Aluminum dynamics on gills of Atlantic salmon fry in the presence of citrate and effects on integrity of gill structures

Abstract The effect of citrate as organic acid anions (A − ) on the accumulation of aluminum (Al) on gills of Atlantic salmon ( Salmo salar ) fry was examined in acidic media. Treatments with (Al−A − ) = +10, 0, and −10 μ eq/1([Al] = 0, 10, 20, 30, 40, 50, 60 μ eq/1 and [citric acid] = 0, 10, 20, 50 μ eq/1) were used. Depuration of gills loaded with Al (10 μeq/l) was also examined in the presence of citric acid (0, 10, 20, 40 μeq/l). Elimination of Al from gills was a much more rapid process ( − and negatively charged binding sites on the gill surface for inorganic Al, whereas short-term depuration of Al was considered to be primarily a physical phenomenon related to the efficiency of the sloughing process. The severity of gill lesions observed by scanning and transmission electron muscopy and supported by morphometrics was related to [Al] in solutions. Slight reductions in gill lesions occurred in the presence of citrate but protection of gills was not complete, indicating a greater bioavailability of Al than predicted. During depuration, the recovery of gill tissues from Al effects was slightly enhanced by increasing [citric acid]. Electron-dense particles on the gill epithelial surface and within chloride cell vesicles in fish exposed to high [Al] and after Al loading were possibly related to Al deposits. These particles were absent from the lamellar surfaces of gills after only 5 d depuration in Al-free media, indicating that removal of particles from the gill surface was rapid and effective. X-ray muanalysis revealed the presence of Al on the gills of fish exposed to Al and its absence after depuration. Probing on the gill surface detected small amounts of Al on epithelial cells and in chloride cell crypts, but most of the Al was in deposits or secretions on the lamellar surface, adding further support to the premise that the majority of Al accumulated on gills over a short time period can be readily sloughed off.