I had a call the other day from an angler who had just caught a fresh run salmon from the Ayr which he described as being covered in about 60 lice. A lice burden of that level is unusual so I nipped up to see the fish which had by that time been gutted. I managed to find a few lice on the fish and was interested to see that there was a mixture of freshwater lice (Argulus)( larger paler ones in the photo below) and sealice, Lepeophtheirus salmonis.
The sealice were males which apparently can survive for up to a week in the river. The presence of the two types of lice on the same fish is unusual, there must be a high density of Argulus in the Ayr this year for this fish to gather so many in just a few days.
In 2006 we sent a sample of freshwater lice from a dying brown trout in the lower River Ayr to Marine Scotland for identification. The report found they were Argulus coregoni, and stated “that heavily infested fish can become listless, emaciated and prone to secondary infection”. An adult salmon could cope with a moderate number of lice but the consequences for smaller fish may be more serious. I have seen heavy infestation on stocked brown trout in the river. These fish will not be as resiliant as the native fish so may attract a higher burden.
It is not often I get to see a dead salmon these days so it was interesting to try and identify the sex from the head of the fish. What do you think?
The angler thought it was a cock but an examination of the carrier bag containing the entrails showed it to be a hen.
Many experienced anglers would have said it was a male; just goes to show you that it is difficult to tell the sex of a fresh run spring/summer fish, especially when it is still alive on the riverbank.
Tend to agree that it is very hard to sex a very fresh fish early in the season.Have had a few fish that I have not been able to sex until gutted.Also surprised about the freshwater lice, never seen them on migratory fish and I have only seen them on a couple of brownies on the Irvine at Hurlford, very interesting!!!!!!!!!!!!!!Do the brownies on the lower beats have a high number of Argulus on them????????????
Freshwater lice have been known on the River Ayr for many years. They tend only to be present on the fish in the spring, particularly during period of low flows. I have notice a reduction in numbers once high flows are restored.
I have seen Argulus on brown trout, salmon parr and grayling and I’m sure they are present on other fish species as well, although this was the first report on an adult salmon.
Regarding its distribution we have only received reports from the Ayr and Irvine, generally in the middle or lower reaches. Not considered to be a problem in rivers unless present in high numbers. There are three different species and can be a problem in small stocked stillwater fisheries
brian ……….. took a 14lb fish today (27/06) from the ayr, it had been in a wee while and no obvious lice on it. However I hosed it down outside and went into the kitchen to wash my hands, lo and behold there were then lice swimming around quite happily in the basin !
They were of the larger type shown in the pic above.
Well spotted David. The larger ones in the photo are the freshwater lice, the mature female sealice can be as big but as you know they fall off quickly on entry into freshwater.
I have often heard ghillies say that salmon become more difficult to catch once the sealice have fallen off but maybe the irritation caused by the freshwater lice makes them more liable to take. Of course an angler of your undoubted skill would be able to catch it anyway, lice or no lice………
I had a quick look at a report on the Tay Foundation website today and they mention that Argulus are rarely found on adult salmon (in the Tay) but obviously not the case in the Ayr.