Wa­ter Qual­ity Re­duces Sports Fish Ed­i­bil­ity

NZ Fish & Game - - Letters - David moate

A COM­MON PER­CEP­TION FROM ang an­glers is that sports fish caught in rivers and lakes that are su suf­fer­ing from wa­ter qual­ity p prob­lems are go­ing to be poor eat­ing. Is this a myth or f fact? I be­lieve this is a myth based on re­cent r re­search con­ducted on a stream in South­land t that suf­fers from poor wa­ter qual­ity and many o other ob­ser­va­tions around the coun­try. First, t trout are a good in­di­ca­tor of wa­ter qual­ity; if t they con­tinue to live in the wa­ter­way or lake th then the wa­ter is not heav­ily pol­luted and it is u un­likely eat­ing the fish will be a health haz­ard. Y Yes, they could con­tain slightly el­e­vated lev­els of chem­i­cals, but un­less you con­sume huge quan­ti­ties it will not be an is­sue. In­fact, fish from the sea are likely to carry higher lev­els. M Most of our trout fish­ery wa­ter qual­ity is­sues are from agri­cul­ture runoff that re­duces wa­ter clar­ity and bio­di­ver­sity. This re­duces the prey avail­able to trout, es­pe­cially mayflies, that has two ob­served con­se­quences on sports fish ed­i­bil­ity. One is a diet mostly made of the more pol­lu­tant tol­er­ant mayflies, like the De­lea­tid­ium species that graze on the alga and pass on the flavour dur­ing the sum­mer months into trout flesh (perch and salmon are not af­fected). This gives that muddy flavour that an­glers com­plain about, but only dur­ing the warmer months. The other is the op­po­site in that trout and perch be­come bet­ter eat­ing as they con­sume fewer mayflies and stone­flies, which are re­duc­ing by in­creased lev­els of ni­trate, and more snails, mol­lusc, shrimp, cray­fish, bait­fish, and cad­dis, which can tol­er­ate el­e­vated lev­els of nu­tri­ents in the wa­ter. All these species are rich in carotene, which gives that rich red-coloured flesh in trout and fat­tens perch. Do not let this myth stop you go­ing fish­ing on your lo­cal low­land wa­ters and en­joy­ing a meal of freshly caught fish.

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