Fish health concerns

In recent weeks we have seen an increase in the number of fish in the river affected by fungus, in this case Saprolegnia, a group  of ubiquitous freshwater fungi which is present all year round and can affect all stages of fish if the conditions are right.  A visit from Marine Scotland fish health inspectors was organised last week in order to establish if there were any other underlying conditions which may have been affecting the fish. We have now had the initial verbal reports from the histopathology samples and can report that the fish sampled were not infected by any other disease or condition.

The feeling on the river is that the situation is already improving perhaps in response to the change in conditions at the weekend. The heavy rain last Saturday resulted in the river rising by about 6″ and it is now carrying a lot more colour, mainly from the two largest tributarties, the Avon & the Dulnain, where the level increased by about 12″. Prior to that rain the river had been unusually low, and clear, for this time of year; a consequence of the virtual absence of a snow reservoir in the hills. The prolonged low and clear conditions, combined with a reasonable head of fish in the river, are exactly the type of conditions under which fungus can spread amongst the stock. It is important to note that we have some fish suffering from fungus every year, often in the late spring, but it invariably clears up, normally at this time of year.

Some of the ghillies on the river are of the opinion that the fluctuating temperatures at this time of year; a feature of the spring river, result in the fish being more prone to fungal infection but that it usually clears up as the temperature increases and stabilises. This would explain why we rarely see fungus in the summer months, even though temperatures are higher.

Adult salmon, sea trout and brown trout have been affected, and we have seen some mortality amongst the smolts.  However, the number of fish affected is small in comparison to the total stock. Whilst it may be concerning for anglers; indeed for anyone with an interest in the river, to see dead fish, it is a natural phenomenon and experience tells us that it will clear up quickly, particularly if conditions change.

The situation can be summarised as follows:

  • Some fish, of all species and ages, have suffered from fungal infection, but there are no other underlying disease issues
  • This is a natural phenomenon, brought on by the unusually low and clear water conditions
  • The number of fish infected is low in comparison to the total stock
  • Experience on the Spey tells us that the situation will improve, indeed the number of dead fish has declined this week
  • A number of other Scottish rivers are experiencing the same issues, some to a much greater extent that on the Spey
  • Anglers are expected to disinfect waders etc on arrival, and should do when leaving the river, but there is no additional requirement to do so at present, fungus is already present in all freshwaters, all it needs is the right conditions under which it can flourish
  • Best catch and release practice should be used when returning fish, any damage to fish can make them more susceptible to fungal infection

 

 

Leave a Reply

Your email address will not be published. Required fields are marked *