Energetic savings and cardiovascular dynamics of a marine euryhaline fish (Myoxocephalus scorpius) in reduced salinity

Abstract

Few studies have addressed how reduced water salinity affects cardiovascular and metabolic function in marine euryhaline fishes, despite its relevance for predicting impacts of natural salinity variations and ongoing climate change on marine fish populations. Here, shorthorn sculpin (Myoxocephalus scorpius) were subjected to different durations of reduced water salinity from 33 to 15 ppt. Routine metabolic rate decreased after short-term acclimation (4–9 days) to 15 ppt, which corresponded with similar reductions in cardiac output. Likewise, standard metabolic rate decreased after acute transition (3 h) from 33 to 15 ppt, suggesting a reduced energetic cost of osmoregulation at 15 ppt. Interestingly, gut blood flow remained unchanged across salinities, which contrasts with previous findings in freshwater euryhaline teleosts (e.g., rainbow trout) exposed to different salinities. Although plasma osmolality, [Na+], [Cl−] and [Ca2+] decreased in 15 ppt, there were no signs of cellular osmotic stress as plasma [K+], [hemoglobin] and hematocrit remained unchanged. Taken together, our data suggest that shorthorn sculpin are relatively weak plasma osmoregulators that apply a strategy whereby epithelial ion transport mechanisms are partially maintained across salinities, while plasma composition is allowed to fluctuate within certain ranges. This may have energetic benefits in environments where salinity naturally fluctuates, and could provide shorthorn sculpin with competitive advantages if salinity fluctuations intensify with climate change in the future.

Continuous gastric saline perfusion elicits cardiovascular responses in freshwater rainbow trout (Oncorhynchus mykiss)

“…This was associated with a trend for a reduced R Sys in the ½ SW treatment compared with the control, as well as significantly larger reductions (% Δ from baseline) in R Sys and R GI in the ½ SW treatment. Again, such reductions in R Sys have previously been documented in acutely transferred (Maxime et al 1991) and SW-acclimated trout (Morgenroth et al 2019;Sundell et al 2021;Olson and Hoagland 2008) and, although it has not been measured directly, accumulating evidence indicates that the systemic vasodilation in SW-acclimated trout can, to a large extent, be explained by reduced R GI (Morgenroth et al 2019;Sundell et al 2018).…”

Temperature‐ and ration‐dependent winter growth in northern‐stock Black Sea Bass juveniles

“…A concurrent decrease in migration distance and warming inshore temperatures, truncating winter length, may result in a small but growing Black Sea Bass contingent overwintering, thus establishing a year-round coastal presence. Lower salinities in estuarine habitats like Long Island Sound could provide additional benefits as demonstrated by multiple experimental studies showing increased survival at low to intermediate salinities due to a reduction in energetic costs (Hettler 1976;Peterson-Curtis 1997;Younes et al 2020;Sundell et al 2021).…”

Role of the kidneys in acid-base regulation and ammonia excretion in freshwater and seawater fish: implications for nephrocalcinosis

“…Moving juvenile fish from FTS to RAS gives a larger degree of control, yet more demanding technology and complex interactions in pH, temperature, alkalinity, oxygen saturation and suspended solids, which in turn have direct consequences on dissolved total CO 2 (DIC), nitrogen, ammonia and nitrate (Daalsgard et al, 2013;Becke et al, 2020;Fossmark et al, 2021;Davidson et al, 2023). In addition, the use of salinity (in feed or water) has implications on kidney function (Hickman and Trump, 1969;Kodzhahinchev et al, 2017) and the cardiovascular system (Olson and Hoagland, 2008;Brijs et al, 2017;Sundell et al, 2018). In humans these systems are intrinsically connected, and the same is probably true in fish.…”