Diet influences salinity preference of an estuarine fish, the killifishFundulus heteroclitus

Abstract

SUMMARYUnderstanding the interplay among the external environment, physiology and adaptive behaviour is crucial for understanding how animals survive in their natural environments. The external environment can have wide ranging effects on the physiology of animals, while behaviour determines which environments are encountered. Here, we identified changes in the behavioural selection of external salinity in Fundulus heteroclitus, an estuarine teleost, as a consequence of digesting a meal. Fish that consumed high levels of dietary calcium exhibited a higher preferred salinity compared with unfed fish, an effect that was exaggerated by elevated dietary sodium chloride. The mean swimming speed (calculated as a proxy of activity level) was not affected by consuming a diet of any type. Constraining fish to water of 22p.p.t. salinity during the digestion of a meal did not alter the amount of calcium that was absorbed across the intestine. However, when denied the capacity to increase their surrounding salinity, the compromised ability to excrete calcium to the water resulted in significantly elevated plasma calcium levels, a potentially hazardous physiological consequence. This study is the first to show that fish behaviourally exploit their surroundings to enhance their ionoregulation during digestion, and to pinpoint the novel role of dietary calcium and sodium in shaping this behaviour. We conclude that in order to resolve physiological disturbances in ion balance created by digestion, fish actively sense and select the environment they inhabit. Ultimately, this may result in transient diet-dependent alteration of the ecological niches occupied by fishes, with broad implications for both physiology and ecology.

On the mismatch between salinity tolerance and preference for an invasive fish: A case for incorporating behavioral data into niche modeling

“…Preference could be an important driver of habitat segregation and niche partitioning among euryhaline species (Bucking et al, 2012). Studies of experimentally-determined salinity preferences are limited, but consistently show that organisms prefer narrower salinity ranges than their known physiological tolerances, in agreement with this study.…”

“…African jewelfish do not fit this general expectation, and instead prefer lower than isosmotic conditions. Preference for non-isosmotic values has been shown in previous work (Bucking et al, 2012;Serrano et al, 2010), which indicates that preference is affected by other biotic and abiotic factors than solely physiological optimization. Further, independently of affecting osmoregulatory energy expenditure, salinity can directly influence swimming behavior, food consumption, digestion and absorption (Boeuf and Payan, 2001), which could influence preference.…”

“…Abiotic preferences measured in this and other studies reflect physiological optima related to the energetics of osmoregulation (e.g., Bucking et al, 2012). Salinity can affect energy consumption as fish allocate energy to osmoregulation (or ionoregulation), in order to maintain uniform plasma ion concentrations despite experiencing salinity fluctuations (Boeuf and Payan, 2001;Plaut, 2000).…”

“…Along with physiological adjustments, behavioral ones are an integral component of how species respond to dynamic environments. Fish can use fine scale movement to compensate for physiological imbalances, integrating behavior and physiology (Bucking et al, 2012;Poletto et al, 2013). However, this vital link between physiology and behavior is largely ignored in current species distribution modeling, and thus we argue for incorporation of preference data, in addition to information on ecophysiological constraints, into the forecasting of nonnative species distributions.…”

What is environmental stress? Insights from fish living in a variable environment

“…Unlike other fish, killifish maintain a seawater-type gill morphology down to salinities very close to freshwater, and make the transition to a freshwater-type morphology only if they remain in freshwater longer than a single tidal cycle (Whitehead et al, 2012), and only the northern subspecies makes a complete transition. In general, F. heteroclitus are found in tidally influenced parts of estuarine marshes, and they have a strong behavioural preference for brackish to full-strength seawater (Bucking et al, 2012), suggesting that they would typically use behavioural strategies to avoid freshwater in nature, but they have at least some capacity to gill remodeling if no other option is available.…”