Hematology of three deep-sea fishes: a reflection of low metabolic rates

The evolution of red blood cell shape in fishes

The size and shape of red blood cells (RBCs) provide key information on life-history strategies in vertebrates. However, little is known about how RBC shape evolved in response to environmental factors, body size and the role of evolutionary rate. Here, we analysed RBC morphometrics in a set of Teleostei (bony fishes) and Elasmobranchii (sharks and rays) species testing the hypothesis that phylogenetic relationship explains species occupation of morphospace. We collected data on cell and nucleus area and volume, nucleus:cytoplasm ratio and shape factor for 65 species belonging to 28 orders. Then, we built phylomorphospaces separately for bony fish and sharks and rays. To test whether phylogenetic relationships predicted phenotypic similarity, we calculated multivariate phylogenetic signal. We also estimated the evolutionary rate of RBC shape for each node and tip using ridge regression. Finally, we tested whether habitat and body size influenced RBC shape using a PGLS. We found a significant phylogenetic signal in RBC shape for bony fish, but not sharks and rays. Saltwater teleost species were more clustered than freshwater ones in the phylomorphospace, suggesting clade disparity. Accordingly, the rate of evolution was highly heterogeneous, with significant decrease in Acanthopterygii. Neither habitat nor body size influenced RBC shape. In conclusion, RBC shape seems to have evolved in fishes in response to multiple selective pressures independent of life-history characters.

More than just the numbers-contrasting response of snake erythrocytes to thermal acclimation

Acclimation to lower temperatures decreases energy expenditure in ectotherms but increases oxygen consumption in most endotherms, when dropped below thermoneutrality. Such differences should be met by adjustments in oxygen transport through blood. Changes in hematological variables in correspondence to that in metabolic rates are, however, not fully understood, particularly in non-avian reptiles. We investigated the effect of thermal acclimation on a snake model, the grass snakes (Natrix natrix). After 6 months of acclimation to either 18 °C or 32 °C hematocrit, hemoglobin concentration, erythrocyte number, and size were assessed. All variables revealed significantly lower values under warm compared to cold ambient temperature. Our data suggest that non-avian reptiles, similarly as birds, reduce erythrocyte fraction under energy-demanding temperatures. Due to low deformability of nucleated erythrocytes in sauropsids, such reduced fraction may be important in decreasing blood viscosity to optimize blood flow. Novel findings on flexible erythrocyte size provide an important contribution to this optimization process.

Evolution of Hemoglobin Genes in Codfishes Influenced by Ocean Depth

Understanding the genetic basis of adaptation is one of the main enigmas of evolutionary biology. Among vertebrates, hemoglobin has been well documented as a key trait for adaptation to different environments. Here, we investigate the role of hemoglobins in adaptation to ocean depth in the diverse teleost order Gadiformes, with species distributed at a wide range of depths varying in temperature, hydrostatic pressure and oxygen levels. Using genomic data we characterized the full hemoglobin (Hb) gene repertoire for subset of species within this lineage. We discovered a correlation between expanded numbers of Hb genes and ocean depth, with the highest numbers in species occupying shallower, epipelagic regions. Moreover, we demonstrate that the Hb genes have functionally diverged through diversifying selection. Our results suggest that the more variable environment in shallower water has led to selection for a larger Hb gene repertoire and that Hbs have a key role in adaptive processes in marine environments.

Hematological and morphometric blood value of four cultured species of economically important tropical foodfish

The use and validation of fish health monitoring tools have become increasingly evident due to aquaculture expansion. This study investigated the hematology and blood morphometrics of Piaractus mesopotamicus, Brycon orbignyanus, Oreochromis niloticus and Rhamdia quelen. The fish were kept for 30 days in 300-liter aquariums, after which they were anesthetized with benzocaine and blood was collected from caudal vessels. In comparison to other species, B. orbignyanus presented the highest hematocrit (Ht), RBC averages and Mean Corpuscular Volume (MCV) with a particular range of data. B. orbignyanus presented lower Ht, Hb, RBC averages and values, and Mean Corpuscular Hemoglobin Concentration (MCHC). Oreochromis niloticus presented lower Ht, Hb, RBC averages and values, and Mean Corpuscular Hemoglobin Concentration (MCHC). Rhamdia quelen and O. niloticus presented higher variation of White Blood Cells (WBC), neutrophils (Nf), lymphocytes (Lf), monocytes (Mf) and thrombocytes (Trb). Data of large axes (LA), minor axes (MA), surface (SF) and volume (VL) are in the same variance range. This study has demonstrated that hematological variances can occur between animals of different species as well as of the same species.

Hematological parameters of Hoplias malabaricus (Characiformes: Erythrinidae) parasitized by Monogenea in lagoons in Pirassununga, Brazil

Hematology is an important pathological and diagnostic tool. This paper describes the hematological parameters of 76 specimens of Hoplias malabaricus infested with monogenean parasites, which were collected from two lagoons. The hematological parameters included: erythrocyte count (Er), microhematocrit (Hct), hemoglobin (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC). The blood parameters showed no significant changes associated with the infestation. Water temperature was found to be negatively correlated with MCV and Hct, with values of rs= -0.52, p<0.0001 and rs= -0.48, p<0.0001, respectively. The mean Relative Condition Factor was Kn=1.01, indicating good health conditions of the fish in these lagoons. No correlation was found between the monogenean infestation and the blood parameters, or between the environmental factors and the monogeneans.

Analysis methods and reference concentrations of 12 minor and trace elements in fish blood plasma

A comprehensive review of the analytical literature revealed substantial under-representation of trace element concentrations in fish blood, particularly for marine species. We describe a simple dilution procedure to measure Li, Mg, K, Ca, Mn, Cu, Zn, Se, Rb, Sr, Ba and Pb concentrations in low volumes of blood plasma of adult plaice (Pleuronectes platessa) using high resolution-inductively coupled plasma-mass spectrometry (HR-ICP-MS). Captive male and female plaice (n = 18) were serially sampled for one year and samples collected outside of the spawning season (n = 157) used to estimate reference ranges for this species. Method accuracy was deemed satisfactory, based on its application to the analysis of a certified reference material. Precision was generally <3%, with the most conservative measure of precision being ≤10% for all elements except Pb (∼20%). This is the first study to analyse fish blood plasma by ICP-MS and includes some of the first reference ranges for trace element concentrations in fish blood.

Regularities of Variation of the Red Blood Indices Characterizing the Respiratory Function of Blood in Selected Fish

There is a large diversity of red blood indices determining oxygen transport ability in vertebrates. In fish this diversity is particularly large, probably due to the great variability in water environments, which impedes the possibility of finding and understanding general patterns. It has been assumed that in mammals, the measure determining the ability of a blood unit to transport oxygen is the ratio of hemoglobin concentration (HB) and total erythrocyte surface area (TSAE). It was also shown that both in mammals and birds the amount of hemoglobin per total surface area unit (Hb/TSAE) conditions maximum use of respiratory pigment in oxygen transport, in different physiological and environmental conditions. In order to check whether this regularity occurs in fish, red blood indices were analyzed in seven species of freshwater fish, differing noticeably in their biology and body mass in two seasons of the year. Notwithstanding this marked seasonal variability to the component variables together determining the total surface area of erythrocytes, the value for TSAE was found to differ in proportion to the higher or lower concentrations of HB. In consequence, the HB/TSAE ratio indicative of the maximal use of haemoglobin in the transport of oxygen was constant in all of the fish studied between analyzed seasons. This constancy - resembling that to be noted in birds - is most probably related to the counter-current gaseous exchange ongoing in the gills of fish.

Development pattern of blood oxygen carrying capacity in rainbow bee-eater nestlings

Growth profile variation among altricial bird species is reflected in variation in development patterns of parameters influencing blood oxygen carrying capacity (O2Cap). Rainbow bee-eater nestlings develop slowly and their asymptotic mass reaches or exceeds adult levels before undergoing prefledging recession (mass overshoot–recession profile, MOR). Erythrocyte count (RBC), blood hemoglobin content (Hb) and hematocrit (Hct) increased 2.5-fold during development. Hatchlings’ erythrocyte volume closely approximated adult levels and decreased by only 1% during development. Erythrocyte hemoglobin content and concentration also increased minimally. RBC and Hb increased throughout development, but Hct increase was restricted to early development, overlapping the mass-gain period by just 37%. Blood parameters influencing O2Cap did not exceed adult levels and then decline during the mass asymptote–recession development stage. Continuing increase in RBC and Hb at this stage contributed to attaining a fledging O2Cap of adult levels. Results were consistent with there being a common mechanism regulating developmental increase in O2Cap in altricial birds. However, features of this development in bee-eater nestlings variously conformed to the patterns of both species with MOR and species with standard growth profiles. Some features shared with other MOR species also differed in timing or pattern in bee-eater nestlings.

Hemoglobin function in deep-sea and hydrothermal-vent endemic fish: Symenchelis parasitica (Anguillidae) and Thermarces cerberus (Zoarcidae)

Deep-sea hydrothermal vents probably provide the harshest physico-chemical conditions confronting metazoan animals in nature. Given the absence of information on hemoglobin (Hb) function in hydrothermal-vent vertebrates, and the complex molecular and functional adaptations observed in hydrothermal-vent invertebrates, we investigated the oxygenation reactions of Hbs from the vent-endemic zoarcid Thermarces cerberus and the deep-sea anguillid Symenchelis parasitica from adjacent habitats. Electrophoretically cathodic and anodic isoHbs from S. parasitica exhibit radical differences in O(2) affinity and pH and organic phosphate (ATP) sensitivities, reflecting a division of labor as in other 'class II' fish that express both Hb types. Remarkably, the cathodic Hb (I) lacks chloride sensitivity, and the anodic Hb (II) shows anticooperativity near half-saturation at low temperature. T. cerberus isoHbs exhibit similar affinities and pH sensitivities ('class I' pattern) but much higher O(2) affinities than those observed in Hbs of the temperate, shallow-water zoarcid Zoarces viviparus, which, unless compensated, reveals markedly higher blood O(2) affinities in the former species. The temperature sensitivity of O(2) binding to T. cerberus Hbs and the anodic S. parasitica Hb, which have normal Bohr effects, is decreased by endothermic proton dissociation, which reduces the effects of ambient temperature variations on O(2) affinity. In the cathodic S. parasitica Hb, similar reduction appears to be associated with endothermic conformational changes that accompany the oxygenation reaction.

Fish at high pressure: a hundred year history

Two main periods can be considered in the history of fish metabolism under pressure. The first period (roughly from 1870 to 1970) was mainly descriptive: survival times and behavior were studied and some authors described an increase in oxygen consumption under pressure; later, the counteracting effects of high temperature on pressure were mentioned. The second period (from 1970 onwards) was more integrative and two major ways were explored. The first was to use shallow-water fish, experimentally exposed to hydrostatic pressure, which can induce a metabolic state resembling histotoxic hypoxia. The second way was to use deep-living fish which have, when compared to surface fish, muscle enzymes with higher structural stability, lower activity (in relationship with habitat depth) and kinetics that are less sensitive to pressure increase. Using this approach, it was also shown that muscle composition and function were somewhat different at depth and that deep fish are well adapted to pressure partly by maintaining membrane fluidity (homeoviscous theory). Since about 1990, the two above-mentioned approaches have still been pursued but by fewer researchers. Studies on deep-living fish are mainly concerned with enzyme kinetics whereas shallow water fish are used mainly for cellular energetic studies. Regarding this topic, it has been shown that yellow freshwater eels are able to acclimate to high-pressure effects, by optimizing membrane fluidity and composition (as achieved by deep-living fish), by improving oxidative phosphorylation (increase of P/O ratio) and the glycolytic pathway.

Comparative hematology in marine fish

1. A comparative study involving 80 species (14 ray, 14 shark and 52 teleost species) of marine fish found at the southeastern Brazilian coast is presented. 2. Active species displayed higher values for all hematological parameters studied when compared to the less active forms. 3. Mean values of hematocrit, hemoglobin concentration and red blood cell counts increased according to the sequence: rays, sharks, teleosts. 4. As a group, cartilaginous fish blood displayed larger and fewer erythrocytes containing more hemoglobin than teleosts; mean cell hemoglobin concentration was significantly higher in rays and sharks than in teleosts. 5. For all but the hemoglobin concentration, the hematological values studied revealed a marked contrast between bony and cartilaginous fishes which suggests distinct ways to accomplish their oxygen demands.

Effects of hydrostatic pressure per se (101 ATA) on energetic processes in fish

Nucleotides concentrations (ATP, ADP, AMP) have been measured in brain and muscle of eels exposed to 101 ATA of hydrostatic pressure (HP) for 3 hr. Survival times (ST) and oxygen arterial content (CaO2) have been measured in trouts exposed to HP = 101 ATA. The results show that at HP = 101 ATA, AMP increases (P less than 0.05) and ATP decreases (-12%; NS) in muscle but are not modified in brain; ST values are similar in normoxic and hyperoxic conditions, and CaO2 are similar at 1 ATA and 101 ATA of HP. It is concluded that HP tends to decrease aerobic production of energy. This phenomenon is not due to a failure in O2 transport from ambient medium to the cell but to a possible perturbation of the aerobic cellular processes leading to energy production (Krebs cycle and/or respiratory chain coupled to oxidative phosphorylation.