Disease Control in Korean Aquaculture

Fish Pathology, 44 (1), 19 23 2009. 3 2009 The Japanese Society of Fish Pathology Disease Control in Korean Aquaculture Soo Il Park* Department of Aquatic Life Medicine, College of Fisheries Sciences, Pukyong National University, Busan 608 737, Republic of Korea ABSTRACT As the mariculture technique had been developed, annual production of shallow water cultures exceeded that of adjacent water fisheries in recent years in Korea. For reducing production losses from infectious diseases in fish aquaculture, various strategies were employed including treatment of effective chemotherapeutics, development of herbal immunostimulants and vaccination, etc. For the treatment of bacterial diseases, 27 antibacterial agents have been used under government license. Frequent use of these drugs was accompanied with occurrence of drug-resistant bacteria. Recently, new bacterial diseases have occurred in cultured fishes. As the studying on the control activities of medicinal herbs to bacterial growth, the wormwood Artemisia asiatica, the Galla rhois Rhus javanica and the veiled lady mushroom Dictyophora indusiata were revealed high antibacterial activities to the Gram-positive and negative bacteria. For the enhancement of nonspecific immune response in mariculture fish, medicinal herbs and other several materials were investigated as immunostimulants. s Paralichthys olivaceus fed on the diet supplemented with 0.1% extract mixture of the wormwood and the barrenwort Epimedium koreanum showed higher relative percent survival (RPS), when they were challenged with bacterial pathogens. To prevent various infectious diseases, two vaccines were developed and commercially available including vaccines on Edwardsiella tarda and Streptococcus iniae. Key words: immunostimulant, vaccine, herbal medicine, fish pathogen The status of disease occurrence in Korea In Korea, as the aquaculture industry had been developed with the advancing scientific technology, production losses were also increased from infection of various diseases in recent years. However, fish mortality is not the only criterion to evaluate the damage effects of fish disease. The morbidity, which leads to weight loss and poor growth in surviving fish also contributes substantial losses to the farmers. Recently, controlling pathogens is taken as the most important factor to maintain healthy stocks to enhance production. Many fish diseases are believed to be caused by bacterial pathogens. They occur in nursery and rearing ponds causing serious concern to fish farmers. Some of them often wipe out the entire population of fish. Some of the important bacterial pathogens are Edwardsiella tarda, streptococci including Streptococcus iniae, Streptococcus parauberis and Lactococcus garvieae, Vibrio anguillarum (Listonella anguillara) and Vibrio harveyi. They have been identified as most com- * Corresponding author E-mail: parksi@pknu.ac.kr This paper was presented in 5th International Symposium of the Japanese Society for Fish Pathology held in Tokyo (October 18 19, 2008). monly encountered agents in fish diseases. In addition, Photobacterium damselae subsp. piscicida, Vibrio ichthyoenteri, Pseudomonas sp. and Tenacibaculum maritimum were also included. Viruses are known as notorious pathogens, which can cause severe fish diseases, especially red sea bream iridoviral disease (RSIVD), viral hemorrhagic septicemia (VHS) and viral nervous necrosis (VNN). Fish can be attacked on their gills and skin by many parasites. The parasites are scuticociliates causing the scuticociliatidosis, Trichodina spp. causing the trichodinosis, Microcotyle sebastis, Dactylogyrus spp., Bivagina tai and Gyrodactyrus spp. causing the monogenean infestation and Allela macrotrachelus causing the crustacean infestation (Table 1). The strategy of the disease control The basic strategies are either by pathogen control with chemotherapeutics, medicinal herbs or by host control with vaccines and immunostimulants. In Korea, 27 antibacterial agents have been used including 23 antibiotics and 4 sulfa drugs. The frequent use of these drugs often results in occurrence of drug-resistant bacteria, remnants of antibiotics in the fish products and environmental contamination. Therefore, the treatment of

20 S. I. Park Table 1. Major diseases of mariculture fishes in Korea Group Disease Causative agent Affected species* Lymphocystis disease Lymphocystis disease virus (LDV) Many fishes Red seabream iridoviral disease Red sea bream, Red sea bream iridovirus (RSIV) (RSIVD) Rock bream Rhabdoviral infection Hirame rhabdovirus (HIRRV) Viral Birnavirus infection Yellowtail ascites virus (YTAV) disease Viral nervous necrosis (VNN) Piscine nodavirus Several fishes Viral ascites Yellowtail ascites virus (YTAV) Yellowtail Viral hemorrhagic septicemia (VHS) Viral hemorrhagic septicemia virus (VHSV) Viral epidermal hyperplasia Flounder herpesvirus (FHV) Vibriosis Vibrio anguillarum (Listonella anguillara), Vibrio harveyi Several fishes Bacterial enteritis Vibrio ichthyoenteri Larvae of olive flounder Bacterial Photobacterium infection Photobacterium damselae subsp. damseke Several fishes disease Pseudomonas infection Pseudomonas sp. Several fishes Edwardsiellosis Edwardsiella tarda Several fishes Gliding bacterial disease Tenacibaculum maritimum Several fishes Streptococcicosis Streptococcus iniae, S. parauberis Lactococcus garvieae, etc. Several fishes Scuticociliatidosis Scuticociliatida Several fishes Trichodinosis Trichodina spp. Several fishes Parasitic Microcotyle sebastis, Bivagina tai Black rockfish disease Monogenean infestation Dactylogyrus spp., Gyrodactyrus spp. Other fishes Crustacean infestation Allela macrotrachelus Several fishes * Red sea bream, Pagrus major ; Rock bream, Oplegnathus fasciatus;, Paralichthys olivaceus; Yellowtail, Seriola quinqueradiata; Black rockfish, Sebastes schlegeli. Table 2. Studies on the antibacterial activity of medicinal herbs to fish pathogens Herb Botanic name Extract Reference Liquorice, etc. Glycyrrhiza uralensis, etc. Hot water, Ethanol Choi et al., 2004 Jung et al., 2001 Galla rhois Rhus javanica* Various solvents Choi et al., 2005a White mulberry Morus alba Hot water Mok et al., 2001b Selfheal, etc. Prunella vulgaris, etc. Hot water Moon et al., 2006 Methanol Moon and Heo, 2007 Cinnamon Cinnamomum cassia Ethanol Mok et al., 2001c Red sage Salvia miltiorriza Ethanol Mok et al., 2001a Green tea Camellia sinensis Dried Park et al., 1999 Veiled lady mushroom Dictyophora indusiata Ethanol Jo et al., 2002 Cactus opuntia Opuntia ficus Hydrolysis compound Jung et al., 2008 * With cocoon of Melaphis chinensis. medicinal herbs and vaccination would be alternative and more promising ways to prevent fish from infectious diseases. Many studies showed that the medicinal herbs and indigenous plants can replace the antibiotics (Table 2). The wormwood Artemisia asiatica, Galla rhois Rhus javanica and veiled lady mushroom Dictyophora indusiata showed strong antibacterial activities both to the Gram negative and to Gram positive bacteria. The hot water extract of wormwood had higher growth inhibition activity to 36 fish pathogenic bacterial strains including vibrios, E. tarda and streptococci. The ethyl alcohol and ethyl acetate extracts of Galla rhois showed the higher antibacterial activities in the tested 19 fish pathogenic bacterial strains (Choi et al., 2005a). MBT-01108 which was hydrolyzed compound of the stem of cactus opuntia Opuntia ficus-indica var. saboten also showed an excellent antimicrobial activity against the tested 18 fish pathogenic bacterial strains (Table 3). Ethanol extract of veiled lady mushroom was found to be the

Review articles of JSFP2008 Disease control in Korea 21 Table 3. Antimicrobial activity of MBT-01108 on the fish pathogenic bacteria (Jung et al., 2008) Microorganisms MBT-01108 (mg) Commercial discs 50 25 10 5 2.5 1 OTC Am Edwardsiella tarda 40 * 34 26 22 13 10 24 22 Vibrio anguillarum 40 38 32 26 20 13 20 Vibrio sp. 46 31 29 25 14 11 15 Lactococcus garvieae 33 28 22 17 12 12 12 Streptococcus parauberis 35 35 27 23 14 10 18 29 Streptococcus iniae 35 32 24 21 15 21 20 MBT-01108, hydrolysis compound of the stem of cactus opuntia Opuntia ficus-indica var. saboten; OTC, oxytetracycline 30 mg/disc; Am, ampicillin 10 mg/disc. * Diameter (mm) of inhibitory zone. most potent antibacterial activity against all the tested fish pathogenic bacteria (Jo et al., 2002). As the host control strategy, we have used vaccines and immunostimulants. Vaccination with good health management appears to be the most effective way to control infectious diseases these days in fish farms. Therefore, vaccination has become a standard procedure to control fish diseases among countries in Europe and North America. Several kinds of vaccines against the viral and the bacterial pathogens were also developed in Korea (Table 4). Vaccines against the bacteria, E. tarda and S. iniae were already developed and commercially available now. The effectiveness of immersion vaccine of E. tarda against edwardsiellosis of olive flounder was evaluated in a field trial test (Table 5). The two-fold diluted E. tarda formalin-killed cells (FKC) was administrated by immersion for two minutes to 3,000 fingerlings and 5,000 juveniles of olive flounder. Relative percent survivals (RPS) for two vaccinated groups of the fingerlings and juveniles were 94.9% and 92.4%, respectively (Bang et al., 2000). Streptococcal infections were also considered as a serious problem because of significant economic losses in fish farm industry. Fortunately, effective Streptococcus iniae FKC vaccine for olive flounder was developed and the fish immunized intraperitoneally with the 0.3% FKC as prime and booster exhibited the RPS of 66.7% and 87.5%, respectively (Cho et al., 2006) (Table 6). Recently, the rock bream iridovirus (RBIV) vaccine with recombinant protein was also developed and showed excellent effect with high RPS (Do et al., 2006). Immunostimulants are valuable for the control of fish diseases and may be useful to fish culture. The immunostimulatory effects of cactus opuntia Opuntia Table 4. Vaccines licensed for aquaculture in Korea Fish Pathogen Administration route Vaccine mode Paralichthys olivaceus Edwardsiella tarda Immersion FKC * Paralichthys olivaceus Rock bream Oplegnathus fasciatus * FKC, formalin-killed cells. Streptococcus iniae Injection FKC Iridovirus Injection Recombinant protein Table 5. Cumulative mortality and relative percent survival (RPS) of olive flounder against edwardsiellosis after vaccination with 0.5% formalin-killed bacterin Fish body Observation Treatment No. of dead fish Cause of death RPS * (%) weight (g) period (month) group (Cumulative mortality, %) 51.4 Jun Oct Edwardsiellosis 6 ( 0.2) 94.8 Vaccination (n = 3,000) (5 months) Other diseases 73 ( 2.4) 93.1 Edwardsiellosis 116 ( 3.9) Control Other diseases 1,060 (35.3) 1.2 Mar Nov Vaccination 63 ( 1.26) 94.4 (n = 5,000) (9 months) Control 1,127 (22.54) * RPS = [1 (cumulative mortality of vaccinated group/cumulative mortality of control group)] 100.

22 S. I. Park Table 6. Cumulative mortality and relative percent survival (RPS) of olive flounder with Streptococcus iniae after vaccination with 0.3% formalin-killed bacterin (Cho et al., 2006) Treatment Fish body No. of fish Cumulative group weight (g) challenged mortality (%) RPS * Prime injection 22 38 20 20 66.7 Booster injection 24 38 20 7.5 87.5 Control ** 24 36 20 60 Fish were challenged with 1 10 8 cells of S. iniae 3 weeks after vaccination. * RPS (see Table 5) **Control fish received physiological saline only. Table 7. The results of screening of dietary supplements as immunostimulant to fish Ingredient Botanical name Fish Effect Reference Chinese wolfberry, Lycium chinense Nile tilapia Hwang et al., 1999 etc. etc. Resistant to E. tarda Jung et al., 2002 Siberian ginseng Eleutherococcus senticosus Resistant to E. tarda and Won et al., 2008 V. anguillarum Red ginseng Panax ginseng Israeli carp Immunity Choi et al., 2005b Mistletoe Viscum album Japanese eel Selfheal Prunella vulgaris Vegetable silkworm Paecilomyces japonica Resistant to A. hydrophila Survival rate Growth Choi et al., 2008 Kim et al., 2007 Lee et al., 2002 Cactus opuntia Opuntia ficus Resistant to E. tarda and Jee et al., 2007 S. iniae * Nile tilapia, Oreochromis niloticus;, Paralichthys olivaceus; Israeli carp, Cyprinus carpio; Japanese eel, Anguilla japonica. ficus, Siberian ginseng Eleutherococcus senticosus, selfheal Prunella vulgaris and various medicinal herbs on fish have been reported (Table 7). These immunostimulants mainly facilitate the function of phagocytic cells and increase their bactericidal activities. Several immunostimulants also stimulate complement, lysozyme and antibody responses of fish. The activities of these immunological functions are associated with increasing the protection capability against infectious disease. Some of their resistances were evaluated to bacterial pathogens such as vibrios, streptococci and E. tarda. One of the results, olive flounder fed on the diet supplemented with 0.1% wormwood and barrenwort mixture exhibited the higher RPS compared with the control after a challenge test of bacterial fish pathogen (Jung et al., 2002). Chinese wolfberry Lycium chinense showed elevated bactericidal activity in the serum of Nile tilapia Oreochromis niloticus and revealed the higher RPS when they were challenged with 1.0 10 7 CFU/mL of E. tarda, intraperitoneally (Hwang et al., 1999). General discussion and future prospects There are many different types of fish diseases caused by various pathogens in Korea including viral, bacterial, parasitic and other diseases causing organisms. The diseases caused by the combined pathogens are dominant cases. To control these fish diseases, various disease control strategies were used in Korea. Basic strategies are the pathogen control with chemotherapeutics or medicinal herbs, and host control with vaccines and immunostimulants. The Korean government licensed the use of the 27 antibacterial agents for aquaculturing use by 2008. However, the government excluded four quinolones by 2008 and has a strong will to reduce more items from the list for the safe food products. The licensed antibacterial agents in Korea are still much higher in number compared with eight antibiotics of EU and four of USA. A typical study revealed that some medicinal herbs had a growth inhibition activity against fish-pathogenic bacteria and it means those can replace chemotherapeutics. Fish fed on the medicinal herbs showed high RPS.

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