Hans Malte

The biology of hagfishes

Evolution, taxonomy and ecology development and pathology the integument and associated glands supporting tissues the muscular system the respiratory system the cardiovascular system the blood and immune system the uro-genital system the endocrine system the nervous system sensory organs.

Silver nanoparticles and silver nitrate cause respiratory stress in Eurasian perch (Perca fluviatilis)

Silver nanoparticles are utilised in an increasing amount of products, and discharge to the aquatic environment is inevitable. Fish gills are in direct contact with the ambient water, making them potential exposed and vulnerable to suspended silver nanoparticles. The present study investigates the effect of silver nanoparticles (average 81 nm) on the oxygen consumption (M(O2)) in Eurasian perch (Perca fluviatilis), expressed by the basal metabolic rate (BMR) and the critical oxygen tension (P(crit)) below which the fish can no longer maintain aerobic metabolism. For comparison, the impact of silver nitrate (AgNO(3)), was examined as well. Perch were exposed to nominal concentrations of 63, 129 and 300 microg L(-1) silver nanoparticles and 39 and 386 microg L(-1) AgNO(3), respectively, plus controls which were not exposed to silver. M(O2) measured by automated intermittent closed respirometry. After one day acclimatization in the respirometer, the pre-exposure BMR was determined together with P(crit). Hereafter, nanoparticles or silver nitrate were added to the test tank and BMR and P(crit) were measured again the following day. The results demonstrate that nanosilver had no impact on the BMR, whereas exposure to 386 microg L(-1) AgNO(3) resulted in a significant raise in BMR. P(crit) was increased approximately 50% after exposure to 300 microg L(-1) nanosilver plus 31% and 48% by 39 microg L(-1)and 386 microg L(-1) silver nitrate, respectively. These findings reveal that exposure to nanosilver results in impairment of the tolerance to hypoxia. Possibly, nanosilver affects the gills externally, reducing the diffusion conductance which then leads to internal hypoxia during low water oxygen tensions (P(O2)).

Aerobic scope does not predict the performance of a tropical eurythermal fish at elevated temperatures

Climate warming is predicted to negatively impact fish populations through impairment of oxygen transport systems when temperatures exceed those which are optimal for aerobic scope (AS). This concept of oxygen- and capacity-limited thermal tolerance (OCLTT) is rapidly gaining popularity within climate change research and has been applied to several fish species. Here, we evaluated the relevance of aerobic performance of juvenile barramundi (Lates calcarifer) in the context of thermal preference and tolerance by (1) measuring standard and maximum metabolic rates (SMR and MMR, respectively) and AS of fish acclimated to 29°C and acutely exposed to temperatures from 23 to 38°C, (2) allowing the fish to behaviourally select a preferred temperature between 29 and 38°C, and (3) quantifying alterations to AS after 5 weeks of acclimation to 29 and 38°C. SMR and MMR both increased continuously with temperature in acutely exposed fish, but the increase was greater for MMR such that AS was highest at 38°C, a temperature approaching the upper lethal limit (40–41°C). Despite 38°C eliciting maximum AS, when given the opportunity the fish selected a median temperature of 31.7±0.5°C and spent only 10±3% of their time at temperatures >36°C. Following acclimation to 38°C, AS measured at 38°C was decreased to the same level as 29°C-acclimated fish measured at 29°C, suggesting that AS may be dynamically modulated independent of temperature to accommodate the requirements of daily life. Together, these results reveal limited power of the OCLTT hypothesis in predicting optimal temperatures and effects of climate warming on juvenile barramundi.

Repeatability of standard metabolic rate, active metabolic rate and aerobic scope in young brown trout during a period of moderate food availability

SUMMARY Standard metabolic rate (SMR) and active metabolic rate (AMR) are two fundamental physiological parameters providing the floor and ceiling in aerobic energy metabolism. The total amount of energy available within these two parameters confines constitutes the absolute aerobic scope (AAS). Previous studies on fish have found SMR to closely correlate with dominance and position in the social hierarchy, and to be highly repeatable over time when fish were provided an ad libitum diet. In this study we tested the temporal repeatability of individual SMR, AMR and AAS, as well as repeatability of body mass, in young brown trout (Salmo trutta L.) fed a moderately restricted diet (0.5–0.7% fish mass day–1). Metabolism was estimated from measurements of oxygen consumption rate () and repeatability was evaluated four times across a 15-week period. Individual body mass was highly repeatable across the entire 15 week experimental period whereas residual body-mass-corrected SMR, AMR and AAS showed a gradual loss of repeatability over time. Individual residual SMR, AMR and AAS were significantly repeatable in the short term (5 weeks), gradually declined across the medium term (10 weeks) and completely disappeared in the long term (15 weeks). We suggest that this gradual decline in repeatability was due to the slightly restricted feeding regime. This is discussed in the context of phenotypic plasticity, natural selection and ecology.

Functional properties of neuroglobin and cytoglobin. Insights into the ancestral physiological roles of globins

Neuroglobin and cytoglobin are two recently discovered vertebrate globins, which are expressed at low levels in neuronal tissues and in all tissues investigated so far, respectively. Based on their amino acid sequences, these globins appear to be phylogenetically ancient and to have mutated less during evolution in comparison to the other vertebrate globins, myoglobin and hemoglobin. As with some plant and bacterial globins, neuroglobin and cytoglobin hemes are hexacoordinate in the absence of external ligands, in that the heme iron atom coordinates both a proximal and a distal His residue. While the physiological role of hexacoordinate globins is still largely unclear, neuroglobin appears to participate in the cellular defence against hypoxia. We present the current knowledge on the functional properties of neuroglobin and cytoglobin, and describe a mathematical model to evaluate the role of mammalian retinal neuroglobin in supplying O2 supply to the mitochondria. As shown, the model argues against a significant such role for neuroglobin, that more likely plays a role to scavenge reactive oxygen and nitrogen species that are generated following brain hypoxia. The O2 binding properties of cytoglobin, which is upregulated upon hypoxia, are consistent with a role for this protein in O2‐requiring reactions, such as those catalysed by hydroxylases. IUBMB Life, 56: 689‐696, 2004

A mathematical model for gas exchange in the fish gill based on non-linear blood gas equilibrium curves

A mathematical model for gas exchange in fish gills is presented, which makes allowance for the non-linear nature of the oxygen and carbon dioxide equilibrium curves of blood, for the uneven distribution of diffusion conductance along the secondary lamellae, and for coupling of oxygen and carbon dioxide exchange through the Bohr and Haldane effects. The model demonstrates that for oxygen loading in the gill the sigmoid equilibrium curve is superior to a linear one, whereas the non-linearity of the carbon dioxide equilibrium curve does not significantly affect carbon dioxide exchange and that the Bohr and Haldane effects have importance only for carbon dioxide exchange. It is also shown that the arterial and expired gas tensions and concentrations are unaffected by whether the bulk of the diffusion conductance is at either the afferent or the efferent end of the individual lamellae, provided that the total conductance is unchanged.

Intraspecific variation in aerobic metabolic rate of fish: relations with organ size and enzyme activity in brown trout.

Highly active animals require a high aerobic capacity (i.e., a high maximum metabolic rate [MMR]) to sustain such activity, and it has been speculated that a greater capacity for aerobic performance is reflected in larger organs, which serve as energy processors but are also expensive to maintain and which increase the minimal cost of living (i.e., the basal or standard metabolic rate [SMR]). In this study, we assessed the extent of intraspecific variation in metabolic rate within a group of brown trout (Salmo trutta L.) and tested whether the observed variation in residual (body-mass-corrected) SMR, MMR, and absolute aerobic scope could be explained by variations in the residual size (mass) of metabolically active internal organs. Residual SMR was found to correlate positively with residual MMR, indicating a link between these two metabolic parameters, but no relationship between organ mass and metabolic rate was found for liver, heart, spleen, intestine, or stomach. Instead, activity in the liver of two aerobic mitochondrial enzymes, cytochrome c oxidase and, to a lesser extent, citrate synthase, was found to correlate with whole-animal metabolic rate, indicating that causes for intraspecific variation in the metabolic rate of fish can be found at a lower organizational level than organ size.

Physiological effects and tissue accumulation of copper in freshwater rainbow trout (Oncorhynchus mykiss) under normoxic and hypoxic conditions

Rainbow trout (Oncorhynchus mykiss) were exposed to a sublethal copper concentration (0.5 ppm) for 9 days in normoxic (PO2 > 130 mmHg) and hypoxic (70 mmHg), hard water ([Ca2+] = 2.15 mM). There were no signs of respiratory dysfunction in any of the exposed fish. A small, transient extracellular alkalosis was induced, which was of metabolic origin in normoxia and of respiratory origin in hypoxia. During copper exposure the plasma concentrations of Na+, K1 and Ca2+ decreased. In hypoxia the decrease in [Na+] continued throughout the experiment, whereas in normoxia [Na+] recovered towards the control values. The concentration of copper increased drastically in mucous and gill, liver and kidney tissues, whereas the copper concentration of white muscle, heart, spleen and whole blood was only marginally affected by copper exposure. There were no significant differences in the degree of tissue copper accumulation between copper/normoxia- and copper/hypoxia-exposed fish.

The Anodic Hemoglobin of Anguilla anguilla MOLECULAR BASIS FOR ALLOSTERIC EFFECTS IN A ROOT-EFFECT HEMOGLOBIN

The functional and structural basis for the Root effect has been investigated in the anodic hemoglobin of the European eel, Anguilla anguilla. This hemoglobin exhibits a large Bohr effect, which is accounted for by oxygen-linked binding of seven to eight protons in the presence of GTP at pH 7.5. Oxygen equilibrium curves show nonlinear lower asymptote of Hill plots, indicating the occurrence of heme-heme interactions within the T state. Analysis of the curves according to the co-operon model (Brunori, M., Coletta, M., and Di Cera, E. (1986) Biophys. Chem. 23, 215–222) reveals that T state cooperativity is positive at high pH and in the stripped hemoglobin (where the T → R allosteric transition is operative) and negative at low pH and in the presence of organic phosphate (where the molecule is locked in the low affinity structure), indicating site heterogeneity. The complete amino acid sequence of eel anodic hemoglobin has been established and compared with that of other fish hemoglobins. The presence of the Root effect correlates with a specific configuration of the α1β2 switch interface, which at low pH would stabilize subunit ligation in the T state without changing the quaternary structure. We propose that the major groups involved in the binding of oxygen-linked protons in eel anodic hemoglobin are located on the β chain and comprise His-HC3 at the C terminus, His-FG4 at the switch interface, and Lys-EF6 and the N terminus at the phosphate-binding site.

The physiological basis of the migration continuum in brown trout (Salmo trutta).

Partial migration is common in many animal taxa; however, the physiological variation underpinning migration strategies remains poorly understood. Among salmonid fishes, brown trout (Salmo trutta) is one of the species that exhibits the most complex variation in sympatric migration strategies, expressed as a migration continuum, ranging from residency to anadromy. In looking at brown trout, our objective with this study was to test the hypothesis that variation in migration strategies is underpinned by physiological variation. Prior to migration, physiological samples were taken from fish in the stream and then released at the capture site. Using telemetry, we subsequently classified fish as resident, short-distance migrants (potamodromous), or long-distance migrants (potentially anadromous). Our results revealed that fish belonging to the resident strategy differed from those exhibiting any of the two migratory strategies. Gill Na,K-ATPase activity, condition factor, and indicators of nutritional status suggested that trout from the two migratory strategies were smoltified and energetically depleted before leaving the stream, compared to those in the resident strategy. The trout belonging to the two migratory strategies were generally similar; however, lower triacylglycerides levels in the short-distance migrants indicated that they were more lipid depleted prior to migration compared with the long-distance migrants. In the context of migration cost, we suggest that additional lipid depletion makes migrants more inclined to terminate migration at the first given feeding opportunity, whereas individuals that are less lipid depleted will migrate farther. Collectively, our data suggest that the energetic state of individual fish provides a possible mechanism underpinning the migration continuum in brown trout.