Embryos of mummichog, Fundulus heteroclitus (L.), were incubated in various combinations of constant salinity (0, 10, 20, 30, 60‰ S) and temperature (15, 20, 25, 30C) from fertilization to completion of hatching. In all instances, the velocity of embryonal development was accelerated at higher temperatures. In salinities of 0, 10, 20, 30‰, higher temperature had a similar accelerating effect on developmental rate throughout the embryonal term. However, the highest salinity (60‰) retarded embryonal development particularly after neurulation. This retarding effect increased with the increasing temperature. The onset of hatching and 50% hatching time were also retarded in 60‰ S. Embryos hatched with difficulty in the lowest incubation combination, 0‰ S, 15C. This observation is discussed in the light of pertinent literature.Highest percentage total hatch and viable (normal) hatch were obtained at 20C in all test salinities. Response surface analysis showed that optimum conditions for survival for mummichog embryos appeared to be associated with salinities and temperature of 19–20‰ and 18C.Larval length was greatest in groups incubated at 15 and 20C and 0–30‰ S.
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.
Cells, structurally identical with branchial chloride-secreting cells, were observed to be broadly distributed in buccal and pharyngeal epithelia and various regions of the trunk epidermis, in early fry of the mummichog, Fundulus heteroclitus L., that had been incubated in embryonal and alevin stages in sea water concentrated by additional salts to 60‰ salinity, at 20 °C. Although there was some proliferation of these cells in the buccal and pharyngeal epithelia, such apparently adaptive hyperplasia and hypertrophy of these cells did not occur in early fry that had previous incubation and rearing in seawater concentrations of 30, 20, and 10‰ salinity (S), and in fresh water (< 0.5‰ S)
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