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

Juvenile brown trout acclimated to fresh water of 0‐3 mEq 1 ‐1 calcium and neutral p H were exposed to p H 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 p H 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 p H 7‐0 in the presence of aluminium at a final concentration of 6‐5 μM. The experiment was repeated at p H 5‐5, and subsequently p H 4‐0. At p H 7‐0, aluminium stimulated chloride efflux by 105% but influx was not affected. At p H 4‐0, efflux was not affected but influx reduced to 55%. At p H 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 p H alone, and the presence of aluminium in natural waters may have a detrimental effect on chloride balance which is most evident at p H 5‐5.