Red Vents on Salmon
Please see below responses from FRS to some recent questions posed by Brian Davidson of the ASFB about fish with bleeding vents. As you will see these are far from conclusive but Brian thought they should at leastbe circulated
- Is there a human health risk to eating the fish? – this has been queried already by anglers, and we understand that the worm is not killed by certain preparations (eg cold smoking). Have the Food Standards Agency been involved in assessing any risk? One major aquaculture producer representative has stated that infected fish must be cooked or else there are health implications for humans. Some anisakids are indeed pathogenic. I am not an expert in food safety, so advice should be sought from the FSA. (I do know that they have advised that cooking fish for at least 2 minutes at a temperature of seventy degrees centigrade will kill any parasites which may be present.)
- Should affected fish be kept or returned by anglers? I guess that that depends upon the policy of the river - catch and release etc. These fish are not infectious, except to other hosts of the parasites - they cannot infect other fish in freshwater by contact or by shedding parasites.
- Is the infection likely to compromise spawning – the worm may be widespread and common but infections this year have been abnormally intense. Whether spawning is affected remains to be seen. In 2006, a small number of affected fish were used by the EA in their broodstock unit, so we know that their progeny are viable. However, the fish were stripped artificially so we don't currently know if they will spawn naturally.
- Is there likely to be any checks on spawning fish later in the year to assess the above? FFL are looking into maintaining some of these fish in freshwater to see if they will spawn naturally, although that in itself is an unnatural environment, which may affect spawning behaviour. I would expect that there will be much interest in spawning behaviour and success all around Scotland.
- Will the fish recover in freshwater? To your last question, the answer is that we don't know. Personally I would be concerned about secondary infections in the most seriously affected fish, but we have no reports of such at the present time. Those which have not suffered prolapse or extensive damage of the area around the vent may recover, but currently we have no evidence either way to support this.
Brian Davidson
ASFB/IFM
2 Hill Street
Edinburgh
EH2 3JZ
Tel office - 0131 226 4955
Tel mob - 07775 918754
Fax - 0131 226 4610
Web - http://asfb.hub.uk.com/