Growth hormone transgenesis and polyploidy increase metabolic rate, alter the cardiorespiratory response and influence HSP expression to acute hypoxia in Atlantic salmon (Salmo salar) yolk-sac alevins

Abstract

Growth hormone (GH)-transgenic Atlantic salmon display accelerated growth rates compared with non-transgenics. GH-transgenic fish also display cardiorespiratory and metabolic modifications that accompany the increased growth rate. An elevated routine metabolic rate has been described for pre-and post-smolt GH-transgenic salmon that also display improvements in oxygen delivery to support the increased aerobic demand. The early ontogenic effects of GH transgenesis on the respiratory and cellular physiology of fish, especially during adverse environmental conditions, and the effect of polyploidy are unclear. Here, we investigated the effects of GH transgenesis and polyploidy on metabolic, heart and ventilation rates and heat shock protein (HSP) levels after exposure to acute hypoxia in post-hatch Atlantic salmon yolk-sac alevins. Metabolic rate decreased with decreasing partial pressures of oxygen in all genotypes. In normoxia, triploid transgenics displayed the highest mass-specific metabolic rates in comparison to diploid transgenics and non-transgenic triploids, which, in contrast, had higher rates than diploid non-transgenics. In hypoxia, we observed a lower massspecific metabolic rate in diploid non-transgenics compared with all other genotypes. However, no evidence for improved O 2 uptake through heart or ventilation rate was found. Heart rate decreased in diploid non-transgenics while ventilation rate decreased in both diploid non-transgenics and triploid transgenics in severe hypoxia. Regardless of genotype or treatment, inducible HSP70 was not expressed in alevins. Following hypoxia, the constitutive isoform of HSP70, HSC70, decreased in transgenics and HSP90 expression decreased in all genotypes. These data suggest that physiological changes through GH transgenesis and polyploidy are manifested during early ontogeny in Atlantic salmon.

Insights into the control and consequences of breathing adjustments in fishes-from larvae to adults

“…However, despite the apparently minor role of the gills in O 2 uptake during early stages of development, zebrafish (Jonz and Nurse, 2005) and rainbow trout (Holeton, 1971) exhibit an obvious HVR as early as 3 and 1 day post fertilization (dpf), respectively. Similar hyperventilatory responses before gill maturation were reported for Arctic char (Salvelinus alpinus; McDonald and McMahon, 1977) and gar (Atractosteus tropicus; Burggren et al, 2016) larvae, although Atlantic salmon (Salmo salar) larvae at 50 dpf do not exhibit a HVR (Polymeropoulos et al, 2014).…”

Automated Non-invasive Video-Microscopy of Oyster Spat Heart Rate during Acute Temperature Change: Impact of Acclimation Temperature

“…The experimental chamber enabled rapid changes in T exp during which cardiac contraction and HR could be assessed relative to T a . The system can provide rapid as well as slow temperature changes, which contrasts with existing reports, where experimental chambers are placed or immersed within large, temperature-controlled water baths to make cardiorespiratory or metabolic measurements (Frappell and Mortola, 2000 ; Polymeropoulos et al, 2014 ).…”

“…By contrast, the thin valves of young spat are amenable to trans-illumination, eliminating physical stressors and attachments, while video microscopy provides an easily verifiable HR signal for the experimenter. Our automated, non-invasive method could be applied to younger or older spat once the limits of microscopic magnification and shell calcification (i.e., animal maturity and size) are defined, or in other species amenable to trans-illumination (e.g., other invertebrates, alevin, Polymeropoulos et al, 2014 ; eggs, Mortola et al, 2010 , 2012 ). We used the minimum light intensity necessary for cardiac visualization; however, near red light sources could be used to determine/minimize the potential impact of light exposure on spat physiology.…”

“…Limited non-invasive methods have been tested in mature invertebrates (Dieringer et al, 1978 ; Depledge et al, 1996 ; Curtis et al, 2000 ). Although innovative methods for zebrafish electrocardiogram (ECG) also rely on invasive approaches to assess cardiac rate (Liu et al, 2016 ), promising results have been reported for HR in Atlantic salmon alevins using microscopy (Polymeropoulos et al, 2014 ). We set out to develop a robust, automated method to non-invasively detect cardiac contraction for HR and heart rate variability (HRV) measurements in oyster spat maintained at different environmental temperatures (10°C vs. 22°C).…”

Repeated measurement ofMo2in small aquatic organisms: a manual intermittent flow respirometer using off-the-shelf components

“…Our MIFR acts as a closed system during the MO 2 measuring phase, but then uses a manually controlled gravity-fed system that allows seawater exchange without damaging the enclosed larvae. The MIFR is based on an off-the-shelf fluorescent optode flow-through cell (PreSens FTC-PSt3) with a fluorescent sensor film that allows contactless measurement, has excellent long-term stability, does not consume oxygen during measurement (16,31), has previously been used in physiological applications (e.g., 7,12,25,28), and allowed high resolution MO 2 measurements from small aquatic animals including larval fishes (5).…”