The effect of prey density on foraging mode selection in juvenile lumpfish: balancing food intake with the metabolic cost of foraging

<p>1: In many species, individuals will alter their foraging strategy in response to changes in prey density. However, previous work has shown that prey density has differing effects on the foraging mode decisions of ectotherms as compared with endotherms. This is likely due to differences in metabolic demand; however, the relationship between metabolism and foraging mode choice in ectotherms has not been thoroughly studied.</p> <p>2:Juvenile lumpfish Cyclopterus lumpus forage using one of two modes: they can actively search for prey while swimming, or they can ‘sit-and-wait’ for prey while clinging to the substrate using a ventral adhesive disk. The presence of these easily distinguishable foraging modes makes juvenile lumpfish ideal for the study of foraging mode choice in ectotherms.</p> <p>3: Behavioural observations conducted during laboratory experiments showed that juvenile lumpfish predominantly use the ‘cling’ foraging mode when prey is abundant, but resort to the more costly ‘swim’ mode to seek out food when prey is scarce. The metabolic cost of active foraging was also quantified for juvenile lumpfish using swim-tunnel respirometry, and a model was devised to predict the prey density at which lumpfish should switch between the swim and cling foraging modes to maximize energy intake.</p> <p>4: The results of this model do not agree with previous observations of lumpfish behaviour, and thus it appears that juvenile lumpfish do not try to maximize their net energetic gain. Instead, our data suggest that juvenile lumpfish forage in a manner that reduces activity and conserves space in their limited aerobic scope. This behavioural flexibility is of great benefit to this species, as it allows young individuals to divert energy towards growth as opposed to activity. In a broader context, our results support previous speculation that ectotherms often forage in a manner that maintains a minimum prey encounter rate, but does not necessarily maximize net energy gain.</p&gt

Ontogeny of predator-sensitive foraging and routine metabolism in larval shorthorn sculpin, Myoxocephalus scorpius

Most animals will reduce foraging activity in the presence of a predatory threat. However, little is known about the onset of this decision-making ability during the early life stages of fishes, and how the trade-off between foraging and predator-avoidance may be affected by changes in metabolic demand during ontogeny. To examine these issues, the foraging behaviour of larval shorthorn sculpin Myoxocephalus scorpius was monitored during visual exposure to a predatory threat (juvenile Atlantic cod, Gadus morhua) throughout development at 3°C (March–April, 2004). Larvae did not respond to predatory exposure during the first week post-hatch, but thereafter showed drastic reductions in foraging activity when exposed to predators. During early development, the mass-specific routine metabolism of shorthorn sculpin larvae displayed a triphasic ontogeny and peaked during metamorphosis. This high mass-specific metabolic demand could make reduced foraging under predation threat very costly during this stage of development. To further investigate this possibility, additional experiments were performed (March–April, 2005) where larvae were reared with visual exposure to predators for 6 h day−1 during the feeding period. At 7-week post-hatch, larvae exposed to predators were smaller (wet mass and SL), showed decreased levels of whole-body lipids and certain fatty acids, and experienced higher rates of mortality as compared to control larvae. In environments where abundant predators cause larval fish to reduce their foraging rate, growth and survival of larvae may be negatively affected

Effect of acute and chronic hypoxia on the swimming performance, metabolic capacity and cardiac function of Atlantic cod (Gadus morhua)

Article exploring the degree to which diminished cardiac function contributes to the reduction in fish swimming performance concomitant with acute exposure to hypoxia and how fish cardiorespiratory physiology is altered by, or adapts to, chronic hypoxia. Results provide important insights into how fish cardiorespiratory physiology is impacted by short-term and prolonged exposure to hypoxia, and highlight the capacity of the fish cardiorespiratory system to deal with environmental challenges

DNA Methylation Dynamics in Atlantic Salmon (Salmo salar) Challenged With High Temperature and Moderate Hypoxia

26 pages, 7 figures, 2 tables, supplementary material https://doi.org/10.3389/fmars.2020.604878.-- Data Availability Statement: The datasets generated for this study can be found in the online repositories. The names of the repository/repositories and accession number(s) can be found below: https://www.ncbi.nlm.nih.gov/geo/, GSE153343; doi: 10.1594/PANGAEA.913696The marine environment is predicted to become warmer and more hypoxic, and these conditions may become a challenge for marine fish species. Phenotypically plastic responses facilitating acclimatization to changing environments can be mediated by DNA methylation through the modulation of gene expression. To investigate whether temperature and hypoxia exposure induce DNA methylation changes, we challenged post-smolt Atlantic salmon (Salmo salar) to increasing temperatures (12 → 20°C, 1°C week–1) under normoxia or moderate hypoxia (∼70% air saturation) and compared responses in the liver after 3 days or 4 weeks at 20°C. DNA methylation was studied in six genes related to temperature stress (cirbp, serpinh1), oxidative stress (prdx6, ucp2), apoptosis (jund), and metabolism (pdk3). Here, we report that exposure to high temperature, alone or combined with hypoxia, affected the methylation of CpG sites within different genomic regulatory elements around the transcription start of these temperature/hypoxia biomarker genes. Yet, we uncovered distinct CpG methylation profiles for each treatment group, indicating that each environmental condition may induce different epigenetic signatures. These CpG methylation responses were strongly dependent on the duration of stress exposure, and we found reversible, but also persistent, CpG methylation changes after 4 weeks of exposure to 20°C. Further, several of these changes in CpG methylation correlated with transcriptional changes, and thus, can be considered as regulatory epigenetic marks (epimarkers). Our study provides insights into the dynamic associations between CpG methylation and transcript expression in Atlantic salmon, and suggests that this epigenetic mechanism may mediate physiological acclimation to short-term and long-term environmental changesFunding for this research was provided to AKG by the Ocean Frontier Institute, through an award from the Canada First Research Excellence Fund (20181007) and was supported by the Spanish Ministry of Science Grants AGL2015-73864-JIN “Ambisex” and RYC2018-024017-I, and an “Interomics” Grant (202030E004) from the Spanish National Research Council (CSIC) to LR. This research was conducted on samples collected through the “Mitigating the Impact of Climate-Related Challenges on Salmon Aquaculture (MICCSA)” project. MICCSA funding was provided by the Atlantic Canada Opportunities Agency (781-9658-205222), Innovate NL (5404-1209-104), and Innovate PEI to AKGWith the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)Peer reviewe

Transcriptional and DNA methylation responses in Atlantic salmon (Salmo Salar) when challenged with increasing temperature and moderate hypoxia

Functional annotation of the Atlantic salmon genome, translation to improved health and performance in Aquaculture, 26-27 August 2019, Canad