Internal fertilization in Lepidogalaxias salamandroides Mees (Pisces: Lepidogalaxiidae)

The gonads of Lepidogalaxias salamandroides are structurally distinctive. A duct, the surface of which is ciliated, is located on the ventral surface of each ovary and may be a modification of the ovarian tunica. The testes are small and the majority of the testicular structure functions as a sperm storage area. Secondary requisite sex characters are present in the male and the function of a modified scale sheath in copulation is unique among teleosts. Fertilization is internal and a viscous mucus mass secreted during copulation may serve as a copulatory plug. It is postulated that internal fertilization within this species has arisen as a response to sperm competition.     

Internal fertilization in Lepidogalaxias salamandroides Mees (Pisces: Lepidogalaxiidae)

The gonads of Lepidogalaxias salamandroides are structurally distinctive. A duct, the surface of which is ciliated, is located on the ventral surface of each ovary and may be a modification of the ovarian tunica. The testes are small and the majority of the testicular structure functions as a sperm storage area. Secondary requisite sex characters are present in the male and the function of a modified scale sheath in copulation is unique among teleosts. Fertilization is internal and a viscous mucus mass secreted during copulation may serve as a copulatory plug. It is postulated that internal fertilization within this species has arisen as a response to sperm competition.     

Seasonality,aestivation and the life history of the salamanderfish Lepidogalaxias salamandroides (Pisces: Lepidogalaxiidae)

Synopsis Changes in the age/length structure of Lepidogalaxias salamandroides populations in temporary waters of south-western Australia were monitored over a 51 month period by regular field sampling. Each year the study area experienced a summer drought of approximately five months duration. During the drought period Lepidogalaxias burrows into the mud and aestivates and substantial mortality occurs during this period. Body lipid reserves decrease during this period suggesting that they are the main energy source used during aestivation. The amount of lipid remaining after aestivation appears to be important in determining when female fish reproduce. Males die after reproduction and achieve a maximum age of only about 12 months. Some females also reproduce and die at this age while others defer reproduction for another year. Fecundity is much higher in these older, larger fish: they must however, survive two drought periods before they reproduce. The evolution of the life history style shown by Lepidogalaxias salamandroides is discussed with respect to the well defined seasonality of the region and it is suggested that selection for reproduction at an early age is balanced by the constraints of offspring survival during the aestivation period.     

The effect of starvation on oxygen consumption and nitrogen excretion inLepidogalaxias salamandroides (Mees)

Summary Measurement of the rates of oxygen consumption and nitrogen excretion in fed and starvedLepidogalaxias salamandroides showed that starvation has no effect on these basal metabolic parameters. A low metabolic rate (50 ml O₂ kg^–1 h^–1) is suggested to account for the lack of such an effect.A high proportion of the total waste nitrogen is excreted as urea and the magnitude of this fraction is also unaffected by starvation. The importance of urea synthesis is consistent with this species' ability to aestivate.The results are discussed with reference to current concepts in fish aestivation.     

Ultrastructure of the spermatozoon of Lepidogalaxias salamandroides and its phylogenetic significance

The spermatozoon of Lepidogalaxias salamandroides possesses an acrosome (putative), one or two perforatoria (putative) but no nine-triplet centrioles. Two elongated mitochondria (12 μm long) are situated in parallel between the nucleus (20 μm long) and the axoneme (53 μm long). The above features are unique among other teleosts with internal fertilization. The presence of an “acrosome” in this primitive teleost supports the hypothesis that this structure has been secondarily lost in teleosts during evolution. The uncertainty of phylogenetic placement of this fish is reflected by its unique sperm ultrastructure.     

Molecular phylogenetics and biogeography of galaxiid fishes (Osteichthyes: Galaxiidae): dispersal,vicariance, and the position of Lepidogalaxias salamandroides

The galaxiid fishes exhibit a gondwanan distribution. We use mitochondrial DNA sequences to test conflicting vicariant and dispersal biogeographic hypotheses regarding the Southern Hemisphere range of this freshwater group. Although phylogenetic resolution of cytochrome b and 16S rRNA sequences is largely limited to more recent divergences, our data indicate that the radiation can be interpreted as several relatively recent dispersal events superimposed on an ancient gondwanan radiation. Genetic relationships contradict the findings of recent morphological analyses of galaxioid fishes. In particular, we examine several hypotheses regarding phylogenetic placement of the enigmatic Lepidogalaxias. Although most workers consider Lepidogalaxias to be an unusual scaled member of the Southern Hemisphere galaxioids, it has also been suggested that this species is related to the Northern Hemisphere esocoids. Our data strongly suggest that this species is not a galaxiid, and the alternative hypothesized esocoid relationship cannot be rejected. The species-rich genus Galaxias is shown to be polyphyletic and the generic taxonomy of the Galaxiinae is reassessed in the light of phylogenetic relationships. Juvenile saltwater-tolerance is phylogenetically distributed throughout the Galaxiinae, and the loss of this migratory phase may be a major cause of speciation.     

Age Composition, Growth and Reproductive Biology of the Salamanderfish Lepidogalaxias salamandroides: A Re-examination

This study has determined the age and size compositions, growth rate and reproductive biology of Lepidogalaxias salamandroides using data for fish of known sex and age and the monthly trends exhibited by various gonadal variables, including the sizes and stages of the oocytes. The results resolve conflicting conclusions drawn by other workers concerning certain aspects of the biology of this freshwater species and expands our knowledge of this teleost. Our results are based on data derived from samples collected from small, ephemeral acidic pools in south-western Australia in 22 consecutive months. Although ca. 78% of the fish caught belonged to the 0+ age class, substantial numbers of the 1+ and 2+ age classes and some 3+ and 4+ fish were caught. Spawning occurs between late May and late August, with peak activity in late July and early August. During the first year of life, growth is initially rapid, but then ceases in the weeks immediately prior to and during the period when the habitat becomes dry and fish aestivate, before recommencing in autumn as the pools again become filled with water. The growth coefficient (K) in the von Bertalanffy growth equation was lower for females (0.63) than males (1.28), reflecting the greater growth undergone by females after the first year of life. Maturity was attained by ca. 28% of the females and ca. 26% of the males that reached the end of their first year of life and by all fish that reached the end of subsequent years of life. The L₅₀s for females and males at first maturity were 43.2 and 38.6mm TL, respectively. The mean fecundity was only 82.4, reflecting a combination of a small body size and a relatively large egg (diameter=1.8mm). Lepidogalaxias salamandroides is a multiple spawner, which increases the chances of some eggs and newly-hatched embryos encountering a period of favourable environmental conditions during the spawning period, which is characterised by bouts of heavy rainfall. The ratio of females to males was essentially parity in the 0+ and 1+ age classes and in all age classes collectively. When testes commence maturing for the first time, the anal fin of males starts to become modified to form a structure that facilitates the transfer of sperm to the female, and it remains modified throughout the rest of life.     

Pituitary cytology of the teleost fish Tilapia mossambica (Peters)

In the pituitary of Tilapia mossambica, eight cell types were identified on the basis of their staining reactions. the RPD consists of erythrosinophils and PbH positive cells. PbH cells border the NH and give amphipilic reaction to tri- and tetrachrome dyes and Halmi's stain. Erythrosinophils are also stained with acid fuchsin and orange G. The PPD is made up of acidophils and cyanophils. The acidophils are stained with orange G, acid fuchsin and erythrosin. These cells form a palisade zone between the neurohypophysis and the cyanophils. The cyanophils are AB, AF, ATh, PAS and aniline blue positive. They include both thyrotrophs and gonadotrophs and cannot be differentiated. The gonadotrophs may be those which are degranulated and vacuolated in the breeding season. The PI is formed of PAS- and PbH positive cells which lack any definite pattern of arrangement. Apart from the chromophils, scattered chromophobes were seen throughout the adenohypophysis. Occasionally, cells resembling the cyanophils of PPD were noticed in the RPD and PI also.     

Proteinase inhibitor(s) in seminal plasma of teleost fish

Anti-proteinase activity has been found in seminal plasma of three teleost fish: rainbow trout, whitefish and yellow perch. The activity was effective against trypsin (bovine and cod) and acrosin (boar), but not bovine chymotrypsin. Inhibitor activity against fish trypsin was nine- to ten-fold higher than against bovine trypsin. All anti-proteinase activity remained in the retentate after filtration through molecular filter with 30 kDa cut-off membrane and eluted from a column of Sephacryl S-200 HR at the volume characteristic for molecular weight of approximately 90 kDa (data for rainbow trout). Inhibitor(s) had low thermal stability (50–60% activity remained after 15 min at 60° C). The discovery of proteinase inhibitor(s) in the seminal plasma of teleosts raised the question of the regulatory function of this protein in the systematic group of fishes having anacrosomal spermatozoa.     

Suppression of osteoclastic activities by calcitonin in the scales of goldfish (freshwater teleost) and nibbler fish (seawater teleost)

Using a tartrate-resistant acid phosphatase (TRACP) activity, the effects of calcitonin (CT) and estradiol-17beta(E(2)) on osteoclastic activities in cultured scales of goldfish (freshwater fish) and nibbler fish (seawater fish) were examined. In mature male and female goldfish, scales were collected and incubated in Earle's minimun essential medium (MEM) supplemented with either CT (100 ng/ml) or E(2) (100 ng/ml). In both sexes, CT suppressed TRACP activities in the scales, whereas E(2) increased them. When CT (100 ng/ml) and E(2) (100 ng/ml) were added simultaneously to MEM, TRACP activities in the scales did not change as compared with the control. Similar results were obtained with the scales of female nibbler fish. In goldfish, furthermore, the activation of scale TRACP by E(2) was suppressed, depending on CT concentrations (100 pg/ml to 1 microg/ml). In fish reproduction, this function of CT may be useful to protect scales from excess degradation of calcium at vitellogenesis.     

Inner retinal photoreceptors (IRPs) in mammals and teleost fish.

Research over the past decade has provided overwhelming evidence that photoreception in the vertebrate eye is not confined to the rods and cones. The discovery of non-rod, non-cone ocular photoreceptors in mammals and fish arose from quite different lines of investigation. In transgenic mice entirely lacking functional rod and cone photoreceptors a range of responses to light, including the regulation of the circadian system and a pupillary light reflex, are preserved. Electrophysiological and imaging approaches were then able to characterise a coupled plexus of directly light sensitive ganglion cells. Most recently action spectroscopy has shown that a novel 'blue-light' sensitive photopigment based upon opsin/vitamin A (OP480) mediates these responses to light. Several candidate genes have emerged for OP480, with melanopsin being by far the strongest. A definitive link, however, between this gene and OP480 has still to be established. In contrast to the mammals, the discovery of inner retinal photoreceptors (IRPs) in fish started with the discovery of a new gene family (VA opsin). The teleost VA opsins form functional photopigments and are expressed in several different types of inner retinal neuron, including retinal horizontal cells. Recent studies have investigated the electrical properties of these photosensitive neurones, but their light-sensing role remains a matter of speculation. Thus the study of IRP is developing along quite separate lines. In the mammals the research is directed towards a molecular identification of the photopigment (OP480) and its cascade, whilst in fish the major effort is directed towards identifying a role for these novel photoreceptors using physiological approaches. The discovery of IRPs in the vertebrates tells us that despite 150 years of research, we still have much to learn about how the eye processes light.     

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.

     

Ovarian germline stem cells in the teleost fish, medaka (Oryzias latipes)

In the mammalian testis germline stem cells keep producing many sperms, while there is no direct evidence for the presence of germline stem cells in the ovary. It is widely accepted in mammals that the mature oocytes are supplied from a pool of primordial follicles in the adult ovary. In other vertebrates, such as fish, however, there has been no investigation on the mechanism underlying the high egg-producing ability. In this review, we introduce the recently identified ovarian germline stem cells and the surrounding unique structure in teleost fish, medaka (Oryzias latipes) [Nakamura S et al. Science. 2010; 328: 1561-1563]. We also discuss about the expression and function of sox9 that characterizes this unique structure.     

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.     

Photokinesis in the teleost fish Danio malabaricus

Summary Photokinesis as shown by the rapidly moving fish Danio malabaricus was examined in two experiments.In Experiment I, which involved sequences of short periods of light and darkness, the Ss for the most part showed a positive relationship between light intensity and level of activity. This reaction included a well differentiated response to abrupt intensity change, the effect of the transition from darkness to light being marked. Level of activity in both light and dark periods tended to fall; after a certain point, however, it rose again in the light but continued to fall in the darkness.In Experiment II, successive increases in the total area of lighted space available were matched by increases in the total length of time spent there by the Ss. The overall reaction, however, was initially photonegative and became more so as the experiment progressed. The range of most frequent periods of time spent in the lighted area increased gradually, while the length of entries into the shaded area gradually decreased, in the course of the experiment. But for a lighted area the Ss' length of entry was shorter than for the corresponding dark area, the choice of period was more precise, there were fewer longer periods, and the range was less. In the last condition, the Ss divided their time approximately equally between the lighted 7/8 and the shaded 1/8 of the area available. The number of times the Ss crossed from one area to the other almost doubled during the experiment.The author wishes to express his gratitude to Prof. G. Thinès for his help and encouragement. He was supported by a research grant from N. A. T. O., administered through the Science Research Council, London. The findings reported formed part of a study submitted as a doctoral dissertation at the Université de Louvain. The raw data is tabulated in this study and may be consulted at the Institut de Psychologie et des Sciences Pédagogiques. Address after 1 October: Department of Psychology, Bryn Mawr College, Bryn Mawr, Pennsylvania, U.S.A.     

Ultrastructure of the spermatozoon of the teleost fish Acanthopagrus schlegeli (Perciformes: Sparidae)

Ultrastructurally the spermatozoon of Acanthopagrus schlegeli (Sparidae) has a spherical, homogeneously electron-dense nucleus with a deep axial nuclear fossa, and an unusual notch, shaped like a bowtie, in the nuclear region. The short midpiece contains four spherical mitochondria and encircles the basal body of the flagellum. It is concluded that the spermatozoon is of a primitive type, although it is characterized by several unique features which may provide useful systematic characters. © 1993 Wiley-Liss, Inc.     

Different aspects of tubulin polymerization in spermatids of cyprinodontidae (fish,teleost)

Our study concerns 10 genera and 26 species of cyprinodontid fish. In the cytoplasm of spermatids tubulin polymerizes in various forms according to species. We have demonstrated the presence of classic microtubules with a diameter of 24 nm and also of tubules of smaller diameter (15 run) and greater diameter (30 to 50 nm). Microtubules are very numerous in the cytoplasm of certain species. They may be arranged without any order or form bundles which may contain several hundred parallel elements. They never form a manchette. In two species (Aplocheilichthys normani and Epiplatys fasciolatus) only spermatids that degenerate show this peculiarity. The microtubules present two kinds of decorations. The first type are small elements composed of MAP which enable two or more microtubules to link up. The second type are curved tubulin elements that give the microtubule that bear them the appearance of an incomplete doublet. Doublets and triplets may also be formed. Cyprinodontidae spermatocytes and spermatids probably synthesize a very large quantity of tubulin which polymerizes in certain species.     

Ultrastructure of granulocytes of teleost fish (Salmoniformes, Cypriniformes, Perciformes)

Analysis of data on ultrastructure of granulocytes of freshwater and marine bony fish of orders Salmoniformes, Cypriniformes, and Perciformes showed that in all studied species there were revealed two types of granulocytes-neutrophils and eosinophils. The exception was the bluefish Pomatomus saltatrix L. whose pronephros hemopoietic tissue was found to contain one type of the granulocyte line-neutrophils. The identification parameters of granular leukocytes are specific granules filling the cytoplasm. The main form of specific granules in neutrophils of bony fish of various phylogenetic groups is an elongated granule with different distribution of fibrils or a granule that has fibrils-formed crystalloid. Eosinophil granules are mainly of large, electron-dense, homogenous form.