Responses of Fishes to a Low pH Environment Page: 4
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variables, such as dissolved oxygen and temperature, affect the ability
of fish to tolerate low pH (Robinson et al., 1976; Falk and Dunson, 1977;
Neville, 1979).
Mount (1973) reported an inability of fathead minnows to acclimate
to low pH levels. Robinson et al. (1976) found low pH tolerance to differ
among strains of brook trout (Salvelinus fontinalis). Hybridization
produced offspring of intermediate acid tolerance in one cross, while
offspring of another cross exhibited increased acid tolerance. These
authors suggested that increased tolerance to low pH could be artificially
selected, producing strains which would be more likely to survive in
acidic lakes.
Two non-mutually exclusive mechanisms have been suggested to explain
fish mortality at low ambient pH levels. (1) Acid induces depletion of
body sodium, resulting in the breakdown of the ion exchange process (Packer
and Dunson 1970; Dunson et al., 1977; Cameron, 1978). Normally, hydrogen
ions leave the body through gill lamellae in exchange for sodium ions up-
taken from the water (Evans, 1975). Net increases in blood acidity occur
with failure of sufficient cation exchange. Tissue anoxia, resulting from
reduced oxygen-carrying capacity of low pH blood, is reported as a probable
cause of death (Packer and Dunson, 1972; Hargis, 1976). (2) Excess mucous
secretion in response to low pH exposure may form a diffusion barrier,
decreasing oxygen transfer across the gills,which could lead to anoxia
and subsequent death (Janssen and Randall , 1975; Ultsch, 1978; Packer,
1978; Ultsch and Gros, 1979). Electron microscopic examinations by
Daye and Garside (1976) of surficial tissues of brook trout exposed to
sub-lethal pH levels revealed alteration of epithelial tissue occurring
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Prete, Philip J. (Philip John). Responses of Fishes to a Low pH Environment, thesis, August 1981; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc663820/m1/10/: accessed July 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .