A novel hyperbaric swimming respirometer allows the simulation of varying swimming depths in fish respirometry studies.

The understanding of swimming physiology and knowledge on the metabolic costs of swimming are important for assessing effects of environmental factors on migratory behavior. Swim tunnels are the most common experimental setups for measuring swimming performance and oxygen uptake rates in fishes; however, few can realistically simulate depth and the changes in hydrostatic pressure that many fishes experience, e.g. during diel vertical migrations. Here, we present a new hyperbaric swimming respirometer (HSR) that can simulate depths of up to 80 m. The system consists of three separate, identical swimming tunnels, each with a volume of 205 L, a control board and a storage tank with water treatment. The swimming chamber of each tunnel has a length of 1.40 m and a diameter of 20 cm. The HSR uses the principle of intermittent-flow respirometry and has here been tested with female European eels (Anguilla anguilla). Various pressure, temperature and flow velocity profiles can be programmed, and the effect on metabolic activity and oxygen consumption can be assessed. Thus, the HSR provides opportunities to study the physiology of fish during swimming in a simulated depth range that corresponds to many inland, coastal and shelf waters.

Hydrostatic pressure affects selective tidal stream transport in the North Sea brown shrimp (Crangon crangon).

The brown shrimp (Crangon crangon) is a highly abundant invertebrate in the North Sea, with its life cycle stages ranging from deep offshore spawning to shallow onshore nursery areas. To overcome the long distances between these two habitats, brown shrimp are suspected to use selective tidal stream transport (STST), moving with the cyclic tide currents towards their preferred water depths. However, it is not known which stimulus actually triggers STST behavior in brown shrimp. In this work, we determined the influence of different hyperbaric pressures on STST behavior of juvenile brown shrimp. Brown shrimp activity was recorded in a hyperbaric pressure chamber that supplied constant and dynamic pressure conditions simulating different depths, with and without a tidal cycle. Subsequent wavelet and Fourier analysis were performed to determine the periodicity in the activity data. The results of the experiments show that STST behavior in brown shrimp varies with pressure and therefore with depth. We further show that STST behavior can be initiated by cyclic pressure changes. However, an interaction with one or more other environmental triggers remains possible. Furthermore, a security ebb-tide activity was identified that may serve to avoid potential stranding in shallow waters and is 'remembered' by shrimp for about 1.5 days without contact with tidal triggers.

"Do-not-resuscitate" preferences of the general Swiss population: Results from a national survey.

AIMS: To assess the do-not-resuscitate preferences of the general Swiss population and to identify predictors influencing decision-making. Methods: A nationwide web-based survey was conducted in Switzerland on a representative sample of the adult population. The primary endpoint was the preference for a "Do Not Resuscitate" order (DNR Code Status) vs. cardiopulmonary resuscitation (CPR Code Status) in a clinical case vignette of an out-of-hospital cardiac arrest. Secondary endpoint were participants' own personal preferences for DNR. Results: 1138 subjects participated in the web-based survey, 1044 were included in the final analysis. Preference for DNR code status was found in 40.5% (n = 423) in the case vignette and in 20.3% (n = 209) when making a personal decision for themselves. Independent predictors for DNR Code Status for the case vignette were: Personal preferences for their own DNR Code Status (adjusted OR 2.44, 95%CI 1.67 to 3.55; p < 0.001), intubation following respiratory failure (adjusted OR 1.95, 95%CI 1.20 to 3.18; p = 0.007), time-period after which resuscitation should not be attempted (adjusted OR 0.91, 95%CI 0.89 to 0.93); p < 0.001), and estimated chance of survival in case of a cardiac arrest (adjusted OR per decile 0.91, 95%CI 0.84 to 0.99, p = 0.02; which was overestimated by all participants. Conclusions: Main predictors for a DNR Code Status were personal preferences and the overestimation of good neurological outcome after cardiac arrest. Overestimation of positive outcomes after cardiac arrest seems to influence patient opinion and should thus be addressed during code status discussions.

Environmental enrichment during early rearing provokes epigenetic changes in the brain of a salmonid fish.

Environmental enrichment is used to increase structural complexity of captive rearing systems and has been shown to provoke a wide range of effects in the kept animals. Here we studied the effects of enrichment on DNA methylation patterns at the whole-genome level in the brain of rainbow trout reared in an aquaculture setting. We investigated the epigenetic effects between different types of enrichment (natural substrate vs. artificial substrate vs. barren) in three developmental stages (egg vs. alevin vs. fry) and as enrichment was discontinued at the fingerling stage by means of the Methylation-Sensitive Amplified Polymorphism (MSAP) technique. While enrichment did not affect growth in body size, we found enrichment to affected global DNA methylation in the brain at the egg and alevin stage, i.e., the period during development where the animals are in close physical contact with the substrate. At these stages, trout reared on the two substrates differed more from the control than the substrates differed from each other. Only minor differences between rearing environments were detected following emergence at the fry stage. When enrichment was discontinued during the rearing of fingerlings, no differences in DNA methylation patterns were observed between the rearing environments. Our results provide further evidence on the effects of enrichment in the captive rearing of fish and show that enrichment can even modulate epigenetic patterns. The effect on the epigenome may be causal for the previously reported effects of enrichment on gene expression, behaviour and brain development.

Metamorphosis and transition between developmental stages in European eel (Anguilla anguilla, L.) involve epigenetic changes in DNA methylation patterns.

The life history of the European eel (Anguilla anguilla, L.) is characterized by a series of metamorphoses and transitions that provoke drastic morphological changes. Most of these changes go along with the catadromous life cycle in eels, involving extensive physiologically adaptations. In this study it was investigated whether these drastic changes have an epigenetic basis by analyzing global methylation patterns in liver, gill and brain tissue from glass eels caught at the British coast as well as yellow and silver eels from River Rhine using methylation-sensitive amplified polymorphisms (MSAP). Analysis of molecular variance (AMOVA) on MSAP data derived from liver tissue revealed only minor differences in methylation patterns between glass, yellow and silver eels, reflecting uniform functioning of the liver throughout the investigated lifespan. In brain and gill tissue, however, marked differences in methylation patterns were found. Principal coordinates analysis (PCoA) revealed yellow eels being partially clustered with silver eels and a more distinct cluster of glass eels based on the methylation patterns in the brain. According to results found in the gills, glass eels were more similar to silver eels whereas yellow eels were found to be clustered separately. From these results it can be concluded that epigenetic changes in gill tissue most likely reflect and are linked with adaptation towards salt- and freshwater conditions. The observed differences in brain methylation patterns, however, might be linked to morphological and physiological changes during metamorphosis and transitions within the life history of European eels potentially affecting subsequent differential gene expression patterns required for such changes.