Aquaculture Health Management in Singapore:
Current Status and Future Directions

Frederic H.C. Chua

Fish Health Section, Animal And Plant Health Inspection Division
Primary Production Department, Singapore.

Chua, F.H.C. 1996. Aquaculture health management in Singapore: current status and future directions. In Health Management in Asian Aquaculture. Proceedings of the Regional Expert Consultation on Aquaculture Health Management in Asia and the Pacific. R.P. Subasinghe, J.R. Arthur & M. Shariff (eds.), p. 115–126. FAO Fisheries Technical Paper No. 360, Rome, FAO. 142 p.

Abstract

Although the total area utilized for aquaculture in Singapore is comparatively small, it annually produces over US$ 30 million worth of ornamental fish and marine foodfish. It has been predicted that, with the introduction of the Agrotechnology Parks concept, the value of aquaculture production in Singapore will reach US$ 42 million by the year 2000. This paper describes the approach taken by the Government of Singapore to ensure production of fish through hygienic methods employing better planned management systems.

INTRODUCTION

The ornamental fish and marine foodfish sectors make up the aquaculture industry in Singapore. Together they produce over US$ 30 million worth of farmed fish a year. The production from the ornamental fish sector accounts for about 75% of this total value. Freshwater foodfish production is insignificant.

Singapore exported a total of US$ 57 million worth of ornamental fish in 1994. This consisted of imported as well as locally farmed fish produced from 107 freshwater farms which cover a land area of 170 ha. By market demand, a diversity of species is cultured. More than 300 varieties can be found, comprising the live bearers (viz., guppy, platys, mollies, swordtail) and egg layers (angelfish, tetras etc.). Most farms culture a few species at a time. Due to competition, there has been a move to concentrate on and upgrade the farming and breeding of a few high-value species such as the varieties of discus and dragon fish (arowana). Nevertheless, the various guppies still form the bulk of production.

While many farms still employ what are considered to be traditional methods, such as growing fish in organically fertilized earthen ponds, there is a shift towards more hygienic production methods employing better planned management systems. This is seen in the establishment of farms within Agrotechnology Parks. In these sites, which have been set up by the Primary Production Department (PPD), land use is optimized through improved site planning and engineering. An increasing number of farms are being located at Agrotechnology Parks, and by the year 2000, a total production area of 260 ha from the Parks is expected to increase production to US$ 42 million a year. As the intensity of farming would increase with this development, the industry would be less reliant on imported fish for its export trade.

Production periods for ornamental fish are generally short, being between one to three months. Most stock are farm bred. Grading and sexing are routinely done during the production cycle.

Farmers use a variety of farm-prepared feeds. Common ingredients used include wheat, oats and fish meal. Live feed, such as Moina and tubifex worms, form part of the diets of some age groups (e.g., fry, broodstock). Commercial pellets such as cel mash and tilapia pellets are also used.

Mariculture development took off after the Marine Fish Farming Scheme was implemented in March, 1981. There are now 79 floating marine netcage farms off the northern coast of Singapore (Johore Straits), which produce over 2000 metric tonnes (mt) of marine foodfish annually. The species farmed include seabass, groupers, siganids, snappers, threadfin, mud crabs, lobsters etc. Perhaps driven by good market demands for live fish in Hong Kong, Taiwan and China, and increasing production costs locally (particularly labor costs), many farms are switching to the transshipment trade. Here market-sized fish are imported from Indonesia, Malaysia and India, held for one to four weeks, and re-exported live. Because of the shorter turnover period, overall risk and production costs are considered to be lower.

The farms stock a variety of species and age groups at a time. Since both transshipment and growout are often carried out simultaneously, the culture periods vary widely, being between one to eight months. Although there are no particular periods of the year during which the introduction of fingerlings for on-growing is preferred, farmers generally avoid stocking fish during the monsoon seasons (June – July and November-January) due to higher post-stocking losses. Most feeding is with trash fish, which is supplied daily from the local port. However formulated diets are slowly finding their way into more farms.

The bulk of fingerlings stocked for growout comes from neighboring countries. However, there is an active program to commercialize the breeding and larviculture of species considered to have better market potential, such as the groupers. A project undertaken by the PPD in conjunction with the National University of Singapore (NUS) aims to produce grouper fry under captivity. There are currently three commercial hatcheries in operation, producing fry of seabass and snappers to supply the local and export markets. With government support, successful breeding of the fourfinger threadfin (Eleutheronema tetradactylum) has been accomplished in one of the hatcheries.

Constrained by limited available coastal areas for farming, mariculture will become more intensive in the future. Coupled with inherently high production costs relative to neighboring countries, increased attention will be given to the more highly priced species, such as groupers and threadfin. The focus is to enhance the development of commercial hatcheries, thereby making available a wider variety of fry for export. New sites for coastal aquaculture will also be developed, such as near the southern islands of Singapore, where water quality is expected to be better and where larger farming units with deeper netcages can be used.

HEALTH PRACTICES IN SINGAPOREAN AQUACULTURE

Some health practices commonly carried out by ornamental fish farms are listed in Table 1. Many ornamental fish farms also practice on-farm quarantine. Newly introduced fish are kept reasonably isolated for a few days to a week before stocking into the rest of the farm. Some farms, such as guppy farms which have developed their own varieties, usually do not find it necessary to introduce stock, as they already have an adequate breeding pool.

There appears to be a difference between farms in the Agrotechnology Parks and those which are not, in disease control measures used and in the rate of success of these measures. In contrast to the more traditional farms, those in Agrotechnology Parks have layouts that facilitate disease control. During a disease outbreak among guppies in 1993 which was due to a possible viral agent, it was observed that 30% of guppy farms in Agrotechnology Parks were affected compared with 70% of farms in the non-agrotechnology areas.

Table 2 summarizes some disease control practices used in 34 marine farms surveyed in 1992. Generally farmers did not separate newly introduced stock from those already present on the farms. However the practice of administering bath antibiotic and parasiticide treatments to new stock was quite common.

CONSTRAINTS

A problem not peculiar to Singapore, but perhaps common to most aquaculture industries in the region, relates to the nature of fish diseases found here and our present level of understanding of them. Conventionally, health programs such as those for domestic animals or farmed salmonids, focus on specific diseases of attributable economic impact, and the use of standard diagnostic procedures along with preventive and control programs. They involve the setting of specific targets e.g., “reducing the prevalence of disease ‘A’ by ‘X’ % within a period,” and are possible by virtue of the relatively comprehensive amount of information available.

Commercial diagnostic kits and vaccines are also available, which encourages disease control. Given the fact that most fish diseases occurring in the region are still poorly understood, these are not yet possible here. Many diseases are considered as “syndromes” involving complex host-environment-pathogen interactions. Moreover, in ornamental fish culture, the numerous species involved could potentially be affected by an equally wide variety of pathogens. Even with the emergence of an increasing number of new pathogens, notably the viruses, it may be difficult to justify the development of new cell lines, diagnostic kits and vaccines to provide for the large number of species groups involved. In most cases, the respective sizes of these species groups, in terms of total market value, are still relatively insignificant.

As previously mentioned, aquaculture is becoming increasingly intensive in Singapore due to the limited availability of land and sea space. Only 1,700 ha of land has been designated for farming, and of that, slightly more than 10% is currently used by over 100 aquaculture farms. Consequently risks from disease will also increase, and must be addressed through improved health management programs.

Another constraint presently encountered is that health records such as mortality figures are often poorly kept by farmers. This makes assessment of mortality patterns during disease outbreaks difficult.

HEALTH PROBLEMS IN SINGAPOREAN AQUACULTURE

Quite loosely, we can classify the diseases seen in Singapore as being either (a) those associated with opportunistic pathogens or (b) those caused by specific agents.

Diseases associated with opportunistic pathogens

These are persistent, endemic diseases generally precipitated by some primary insult to the host. They become more significant with increased farming intensity and poor husbandry. They are often presented as disease syndromes involving fluctuating or poor water quality, unsuitable soil conditions, poor nutrition and usually concomitant infections by multiple opportunistic agents. Nonetheless they constitute a larger overall economic impact in comparison with problems caused by specific agents. Conditions in this category which are commonly seen include gill hyperplasia, erosive and ulcerative dermatitis of the fins and general body surface, bacterial septicemia, ectoparasitic infections, endoparasitic encystments and parasitic enteritis.

Common parasites found among ornamental fish cases include members of the genera Ichthyobodo, Dactylogvrus, Gyrodactylus, Trichodina, Ichthyophthirius and Piscinoodinium. Those commonly found affecting marine foodfish include Benedenia, Cryptocaryon, and Trichodina.

The bacteria isolated from many disease cases were mixed, and were usually considered to be insignificant. Tables 3 and 4 summarize the bacteria recently isolated from ornamental and marine fish by the Central Veterinary Laboratory and the Fish Health/Environment Unit (PPD), respectively. The interpretation of bacteriological and parasitological findings can be baffling; as a result much attention has been given to case histories, post-mortem findings and histopathology.

Recent observations suggest that there may be specific strains of bacteria, such as some Vibrio harveyi which are pathogenic to seabass, indicating some promise for the development of bacterial vaccines for marine foodfish. It is also likely that certain strains of Aeromonas may be more pathogenic than others to freshwater ornamental fishes, however, this needs further investigation. Likewise, outbreaks which have been attributed to certain parasites such as Argulus, Lernaea and Hexamita have been observed. Because these parasitic infections respond to specific treatments (e.g., metronidazole to treat Hexamita infections), they are thought to be primary diseases under certain circumstances.

Diseases caused by specific agents

These include the new diseases and are characterized by some or all of the following:

• they affect apparently healthy stocks in relatively well-managed farms

• they cause mortalities of epizootic proportions

• many farms are affected concurrently

• they present with specific, often pathognomonic gross or histopathological signs or lesions

• both young and growout stocks are affected.

In Singapore, viral diseases have dominated this category. Some of them are novel diseases and have caused epizootics in specific species and age groups. The following have been observed:

Marine foodfish

• Lymphocystis of seabass (Chao, 1984)

• Rabbitfish viral hepatopathy (unpubl. obs.)

• Red grouper reovirus infection (Chew-Lim et al., 1992)

• Viral nervous necrosis (VNN) of brownspotted grouper (Spinning Grouper Disease) (Chua et al., 1993)

• VNN of seabass (unpubl. obs.)

• Bent body syndrome/swimbladder syndrome of brownspotted grouper (Chua et. al., 1993)

• Sleepy grouper disease of brownspotted grouper (Chua et. al., 1994)

Freshwater ornamental fish

• An infectious disease affecting angelfish in 1988 (Lim S.J., pers. comm.).

• An infectious disease affecting guppies in 1993 (unpubl. obs.).

DRUG AVAILABILITY AND USAGE

Importers of drugs for aquaculture use must be licensed under the Poisons Act, which is administered by the Ministry of Health (MOH). As a condition before purchase of drugs, farmers must produce their farm license; details of the purchase, such as quantity and date of purchase are recorded and maintained by the supplier.

These records are checked periodically by MOH officials. For importation of new drugs or chemicals, advice from the PPD is first sought.

Drugs and chemicals are commonly used during husbandry operations such as grading and sexing, or in between transfer into new tanks/nets. Many farmers carry out preventive treatment of newly introduced stocks. Exporters of ornamental fish sometimes add antibiotics and antiseptics to the packing water used for transportation. In such prophylactic procedures, broad spectrum medications are used, targeting bacteria and ectoparasites. Table 5 lists the commonly used drugs and chemicals. Both generic and nongeneric drugs are used.

Culture-sensitivity tests conducted for bacteria isolated from marine fish over the last two years indicate consistent in-vitro resistance of many Vibrio isolates to tetracycline and oxytetracyline. There was little or no resistance to the other antibiotics tested (amoxycillin, chloramphenicol, erythromycin, trimethoprim and furazolidone).

GOVERNMENT APPROACH TO HEALTH MANAGEMENT

The primary aims of aquatic health management in Singapore are to reduce the prevalence of diseases due to opportunistic pathogens and to minimize the impact of introduced diseases. Under the Fisheries Act, the PPD may enforce legislative controls to prevent the introduction and spread of diseases when deemed necessary. Import regulations require the licensing of all fish importers and the declaration of every consignment of imported fish.

A farm Accreditation Scheme was established in 1989 to cater to the export trade. Under the scheme, the PPD routinely inspects farms to ensure that minimum standards of disease control, such as quarantine facilities and procedures, are in place. Fish are routinely sampled at the point of export for clinical and laboratory examinations.

A fish health surveillance program which will involve the regular monitoring of a wide spectrum of farms is being studied. In particular, certain farms (sentinel farms) may be selected in rotation for closer monitoring of disease and mortality patterns, and of on-farm disease control systems. Particular batches of fry may be followed through to harvest to help further understand disease trends. The emphasis would also be on strategic sampling of stock for routine examination. High risk groups, such as fry, would be identified so that their monitoring may be concentrated during high risk periods (e.g., during dry spells or monsoons). The push for on-farm quarantine in inland farms (e.g., ornamental fish farms) and prestocking treatment of introduced marine fish will continue. Standardization of such procedures will be considered.

Improved facilities for clinical observation of fish, particularly in the study of new diseases, are being planned. Information transfer is also carried out during visits to farms, and seminars are held periodically.

The government's approach to research and development in fish disease is to link up with academic institutions and the private sector. Typically, research areas are identified by the government. Thereafter, the basic research component, such as molecular work, may be taken up by academic institutions, and subsequent development of product lines (e.g., diagnostic kits, vaccines) by private companies. Currently, the PPD is collaborating with Ngee Ann Polytechnic in the serotyping and genetic fingerprinting of Vibrio isolates from marine foodfish. Another project between the PPD, the NUS and a private company dealt with the development of fish cell lines and the isolation and identification of certain fish viruses.

A major spin-off from the establishment of Agrotechnology Parks by the PPD is that health management can be better facilitated. In thsese parks, farms can be kept reasonably isolated and quarantined should the need arise. The quality of effluent can also be monitored and controlled more easily. Within the farms, water recycling systems are being developed. It is also more feasible to put into place systems which isolate culture units, provide for more efficient treatment procedures and segregate batches of stock in these farms. This Agrotechnology Park concept will continue to shape the nature of fish farming in Singapore.

CONCLUSIONS

While Singapore's production base remains modest by virtue of its limited area for agricultural development, aquatic animal health management is nevertheless a high priority. As the approach adopted is principally that of “high-tech farming” or agrotechnology, the justification for development and production of high-value stock with good halth status is even greater. Increased health vigilance is anticipated with the expected increase in aquaculture trade between Singapore and her neighbors in the Asia-Pacific.

ACKNOWLEDGMENTS

I thank the Director of Primary Production for permission to present this paper, and Miss Julie Goh for her assistance in preparing the manuscript.

REFERENCES

Chao, T.M., 1984. Studies on the transmissibility of lymphocystis disease occurring in seabass, Lates calcarifer (Bloch). Singapore J. Pri. Ind. 12: 11–16.

Chew-Lim, M., G.H. Ngoh, S.Y. Chong, F.H.C. Chua, J.L.C. Howe and E.W. Lim, 1992. Description of a virus isolated from the grouper Plectropomus maculatus (L). J.Aquat. Anim. Health, 4: 222–226.

Chua F.H.C., J.J.Loo, J.Y. Wee and M. Ng, 1993. Findings from a fish disease survey: an overview of the marine fish disease situation in Singapore. Singapore J. Pri. Ind. 21: 26–37.

Chau F.H.C., M.L.Ng, K.L. Ng, Loo, and J.Y. Wee, 1994. Investigation of outbreaks of a novel disease, ‘Sleepy Grouper Disease’, affecting the brown-spotted grouper, Epinephelus tauvina, Forskal. J. Fish Dis. 17: 417–427.