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

Abstract

Environmental hypoxia has effected numerous and well-documented anatomical, physiological and behavioural adaptations in fishes. Comparatively little is known about hypoxia's impacts on sensing because it is difficult to quantify sensory acquisition in vivo. Weakly electric fishes, however, rely heavily on an easily-measurable sensory modality-active electric sensing-whereby individuals emit and detect electric organ discharges (EODs). In this study, hypoxia tolerance of a mormyrid weakly electric fish, Marcusenius victoriae, was assessed by examining both its metabolic and EOD rates using a critical threshold (p crit ) paradigm. The routine metabolic rate was 1.42 mg O 2 h −1 , and the associated critical oxygen tension was 14.34 mmHg.Routine EOD rate was 5.68 Hz with an associated critical tension of 15.14 mmHg.These metabolic indicators of hypoxia tolerance measured in this study were consistent with those in previous studies on M. victoriae and other weakly electric fishes. Furthermore, our results suggest that some aerobic processes may be reduced in favour of maintaining the EOD rate under extreme hypoxia. These findings underscore the importance of the active electrosensory modality to these hypoxia-tolerant fish. K E Y W O R D Scritical threshold, electric organ discharge, Lake Victoria, Marcusenius victoriae, mormyrids, respirometry

A Spark in the Dark: Uncovering Natural Activity Patterns of Mormyrid Weakly Electric Fish

“…These fishes are protected from predation by Nile perch, as this species does not penetrate the dense swamp and is sensitive to hypoxia (Chapman et al, 2002). Inundation levels, water temperature and DO in the wetland show seasonal and diel variation, though DO remains generally low (previously reported diurnal ranges: 1.06-2.63 mg O 2 L-1, Reardon and Chapman, 2008; 0.69-0.82 mg O 2 L-1, Moulton et al, 2020), and water conductivity is very low (10-20 µS cm 1 , measured manually during sampling). All research conducted in Uganda was approved by the Uganda National Council for Science and Technology (research clearance nr.…”

“…The lake is surrounded by an extensive wetland area (Lwamunda Swamp), which is dominated by the emergent grass Miscanthidium violaceum that transitions to water lilies (Nymphaea lotus and N. carulea) or hippo grass (Vossia cuspidata) at the lake edge (Chapman et al, 1996a;Chrétien and Chapman, 2016). Various fish species occur deep within the wetland (see species list in Chapman et al, 1996b), including P. degeni and M. victoriae (Chapman et al, 1996b(Chapman et al, , 2002Chapman and Hulen, 2001;Moulton et al, 2020). These fishes are protected from predation by Nile perch, as this species does not penetrate the dense swamp and is sensitive to hypoxia (Chapman et al, 2002).…”

“…The aim of this study was to investigate and compare activity and habitat use of mormyrid weakly electric fish in the laboratory and in the wild. Marcusenius victoriae and Petrocephalus degeni occur in a severely hypoxic swamp habitat in Uganda and show a high degree of hypoxia tolerance (Chapman and Chapman, 1998;Clarke et al, 2020;Moulton et al, 2020). They belong to different subfamilies of the Mormyridae, Mormyrinae and Petrocephalinae, respectively, and differ in their electrosensory anatomy, overall morphology, and social behavior (Carlson, 2016).…”

Multi-omics analysis reveals the glycolipid metabolism response mechanism in the liver of genetically improved farmed Tilapia (GIFT, Oreochromis niloticus) under hypoxia stress

“…Fish adapt to hypoxia stress through a series of complex physiological and biochemical processes, including a reduction in the metabolic rate, changes in metabolic pathways, and an improvement in the oxygen transport capacity [9,10]. Many studies have found that when an organism is in an anoxic environment, glycolipid metabolism undergoes a series of changes [11][12][13][14]. Anaerobic metabolism can reduce oxygen consumption and quickly provide energy under hypoxia stress [15].…”

The weakly electric fish,Apteronotus albifrons, avoids hypoxia before it reaches critical levels

“…Their EODs are easy to measure, which makes them particularly well suited to research on the energetics of sensation and communication (e.g. Julian et al, 2003;Markham et al, 2016;Moulton et al, 2020;Reardon et al, 2011;Salazar et al, 2013).…”