The Hazards of the Salmon Farming Industry

[Guest guest]

The Hazards of the Salmon " Farming " Industry

 

 

Drugs used in the salmon farming industry

A variety of chemicals, including antibiotics, pesticides and

fungicides are used on salmon farms to treat disease outbreaks.

These drugs are often administered to the fish through their feed.

 

Since salmon are mostly raised in open marine netcages, most of the

drug, or its metabolic byproducts, end up in the marine environment

through uneaten feed or the salmon's excrements (1). The

distribution and environmental impact of these chemicals is a cause

of great concern.

 

Antibiotics-

The most common antibiotic used is oxytetracycline, with 6.4 metric

tonnes used on B.C. salmon farms in 1998 (2).

 

Others include fluorfenicol and a class known as sulfonamides. It

has been shown

that oxytetracycline is poorly absorbed by the intestinal tract of

the salmon (3).

 

Consequently much of the drug is excreted unchanged

into the marine environment, where it distributes itself between the

sediment and water column, or is ingested by wild sealife (4).

Studies show that some antibiotics, including oxytetracycline and

fluorfenicol, persist in the environment, and marine sediment acts

as a long-term reservoir for them (5).

 

Not surprisingly, investigators have shown that antibiotics can

significantly alter the microbial community found in marine

sediment. Not only can the total amount of bacteria be reduced, but

also the relative abundance among the different species is altered.

Sediment-dwelling bacteria provide a number of key services, in

particular the cycling of nutrients such as nitrogen, phosphorous

and sulfur. Measurements reveal that antibiotics found in marine

sediment near salmon farms lower the conversion rates for sulphates

and nitrates.

 

What consequences may arise from an altered marine microbial

community has not been studied. There is also the question of the

possible effects of any chemicals produced when the fish

metabolically convert the administered antibiotic. For example, when

salmon ingest florfenicol, the fish converts some of the antibiotic

to florfenicol amine. There are no studies on how this, or other

antibiotic metabolites, can affect the natural marine community.

 

One area that has received a great deal of study, is the increase in

antibiotic-resistant bacteria in sediment under fish farms, in

farmed salmon, and in wild organisms caught near salmon farms. The

implications that this has for human health is covered in some of

our other information sheets.

With respect to the marine

environment, however, it should be mentioned that increases in

antibiotic-resistant bacteria leads to increased use of antibiotics

on the salmon farm, increasing the environmental risks.

 

Pesticides-

Sea lice infestations often cause problems at salmon farms, and are

the primary reason that pesticides are used. The fish are treated

with these chemicals in one of two ways. One is by using a tarpaulin

to isolate the fish within the netcage and then adding the chemical

in the seawater. After 30-60 minutes, the tarpaulin is removed and

the solution is released to the marine environment (6). This method

is used for pesticides such as cypremethrin , dichlorvos and

azamethiphos. Other pesticides, such as ivermectin, are administered

within the feed.

 

The Canadian Pest Management Regulatory Agency has only approved

azamethiphos for use against sea lice. Although not approved, the

other pesticides are used with the permission of a veterinarian,

often with little or no data available on their effects on the

marine environment.

 

Sealice and Ivermectin

 

In BC, sealice are often treated using ivermectin. A high proportion

of the administered chemical is excreted unchanged by the salmon,

and accumulates in marine sediment beneath and in the vicinity of

the fish farm. It can take 90 - 240 days for just half of the

chemical in the sediment to decompose. Recent analysis of sediment

under salmon farms has shown levels of ivermectin up to 6.8

milligrams (mg) per kilogram of sediment. This concentration went

down with distance from the farm, but in some samples still showed a

concentration of 5.4 mg per kg of sediment 35 metres from the

netcage. The accumulation of ivermectin was also expressed as amount

per unit area. This gave figures of .675 mg per square metre (m-2)

for under the cage and .357 mg m-2 for the sample at 35 metres from

the netcage.

 

Ivermectin has the ability to disrupt neurological processes. It

also can bind to biological membranes, increasing their permeability

to chloride ions (a main component of sea water) (7). It therefore

has the potential to be toxic to a wide variety of marine organisms.

To date studies have shown the chemical to be very toxic to many

species that live in or on the seabed.

 

 

Table 1: Studies which show lethal effects of ivermectin on various

marine organisms

 

Asterias rubens(a starfish)(7) 5 mg/kg

Corophium Íolutator ( sediment worm)(7) 0.05 mg/kg</td>

Crangon septemspinosa (a shrimp)( 8.5 micrograms per gram of feed

shrimp has access to.

Arenicola marina (a marine worm)(9) 0.018mg/kg

8 species of polychaetes (a class of marine worms)(10) 8 - 80 mg/

sq. metre depending on species.

 

Table 1 lists some of the species that have been tested and the

concentrations of ivermectin for which the species begins to die

off. It can be seen that the concentrations that are lethal to these

organisms are in the range of what has been measured under and near

salmon farms (see paragraph above).

 

The lethal effect of ivermectin on the polychaetes is particularly

interesting. This large class of marine worms is often a crucial

part of many marine food chains. They also are key to the

decomposition of accumulated organic matter, such as fish feces and

uneaten feed that accumulates under salmon farms. The worms

constantly turn over the marine sediment allowing oxygenated water

to reach aerobic decomposing bacteria. Without these worms, the

marine sediment can become depleted in oxygen and proper

decomposition cannot occur.

 

Two of the other pesticides, cypermethrin and azamethiphos, used on

salmon farms have also been shown to have toxic effects on marine

organisms.

A recent study showed that cypermethrin is lethal to

lobster larvae at concentrations of 0.06 to 0.16 micrograms per

litre of seawater (11).

The same study showed that azamethiphos

killed shrimp and adult lobster at concentrations of 50 micrograms

per litre of seawater. Sub-lethal concentrations of azamethiphos at

5 and 10 micrograms per litre were also shown to reduce spawning in

female lobster.

 

The use of pesticides on salmon farms results in negative impacts on

marine organisms found near the salmon farm.

The effect on many more

marine organisms needs to be studied, as well as the effects of sub-

lethal concentrations, which has received very little attention.

 

 

References

1. Lunestad, B.T., 1992. Fate and effects of antibacterial agents in

aquatic environments. In: Michel, C.M., Alderman, D.J. Eds. ,

Chemotherapy in Aquaculture: From Theory to Reality. Office

Internationale des Epizooties, Paris, pp. 151–161.

 

2. Paone, S. Farmed and Dangerous:Human Health Risks Associated With

Salmon Farming. A Report Prepared for Friends of Cloyoquot Sound,

November, 2000

 

3. Samuelsen, 1994.

 

4. GESAMP 1997.

 

5. Samuelsen, 1994

 

6. Haya, K., et. al., Environmental impacts of chemical wastes

produced by the salmon aquaculture industry. ICES Journal of Marine

Science, 58, 492-496, 2001.

 

7. Davies, I.M., et. al., Environmental risk of ivermectin to

sediment dwelling organisms. Aquaculture, 163: 29-46, 1998.

 

8. Davies, I.M., A review of the use of ivermectin as a treatment

for sea lice [Lepeophtheirus salmonis (Kroyer) and Caligus elongatus

Nordmann] infestation in farmed Atlantic salmon (Salmo salar L.).

Aquaculture Research, 31: 869 - 883, 2000.

 

9. Thain, J., et. al. Acute Toxicity of ivermectin to the lugworm

Arenicola marina. Aquaculture, 159: 47-52, 1997.

 

10. Collier, L. An assessment of the acute impact of the sea lice

treatment ivermectin on a benthic community. Journal of Experimental

Marine Biology and Ecology, 230: 131-147, 1998.

 

11. Haya, K., et. al. Environmental impact of chemical wastes

produced by the salmon aquaculture industry. ICES Journal of Marine

Science, Vol. 58: pp. 492-496, 2001.

 

http://www.davidsuzuki.org/Oceans/Fish_Farming/Salmon/Drugs.asp