Bruce D. Sidell

When bad things happen to good fish: the loss of hemoglobin and myoglobin expression in Antarctic icefishes.

SUMMARY The Antarctic icefishes (Family Channichthyidae) provide excellent examples of unique traits that can arise in a chronically cold and isolated environment. Their loss of hemoglobin (Hb) expression, and in some cases, loss of myoglobin (Mb) expression, has taught us much about the function of these proteins. Although absences of the proteins are fixed traits in icefishes, the losses do not appear to be of adaptive value. Contrary to some suggestions, loss of Hb has led to higher energetic costs for circulating blood, and losses of Mb have reduced cardiac performance. Moreover, losses of Hb and Mb have resulted in extensive modifications to the cardiovascular system to ensure adequate oxygen delivery to working muscles. Recent studies suggest that losses of Hb and Mb, and their associated nitric oxide (NO)-oxygenase activities, may have accelerated the development and evolution of these cardiovascular modifications. The high levels of NO that should occur in the absence of Hb and Mb have been shown in other animal groups to lead to an increase in tissue vascularization, an increase in the lumenal diameter of blood vessels, and an increase in mitochondrial densities. These characteristics are all hallmark traits of Antarctic icefishes. Homeostatic feedback mechanisms thus may have accelerated evolution of the pronounced cardiovascular traits of Antarctic icefishes.

Time course of thermal acclimation in goldfish

Summary1.The time course of acclimation from 15 ° C to 5 ° C and from 15 ° C to 25 ° C was measured for two compensating enzymes (cytochrome oxidase and succinic dehydrogenase) from epaxial muscle of goldfish (Carassius auratus L.). The time course of acclimation from 15 ° C to 25 ° C was measured for one inversely compensating enzyme (catalase).2.The transition from one acclimation state to another shows initial oscillations before reaching a new steady state at from 3–4 weeks. The time necessary to reach the new steady state is shorter for small than for larger fish. The oscillations in activity cannot be attributed to the feeding schedule of the animals.

Thermal Tolerance of Antarctic Notothenioid Fishes Correlates with Level of Circulating Hemoglobin

The West Antarctic Peninsula region is experiencing some of the most rapid elevations in temperature of any marine environment. We assessed thermal tolerance of white- and red-blooded Antarctic notothenioid fishes inhabiting these waters, using a modified critical thermal maximum (CTmax) design. Temperature was elevated acutely from ambient at a constant rate of 3.6°C h−1, and CTmax was defined as the temperature where animals lost righting response. CTmax temperatures of white-blooded icefishes Chionodraco rastrospinosus (C) and Chaenocephalus aceratus (C) were significantly lower than those of red-blooded fishes Gobionotothen gibberifrons (C) and Notothenia coriiceps (C). Lepidonotothen squamifrons, a red-blooded species with low hematocrit, exhibited a CTmax (C) that was significantly lower than that of the other red-blooded animals and similar to that of icefishes. A strong relationship between CTmax and hematocrit () suggests that the oxygen-carrying capacity of blood may partially dictate acute lethal temperature. Despite a short treatment duration, we detected a rise in the mRNA level of hypoxia response gene HIF-1α in N. coriiceps heart tissue. One-week exposure to 4°C had no effect on the CTmax of N. coriiceps, indicating an inability to compensate for rising temperature under these experimental conditions. Our results suggest that icefishes are particularly sensitive to temperature elevation because of a lack of hemoglobin and may be a sentinel taxon for climate change.

Morphometry of retinal vasculature in Antarctic fishes is dependent upon the level of hemoglobin in circulation

SUMMARY We quantitatively assessed ocular vascular patterns of six Antarctic notothenioid fishes that vary in their expression of the circulating oxygen-binding protein, hemoglobin (Hb). Digital image analyses revealed marked differences in vessel morphometries among notothenioid species. Hemoglobinless (–Hb) icefishes display mean vessel length densities that are greater (Chaenocephalus aceratus, 5.51±0.32 mm mm–2; Champsocephalus gunnari, 5.15±0.50 mm mm–2) than those observed in red-blooded (+Hb) species (Gymnodraco acuticeps, 5.20±0.46 mm mm–2; Parachaenichthyes charcoti, 4.40±0.30 mm mm–2; Trematomus hansoni, 3.94±0.08 mm mm–2; Notothenia coriiceps, 2.48±0.21 mm mm–2). –Hb fishes also have mean vessel diameters that are ∼1.5 times greater than vessel diameters of +Hb species (–Hb, 0.193±0.006 mm; +Hb, 0.125±0.005 mm). Vascular density index (VDI), a stereological index that is affected by both vessel number and length, is greatest in –Hb C. aceratus (3.51±0.20) and lowest in +Hb N. coriiceps (1.58±0.14). Among four +Hb species, there is a direct relationship between red blood cell content and retinal vasculature. Hematocrit (Hct) is inversely correlated to vascular density (r2=0.934) and positively correlated to intervessel distance (r2= 0.898) over a >2.3-fold range of Hct. These results indicate that anatomical capacity to supply blood to the retina increases to compensate for decreases in oxygen-carrying capacity of the blood.

Phenylhydrazine-induced anemia causes nitric-oxide-mediated upregulation of the angiogenic pathway in Notothenia coriiceps.

SUMMARY Antarctic icefishes possess several cardiovascular characteristics that enable them to deliver oxygen adequately in the absence of hemoglobin (Hb). To gain insight into mechanisms driving development of these cardiovascular characteristics of icefish, we chemically induced severe anemia in a red-blooded notothenioid, Notothenia coriiceps. After 10 days of treatment with phenylhydrazine HCl, the hematocrit and Hb concentration of N. coriiceps decreased by >90% and >70%, respectively. Anemic fish exhibited a significantly higher concentration of nitric oxide (NO) metabolites in their plasma compared with that of control animals, indicating that corporeal levels of NO are higher in anemic animals than in control fish. The activity of nitric oxide synthase (NOS) was measured in brain, retina, pectoral muscle and ventricle of control and anemic animals. With the exception of retina, no significant differences in NOS activities were observed, indicating that the increase in plasma NO metabolites is due to loss of Hb, which normally plays a major role in the degradation of NO, and not due to an overall increase in the capacity for NO production. To determine whether loss of Hb can stimulate remodeling of the cardiovascular system, we measured expression of HIF-1α, PHD2 and VEGF mRNA in retinae of control and anemic fish. Expression of all three genes was higher in anemic animals compared with control N. coriiceps, suggesting a causative relationship between loss of Hb and induction of angiogenesis that probably is mediated through nitric oxide signaling.

Clifford Ladd Prosser

This tribute is not intended to be an exhaustive accounting of Ladd Prosser’s life (1907–2002) and professional accomplishments. Such accountings have been published previously (Prosser et al. 2002; http://www.the-aps.org/membership/ obituaries/ladd_prosser.htm; Feng and Meinertzhagen 2002). Instead, we draw primarily from the recollections of his doctoral students and present a subjective and personal account of the diverse ways in which Ladd Prosser touched and influenced our lives and scientific careers. Nevertheless, it is appropriate for us to begin the tribute with a brief summary of Ladd’s life accomplishments in order to provide an appropriate perspective for what follows. Ladd was born in Avon, New York, in 1907. He grew up in a small town environment and worked in his father’s general store. Ladd attributes his early appreciation for nature to Sunday afternoon walks with his father through meadows and woods: “I set up a table on our back porch where I mounted insects and pressed flowers. I also raised some moths and butterflies from eggs. I used to hike in woods. ... I carried a piece of bread and bacon and when I became hungry I lit a fire of