Salinity affects growth but not thermal preference of adult mummichogs Fundulus heteroclitus

Abstract

The effects of an ecologically relevant range of salinities (2, 12, 22, 32) on thermal preferences and growth of adult mummichogs Fundulus heteroclitus were determined for fish from a southern Chesapeake Bay population. Salinity did not affect the mean temperature selected by F. heteroclitus in a thermal gradient, which was identified as 26.6°C based on observations of 240 individuals. Salinity and temperature had significant and interacting effects on growth rates of F. heteroclitus measured over 12 weeks. Growth rates were highest overall and remained high over a broader range of temperatures at moderate salinities (12 and 22), while high growth rates were shifted toward lower temperatures for fish grown at a salinity of 2 and higher temperatures at a salinity of 32. Significant reductions in growth relative to the optimal conditions (28.6°C, salinity of 22) were observed at the coolest (19.6°C) and warmest (33.6°C) temperature tested at all salinities, as well as temperatures ≥ 26.6°C at a salinity of 2, ≥ 28.6°C at a salinity of 12 and ≤ 26.6°C at a salinity of 32. Growth rates provide a long‐term, organismal measure of performance and results of this study indicate that performance may be reduced under conditions that the highly euryhaline F. heteroclitus can otherwise easily tolerate. The combination of reduced salinity and increased temperature that is predicted for temperate estuaries as a result of climate change may have negative effects on growth of this ecologically important species.

Fast‐start escape performance across temperature and salinity gradients in mummichog Fundulus heteroclitus

“…In response to drops in salinity, mummichogs from brackish or seawater exhibit gill remodelling (Daborn et al ., ; Laurent et al ., ; Mancera & McCormick, ; Wood & Grosell, ; Wood & Marshall, ), changes in gene expression (Scott et al ., ; Scott & Schulte, ; Whitehead et al ., ), reduced muscle function (Grove et al ., ) and increased energetic costs (Kidder III et al ., ), although we note that these effects have only been shown for salinities below ~0.5 ppt, which is lower than the minimum salinity tested in this study. Moreover, changes in multiple environmental factors can result in synergistic effects on physiology and performance (Schulte, ), and in fact temperature and salinity have interacting effects on mummichog growth (Thompson, ), which can be interpreted as a long‐term measure of organismal performance. We tested fish at a range of salinities above freshwater that these fish would realistically experience in their environment, and our results demonstrate that mummichog escape performance is highly robust to this level of variation when fish are allowed to acclimate to a particular salinity prior to testing.…”

“…Mummichogs are well suited to these dynamic environments, exhibiting broad thermal and salinity tolerances (Nordlie, 2006) and labile physiology (Burnett et al, 2007;Fangue et al, 2006;Whitehead et al, 2011). By several measures, mummichogs sustain performance across the environmental gradients they experience; they exhibit similar critical swimming speeds (Brennan et al, 2016;Fangue et al, 2008;Yetsko & Sancho, 2015) and growth rates (Thompson, 2019) across a range of temperatures and salinities. Moreover, mummichogs are abundant where they occur and serve as important prey for a variety of estuarine predators (Able & Fahay, 2010;Kneib, 1986a).…”

Ontogenetic Changes in Behavioral and Energetic Responses of Juvenile Atlantic Croaker to an Estuarine Salinity Gradient

“…Studies of salinity effects on the energetics of marine and freshwater fishes often reveal lower metabolic rates and higher somatic growth rates at intermediate salinities (Boeuf and Payan 2001;Bernatzeder et al 2010;Thompson 2019). This pattern is commonly attributed to decreased osmoregulatory costs at intermediate (isosmotic) salinities (Ern et al 2014).…”