The differential leucocyte landscape of four teleosts: juvenile Oncorhynchus kisutch, Clupea pallasi, Culaea inconstans and Pimephales promelas

The appearance and proportions of morphologically distinct leucocytes (monocytes, thrombocytes, lymphocytes and diverse forms of granulocytes) encountered in the blood of four teleost species: coho salmon Oncorhynchus kisutch , Pacific herring Clupea pallasi , brook stickleback Culaea inconstans and fathead minnow Pimephales promelas , are presented, along with examples of how water quality influenced their relative proportions. The results clearly show that relative leucocyte number responds significantly and differently to changes in water quality. The value of using differential white cell counting as a quick and inexpensive component of assaying immune system alterations is discussed.     

Kinematics and hydrodynamics of linear acceleration in eels, Anguilla rostrata

The kinematics and hydrodynamics of routine linear accelerations were studied in American eels, Anguilla rostrata, using high-speed video and particle image velocimetry. Eels were examined both during steady swimming at speeds from 0.6 to 1.9 body lengths (L) per second and during accelerations from -1.4 to 1.3 L s(-2). Multiple regression of the acceleration and steady swimming speed on the body kinematics suggests that eels primarily change their tail-tip velocity during acceleration. By contrast, the best predictor of steady swimming speed is body wave speed, keeping tail-tip velocity an approximately constant fraction of the swimming velocity. Thus, during steady swimming, Strouhal number does not vary with speed, remaining close to 0.32, but during acceleration, it deviates from the steady value. The kinematic changes during acceleration are indicated hydrodynamically by axial fluid momentum in the wake. During steady swimming, the wake consists of lateral jets of fluid and has minimal net axial momentum, which reflects a balance between thrust and drag. During acceleration, those jets rotate to point downstream, adding axial momentum to the fluid. The amount of added momentum correlates with the acceleration, but is greater than the necessary inertial force by 2.8+/-0.6 times, indicating a substantial acceleration reaction.     

Risk-taking behavior in weight-compensating coho salmon, Oncorhynchus kisutch

The effects of food restriction on predation risk-taking behaviorwere studied in juvenile coho salmon, Oncorhyndtus kisutch,during the period before seawater migration in the spring. Aradiographic technique enabled the study of individual foodintake in a safe and risky food patch before and after exposureto a piscivorous predator. The study revealed a significantincrease in food intake and specific growth rate in the weeksfollowing deprivation, resulting in compensatory growth anda recovery of the weight loss caused by dietary restriction.The increase in food intake resulted from a change in risk-takingbehavior. Following a period of diet restriction, the fish habituatedfalter after predator exposure, and the proportion of fish inthe risky patch was significantly higher than before deprivation.Deprived fish took greater shares of the group meal comparedwith control fish, and the pattern of the individual share ofthe group meal after food restriction indicated a change inthe social hierarchy. This study indicates that risk-takingbehavior is state dependent and changes temporarily to compensatefor a period of food restriction. The results are discussedin terms of tradeoffs between food and risk in a period leadingup to an ontogenetic habitat shift.     

The ultrastructure of the integument of the American eel,Anguilla rostrata

Summary The morphology and ultrastructure of the lateral body integument of the leptocephalus, glass eel, pigmented elver, and adult stages of the American eel, Anguilla rostrata, were examined with light and electron microscopy. The integument consists of an epidermis separated by a basal lamina from the underlying dermis. Three cell types are present in the epidermis in all stages. Filament-containing cells, which are the principal structural cell type, are increasingly numerous at each stage. Mucous cells, which secrete the mucous that compose the mucous surface coat, are also more numerous in each subsequent stage and are more numerous in the anterior lateral body epidermis than in the posterior lateral body epidermis of the adult. Club cells, whose function is unknown, are most numerous in the glass eel and pigmented elver. Chloride cells are common in the leptocephalus which is marine and infrequent in the glass eel. They are not present in the pigmented elver and adult which inhabit estuaries and fresh-water. Lymphocytes and melanocytes are also present in some stages. The dermis comprises two layers: a layer of collagenous lamellae, the stratum compactum, and an underlying layer of loose connective tissue, the stratum spongiosum.There is a progressive increase in epidermal thickness at each stage which is paralleled by an increase in the thickness of the stratum compactum. Rudimentary scales are present in the dermis of the adult. The increase in the number of epidermal filament-containing cells, epidermal thickness and stratum compactum thickness is correlated with an increased need for protection from abrasion and mechanical damage as the eel moves from a pelagic, oceanic habitat to a benthic, freshwater habitat. The increase in mucous cell numbers is likewise correlated with an increased need for the protective and anti-bacterial action of the mucous surface coat in the freshwater environment.This investigation was supported by NIH research grant NS-11276 from National Institute of Neurological Diseases and Stroke to Dr. J.D. McCleave and by N.S.F. Grant GD 38933 to the Bermuda Biological Station, St. Georges West, Bermuda. Bermuda Biological Station Contribution No. 668     

Catecholaminotropic effects of catecholamines in a teleost fish,Anguilla rostrata

Summary Injections of physiological and supraphysiological doses of epinephrine (E) into cardiaccannulated eels cause a dose-related increase of plasma dopamine (DA) and norepineprine (NE) within 3 min. Likewise, both exogenous DA and NE increase the plasma titers of the respective other two catecholamines (CAs). The baseline titers of NE and E are closely correlated. Lack of a correlation of the baseline titers of NE and E with that of DA appears to be due to a faster disappearance rate of DA from the circulation. E is strongly hyperglycemic, and the weaker glycemic action of NE may be mediated via E release. The effects of E seem to depend on a spurt-like increase rather than its titer per se. The ability of the eel to cope with very fast, excessive increases of plasma CAs raises the question of the underlying mechanisms.Abbreviations CA(s) catecholamine(s) - DA dopamine - NE norepinephrine - E epinephrine     

The oxygen equilibrium of the hemoglobin of the eel,Anguilla rostrata

Kawamoto had reported that eel hemoglobin has a hyperbolic oxygen equilibrium function, with n in the Hill equation equal to 1. On the basis of Kawamoto's data and with new measurements, it is shown that the equilibrium function is in fact S-shaped, as in most other vertebrates, and n in Hill's equation equals 1.8.     

Evidence for Environmental Sex Determination in the American eel, Anguilla rostrata

Males have predominated among migrating silver eels in the Annaquatucket River, Rhode Island, for at least two decades, with no significant variation in mean total length in either sex. Because the species is panmictic (random breeding), this consistency suggests environmental sex determination (ESD). Most yellow (feeding phase) eels <300mm total length in the Annaquatucket are sexually undifferentiated, and in contrast to all other published sex ratios, males greatly outnumber females (3:1) among differentiated yellow eels. Estimates of yellow eel population densities are 4–10 times greater than published values for other habitats. We propose that this crowding results in a long period of undifferentiation and the suppression of femaleness. Published field and experimental evidence indicates that high population density results in high proportions of males in Atlantic Anguilla, and that low population density results in the predominance of females. This ESD may be adaptive, resulting in vast numbers of small males in coastal habitats, relatively close to the spawing area, and much larger and more fecund females that occupy most of the available eel habitat.     

Growth hormone and seawater adaptation in coho salmon, Oncorhynchus kisutch

1. Effects of growth hormone (GH) were examined on short-term aspects of seawater adaptation in coho salmon smolts. 2. Injection of somatostatin (SRIF) immediately prior to seawater entry suppressed plasma GH levels, but did not have any significant effects at 6 or 12 hr on hematocrits, plasma glucose or plasma Na+ levels. 3. Plasma GH levels increased 250% within 36 hr after seawater exposure. 4. Plasma glucose levels, in contrast, were significantly lower in the seawater fish after 36 hr post-exposure. 5. Plasma Na+ levels increased to 190 mEq/1 by 24 hr but subsequently returned to freshwater levels while hematocrits showed no significant changes over the 72 hr of exposure. 6. The significance of these results is discussed in terms of successful seawater adaptation in coho salmon.     

Draft genome of the American Eel (Anguilla rostrata)

Freshwater eels (Anguilla sp.) have large economic, cultural, ecological and aesthetic importance worldwide, but they suffered more than 90% decline in global stocks over the past few decades. Proper genetic resources, such as sequenced, assembled and annotated genomes, are essential to help plan sustainable recoveries by identifying physiological, biochemical and genetic mechanisms that caused the declines or that may lead to recoveries. Here, we present the first sequenced genome of the American eel. This genome contained 305 043 contigs (N50 = 7397) and 79 209 scaffolds (N50 = 86 641) for a total size of 1.41 Gb, which is in the middle of the range of previous estimations for this species. In addition, protein‐coding regions, including introns and flanking regions, are very well represented in the genome, as 95.2% of the 458 core eukaryotic genes and 98.8% of the 248 ultra‐conserved subset were represented in the assembly and a total of 26 564 genes were annotated for future functional genomics studies. We performed a candidate gene analysis to compare three genes among all three freshwater eel species and, congruent with the phylogenetic relationships, Japanese eel (A. japanica) exhibited the most divergence. Overall, the sequenced genome presented in this study is a crucial addition to the presently available genetic tools to help guide future conservation efforts of freshwater eels.     

Monoamine oxidase in the hypothalamo-hypophysial region of the teleosts,Anguilla japonica and Oryzias latipes

Summary Distribution of monoamine oxidase (MAO) was histochemically examined in the hypothalamo-hypophysial region of the eel (Anguilla japonica) and the medaka (Oryzias latipes) with a modified Glenner's tryptamine-tetrazolium method. The hypothalamic neurosecretory cells showed very weak MAO activity in their perikarya. MAO-positive fibers were present in close contact with the neurosecretory cells, suggesting that monoaminergic fibers participate in the control of neurosecretory cell activity. The nucleus lateralis tuberis (NLT) contained cells exhibiting strong MAO activity. These cells must be monoaminergic neurons.In the anterior region of the neurohypophysis of both eel and medaka, two bundles of MAO-positive fibers originating from the NLT proceed down along each side of the third ventricle into the pars distalis. This suggests that monoaminergic neurons of the NLT are involved in the release of hormones from the pars distalis. In addition to these tracts, numerous MAO-positive fibers proceed backward from the post-optic area and end around the blood capillaries located between the neurohypophysis and the pars intermedia in both species.I wish to express my gratitude to Prof. H. Kobayashi for his valuable advice during the course of this study. I am indebted to Prof. S. Uchida, Ocean Research Institute, University of Tokyo, for supplying the eels.     

Discovery and characterization of single nucleotide polymorphisms in coho salmon,Oncorhynchus kisutch

Molecular population genetic analyses have become an integral part of ecological investigation and population monitoring for conservation and management. Microsatellites have been the molecular marker of choice for such applications over the last several decades, but single nucleotide polymorphism (SNP) markers are rapidly expanding beyond model organisms. Coho salmon (Oncorhynchus kisutch) is native to the north Pacific Ocean and its tributaries, where it is the focus of intensive fishery and conservation activities. As it is an anadromous species, coho salmon typically migrate across multiple jurisdictional boundaries, complicating management and requiring shared data collection methods. Here, we describe the discovery and validation of a suite of novel SNPs and associated genotyping assays which can be used in the genetic analyses of this species. These assays include 91 that are polymorphic in the species and one that discriminates it from a sister species, Chinook salmon. We demonstrate the utility of these SNPs for population assignment and phylogeographic analyses, and map them against the draft trout genome. The markers constitute a large majority of all SNP markers described for coho salmon and will enable both population‐ and pedigree‐based analyses across the southern part of the species native range.     

Cholinoceptor-mediated control of catecholamine release from chromaffin cells in the American eel,Anguilla rostrata

The cholinergic agonist-induced secretion of catecholamines from chromaffin cells in the American eel, Anguilla rostrata, was assessed using a salineperfused posterior cardinal vein preparation. Direct membrane depolarization with 60 mmol·l^-1 K⁺ caused a significant release of catecholamines (adrenaline + noradrenaline) into the perfusate which was unaffected by pre-treatment with the ganglion blocker, hexamethonium (final concentration = 10^-3 mol · l^-1). The nicotinic receptor agonist, 1,1-dimethyl-4-phenylpiperazinium iodide, evoked catecholamine release in response to several doses exceeding 10^-7 mol; at 10^-5 mol the response was abolished by pre-treatment with the ganglion blocker, hexamethonium (final concentration = 10^-3 mol · l^-1). The muscarinic receptor agonist, pilocarpine, did not elicit catecholamine release in response to any of the doses administered (10^-8–10^-4 mol). A single injection of the mixed nicotinic/muscarinic cholinoceptor agonist, carbachol (10^-5 mol), caused the release of catecholamines which was abolished by pre-treatment with hexamethonium but which was unaffected by pre-treatment with the muscarinic receptor antagonist atropine (final concentration = 10^-5 mol · l^-1). The results of this study indicate that the process of cholinergic agonist-induced catecholamine secretion from the chromaffin cells in the American eel is mediated exclusively by activation of nicotinic receptors with no involvement of the muscarinic receptor.Abbreviations DMPP 1,1-dimethyl-4-phenylpiperazinium iodide - MS222 ethylaminobenzoate - HPLC high-performance liquid chromatography - PCV posterior cardinal vein - SEM standard error of the mean     

Electrophysiological responses from the peripheral olfactory system of the American eel,Anguilla rostrata

Summary A method is described for recording with microelectrodes from central neurones in locusts,Schistocerca gregaria americana, that are free to perform a large fraction of their behavioural repertoire. This tethered preparation has been used to examine the individual responses of large neurones in the neck connectives to a range of sensory stimuli.From differences in the responses of the units examined and from their positions in the connective, as determined by dye iontophoresis, 31 separate neurones have been identified. The axons of these cells had relatively constant diameters and cord positions in different animals and appeared in both right and left connectives but with their positions mirror reversed. The majority of these 31 cells carried descending information from the head ganglia and under our experimental conditions, 7 were found to have wind stimulation as their strongest sensory input, 17 had visual stimulation, 4 had sound stimulation and 3 had proprioceptive input.Abbreviations DCMD descending contralateral movement detector (neurone) - DIMD descending ipsilateral movement detector (neurone)