Rapid changes in renal morphometrics in silver sea bream Sparus sarba on exposure to different salinities
The kidney histology of silver sea bream Sparus sarba adapted to different salinities was studied. Renal glomeruli in silver sea bream were grouped into clusters and two distinct types of glomeruli could be discerned. Expanded glomeruli were highly vascular, probably related to an active filtering role, while collapsed glomeruli had a shrunken appearance, probably related to an abated filtering role. Collecting tubules were lined by tall columnar cells and were more prominent and muscular in hypo-osmotic media. Chronic adaptation across a broad spectrum of salinities (0, 6, 12, 33 and 50) caused significant modifications in renal morphology. In hypo-osmotic media, a significant increase in glomerular number, size and percentage expanded glomeruli were found, which could facilitate water excretion. Collecting tubules exhibited an increase in thickness, diameter and muscularity that tended to favour a faster glomerular filtrate flow upon hypo-osmotic adaptation. Abrupt hypo-osmotic exposure induced rapid changes in the morphology of renal tubules. There was an increase in diameter and thickness of collecting tubules, suggesting increased glomerular filtrate flow was stimulated by hypo-osmotic exposure. The data suggested that the rapid change in kidney morphology is one of the osmoregulatory strategies of silver sea bream that may contribute to its ability to withstand abrupt hypo-osmotic challenge. A fast-acting mechanism that could be triggered within several hours could reorganize silver sea bream kidney so that the renal machinery is highly responsive to changes in environmental salinities.
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