Fish blood osmolality, gill histology and oocyte atresia as early warning acid stress indicators
Juvenile yellow perch, rock bass, black crappie and largemouth bass exposed to acidified soft water ranging from pH 7.0 to 4.5 maintained blood osmotic homeostasis for up to 30 days. At pH 4.0 blood osmotic homeostasis was lost and all but the yellow perch died within 30 days. Blood osmolality decreased from a normal value of 280-320 mmol/kg to \textless= 200 a few days before death. Yellow perch exposed to pH 4.1 were emaciated and near death within 58 days. Gill hyperplasia and chloride cell proliferation were observed in these species at pH 4.5 and 4.0. In fathead minnows exposed to acidifgied water, the choloride cells developed apical pits and evaginations at pH 5.5. The incidence of these chloride cell changes was progressively greater at lower pH values, particularly at pH 5.0. Abnormally high numbers of atretic oocytes observed in acid exposed fathead minnows were most prevalent in the latter part of the spawning season.