How much do we re­ally know?

Fish Farmer - - Aqua Nor preview - BY NICK JOY

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 That chart be­came out of date when, af­ter about 50 years, our in­dus­try dis­cov­ered that two stages of the life­cy­cle didn’t ex­ist.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.

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