An Overview of Health Management of
Coldwater Fish and Shrimp in Japanese Aquaculture

K. Inouye

National Research Institute of Aquaculture
Tamaki, Mie 519 04, Japan

Inouye, K. 1996. An overview of health management of coldwater fish and shrimp in Japanese aquaculture. 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. 104–114. FAO Fisheries Technical Paper No. 360, Rome, FAO. 142 p.

Abstract

Disease problems has been an important consideration in Japanese aquaculture over the past decade. Most of the disease outbreaks are caused by the environmental problems stemming from over stocking and entry of new exotic pathogens. In 1992 alone, Japan lost US$ 264 million due to diseases in aquaculture. Japan's approach to aquaculture health management consists of three major components: provision of facilities for diagnosis and prevention, implementation of appropriate rules and regulations, and improvement of infrastructure. This paper describes the manner in which health management of coldwater cultured fish and shrimp is being conducted.

INTRODUCTION

In Japan, aquaculture production in 1992 was 1 397 000 metric tonnes (mt), worth US$ 8.4 billion, and amounting to 15.7% of the total fishery production. Aquaculture production of coldwater finfish and shrimp in 1992 was 47 091 mt, or 3.4% of the total aquaculture production. The major species of cultured coldwater finfish and shrimp are coho salmon (Oncorhynchus kisutch), which are cultured in fresh water until smoltification and then raised in sea water, kuruma shrimp (Penaeus japonicus), which are reared in marine systems, and rainbow trout (O. mykiss) and Japanese native salmonids (landlocked salmon, O. masou; dwarf rill trout, O. rhodurus; and mountain trout, Salvelinus pluvius), which are raised in fresh water. Coho salmon is a species whose production has increased rapidly in the last 10 years. In 1992, it was the highest in production, with 25 519 mt, followed by the freshwater salmonids and kuruma shrimp, with 19 385 mt and 2 187 mt, respectively.

The very rapid development of aquaculture has been accompanied by disease problems. These problems are partly caused by environmental deterioration and overstocking, which lead to health disorders in cultured fish, and are partly due to the entry of exotic pathogens.

Table 1 shows the major diseases of fish and shrimp, their causative agents, and the year of their first occurrence. Infectious pancreatic necrosis (IPN), infectious hematopoietic necrosis (IHN), erythrocyte inclusion body syndrome (EIBS) and bacterial kidney disease (BKD) have been introduced from abroad with imported eggs. Recently, mass mortalities caused by a new baculovirus occurred in kuruma shrimp farms in Japan. The causative virus of this disease was also introduced from abroad.

The Fisheries Agency regularly evaluates the damage caused by fish disease in intensive aquaculture. Each year the Agency has prefectural governments send out questionnaires to all aquaculturists and inform the Agency of the results. The damage caused by disease in finfish and shrimp aquaculture in 1992 was estimated to be 18 269 mt, worth US$ 264 million, compared to a total production of 356 154 mt, worth US$ 4 376 million. Thus, about 5% of the total production of finfish and shrimp was lost to disease in 1992.

Losses due to disease suffered by coldwater finfish and shrimp culture (% total production) were on the order of 2.5% for coho salmon, 6.2% for rainbow trout, 5.3% for Japanese native salmonids and 13.3% for kuruma shrimp. The loss of coho salmon due to disease in 1992 was estimated to be 733 mt, worth US$ 4.6 million. EIBS caused the largest loss (289.1 mt), followed by vibriosis (197.7 mt) and BKD (162.9 mt) (Table 2). The loss of rainbow trout in 1992 was estimated to be 630.2 mt, worth US$ 6.2 million. IHN caused the largest loss (199.3 mt), followed by saprolegniasis (109.0 mt), bacterial gill disease (BGD) (64.7 mt), ichthyophonosis (51.7 mt) and vibriosis (42.9 mt) (Table 3). Losses of Japanese native salmonids were estimated to be 266.4 mt, worth US$ 1.8 million. Furunculosis caused the largest loss (95.6 mt), followed by saprolegniasis (27.5 mt), vibriosis (26.0 mt), ichthyophthiriasis (white spot disease) (22.0 mt) and BGD (18.9 mt) (Table 4).

Vibriosis caused the largest loss in kuruma shrimp production in 1992, the damage amounting to 149.5 mt, worth US$ 26.8 million. In 1993, a new baculovirus disease occurred in major kuruma shrimp farms in Japan. The loss of shrimp caused by this disease was estimated to be 320 mt, worth US$ 24 million.

DIAGNOSIS AND PREVENTION

Diagnosis of fish diseases is made mainly by staff of fisheries experimental stations or of the fish diseases control centers of the prefectural governments. A small number of staff at the Fisheries Co-operation Association who have followed a training course in fish disease control also make diagnoses.

When a disease breaks out, chemotherapy is important. At present, 29 antibacterials are permitted for fisheries usage in Japan: 5 sulfa drugs, 2 nitrofurans, 7 other synthetic antimicrobial drugs, and 15 antibiotics. Oxytetracycline hydrochloride (OTC), oxolinic acid (OA), sulfamonomethoxine (SMM) or its sodium salt (SMM-Na), and florfenicol (FF) are used to treat bacterial diseases of coho salmon. OTC, OA, sulfadimetoxine (SDM) or its sodium salt (SDM-Na), SMM, SMM-Na, FF and sulfisozole (SIZ) are used for rainbow trout; OTC, OA, SMM, SMM-Na, FF and piromidic acid (PA) for dwarf rill trout; and OTC and OA are used for treating kuruma shrimp (Table 5).

Only one commercial vaccine for salmonid vibriosis has been approved for use in Japan. The bath vaccination method is currently employed.

Several germicides are used in aquaculture for the prevention of diseases such as IHN, IPN and vibriosis (Table 6), iodophor being the most commonly used. Living salmonid eggs are disinfected by iodophor immediately after importation. When eggs are introduced from a domestic hatchery, the fish culturist uses germicides for their disinfection in the same way. Farmers use several kinds of invert soaps, cresol, sodium hypochlorite and bleaching powders to sanitize aquacultural materials and facilities. Recently, some new methods, such as treatment using ultraviolet light and ozone, are employed in some hatcheries for sanitizing the water supply.

RULES AND REGULATIONS

Quarantine

No regulations for fish quarantine have been established in Japan. However, to avoid the entry of pathogens from abroad, the Fisheries Agency has requested that certain steps be taken through the prefectural governments. Namely, at importation of live eggs or juveniles, the importers are requested to a) attach a health certificate issued by the governmental authority of the exporting country stating that the eggs or juveniles are not infected, b) have juveniles or eggs examined for pathogens at the time of importation, and c) disinfect juveniles or eggs immediately after importation. Examination for pathogens at the time of importation is entrusted to the Japanese Fisheries Resource Conservation Association (JFRCA) by the Fisheries Agency. Voluntary inspections of eggs and fingerlings are performed for viruses, bacteria and parasites by JFRCA in cooperation with universities and the National Fisheries Research Institute.

Information on disease occurrence

To prevent the spread of pathogens within the country, measures are taken by Fishery Experimental Stations and Fish Disease Control Centers. On request, they examine for pathogens and make diagnoses when juveniles and eggs are transferred between prefectures. Prefectural governments gather information on the occurrence of diseases from aquaculturists and Fisheries Co-operative Associations and distribute this information to other Fisheries Co-operative Associations and prefectural governments as the occasion demands. A computerized network linking the Fisheries Agency, JFRCA and the prefectural governments is being established.

Restrictions on the use of drugs in aquaculture

All drugs should be controlled by the Central Pharmaceutical Affairs Council before being approved for manufacture by the Ministry for Agriculture, Forestry and Fisheries. The examination is based on the Pharmaceutical Affairs Law for the safety and efficiency of medicines. Usage of fishery medicines is also regulated by The Standard to be Observed by User, which is based on the Pharmaceutical Affairs Law and indicates the administration method, dosage, withdrawal period etc.

INFRASTRUCTURE

Institutions

• The Fisheries Agency

The Fisheries Agency belongs to the Ministry of Agriculture, Forestry and Fisheries, and has jurisdiction over fisheries administration, including disease control and aquaculture promotion. The Fisheries Agency has nine national research institutes and the Shimonoseki University of Fisheries. These facilities carry out research or training in fisheries.

The National Research Institute of Aquaculture (NRIA) belongs to the Fisheries Agency, and was established in 1979 to promote basic research on aquaculture. There are five research divisions in NRIA, one of which is the Fish Pathology Division. This division has 12 researchers working in four research sections: the Pathogen Section, the Pathophysiology Section, the Pharmacology Section and the Immunology Section.

Since 1973, when losses due to disease began to be recognized as a serious problem to aquaculture, the Fisheries Agency has practiced systematic measures for the prevention of fish disease. These measures can be roughly divided into two parts: one is to support the work carried out by the prefectural governments and the Fisheries Co-operative Associations, and the other is the work entrusted to the Japan Fisheries Resource Conservation Association. The Fisheries Agency is taking broad countermeasures for the prevention of fish diseases by working together with the prefectural governments, fishermen's cooperatives and aquaculturists.

• Prefectural Governments

The fishery sections of prefectural governments exercise jurisdiction over fisheries administration mainly within their prefectures and coastal areas. As for disease prevention, measures taken at the actual aquacultural sites are very important. Prefectural governments play a very important role in guiding farmers, either directly or through the fishermen's cooperatives.

There are a total of 96 Fishery Experimental Stations in Japan, each prefecture having at least one station. At each station, some divisions of carry out research for aquaculture and the control of fish diseases. In most prefectures where disease causes severe damage to aquaculture, there are Fish Disease Control Centers (20 in total), either as a part of the Fishery Experimental Stations or as independent organizations. Prefectural governments have also established Fisheries Extension Offices to give technical guidance to fishermen. These offices and the Fishery Experimental Stations work together to take preventive measures against fish diseases.

The total number of staff of prefectural governments engaged in disease prevention was 470 in 1992. In addition, 30 staff from cities, towns and villages are also engaged in these measures.

• Fisheries Co-operative Associations

Fish farmers often establish their facilities quite close to each other. In marine aquaculture, farms are usually set up within a rather confined area, such as a bay, and in freshwater aquaculture, farms often utilize the same source of water. Therefore, the Fisheries Co-operative Association, which gives guidance to fishermen and controls the local fishing ground, plays an important role in fish disease prevention. However, many of these associations are on a very small scale and thus the level of guidance varies greatly according to the association. The total staff of all associations engaged in disease prevention measures in 1992 was only 80.

• Japan Fisheries Resource Conservation Association (JFRCA)

Since 1984, the Fisheries Agency has carried out some activities by entrusting JFRCA to establish uniform techniques for disease prevention. The undertaking involve promotion of measures for disease prevention, technical extension, training, improvement of diagnostic methods and voluntary inspection of imported living fish and eggs for pathogens. In carrying out these undertakings, JFRCA also receives advice and support from the National Research Institute of Aquaculture, the universities and the fishery experimental stations.

• Universities

Seventeen universities having fishery faculties (including the Shimonoseki University of Fisheries belonging to the Fisheries Agency), and another 16 universities with veterinary faculties have educational research facilities for fish disease.

Establishment

The Fisheries Agency provides financial support to the prefectural governments and the Fisheries Co-operative Associations for establishing facilities for disease prevention.

Training

At the farm level, fish disease specialists are indispensable in order to carry out disease prevention measures, such as providing advice to farmers, making diagnoses, and disinfecting facilities and equipment. Therefore, since 1973 the Fisheries Agency has trained staff from prefectural governments and, since 1984, staff from the Fisheries Co-operative Association have been included in this training. This training is aimed at educating fish disease specialists and improving their quality. In recent years, the Fisheries Agency has entrusted this training to JFRCA.

In Japan, the training of fish disease technical workers is carried out separately in both fishery and veterinary fields, with aquacultural guidance and leadership being mainly carried out in the fishery field. There are several training courses. A basic course consists of lectures and practical exercises given 20 days each year for a duration of three years. In 1989, there were 30 to 40 trainees for each yearly course; altogether 100 staff participated in the training. Other training for fish disease technical workers is also carried out, depending on the circumstances. Since 1974, the Japan Veterinary Medical Association has individually carried out annual fish disease training via post-graduate education of veterinarians.

Extension

Countermeasures for disease prevention need to be uniformly applied. To achieve this, extension activities with respect to disease countermeasures are implemented as follows: JFRCA distributes textbooks on diagnosis and techniques of disease prevention and lends out movies and VTR to prefectural staff who are in charge of guiding farmers. The prefectural governments also offer courses and distribute textbooks and pamphlets on fish diseases. These steps are taken to extend knowledge on fish disease, disease prevention and the use of chemotherapeutants.

National programs and development plans

Disease prevention measures should be taken cooperatively by the national and prefectural governments, the Fisheries Co-operative Associations and aquaculturists. In addition, disease control systems for the farms and a rapid and appropriate response by farmers to disease problems are important.

To promote an efficient disease prevention plan, the Fisheries Agency, prefectural governments and Fisheries Co-operative Associations hold meetings on disease prevention. These meetings cover the regulations and administrative policy of each agency or organization and are designed to ensure that the prefectural organizations and farmers follow the overall administrative plans of the Fisheries Agency.

The following activities should be undertaken by the Fisheries Agency to promote fish disease prevention:

• Studies are needed to elucidate the mechanisms and the causes of fish diseases, and to develop disease prevention techniques such as vaccines.

• New medicines applicable to different species of fish, and to diseases that are resistant to medicines currently used in aquaculture need to be developed.

• Husbandry techniques for fish health management by farmers need to be improved, and a fish-disease control system by the Fisheries Co-operative Associations should be established.

¹ Year of first occurrence.