M.E. Mueller | Geology Reports

USGS1991

Nature and time course of acclimation to aluminum in juvenile brook trout ( Salvelinus fontinalis ): II. Gill histology

Gill samples from juvenile brook trout ( Salvelinus fontinalis ) acclimated to low-level aluminum at pH 5.2 showed severe damage by day 4, with necrosis and fusion of secondary lamellae and hyperplasia and hypertrophy of mucous cells. Over the following 20&ensp;d, there was a continual process of repair with proliferation and hypertrophy of mucous cells. Qualitative analysis of gill samples plus physiology and mortality data collected in a companion study indicated progressive development (by day 10 onward) of increasing acclimation to Al. Quantitative analysis of gill samples on day 13 showed that mucous cell volume density had tripled and mucous cell area had doubled in Al-exposed fish compared with control fish. A lamellar fusion index showed evidence of fusion in Al-exposed fish by day 4 with recovery to nearly control levels by day 13. Physiological disturbances appear to be directly related to the histological changes observed in the gill epithelium. At the cellular level, changes in either mucous cell production and secretion or changes in mucus chemistry contribute, in part, to acclimation to Al.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS1989

Sensitivity of endemic Snake River cutthroat trout to acidity and elevated aluminum

Acidic episodes in waters of the western USA, do not last as long and are not as intense as those in the eastern USA, but we found that the native western cutthroat trout Oncorhynchus clarki is sensitive to even brief reductions in pH. In laboratory studies, fish were exposed to acidity (pH 4.5–6.5) alone or in the presence of aluminum during the first 7 d of the freshly fertilized egg, eyed embryo, alevin, or swim-up larva stages of development. Following exposure to acidity and aluminum, eggs and fish were held under control water quality conditions to 40 d posthatch to assess effects of the exposure on subsequent development. Reductions in pH from 6.5 to 6.0 in low-calcium water (1.4 mg/L) did not affect survival, but reduced growth offish in the early life stages. The presence of as little as 50 μg A1/L at low pH further decreased growth and reduced survival. The most sensitive indicators of stress were loss of ions (determined from whole-body sampling) and reduced swimming in alevins, reduction in the ratio of RNA:DNA, feeding inhibition, and pathology of gill tissue in swim-up larvae. A pH of 6.0 and 50 μg Al/L reduced whole-body sodium by 72% and potassium by 50% in alevins. Reductions in the RNA: DNA ratio, correlated with lower growth rates, were observed in swim-up larvae exposed to pH 5.5 and 50 μg Al/L. Exposure to 50 μg Al/L at pH 6.0 reduced swimming activity of alevins by 68% and feeding rates of swim-up larvae by 67%. In the presence of 50 μg A1/L, pathological changes in gill tissue were observed in swim-up larvae exposed to pH 6.0 or less. Although acidification is not widespread in the western USA, cutthroat trout have a narrow margin of safety between conditions that currently exist and those at which pH and aluminum reduce survival and growth.

Transactions of the American Fisheries Society↗