Mr H. A. Iiorsfieli) Reply to Objections Conceri\Ing F.Ish Disease

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NEW ZEALAND FRESIIWATER FISHERIES MISCELLAIIEOUS REFORT NO. 95

\ryATER RIGHT APPLICATIONS OF MR H. A. IIORSFIELI) REPLY TO OBJECTIONS CONCERI\ING F.ISH DISEASE

N.C. Boustead

Report to: Mr H.A. Horsfïeld, Wellington

Freshwater Fisheries Centre

MAF Fisheries

PO Box 8324

CHRISTCHT]RCII

Semicing freshwarer fisheries and aquacukure

JULY l99r NE\ry ZEALAIID FRESHWATER FISHERIES MISCELLANEOUS REPORTS

This report is one of a series initiated in January 1989, and issued by the Freshwater Fisheries Centre, MAF Fisheries. The series was established to ensure that reports prepared for clients, tribunal hearings, internal use, etc., are collected together and available to future users. They are for limited circulation, and some may be confrdential. rsBN 0-477-08440-0

MAF Fisheries is the fisheries business group of the New Zealand Ministry of Agriculture and Fisheries. The name MAF Fisheries was formalised on 1 Novembe¡ 1989 and replaces MAFFish, which was established on 1 April 1987. It combines the functions'of the former Fisheries Resea¡ch and Fisheries Management Divisions, and the fisheries functions of the former Economics Division of MAF.

Enquiries to: The Libra¡ian Freshwater Fisheries Centre PO Box 8324 Riccarton, Christchurch New Zealand RISKS TO HTJMAN HEALTH FROM SALMON DISEASES

None of the hsh diseases that may possibly occur in freshwater farmed salmon in New Zealand pose any risk to human health.

There are diseases of f,rsh that can infect people but these diseases will not occur on this proposed farm. This is clear from knowledge of the particular diseases concerned. Examples are as follows:

Fish mycobacteriosis

This has been found on warm water ornamental aquarium f,tsh and is recorded infecting the skin of three people in New Zealand (Black et al. l97L). It is a disease of tropical fish, and would not proliferate on salmon because of the cool temperatures of salmon.

Anisakis

This is a marine roundworm that can cause stomach ulcers when fish are eaten raw. It does not occur in freshwater and the feeding of unprocessed marine f,rsh wastes to farmed fish is prohibited by the Freshwater Fish Farming Regulations.

DISEASE RISKS TO \ryILD STOCKS

The disease risk to wild stocks was addressed in the report to Mr Horsfield (Field-Dodgson and Boustead 1991). To summarise, diseases on fish farms come from either the parasites and microbes already present on wild fish in the water supply or are introduced with the fish. The possibility of introducing an infectious disease with the fish, that is not already present in wild stocks, is remote for the following reasons. o The number of indigenous infectious salmon diseases is very low and these diseases are not serious threats.

The prospects of exotic diseases becoming established is remote due to the border controls on import of live and chilled salmonids. o Statutory controls exist in the Freshwater Fish Farming Regulations to prohibit the movement of diseased f,rsh. These controls are used and complied with. o The sockeye salmon originated from wild stock in this area only a few generations ago. Thus any diseases farmed fish may have are likely to have come from the wild f,rsh in the area.

In the event of a disease occurring on the farm the prospect of it having a deleterious effect on wild stocks is remote. This is because disease outbreaks are greatly influenced by the environment the hsh are in. Wild fish are not subject to the same space constraints, artificial feeding and fixed location of farmed fish. Furthermore, for the freshwater salmon diseases known in New ZenJand there are no documented cases of these diseases affecting sports 2 fisheries, either here or overseas. It is acknowledged that wild and fa¡med salmonids in Norway are affected by a parasite, Gyrodactylus salaris. This has developed due to the import of live infected fish into Norway without quarantine. Potential for similar disease introductions into New Zealand is addressed under provisions of the Animals Act 1967. Stringent restrictions and conditions apply to the import of live salmonids. MAF policy is to ensure such disease transfers will not occur here.

SOCKEYE SALMON DISEASE SUSCEPTIBILITY

Concerns were raised that sockeye salmon were reported to be unable to be cultured overseas due to disease problems and that this could also apply here. Objectors found Mr Horsfield's reported belief that he could overcome this as inadequate.

This belief that disease problems can be overcome is very soundly based on experience and research in New Zealand. Furthermore application of proper disease control measures has overcome the disease problems reported overseas and sockeye salmon are now being cultured in Alaska (Meyers et al. 1990) and Canada.

There is considerable experience of successful sockeye salmon culture in New Zealand. Sockeye salmon are already being cultured at three licensed salmon farms and have been cultured by the Freshwater Fisheries Centre of MAF Fisheries, beginning in 1976 and continuously from 1982 (Graynoth and Hawke 1984). The diseases encountered have been described and their risks assessed as low (Field-Dodgson and Boustead 1991, Boustead 1989).

The primary cause of disease problems in rearing sockeye salmon overseas has been the viral disease, infectious haematopoietic necrosis (IHN). The Freshwater Fisheries Centre of MAF Fisheries has conducted extensive investigations of wild and farmed stocks to assess if this disease is present. Investigations of 89 wild fish and 306 hatchery fish over the years 1986 to 1991 have found no evidence of this disease in this country (N. Boustead, unpublished data).

This experience and research shows that the belief that these sockeye salmon can be cultured without signihcant disease problems is very soundly based.

FTJRT]NCULOSIS AND ENTERIC REDMOUTII DISEASE

The statement in one of the submissions received that furunculosis has been found in New Zealand is not correct. MAF has no evidence that this disease is present in this country.

The situation regarding enteric redmouth disease in New ZetaIand has been addressed by Boustead and Anderson (Boustead and Anderson 1990). That report provides details showing ERM is not a signif,rcant threat to salmon farming and there is no evidence of it affecting wild fisheries. 3 DO\ryNSTREAM IMPACT OF CHEMICAL TREATMENTS

To address this issue it is necessary to consider the specific diseases that may be encountered and the remedies that may be applied. The diseases are listed in the report. Of these, the only remedies that might be used are Chloramine T for bacterial gill disease, a combination of formalin and malachite green for whitespot, and the antibiotic oxytetracycline for ERM.

The anticipated use of these chemicals is very low as indicated in the report to Mr Horsfield. I consider it unlikely either bacterial gill disease or whitespot would occur at all. Furthermore use of such chemicals in operating farms in New Zealand is very low. Most farms do not have any need for these chemicals on fish of the size envisaged. Should it be necessary to use these remedies, they would be required to be entrapped for treatment by surrounding the cage with a watertight liner.

These treatments are applied to live fish at dilutions which clearly must not be lethal to the f,rsh being treated. Following treatment these chemicals would be released and diluted to harmless levels by the considerable flows in the canals. These substances are inactivated by organic matter which would further reduce any possible impact. The dilution and inactivation of these chemicals mean they would not be a risk to human health downstream of the farm.

Any occurrence of enteric redmouth disease may require the use of oxytetracycline. However, in some cases of ERM both here and overseas, no treatment is applied as losses are insignificant. The use of oxytetracycline and other drugs is controlled by legislation. This means oxytetracycline can only be used when prescribed by a veterinarian which provides control on its use. Oxytetracycline is administered orally by incorporation into the food and is ingested by the fish. With sensible feeding regimes only negligible quantities would enter the waterway.

MONITORING FOR DISEASE

Legislative controls relating to the notification and control of diseases on salmon farms is contained in two Acts, the Freshwater Fish Farming Regulations 1983/278 of the Fisheries Act and in the Animals Act 1967. These regulations specify comprehensive provisions for disease control which must be adhered to. Knowledge and compliance with these regulations is required as part of the licensing of the farm. The regulations give MAF wide powers to act to contain any serious disease problems and require the licensee of the hsh farm to notify MAF of specifrc diseases of concern.

In order to export salmon to the United States the US authorities require that salmon are tested and found free of specific diseases, namely VHS (viral haemorrhagic septicaemia) and whirling disease. To meet these requirements the Quality Management group of MAF carries out regular inspections of farms every three months for disease and tests samples for VHS and whirling disease annually. Tests are carried out to detect asymptomatic or latent infections. As it is proposed that product from this farm may go to the USA this surveillance will be carried out. This provides another mechanism for detection and notification of disease. REFERENCES

Black, H., Rush-Munroe, F. M. Woods, G. 1971. Mycobacterium marinum infections acquired from tropical hsh tanks. Australasian Journal of Dermatology 12: 155-164.

Boustead, N. C. 1989. A Guide to diseases of salmon in New Zealand. New Zealand Freshwater Fisheries Report No 112.

Boustead N. C. and Anderson C. 1990. Enteric redmouth disease in New Zeala¡d. New Zealand Freshwater Fisheries Miscellaneous Repon No. 71.

Field-Dodgson, M. S. and Boustead, N. C. 1991. The feasibility of rearing salmon in hydro canals. New Zealand Freshwater Fisheries Miscellaneou.s Report No 83.

Graynoth E. and Hawke L. J. 1984. Hatchery rearing of sockeye salmon in New Zealand. In: Proceedings of the salmon farming conference. Fisheries Research Division Occasional Publication No. 47.

Meyers T. R., Thomas, J. B., Follett, J.E., and Saft, R. R. 1990. Infectious haematopoietic necrosis virus: trends in prevalence and the risk management approach in Alaskan sockeye salmon culture. Journal of Aquatic Animal Health 2: 85-98.