water ▁e cor eg ion , ▁which ▁supports ▁almost ▁ 4 0 ▁species ▁of ▁fresh water ▁fish . ▁These ▁include ▁several ▁types ▁of ▁lamp re ys , ▁st ur ge ons , ▁sun fish , ▁per ch ▁and ▁various ▁an ad rom ous ▁fish ▁species ▁such ▁as ▁sal mon ▁and ▁steel head . ▁Some ▁of ▁these ▁fish ▁are ▁believed ▁to ▁have ▁desc ended ▁from ▁fish es ▁of ▁the ▁Columbia ▁Bas in ▁in ▁ge olog ically ▁ancient ▁times , ▁when ▁the ▁upper ▁reaches ▁of ▁the ▁Sac r amento ▁River ▁waters hed ▁were ▁connected ▁with ▁that ▁of ▁the ▁S nake ▁River . ▁Up ▁to ▁ 7 5 ▁percent ▁of ▁the ▁historic ▁species ▁were ▁en demic ▁to ▁the ▁Sac r amento - San ▁Jo aqu in ▁bas in . ▁Most ▁native ▁fish ▁stock s ▁have ▁suffered ▁because ▁of ▁pred ation ▁by ▁introduced ▁species ▁and ▁dam ▁construction . ▁In ▁a ▁study ▁from ▁ 1 9 9 3 ▁to ▁ 1 9 9 5 , ▁it ▁was ▁found ▁that ▁the ▁main ▁stem ▁of ▁the ▁San ▁Jo aqu in ▁River ▁was ▁mainly ▁populated ▁by ▁fat head ▁min now , ▁red ▁sh iner , ▁thread fin ▁sh ad ▁and ▁in land ▁sil vers ide , ▁all ▁of ▁which ▁were ▁introduced . ▁Down stream ▁port ions ▁of ▁the ▁river ' s ▁main ▁trib ut aries ▁were ▁populated ▁mainly ▁by ▁larg em outh ▁and ▁small mouth ▁bass , ▁re de ar ▁sun fish ▁and ▁white ▁cat fish , ▁while ▁native ▁species ▁have ▁surv ived ▁relatively ▁well ▁in ▁the ▁upper ▁reaches ▁of ▁the