Hypoxia delays hematopoiesis: retention of embryonic hemoglobin and erythrocytes in larval rainbow trout,Oncorhynchus mykiss, during chronic hypoxia exposure

Abstract

SUMMARYIn rainbow trout development, a switch occurs from high-affinity embryonic hemoglobin (Hb) and round, embryonic erythrocytes to lower-affinity adult Hb and oval, adult erythrocytes. Our study investigated the early ontogeny of rainbow trout blood properties and the hypoxia response. We hypothesized that hypoxia exposure would delay the ontogenetic turnover of Hb and erythrocytes because retention of high-affinity embryonic Hb would facilitate oxygen loading. To test this hypothesis we developed a method of efficiently extracting blood from individual embryos and larvae and optimized several techniques for measuring hematological parameters on microliter (0.5-2.0 μl) blood samples. In chronic hypoxia (30% of oxygen saturation), stage-matched embryos and larvae possessed half the Hb concentration, erythrocyte counts and hematocrit observed in normoxia. Hypoxia-reared larvae also had threefold to sixfold higher mRNA expression of the embryonic Hb α-1, β-1 and β-2 subunits relative to stage-matched normoxia-reared larvae. Furthermore, in hypoxia, the round embryonic erythrocytic shape persisted into later developmental stages. Despite these differences, Hb-oxygen affinity (P 50 ), cooperativity and the Root effect were unaltered in hypoxia-reared O. mykiss. The data support our hypothesis that chronic hypoxia delays the ontogenetic turnover of Hb and erythrocytes, but without the predicted functional consequences (i.e. higher than expected P 50 ). These results also suggest that the Hb-oxygen affinity is protected during development in chronic hypoxia to favor oxygen unloading at the tissues. We conclude that in early trout development, the blood-oxygen transport system responds very differently to chronic hypoxia relative to adults, possibly because respiration depends relatively more on oxygen diffusion than convection.

Developmental Hypoxia Has Negligible Effects on Long-Term Hypoxia Tolerance and Aerobic Metabolism of Atlantic Salmon (Salmo salar)

“…The M Á O 2 min of rainbow trout embryos was not affected during developmental hypoxia exposure in one study (Miller et al 2008), but recent work suggests an increase in M bow trout was lower for up to 48 d following developmental hypoxia (Johnston et al 2013). Also, developmental hypoxia has been shown to affect blood properties, heart rate programming, and muscle development in salmonids, although the longevity of these changes is unknown (Matschak et al 1997;Miller et al 2011;Bianchini and Wright 2013). Given the evidence for cardiovascular plasticity in salmonids exposed to developmental hypoxia, it is possible that fish exposed to developmental hypoxia in our study underwent plastic changes during development but transitioned back to a normal phenotype once returned to normoxic conditions.…”

Phenotypic flexibility in respiratory traits is associated with improved aerial respiration in an amphibious fish out of water

“…Rows were randomly selected by assigning each row a number and using a random number generator to determine which row to count. Unfortunately, we were unable to measure Hb-O 2 affinity as in previous studies (Bianchini and Wright, 2013;Turko et al, 2014) owing to equipment failure.…”

“…Hct was measured after centrifugation (International Clinical Centrifuge, Model CL, International Equipment) at 5200 g for 2 min. Because blood volumes were minute (<1 µl per fish), images were taken of the microhematocrit tubes using a dissecting microscope (Wild of Canada Limited) and the proportion of packed red blood cells was determined using ImageJ (Bianchini and Wright, 2013). To measure the number of red blood cells (n RBC ), whole blood was diluted in a 1:400 dilution (whole blood: Cortland's isotonic saline) (Wolf, 1963) and then further diluted 1:1 with 0.4% Trypan Blue solution to stain for non-viable red blood cells (Turko et al, 2014).…”

Fish embryos on land: terrestrial embryo deposition lowers oxygen uptake without altering growth or survival in the amphibious fishKryptolebias marmoratus

“…Hypoxia delays development in fishes (e.g. Alderdice et al, 1958;Garside, 1959Garside, , 1966Silver et al, 1963;Miller et al, 2011;Bianchini and Wright, 2013;Robertson et al, 2014). In contrast, embryos of amphibious fishes may experience relatively high oxygen availability if deposited out of water because the diffusion coefficient of oxygen in air is ∼8000 times higher than in water, and boundary layers in air are also much smaller (Dejours, 1988).…”