The effects of aluminium and low pH on chloride fluxes in the brown trout, Salmo trutta L.

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Abstract
Juvenile brown trout acclimated to fresh water of 0‐3 mEq 1‐1 calcium and neutral pH were exposed to pH 4‐0 for 2 h at 10°C. Chloride influx was reduced by 66% and a 144% stimulation of chloride efflux recorded. The effect on chloride influx was reversed by returning the medium pH to 7‐0, restoring the influx rate to 89% of its former value.After a control period without aluminium, chloride influx and efflux were measured at 10°C at pH 7‐0 in the presence of aluminium at a final concentration of 6‐5 μM. The experiment was repeated at pH 5‐5, and subsequently pH 4‐0. At pH 7‐0, aluminium stimulated chloride efflux by 105% but influx was not affected. At pH 4‐0, efflux was not affected but influx reduced to 55%. At pH 5‐5, influx was reduced by 62% and efflux was increased by 67‐5%.Thus, the effects of aluminium on chloride fluxes are shown to be separate from those of low pH alone, and the presence of aluminium in natural waters may have a detrimental effect on chloride balance which is most evident at pH 5‐5.