Adrenergically induced translocation of red blood cell β-adrenergic sodium-proton exchangers has ecological relevance for hypoxic and hypercapnic white seabass

White seabass (Atractoscion nobilis) increasingly experience periods of low oxygen (O2; hypoxia) and high carbon dioxide (CO2, hypercapnia) due to climate change and eutrophication of the coastal waters of California. Hemoglobin (Hb) is the principal O2 carrier in the blood and in many teleost fishes Hb-O2 binding is compromised at low pH; however, the red blood cells (RBC) of some species regulate intracellular pH with adrenergically-stimulated sodium-proton-exchangers (β-NHE). We hypothesized that RBC β-NHEs in white seabass are an important mechanism that can protect the blood O2-carrying capacity during hypoxia and hypercapnia. We determined the O2-binding characteristics of white seabass blood, the cellular and sub-cellular response of RBCs to adrenergic stimulation, and quantified the protective effect of β-NHE activity on Hb-O2 saturation. White seabass had typical teleost Hb characteristics, with a moderate O2 affinity (PO2 at half-saturation; P50 2.9 kPa) that was highly pH-sensitive (Bohr coefficient -0.92; Root effect 52%). Novel findings from super-resolution microscopy revealed β-NHE protein in vesicle-like structures and its translocation into the membrane after adrenergic stimulation. Microscopy data were corroborated by molecular and phylogenetic results, and a functional characterization of β-NHE activity. The activation of RBC β-NHEs increased Hb-O2 saturation by ~8% in normoxic hypercapnia, and by up to ~20% in hypoxic normocapnia. Our results provide novel insight into the cellular mechanism of adrenergic RBC stimulation within an ecologically relevant context. β-NHE activity in white seabass has great potential to protect arterial O2 transport during hypoxia and hypercapnia but is less effective during combinations of these stressors.

Quality considerations and malformation surveillance in a marine stocking program

Marine enhancement programs can be helpful for the conservation of important species. Many variables are considered in managing a marine enhancement program, and external fish quality prior to release should be one of them. Quality assessment aids in understanding the influence of rearing variables, limits a recognizable cultured fish phenotype, and maximizes the success of the conservation program by emulating the survivorship potential of wild stocks. We rear white seabass, Atractoscion nobilis, for stock enhancement and developed a semiquantitative assessment and control program to document and reduce the incidence of abnormal physical attributes prior to their release. Clearing and staining techniques were used to define normal processes of ossification, and wild fish surveys were performed to understand variability in natural stock morphology. In the hatchery, A. nobilis were examined in lots of 125 fish cohort−1 at 50 and 80 d post hatch of their development. Specimens evaluated were normal or classified as having malformations involving the bone or cartilage (13 categories) ranked 1–3, mild to severe. Malformations that were unique or differed substantially from wild A. nobilis specimens were culled from the cultured cohort as part of a quality control process prior to release. The most common malformations involved the head region, which accounted for 98% of all hard tissue malformations. Malformations of the jaws accounted for 30% of observed malformations and lower jaw prognathism was the most common observation. This program has proven useful for identifying malformations and minimizing the release of affected cultured marine fish.