Effects of hypoxia on swimming and sensing in a weakly electric fish

Abstract

Low dissolved oxygen (hypoxia) can severely limit fish performance, especially aerobically expensive behaviours including swimming and acquisition of sensory information. Fishes can reduce oxygen requirements by altering these behaviours under hypoxia, but the underlying mechanisms can be difficult to quantify. We used a weakly electric fish as a model system to explore potential effects of hypoxia on swim performance and sensory information acquisition, which enabled us to non-invasively record electric signalling activity used for active acquisition of sensory information during swimming. To quantify potential effects of hypoxia, we measured critical swim speed () and concurrent electric signalling activity under high- and low-dissolved oxygen concentrations in a hypoxia-tolerant African mormyrid fish, Fish were maintained under normoxia for 6 months prior to experimental treatments, and then acclimated for 8 weeks to normoxia or hypoxia and tested under both conditions (acute: 4 h exposure). Acute hypoxia exposure resulted in a significant reduction in both and electric signalling activity in fish not acclimated to hypoxia. However, individuals acclimated to chronic hypoxia were characterized by a higher under both hypoxia and normoxia than fish acclimated to normoxia. Following a 6 month re-introduction to normoxia, hypoxia-acclimated individuals still showed increased performance under acute hypoxic test conditions, but not under normoxia. Our results highlight the detrimental effects of hypoxia on aerobic swim performance and sensory information acquisition, and the ability of fish to heighten aerobic performance through acclimation processes that can still influence performance even months after initial exposure.

Effects of hypoxia on aerobic metabolism and active electrosensory acquisition in the African weakly electric fish Marcusenius victoriae

“…() were conducted on fish up to 3 weeks postcapture, compared with 2–6 days postcapture in this study. Longer acclimation to normoxia may have resulted in a higher RMR, as this has been found to lower the critical swim speed of M. victoriae under hypoxic conditions (Ackerly et al ., ). In a recent study of the mormyrid Petrocephalus degeni (Boulenger 1906), however, Clarke et al .…”

“…The aim of this study was to quantify hypoxia tolerance of a population of mormyrid weakly electric fish, Marcusenius victoriae (Worthingon 1929), shortly after removing them from their hypoxic environments. Rather than allowing fish to acclimate to normoxic lab conditions over a period of weeks, which could affect morphophysiological and behavioural hypoxia‐coping mechanisms (Ackerly et al ., ; Sollid et al ., ; Sollid & Nilsson, ), fish were tested within 2–6 days following their capture. Metabolic and EOD rates were evaluated under acute hypoxia exposure using a critical threshold paradigm in order to assess EOD's role in hypoxia tolerance.…”

Effects of dissolved oxygen concentration on freshwater fish: A review

“…Chronic exposure to hypoxia reduces some of the hypoxia's swimming-limiting effects. Therefore, chronic hypoxia acclimation provides long-term benefits (Ackerly et al, 2018) [55] . [56,57,52] .…”

“…Hypoxia also affects predator-prey interactions, lowering faststart performance in particular species (Domenici et al, 2013) [63] . The effects of hypoxia on aerobic swim performance and sensory information acquisition, as well as the ability of fish to enhance aerobic performance through acclimation processes, might affect performance months after first exposure (Ackerly et al, 2018) [55] . Hypoxia tolerance was assessed using the aquatic surface respiration (ASR50) and loss of equilibrium (LOE50) values, swimming performance was assessed using the critical swimming speed (U crit ), aerobic capacity or space was assessed using the maximum metabolic rate.…”

Fish Behavior as a Neural Proxy to Reveal Physiological States

“…Low oxygen levels reduced the structure and size of schools to prevent an exacerbation of hypoxic conditions in herring ( Domenici et al, 2002 ) and C. auratus ( Israeli and Kimmel, 1996 ). Weakly electric fish ( Marcusenius victoriae and Petrocephalus degeni ) decreased the active acquisition of sensory information to save energy in a hypoxic condition ( Ackerly et al, 2018 ; Clarke et al, 2020 ). Escape responses in fish are facilitated by anaerobically fueled muscles ( Domenici and Blake, 1997 ; Marras et al, 2011 ; Marras et al, 2013 ); thus, the behavioral alteration is most probably due to a malfunctioning at the neurosensory level rather than to an impairment of muscle function ( Domenici et al, 2007 ).…”