How much do we really know?
IUSED to have a sign over my desk showing the lifecycle of a sea louse with the tag ‘Public enemy number one’ written over it. I put that sign up there in 1993 and it stayed for nearly 20 years before it was taken down by the new incumbent. That chart became out of date when, after about 50 years, our industry discovered that two stages of the lifecycle didn’t exist.
Is this a criticism of us, that we don’t understand parasitic lifecycles as well as we need to? Perhaps so but the story of husk (Dictyocaulus viviparus) in cattle is pertinent.
When I was in agricultural college we had just begun to under to understand the lifecycle. The larvae needed dew to travel up the grass in the morning. If you avoided putting your cattle out then, you reduced the risk enormously.
Nowadays, the pressure to use these pastures is seeing a rise in the
The question about husk is rather like furunculosis; how much of the improvement was down to medicine and how much was down to changes in practice?
There is no doubt that we learnt a huge amount from the reduction in furunculosis in the industry but have we applied that learning?
We should not criticise ourselves too much in such a young industry when such an old one took so long to solve a similar problem. However, we must accept the need to grow our knowledge. The
Our output is measured in kilos not in growth of knowledge. Research tends to be very near market and thus market driven.
All of this is entirely understandable or even reasonable except that because we are a young industry, knowledge is so much more critical to us.
We are facing many new challenges and some old ones and if there is anything I have learnt from such a long career in aquaculture, it is that there will be new challenges tomorrow.
If we do not start to try and increase our knowledge we will be to husk is so apt as we don’t really understand the parasite and we don’t really understand the host.
Let me ask some questions of you and I will be thrilled if someone writes back with research to answer them. Why do sea lice larvae rise and fall with light? It is not enough to suggest that this is purely an artefact of the louse. This is an extremely adapted parasite. If it does this then it does it for a reason. If we can surmise the reason, then we can adapt our practices to minimise its success. How do sea lice travel distance? Clearly they move with the tide and current. Maybe also with wind in the top layers of the water but somehow these mechanisms don’t seem to be quite enough to explain some of the instances seen throughout the industry. Why do some salmon, even in affected pens, get no sea lice? Some will say it is genetic but if so, what are they producing or what is the louse unable to recognise? There are companies that say they are breeding resistance but how is that affecting the parasite/host relationship.
Why do we see infections that come from nowhere or come in bursts?
Are lice timed to a lunar cycle? Tides are illogical. If they are adapted to lunar cycles or maybe barometric pressure then how can we use this?
I could go on a great deal more. This parasite is vulnerable, like all living things, if we can work out exactly how it interacts with its host.
Sometimes I think there is an air of hopelessness about this issue. It has pressured solution offered and hope desperately that this is the silver bullet. I don’t believe there is one.
I once remember one of our biologists say to me, ‘We will win. We have to! We have to remember that this parasite is adapted whereas we are intelligent!’ In this statement lies a clear truth but only if we use our intelligence and develop our knowledge.