria: Bacterial disease, especially Vibrio is common in aquaculture. An epidemic disease of abalone occurred first in Dalian, northern China in 1993. It is called "pustule disease". The pathogens are V. fluvialis and V. campbellii (Nie et al. 1995a, Ma et al. 1996). The outbreak that summer caused the loss of 60 tonnes of adult abalone (~5cm-8cm). Following that event the epidemic diseases caused by V. vulnificus, V. alginolyticus, and V. metschinikovii were successively identified in Fujian and Guangdong (Nie & Wang 2000) (Figs. 1, 2, 3). Additionally a Flexibacter spp. disease has occurred in Guangdong (unpublished data). All are capable of causing high mortality in some situations.

[FIGURES 1-3 OMITTED]

Virus: So far the most serious disease caused by a virus epidemic occurred in the spring of 1999 in Dongshan County, the south of Fujian. It caused 100% mortality at 22 farms within 43 days. A globular virus of dimension 5-80 x 120-150 nm was identified (Huang et al. 1999) (Fig. 4). In the early winter from 1999 to 2002, at about 21[degrees]C water temperature, it reappeared at Dongshan and spread to Guangdong. Many farms were infected.

[FIGURE 4 OMITTED]

Those farms that were infected could not escape another outbreak the next winter (unpublished data). It is clearly a terrible disease for abalone. The clinical signs include; tank water turbid and bubbly because of vomit; after death an atrophied and dark foot muscle still settles on the wall (or basket) of the tank (Huang et al. 1999).

Polychaeta: Polydora spp. occurs in the shell of abalone at some farms in the south. They live on the surface of the inside of the shell or in a cave in the rear ventral edge of a shell. The abalone secretes nacre in an attempt to form shell to resist the worms harassment (Fig. 5). The infected abalone becomes very lean and death finally occurs. The smallest infected abalone found was 17-mm shell length H. diversicolor aquatilis. This animal had a cave of the worm, 12-mm in length (Nie & Wang 2000). Another clinical sign associated with Polydora is rupturing of the mantle at the point of the visceral mass (unpublished data) (Fig. 6). This is called "ruptured abdominal disease." An infection of Polydora also caused high mortality at some farms. It is possible that the high mortality occurred as a result of an infection with Vibrio synchronously.

[FIGURES 5-6 OMITTED]

In addition to the above diseases, notable but occasional attacks of parasitic protozoans such as Sporozoa (unpublished data) (Figs. 7, 8), ciliata (Li et al. 19991 have occurred. Another virus disease called "crack shell" caused by a globular virus of 90-140 nm (Li et al. 1998) occurs occasionally.

[FIGURES 7-8 OMITTED]

Cure and Prevention

Some antibiotics such as chloramphenicol, furazolidone, ciprofloxacin and cotrimoxzole, and similar are effective for inhibition of bacteria in seawater. Among these the first 2 are the most effective, however, they are no longer allowed in China. They do not usually cause antimicrobial resistance, and they are both cheap (Nie & Wang 2000). In tank culture the animals are soaked and aerated continually in a 3-4 ppm solution of an equal mix of chloramphenicol and furazolidone for 4-6 h a day. A course of cure takes 3-5 days (Nie et al. 1995a, Nie & Wang 2000). In cases of very high mortality it can be treated twice a day (unpublished data). In most cases the deaths can be controlled. In addition to increasing the frequency of use of the drug, the dose can also be gradually increased. Some effects are obtained by combination of the above antibiotics with a bactericide, such as chlorine dioxide (Cl[O.sub.2]), sodium dichloroisocyanurate, and bromochlorodimethylhydanto all soaked simultaneously with the antibiotic (Nie & Wang 2000). To this date there is no way known to treat the Polydora and virus diseases.

Consumers and Pricing

Most products are sold live in domestic markets. A few are consumed frozen and as dry food. The people of Guangdong are the highest consumers. Recently abalone are not only sold to restaurants but also to families. Large cities near the coasts have become the second largest consumers. Some H. discus hannai is exported to Japan and South Korea. Some live and canned abalone is also imported from Australia and South Africa. The price of small abalone has declined to US$ ~10-25 [kg.sup.-1] whereas H. discus hannai and H. discus discus are selling at around US$ ~36-46 [kg.sup.-1].

Prospects

The development of abalone culture is expected to be slow in the future, with output remaining steady. In the north, the extensive cultivation by releasing seed on the sea bed will be increased under the "Law of Use and Administration of Sea Areas." Producers will be expected to pay more attention to the prevention and cure of disease and to breeding technology for improvement of culture quality and disease resistance.

ACKNOWLEDGMENTS

The authors thank Dr. Steve Edwards for rewriting the paper and his helpful criticism.

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ZONGQING NIE * AND SUPING WANG

Fuzhou Fisheries Research Institute, 3 Gule Rd., Fuzhou 350005 People's Republic of China

* Corresponding author.