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.

Bone resorption and body reorganization during maturation induce maternal transfer of toxic metals in anguillid eels.

During their once-in-a-lifetime transoceanic spawning migration, anguillid eels do not feed, instead rely on energy stores to fuel the demands of locomotion and reproduction while they reorganize their bodies by depleting body reserves and building up gonadal tissue. Here we show how the European eel (Anguilla anguilla) breaks down its skeleton to redistribute phosphorus and calcium from hard to soft tissues during its sexual development. Using multiple analytical and imaging techniques, we characterize the spatial and temporal degradation of the skeletal framework from initial to final gonadal maturation and use elemental mass ratios in bone, muscle, liver, and gonadal tissue to determine the fluxes and fates of selected minerals and metals in the eels' bodies. We find that bone loss is more pronounced in females than in males and eventually may reach a point at which the mechanical stability of the skeleton is challenged. P and Ca are released and translocated from skeletal tissues to muscle and gonads, leaving both elements in constant proportion in remaining bone structures. The depletion of internal stores from hard and soft tissues during maturation-induced body reorganization is accompanied by the recirculation, translocation, and maternal transfer of potentially toxic metals from bone and muscle to the ovaries in gravid females, which may have direct deleterious effects on health and hinder the reproductive success of individuals of this critically endangered species.

Condition-dependent physiological and behavioural responses to anthropogenic noise.

Anthropogenic (man-made) noise, a global pollutant of international concern, is known to affect the physiology and behaviour of a range of organisms. However, experimental studies have tended to focus on trait means; intra-population variation in responses are likely, but have rarely been explored. Here we use established experimental methods to demonstrate a condition-dependent effect of additional noise. We show that juvenile European eels (Anguilla anguilla) in good condition do not respond differently to playbacks of ambient coastal noise and coastal noise with passing ships. By contrast, the additional noise of ship passes caused an increase in ventilation rate and a decrease in startling to a looming predatory stimulus in poor condition eels. Intra-population variation in responses to noise has important implications both for population dynamics and the planning of mitigation measures.

Dietary Korean mistletoe enhances cellular non-specific immune responses and survival of Japanese eel (Anguilla japonica).

The present study was performed to investigate the immunostimulatory effects of Korean mistletoe extract (KM-110; Viscum album Coloratum) on the non-specific immune response and protection against Aeromonas hydrophila infection in Japanese eel (Anguilla japonica). Eels were fed under 4 regimes, 0%, 0.1%, 0.5% and 1.0% KM-110 mixed diet. On day 14 after feeding, 15 fish from each group were injected i.p. with live A. hydrophila (3 x 10(6)CFU) and the remaining unchallenged fish from each group were used to study the innate immune response. On 14 days post-infection, the total survival rates were 26.6% in control, and 33.3%, 66.6% and 80% in 0.1%, 0.5% and 1% KM-110-treated groups, respectively. The maximum lysozyme activity was observed in the 1% KM-110-treated group. There was no significant difference of lysozyme activity between 0.1% and 0.5% KM-110 group. Superoxide anion (O(2)(-)) production was significantly (p<0.05) augmented in the 0.5% and 1% KM-110 groups compared to the control and 0.1% KM-110 group. No significant difference of (O(2)(-) production was found between 0.5% and 1% KM-110 group. Likewise, there was a significant increase in phagocytic activity in the 0.5% KM-110 group compared with the 0.1% group (p<0.05), but no significant difference between the 0.5% and the 1% KM-110 group indicating that 0.5% KM-110 concentration is suitable for stimulating maximum phagocytic activity resulting in a high amount of ROI production. Considering the present results, KM-110 could be utilized as a promising immunostimulating substance for a diet in aquaculture.

Electrostimulation of catecholamine release in the eel: modulation by antagonists and autocrine agonists.

The innervated chromaffin cells of the eel (Anguilla rostrata) release norepinephrine (NE) and epinephrine (E), while a component of the macrovascular wall releases dopamine (DA). The release of the three catecholamines is governed by complex controls which include adrenergic, nicotinergic, muscarinergic, and opioid mechanisms. To gain insight into the interactions between neural and autocrine factors in stimulated catecholamine release, we investigated the effect of adrenergic (phentolamine and propranolol) and muscarinergic (atropine) receptor antagonists, and of autocrine opioids (met-enkephalin, codeine, and morphine) on electrostimulated catecholamine secretion in situ. The hind brain (close to the root of nerve IX) of anesthetized eels was stimulated at four different time points, and segments of the posterior cardinal vein or the caudal vein were perfused with a saline solution, with or without test substances. Electrostimulation (30 s) four times within a total study duration of 14 min increased the release of DA, NE, and E into the perfusate of the cardinal vein. The vessel contains the innervated adrenomedullary equivalent. In the noninnervated caudal vein electrical stimulation had no impact on total DA release, while there was a slight decrease of NE release and a slight increase of E release. In the cardinal vein, both the alpha-adrenergic receptor antagonist phentolamine and the beta-adrenergic receptor antagonist propranolol strongly reduced the effect of electrostimulation on catecholamine release. Met-enkephalin reduced the release of all three catecholamines to a similar degree; its impact on NE release was especially strong. Codeine reduced the catecholamine release moderately, while morphine had no effect. Atropine reduced the release of all three catecholamines in a pattern similar to that of met-enkephalin. The findings on the posterior cardinal vein indicate that neurally stimulated NE and E release (1) involves autocrine/paracrine adrenergic mechanisms, (2) involves a muscarinergic mechanism, and possibly also endogenous codeine and morphine; and (3) is antagonized by met-enkephalin. The findings on the caudal vein are further evidence that macrovascular DA release is not under direct neural control.

Fish testicular 11beta-hydroxylase: cDNA cloning and mRNA expression during spermatogenesis.

We isolated and characterized a cDNA encoding testicular 11beta-hydroxylase, cytochrome P450(11beta) from the Japanese eel (Anguilla japonica) testis. The cDNA contains an open reading frame that encodes a protein of 511 amino acids. The predicted amino acid sequence shares 38-48% homology with those of adrenal P450(11beta) from mammals and frog. Transient expression in COS 1 cells confirmed that the protein encoded by this cDNA had P450(11beta) activity. Northern blotting revealed a single 1.8 kb long transcript of P450(11beta). This transcript was not found in immature eel testes prior to an injection with human chorionic gonadotropin (hCG), but it was present in eel testes after hCG injection.

Primary sequence, tissue specificity and expression of the Na+,K(+)-ATPase alpha 1 subunit in the European eel (Anguilla anguilla).

The entire cDNA nucleotide sequence of the Na+,K(+)-ATPase alpha 1 isoform was cloned from the gills of the European eel (Anguilla anguilla) by a PCR based method. The amino acid sequence translated from the sequence shared 89.4 and 85.6% homology respectively with previously published Na+,K(+)-ATPase alpha subunit sequences from elasmobranch (Torpedo californica) and teleost (Catostomus commersoni) fish. The size of Na+,K(+)-ATPase alpha 1 mRNA transcripts in eel tissues was demonstrated to be 3.5 kb, except in the ovary where a 3.7 kb transcript existed. Na+,K(+)-ATPase alpha 1 mRNA was present at some level in all tissues investigated with the exception of cardiac and skeletal muscle where no Na+,K(+)-ATPase alpha 1 mRNA was detectable. The level of branchial Na+,K(+)-ATPase alpha 1 mRNA increased after the adaptation of freshwater eels to normal or double concentration seawater.

Melanin concentrating hormone inhibits the release of alpha MSH from teleost pituitary glands.

A radioimmunoassay was developed for salmonid melanin concentrating hormone (MCH) and used to measure immunoreactive (ir)MCH in the hypothalamus and pituitary of trout (Salmo gairdneri) and eels, (Anguilla anguilla) maintained under different regimes of background color. In trout, 95% of the total irMCH was located in the pituitary gland. The amount of MCH in both pituitary and hypothalamus was increased when white-adapted trout were transferred to a black background. In eels, a similar change of background led to an accumulation of MCH in the pituitary but not in the hypothalamus. The results suggest that MCH is released from the neurohypophysis in association with physiological color change. Neurointermediate lobes of trout and eels released both ir alpha MSH and irMCH when they were cultured in vitro. The release of alpha MSH was significantly enhanced when endogenous MCH was immunoabsorbed by MCH antiserum added to the culture medium. The results indicate that MCH can induce pallor in fish not only by its peripheral effect on the melanophores but also by an inhibitory action on the release of alpha MSH from the pituitary.

Evidence for the participation of a melanin-concentrating hormone in physiological colour change in the eel.

The hormonal and nervous control of colour change in the eel has been investigated. The only bioactive forms of MSH found in eel pituitary extracts or secreted by eel pituitary cultures were forms of alpha-MSH; no beta-MSH was detected. After transfer of eels from a black to a white background, the melanin concentration in skin melanophores was accompanied by a rapid decline in plasma alpha-MSH titres. Hypophysectomy resulted in melanin concentration, and pituitary extracts injected into hypophysectomized eels caused melanin dispersion. This effect was eliminated if the pituitary extracts were first incubated with a specific alpha-MSH antiserum or if the antiserum was injected into the hypophysectomized eel. However, injection of alpha-MSH antiserum into intact, black-adapted eels failed to result in melanin concentration although the same antiserum was effective in causing pallor in black-adapted toads. Partially purified preparations of teleost melanin-concentrating hormone (MCH), free from catecholamines, induced melanin concentration when injected into black-adapted eels and this effect was significantly potentiated by injections of alpha-MSH antiserum. The denervation of melanophores on the pectoral fin had only a slight effect on the responses of the melanophores to humoral agents. It is concluded that the control of physiological colour change in the eel is largely hormonal, and involves the antagonistic effects of alpha-MSH and a melanin-concentrating agent which is probably MCH.