Responses of the teleost Hoplias malabaricus to hypoxia

Synopsis Oxygen uptake (VO₂) during graded hypoxia, rate of hypoxia acclimation, breathing frequency (f_R), breath volume (V_{S, R}) and gill ventilation (V_G) were measured in Hoplias malabaricus. Normoxia and hypoxia acclimated fish had similar and constant VO₂ and V_G in a range of water PO₂ from 150 to 25 mmHg. Hypoxia acclimated fish showed significantly higher VO₂ in severe hypoxia (PO₂ <15 mmHg). Normoxia acclimated fish showed symptoms similar to hypoxic coma after 1 h of exposure to water PO₂ of 10 mmHg whereas the same symptoms were observed only at PO₂ of 5 mmHg for fish acclimated to hypoxia. Fish required 14 days to achieve full acclimation to hypoxia (PO₂ ≥25 mmHg). Lowering of water PO₂ from 150 to 25 mmHg resulted in normoxic fish showing a 3–2 fold increase in V_G. The increase was the result of an elevation in V_{S, R} rather than f_R. Among normoxia acclimated specimens, small fish showed a higher V_G per unit weight than the large ones in both normoxia (PO₂ =150 mmHg) and hypoxia (PO₂ = 15 mmHg). A decrease in the ventilatory requirement (V_G/VO₂) with increased body weight was recorded in hypoxia (PO₂ = 15 mmHg).     

Enameloid in the teleost fish Lophius

Summary The ultrastructural and chemical differences between mature enameloid and dentine in the teleost fish Lophius were demonstrated using transmission (TEM) and scanning (SEM) electron microscopy, X-ray diffraction analysis, electron diffraction analysis and electron microprobe analysis. An enameloid cap (about 50 m thick) and a thin layer (1 m thick) of collar enameloid were revealed in the scanning (SEM) and transmission (TEM) electron microscopes. Collar enameloid, structurally different from dentine both in SEM and TEM, proved to be less mineralized than the cap as revealed by electron microprobe analysis. The enameloid cap was seen to differ from dentine by (i) its electron density in TEM; (ii) the structural arrangement perpendicular to the underlying dentine, observed in SEM and TEM and corroborated by electron diffraction data, which showed a preferred orientation of enameloid crystallites; (iii) its higher F content decreasing gradually from the apex of the tooth to the junction with dentine and falling suddenly below this junction; and (iv) its lower Mg content. Establishment of a classification of enameloids is proposed, similar to that for dentines, in which selachian enameloid would be a reference standard.

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Résumé La microscopie électronique à transmission, la microscopie électronique à balayage, la diffraction X, la diffraction électronique et l'analyse par microsonde ont prouvé l'existence d'un émailoïde, ultrastructuralement et chimiquement différent de la dentine, chez la baudroie. La microscopie électronique à balayage et la microscopie électronique à transmission ont mis en évidence un chapeau d'émailoïde, d'environ 50 m d'épaisseur, et une couche fine (1 m) d'émailoïde du collet. L'émailoïde du collet, dont l'ultrastructure différente de celle de la dentine a été mise en évidence en microscopie électronique à transmission et en microscopie électronique à balayage, apparaît, après analyse par microsonde, moins minéralisé que le chapeau. Le chapeau d'émailoïde diffère de la dentine par (i) sa densité aux électrons en microscopie électronique à transmission; (ii) sa structure perpendiculaire à celle de la dentine sous-jacente, visible en microscopie électronique à transmission et en microscopie électronique à balayage et confirmée par la diffraction électronique, qui montre une orientation préférentielle des cristaux; (iii) son contenu en fluor plus élevé, qui diminue progressivement de l'apex à la jonction avec la dentine et chute brutalement au-dessous de cette jonction; (iv) sa teneur plus basse en magnésium. Les auteurs proposent que soit établie une classification des émailoïdes analogue à celle des dentines et dans laquelle l'émailoïde de Sélaciens constituerait un standard de référence.

     

Filial cannibalism in teleost fish

This review summarizes information on filial cannibalism (the act of eating one's own offspring) in teleost fish. Cannibalistic parents can either consume their whole brood (total filial cannibalism), or eat only some of the eggs in the nest (partial filial cannibalism). Offspring consumption has been argued to be adaptive under the assumption that offspring survival is traded against feeding, and that offspring can act as an alternative food source for the parents. The evidence supporting the basic predictions formulated under these assumptions is summarized for both total and partial filial cannibalism. These two forms of cannibalism differ significantly since the former represents an investment only in future reproductive success, whereas the latter can affect both present and future reproductive success. Despite a few inconsistencies in the data from laboratory and field studies, the energy-based explanation appears valid for both forms of cannibalism. Alternative non-energy-based explanations are considered, but they are unable to account for the wide distribution of this behaviour in teleosts. The intersexual conflict arising from attempts of the non-cannibal sex to minimize the cost of filial cannibalism is also discussed, together with the potential effect of this behaviour on the operational sex ratio at a population level.     

Sacciform cells in the skin of teleost fish

The fine structure of sacciform gland cells of the epidermis is described in the number of species of teleost fish. In some of these the cell type had either not been found, or not recognized as such, before. Some histological and histochemical results are also reported. Despite considerable differences in the histochemistry and in the morphology of the sacciform cells over the range of species studied, some features of the fine structure are constant and can be used as diagnostic characters. The nucleus is peripheral, and there is a large membrane-limited lumen, into which the secretion is released from membrane-bounded vacuoles at the margin of the cytoplasm. It is probable that the secretion originates mainly in channels of endoplasmic reticulum which become swollen to form the vacuoles. Most sacciform cells open at the surface of the skin by an apical pore, but some have not been seen to open. The classification of the various unicellular glands of teleosts is discussed and it is concluded that attempts to categorise them by the nature of the secretion alone are unsatisfactory.     

Iron acquisition by teleost fish

Iron is a vital micronutrient for teleost fish, being an integral component of proteins involved in cellular respiration and oxygen transfer. However, in excess iron is toxic, and fish need to balance uptake to prevent deficiency vs. potential toxicity. This review assesses the current physiological and molecular knowledge of the mechanisms of iron acquisition in the teleost fish. It focuses on freshwater teleost fish when assessing the gill as a possible site for iron acquisition, and includes a summary of geochemical processes that govern aquatic iron bioavailability. It focuses on marine teleost fish for assessing the mechanism of intestinal iron uptake. Physiological evidence indicates that iron preferentially crosses the apical membrane of both the gills and intestine in the ferrous (Fe2+) state. Molecular evidence supports this, demonstrating the presence of homologues in fish to the large Slc 11a family of evolutionary conserved proteins linked to Fe2+ transport. This symporter is probably linked to a reductase, which reduces either ferric (Fe3+) or organic complexed iron to Fe2+ prior to uptake.     

Neuropharmacology of adrenergic neurons in teleost fish

Although this brief review is based on relatively few types of experiments in few species of teleosts, it is possible to summarize some points of interest regarding the similarities and differences in the mechanisms of adrenergic neurotransmission in fish compared to the higher vertebrates. 1. There is a substantial mixing of cranial autonomic ("parasympathetic") and spinal autonomic ("sympathetic") pathways in the cranial nerves. This close relationship between the two systems and the differences in the nature of the neurons of cranial origin (cholinergic, and non-adrenergic, non-cholinergic) and spinal origin (adrenergic, cholinergic and mixed "polynergic") gives a basis in fish also for a complex pattern of innervation of the various organs. 2. Adrenaline is the major transmitter substance in the adrenergic neurons of most teleosts studied, but there are exceptions within the same species. For instance, in the swimbladder mucosa of the cod, noradrenaline dominates, while adrenaline is the major catecholamine in most other organs innervated by adrenergic neurons. The reasons for the regional differences are not known and further studies of the rate of catecholamine turn-over in the adrenergic neurons of fish are clearly indicated. 3. Adrenoceptors of both the alpha- and the beta-type show great similarities with those of mammals. Some differences in the potencies of certain compounds (e.g., clonidine and methoxamine) exist and receptor binding studies should add valuable information about the adrenoceptors of teleosts. The existence of a subtype of beta-adrenoceptor (beta 2) has been proposed and further work is needed to confirm or deny the applicability of the beta 1/beta 2 adrenoceptor terminology in fish. 4. There appears to be some differences in the mode of action of the so called "indirectly acting amines", such as tyramine, between teleosts and mammals. While the uptake of tyramine into the nerve terminals in mammals appears to take place via the cocaine-sensitive neuronal uptake system which is also responsible for catecholamine uptake (uptake 1), tyramine uptake in cod neurons appears to be via a separate pathway. 5. Presynaptic supersensitivity of the type seen in mammals has also been demonstrated in teleost adrenergic neurons. Both denervation (chemical or surgical) and blockade of the neuronal uptake mechanism by cocaine or desipramine produce this type of supersensitivity, while post-synaptic supersensitivity has so far not been described in teleosts. The effects of removal of the uptake system shows that the uptake process may be as important in teleosts as in mammals in the removal of adrenergic transmitter from the synaptic cleft. 6. In the total picture of adrenergic functions in fish, the circulating catecholamines take a special role...     

Sexual determination and differentiation in teleost fish

The present work reviews the latest information on the cellular, molecular and physiological aspects of sexual determination and differentiation in teleost fish. The group exhibits a large variety of mechanisms of sexual determination. These may be genetic, or depend on environmental conditions such as temperature, pH, and social factors, all of which can influence the proportion of the sexes. Additionally, sex steroids play an important role in the regulation of sexual differentiation. The patterns of gonadal sexual differentiation are diverse, and species may be hermaphroditic or gonochoristic, some of the latter displaying juvenile hermaphroditism. In recent years, several genes involved in the sexual determination and differentiation pathways in vertebrates, particularly in mammals, have also been characterized in teleosts. Conserved as well as diversified functions have been proposed.     

The hapten-carrier effect in teleost fish.

The sea robin (Prionotus evolans), a representative teleost fish, was found to undergo the hapten-carrier effect, suggestive of T-B cell cooperativity, in vivo with dinitrophenyl as the hapten and bovine gamma-globulin or bovine serum albumin as carriers. In contrast to mammalian systems, the secondary anti-hapten response in the sea robin was found to involve exclusively high molecular weight antibody.     

Field studies of hearing in teleost fish

Summary 1. Field measurements of hearing in haddock,Melanogrammus aeglefinus, pollack,Pollachius pollachius and ling,Molva molva, show that they are sensitive to sounds in the frequency range from 30 to 500 Hz, with greatest sensitivity from 100 to 300 Hz.2. At the most sensitive frequencies the thresholds varied between — 15 to — 25 dB relative to a sound pressure of 1µbar.3. In all three species, the thresholds at some frequencies were affected by the level of ambient sea noise. A direct correlation between the thresholds and the spectrum level of sea noise was obtained in haddock and pollack.4. The masking effect of sea noise was confirmed in some experiments on cod,Gadus morbua and haddock, where the background noise level was raised artificially. It was found that the masking of a tone signal was reduced by about 8 dB when the tone and noise were from different directions (85° apart), suggesting that directional discrimination may be well developed in these fish.

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Freilandversuche über das Hörvermögen bei Teleostiern

Kurzfassung Versuche über das Hörvermögen verschiedener mariner Fische — des Schellfischs(Melanogrammus aeglefinus), des Pollacks(Pollachius pollachius), des Kabeljaus(Gadus morhua) und des Lengs(Molva molva) — wurden im Biotop, und zwar in 20 m Tiefe bei Loch Torridon (Schottland) durchgeführt. Die Reaktionen der Fische wurden mit Hilfe einer besonderen Dressurtechnik getestet, wobei dem Tonreiz ein leichter elektrischer Schock folgte; wurde das akustische Signal wahrgenommen, traten Veränderungen im Elektrokardiogramm der Fische auf. Alle 4 Arten wiesen ein ähnliches Hörvermögen auf. Im Niederfrequenzbereich von etwa 60–300 Hz wurde die höchste Empfindlichkeit registriert. Bei höheren Frequenzen stellte sich eine Verminderung der Empfindlichkeit ein; nurMolva molva konnte zuverlässig auf einen Ton von 550 Hz abgerichtet werden. Im Bereich niederer Frequenzen waren alle Fische äußerst empfindlich; es ergaben sich Hinweise, daß die Hörschwellen vom Eigenrauschen des Meeres maskiert wurden. Dies wurde durch Versuche bestätigt, bei denen die Intensität des Eigenrauschens vergrößert wurde, die Mithörschwellen aber in konstantem Abstand zum Störpegel blieben. Ferner wurde festgestellt, daß die Verdeckung reiner Töne wesentlich vermindert wurde, wenn Ton und Störpegel aus verschiedenen Richtungen (im rechten Winkel zueinander) abgestrahlt wurden. Daraus ist zu schließen, daß die Fähigkeit, die Richtung der Schallquellen zu unterscheiden, gut entwickelt sein dürfte.

     

Genome evolution and biodiversity in teleost fish

Teleost fish, which roughly make up half of the extant vertebrate species, exhibit an amazing level of biodiversity affecting their morphology, ecology and behaviour as well as many other aspects of their biology. This huge variability makes fish extremely attractive for the study of many biological questions, particularly of those related to evolution. New insights gained from different teleost species and sequencing projects have recently revealed several peculiar features of fish genomes that might have played a role in fish evolution and speciation. There is now substantial evidence that a round of tetraploidization/rediploidization has taken place during the early evolution of the ray-finned fish lineage, and that hundreds of duplicate pairs generated by this event have been maintained over hundreds of millions of years of evolution. Differential loss or subfunction partitioning of such gene duplicates might have been involved in the generation of fish variability. In contrast to mammalian genomes, teleost genomes also contain multiple families of active transposable elements, which might have played a role in speciation by affecting hybrid sterility and viability. Finally, the amazing diversity of sex determination systems and the plasticity of sex chromosomes observed in teleost might have been involved in both pre- and postmating reproductive isolation. Comparison of data generated by current and future genome projects as well as complementary studies in other species will allow one to approach the molecular and evolutionary mechanisms underlying genome diversity in fish, and will certainly significantly contribute to our understanding of gene evolution and function in humans and other vertebrates.     

Strategic egg allocation in the zebra fish, Danio rerio

Females across a range of taxa have been shown to differentiallyallocate their reproductive resources according to the attractivenessof their mate. Previous studies demonstrated a female preferencefor larger males in the zebra fish but have so far failed touncover a size-mediated difference in male mating success, possiblydue to the effects of male–male competition. By controllingfor male–male competition in the present study, we showthat females strategically allocate their reproductive resources(i.e., eggs) toward larger males. When females were mated sequentiallywith a large and small male, they released a greater numberof eggs to the second male when he was large than when he wassmall. Furthermore, there was also a trend for females to releasea greater proportion of their eggs to the first male when hewas large. Across females, the total number of eggs laid byeach female increased with the average standard length of themale pair, whereas the number of eggs laid to the second malealso increased with his standard length. This study representsone of the first attempts at identifying differential allocationin a resource-free egg scatterer and suggests that female preferencesmay play a greater role in the reproductive success of malesin this species than previously envisaged.     

The interferon system of teleost fish

Interferons (IFNs) are secreted proteins, which induce vertebrate cells into an antiviral state. In mammals, three families of IFNs (type I IFN, type II IFN and IFN-lambda) can be distinguished on the basis of gene structure, protein structure and functional properties. Type I IFNs, which include IFN-alpha and IFN-beta, are encoded by intron lacking genes and have a major role in the first line of defense against viruses. The human IFN-lambdas have similar biological properties as type I IFNs, but are encoded by intron containing genes. Type II IFN is identical to IFN-gamma, which is produced by T helper 1 cells in response to mitogens and antigens and has a key role in adaptive cell mediated immunity. IFNs, which show structural and functional properties similar to mammalian type I IFNs, have recently been cloned from Atlantic salmon, channel catfish, pufferfish, and zebrafish. Teleost fish appear to have at least two type I IFN genes. Phylogenetic sequence analysis shows that the fish type I IFNs form a group separated from the avian type I IFNs and the mammalian IFN-alpha, -beta and -lambda groups. Interestingly, the fish IFNs possess the same exon/intron structure as the IFN-lambdas, but show most sequence similarity to IFN-alpha. Recently, IFN-gamma genes have also been cloned from several fish species and shown to have the same exon/intron structure as mammalian IFN-gamma genes. The antiviral effect of mammalian type I IFN is exerted through binding to the IFN-alpha/beta-receptor, which triggers signal transduction through the JAK-STAT signal transduction pathway resulting in expression of Mx and other antiviral proteins. Putative IFN receptor genes have been identified in pufferfish. Several interferon regulatory factors and members of the JAK-STAT pathway have also been identified in various fish species. Moreover, Mx and several other interferon stimulated genes have been cloned and studied in fish. Furthermore, antiviral activity of Mx protein from Atlantic salmon and Japanese flounder has recently been demonstrated.     

Consequences of hoxb1 duplication in teleost fish

Vertebrate evolution is characterized by gene and genome duplication events. There is strong evidence that a whole-genome duplication occurred in the lineage leading to the teleost fishes. We have focused on the teleost hoxb1 duplicate genes as a paradigm to investigate the consequences of gene duplication. Previous analysis of the duplicated zebrafish hoxb1 genes suggested they have subfunctionalized. The combined expression pattern of the two zebrafish hoxb1 genes recapitulates the expression pattern of the single Hoxb1 gene of tetrapods, possibly due to degenerative changes in complementary cis-regulatory elements of the duplicates. Here we have tested the hypothesis that all teleost duplicates had a similar fate post duplication, by examining hoxb1 genes in medaka and striped bass. Consistent with this theory, we found that the ancestral Hoxb1 expression pattern is subdivided between duplicate genes in a largely similar fashion in zebrafish, medaka, and striped bass. Further, our analysis of hoxb1 genes reveals that sequence changes in cis-regulatory regions may underlie subfunctionalization in all teleosts, although the specific changes vary between species. It was previously shown that zebrafish hoxb1 duplicates have also evolved different functional capacities. We used misexpression to compare the functions of hoxb1 duplicates from zebrafish, medaka and striped bass. Unexpectedly, we found that some biochemical properties, which were paralog specific in zebrafish, are conserved in both duplicates of other species. This work suggests that the fate of duplicate genes varies across the teleost group.     

The role of aquaporin 3 in teleost fish

The aquaporin isoform, AQP3 has now been identified in a number of different teleost fish species, with additional DNA sequence information on AQP3 genes in further fish species available in genome databases. In zebrafish (Danio rerio), the AQP3 gene is present as two duplicate isoforms resulting from a teleostean fish genome-wide duplication. A further splicoform/isoform has also been identified in rainbow trout (Oncorhynchus mykiss). The identification of these AQP3 isoforms in other fish species is consequently explored. The role of AQP3 in physiological/osmoregulatory processes, in various teleost organs is then described. In teleost gill, AQP3 is expressed in 'chloride' cells, and in some species, in other epithelial cell types, where it may have a number of different functions including the prevention of dehydration. In eel esophagus, immunohistochemistry shows that AQP3 is expressed in surface epithelial cells in the anterior esophagus, but in mucus cells within the epithelium of the posterior esophagus. In eel intestine, AQP3 is found in macrophage-like cells and probably plays no part in osmoregulatory processes. In the rectum, as in the posterior esophagus AQP3 is expressed in mucus cells. In eel kidney, AQP3 is expressed in a subset of renal tubules, and localizes to the apical pole of tubule cells. There is no apparent change in the location or protein abundance of renal AQP3 following the acclimation of eels from freshwater to seawater.