A fish out of water

Trout Fisherman (UK) - - News & Views -

I HAVE just read Peter Cock­will’s ar­ti­cle in is­sue 501, where he ex­tracts gems from “The Fish­er­man’s Vade Me­cum”, which I am pleased to have on my own book­shelf. Most of the con­tent is sci­en­tif­i­cally ac­cu­rate and pro­vides valu­able knowl­edge for to­day’s an­glers. It might be worth an ar­ti­cle ex­pand­ing on the ef­fects of tem­per­a­ture on large bodies of water to in­clude the de­vel­op­ment of a ther­mo­cline and the ef­fects of wind di­rec­tion on the ‘tilt­ing’ of the ther­mo­cline. This can ex­plain the ad­van­tage of fish­ing on the lee­ward shore es­pe­cially early in the sea­son. The only thing I would take is­sue with is the com­ment that fish suf­fer out of water be­cause there is too much oxy­gen. Not so! The gills of fish are de­signed to ex­tract oxy­gen from water by hav­ing a large sur­face area pro­vided by the in­di­vid­ual gill fil­a­ments. Blood is pumped through th­ese fil­a­ments in a flow op­po­site to the flow of water through the gills- a counter-cur­rent sys­tem de­signed to main­tain a con­cen­tra­tion gra­di­ent between the water and blood. When a fish is re­moved from water, the del­i­cate gill fil­a­ments stick to each other, con­sid­er­ably re­duc­ing the sur­face area for gas ex­change. Even though the oxy­gen con­tent of the air is thou­sands of times higher than water, very lit­tle can be ab­sorbed. Since there is no flow over the gills, the dif­fu­sion gra­di­ent can­not be main­tained. The fish will ‘suf­fo­cate’ and die from lack of oxy­gen. Thank you, Peter, for in­tro­duc­ing read­ers to GW Maun­sell’s book. There is very lit­tle new when it comes to fish­ing knowl­edge. Keith Hat­field, Presteigne, Powys

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