Lack­ing a sex drive

Trout & Salmon (UK) - - Letters -

I read with in­ter­est the an­swer from Ron­nie Glass (“Trout Surgery”) re­gard­ing less ag­gres­sion in to­day’s rain­bow trout. The rea­sons he gives for the less ag­gres­sive na­ture of rain­bows may be true, but I be­lieve there is a more ge­netic an­swer. I re­mem­ber many years ago dis­cussing the mer­its or not of triploid rain­bow trout with Doc­tor Ted Wise when he ran Cold­ing­ham Loch. Ted had in­tro­duced triploids and was in­ter­ested to see how they fared com­pared to the diploid rain­bows that had been stocked pre­vi­ously. As I re­call, he no­ticed the per­cent­age of triploids be­ing caught shortly af­ter stock­ing de­creased more rapidly than diploid rain­bows. The spec­u­la­tion was that they were less ag­gres­sive and con­se­quently did not chase lures for as long af­ter be­ing stocked as diploids. Male and fe­male trout are prob­a­bly more ag­gres­sive due to be­ing sex­u­ally ma­ture whereas a sex­less trout prob­a­bly does not have the same level of drive and ag­gres­sion. Although the phys­i­cal rea­sons for hav­ing less sex drive and ag­gres­sion are dif­fer­ent, look no fur­ther than geld­ings in the horse world or bul­locks in the cat­tle world to see what the lack of a sex drive does: they are more docile. As the world has moved on, most fish­eries stock triploid rain­bows ex­clu­sively and there are few if any sexed rain­bows in our still­wa­ters. If to­day’s triploids are less ag­gres­sive than those of pre­vi­ous decades then it is no won­der that heav­ing the Viva is less ef­fec­tive.

Colin Mcisaac, Ed­in­burgh

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