Compensatory embryogenie responses in osmoregulative structures of mummichog Fundulus heteroclitus L. incubated at constant temperature and various constant levels of salinity

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Abstract
The number of glomeruli (renal corpuscles) in the opisthonephros of fry of the mummichog Fundulus heteroclitus L. (10–21 mm total length), incubated continuously from fertilization to hatching and subsequently maintained variously in fresh water (<0.5‰ salinity (S)), 10, 20, 30, and 60‰ S, at 20 °C, increased significantly with increased kidney volumes which in turn were correlated positively with total length (TL). Mean densities of glomeruli did not differ among the five samples. However, mean relative glomerular volume and mean relative net intracapsular space decreased significantly with increased salinity, as did mean relative total and lumenal cross-sectional areas of the proximal convoluted tubules. The differences between these last two measurements also decreased, indicating decreased cell size of the tubule wall.The number of branchial chloride-secreting cells increased significantly with increased branchial sectional surface, and branchial sectional surface increased significantly with increased TL. The number and the mean aggregate sectional area of chloride cells per unit branchial sectional surface increased significantly with increased salinity, independently of fish size.Mummichog are frequently acknowledged to be extremely haloplastic. Some of this functional plasticity appears to be derived from structural compensation induced during embryogeny.