Fine structure and metabolism of multiply innervated fast muscle fibres in teleost fish

Summary Both the fast and slow muscle fibres of advanced teleost fish are multiply innervated. The fraction of slow-fibre volume occupied by mitochondria is 31.3%, 25.5% and 24.6%, respectively, for the myotomal muscles of brook trout (Salvelinus fontinalis), crucian carp (Carassius carassius), and plaice (Pleuronectes platessa), respectively. The corresponding figures for the fast muscles of these species are 9.3%, 4.6% and 2.0%, respectively. Cytochrome-oxidase and citrate-synthetase activities in the fast muscles of 9 species of teleost range from 0.20–0.93 moles substrate utilised, g wet weight muscle^-1 min^-1 (at 15° C) or around 4–17% of that of the corresponding slow fibres. Ultrastructural analyses reveal a marked heterogeneity within the fast-fibre population. For example, the fraction of fibres with <1% or >10% mitochondria is 0,4,42% and 36, 12 and 0%, respectively, for trout, carp and plaice. In general, small fibres (<500 m²) have the highest and large fibres (>1,500 m²) the lowest mitochondrial densities. The complexity of mitochondrial cristae is reduced in fast compared to slow fibres.Hexokinase activities range from 0.4–2.5 in slow and from 0.08–0.7 moles, g wet weight^-1 min^-1 in fast muscles, indicating a wide variation in their capacity for aerobic glucose utilisation. Phosphofructokinase activities are 1.2 to 3.6 times higher in fast than slow muscles indicating a greater glycolytic potential. Lactate dehydrogenase activities are not correlated with either the predicted anaerobic scopes for activity or the anoxic tolerances of the species studied. The results indicate a considerable variation in the aerobic capacities and principal fuels supporting activity among the fast muscles of different species. Brook trout and crucian carp are known to recruit fast fibres at low swimming speeds. For these species the aerobic potential of the fast muscle is probably sufficient to meet the energy requirements of slow swimming.     

Early development of the motor and premotor circuitry of a sexually dimorphic vocal pathway in a teleost fish

The plainfin midshipman fish (Porichthys notatus) has a caudal hindbrain vocal motor circuit that has been proposed to share a common embryonic origin with the hindbrain vocal networks of other vertebrates. In midshipman, this vocal circuit includes three groups of neurons: sonic motor, pacemaker, and ventral medullary. Here, transneuronal transport of biocytin or neurobiotin was used to delineate the early ontogeny of the three hindbrain vocal nuclei and their pattern of connectivity. The organization of the vocal nuclei was studied in animals beginning soon after hatching until the nuclei have the adult phenotype at the time fish become free-swimming. There is a clear sequence of events whereby motoneurons establish their connections with the sonic muscle prior to establishing connections with premotor neurons; developmental milestones of the vocal pathway parallel those of the sonic muscle. The results also indicate that sexual differentiation of the vocal motor system in midshipman begins early in development, well before any evidence of sexual maturation. Embryonic males and females differ in the relationship between soma size and body length for the three hindbrain nuclei. Males are also more variable than females in body mass, volume of the sonic motor nucleus, and motoneuron cell size.     

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     

Aromatase activity in hindbrain vocal control region of a teleost fish: divergence amoung males with alternative reproductive tactics

Type I male midshipman fish acoustically court females, whereas type II males do not but instead sneak or satellite spawn to compete with type I males for fertilizations. ''Singing'' type I males diverge from type II males and females in the organization of an expansive hindbrain pacemaker–motoneuron circuit that establishes the physical attributes of vocalizations. Here, levels of aromatase activity were determined in homogenates of brain by measuring the conversion of ³H-androstenedione (AE) to ³H-oestrone (E₁) and ³H-oestradiol (E₂). Levels were highest in the telencephalon–preoptic area and similar for all morphs. Lower levels were in a region including the diencephalon, midbrain and cerebellum, although levels were significantly higher in females compared with type I males. In the vocal hindbrain region, aromatase levels were three- to five-fold higher in type II males and females than in type I males, and in castrated type II males than in castrated type I males. Conversion of testosterone to oestrogen in type II males and females may effectively prevent testosterone-induced maturation of the vocal system that characterizes type I males. Aromatase may thus be a key enzyme regulating the expression of individual-specific brain circuitry and behaviours among members of one sex.     

The effects of lowered temperature on spontaneous eye movements in a teleost fish

A new opto-electronic method has been used to measure spontaneous eye movements in a lightly restrained unanaesthetized marine teleost fish (Parore). The normal scanning pattern of eye movement is similar to that previously described in goldfish. The effects of cooling on eye movements were investigated by 2 degrees C step changes down from ambient temperature (13-14 degrees C). Lowered temperature altered the scanning pattern, decreased saccade velocity, increased mean saccade amplitude and impaired the ability of the fish to hold the eye stationary between saccades. All eye movements stopped at temperatures around 6 degrees C, but could be restored by subsequent warming.     

Early events in myofibrillogenesis and innervation of skeletal,sound-generating muscle in a teleost fish

The plainfin midshipman, Porichthys notatus, generates acoustic communication signals through the rapid contraction of a pair of vocal (sonic) muscles attached to the walls of the swimbladder. Light and electron microscopic methods were used to study two aspects of sonic muscle ontogeny: (1) the development and transformation of myotubes into muscle fibers and (2) innervation, including the formation of sonic neuromuscular junctions and the myelination of sonic motor axons. Sonic motor axons are associated with sonic mesenchyme during its initial migration away from occipital somites. However, myofibrillogenesis, the formation of neuromuscular junctions, and axon myelination do not occur until sonic mesenchyme reaches its final destination (i.e., the swimbladder). A continuum of developing myotubes is present rather than two temporally distinct populations of primary and secondary myotubes as observed for skeletal muscles in mammalian and avian species. Potential reasons for the lack of primary and secondary myotubes are considered, including the functional homogeneity of the sonic motor system and the sonic muscle's unique architecture, namely its direct attachment to the wall of the swim-bladder. © 1993 Wiley-Liss, Inc.     

Sexual dimorphisms in the vocal control system of a teleost fish: morphology of physiologically identified neurons

In one species of vocalizing (sonic) fish, the midshipman (Porichthys notatus), there are two classes of sexually mature males--Types I and II--distinguished by a number of traits including body size, gonad size, and reproductive tactic. The larger Type-I males (unlike Type-II males and females) build nests, guard eggs, and generate several types of vocalizations. Sound production by Type-I males is paralleled by a proportionate increase of 600% in their sonic muscle mass. The motor volley from ventral occipital roots innervating the sonic muscles establishes their contraction rate and, in turn, the fundamental frequency of emitted sounds. Electrical stimulation of the midbrain in every male and female elicited a rhythmic sonic discharge as recorded in the occipital roots; however, the fundamental frequency was slightly, but significantly, higher (20%) in Type-I males. Intracellular recording from identified motoneurons and presumed presynaptic "pacemaker" neurons showed their synaptic and action potentials had the same frequency as that of the nerve volley in every male and female. Reconstructions of physiologically identified motoneurons and pacemaker neurons following intracellular horseradish-peroxidase (HRP) filling showed their somata and dendrites to be 100-300% larger in Type-I males. These data unambiguously show that the size of a target muscle is correlated with the size of both the respective motoneurons and their presynaptic afferent neurons. As discussed, this implies that the dramatic increase in neuron size in the sonic motor system of Type-I males is causally dependent upon expansion of the sonic muscle. It is further likely that the more modest sex difference in the rhythmic central discharge is established by the intrinsic membrane properties of sonic neurons. These results also corroborate, at a number of behavioral, morphological, and neurophysiological levels, that the sonic motor system of "sneak spawning" Type-II males is similar to that of females. Thus, unlike the vocalizing Type-I males, sexual differentiation of the reproductive system in Type-II males is not linked to concomitant changes in the neurophysiological and morphological features of the sonic motor circuit.     

The effects of cortisol administration on intermediary metabolism in teleost fish

• 1.1. This Mini Review deals with the metabolic consequences of administration of the hormone cortisol on proteins, carbohydrates and lipids in teleost fish.
• 2.2. Many effects of administered cortisol on intermediary metabolism in fish have been reported: inhibition of protein synthesis and/or catabolism of tissue protein which result in higher availability of amino acids, induction of gluconeogenesis and of liver aminotransferases, hyperglycemia and glycogen deposition in the liver, induction of gluconeogenic enzymes, liberation of free fatty acids and deposition of liver lipids. All these effects are observed to a greater or less extent. However, the experimental data show that some effects are inconsistent.
• 3.3. Some explanations for the inconsistencies are given.

     

The structure of the coeliac ganglion of a teleost fish Myoxocephalus scorpius

Summary In order to compare the structure of a teleost sympathetic ganglion with those of other vertebrates, light, fluorescence histochemical and electron microscopy were carried out on the coeliac ganglion of the scorpion fish, Myoxocephalus scorpius. In common with studies on other vertebrates, fluorescence histochemistry distinguished two cell types: a) principal neurones which exhibited low levels of specific catecholamine fluorescence and comprise the majority of neurones in the ganglia, and b) smaller intensely fluorescent cells, some of which had processes tens of micrometers long.With the electron microscope, the principal cells were seen to make axodendritic and axosomatic synapses with axons containing mainly 30 nm agranular vesicles at the synaptic site while in other vertebrates usually only one or other synaptic association is present.Both the somata and the processes of intensely fluorescent cells contain 300–600 nm diameter vesicles many of which have electron dense cores. These cells are also innervated by axons containing 30 nm agranular vesicles.     

The fine structure of calcified Mandl's corpuscles in teleost fish scales

Calcified Mandl's corpuscles present in the internal layer (or fibrillary plate) of the teleost fish scale were studied by transmission and scanning electron microscopy for a better understanding of this special type of mineralization process. The corpuscles show a great variability in their structure, form and surface features depending on the arrangement of the collagen fibrils in the internal layer of the different fish species studied, on the localization of the corpuscles in the scale and on the technical treatment to which the scale is subjected.     

Blackcaps Sylvia atricapilla stopping over at the desert edge; inter- and intra-sexual differences in spring and autumn migration

Spring and autumn Palaearctic-African migration patterns of Blackcaps Sylvia atricapilla during stopover at Elat, Israel, showed that males appeared significantly earlier than females during spring but not during autumn migration, suggesting that in males there is a stronger drive to reaching breeding territories early. The difference in mean appearance dates between sexes in spring tended to be greatest in years when the males appeared earliest. Longer spread of passage (the dates between which the central 50% of individuals were captured) for each sex in spring was found in years with an early mean passage datebut was significant only for females. These observations suggest that the timing of Blackcap migration is governed not only by endogenous factors but also by exogenous factors, and when the environmental conditions are unfavourable, the differences in passage dates between sexes decrease and the passage lengths shorten. The early individuals (both males and females) that stopped over at Elat in spring were those with relatively small body size (as indicated by relatively short wings) and relatively large fat reserves and in good body condition (as indicated from fat score and body mass/wing-length ratio). No differences in body size between early and late transients were detected during the autumn migration, but late birds of both sexes carried larger fat reserves. These phenomena may be explained either by leap-frog migration or by differential fitness among wintering males and females or both, with only the fittest Blackcaps being capable of an early departure. These individuals probably face much less intensive intra- and interspecific competition with residents and other transients in stopover sites than do later transients.     

真骨鱼类DMRT基因家族的连锁结构及其系统发生

利用已经报道的多个物种基因组序列资源,我们通过比较真骨鱼类（Teleost fish）共有的DMRT1-5基因所在染色体位置的基因组结构特征,从基因组水平证明了真骨鱼类和四足动物的相应DMRT基因的直系同源关系,揭示了DMRT4和DMRT5是因为真骨鱼类和四足动物的共同祖先发生了染色体重复事件而由同一基因分歧演变形成的。同时通过基因连锁分析,探测到包括SNF2和elavL家族基因在内的多个可能与DMRT基因功能密切相关的基因,为进一步研究DMRT基因和它们之间可能存在的调控机制提供了新的线索。     

Temperature adaptation and the contractile properties of live muscle fibres from teleost fish

Summary The contractile properties of swimming muscles have been investigated in marine teleosts from Antarctic (Trematomus lepidorhinus, Pseudochaenichthys georgianus), temperate (Pollachius virens, Limanda limanda, Agonis cataphractus, Callionymus lyra), and tropical (Abudefduf abdominalis, Thalassoma duperreyi) latitudes. Small bundles of fast twitch fibres were isolated from anterior myotomes and/or the pectoral fin adductor profundis muscle (m. add. p). Live fibre preparations were viable for several days at in vivo temperatures, but became progressively inexcitable at higher or lower temperatures. The stimulation frequency required to produce fused isometric tetani increased from 50 Hz in Antarctic species at 0°C to around 400 Hz in tropical species at 25°C. Maximum isometric tension (P_o) was produced at the normal body temperature (NBT) of each species (Antarctic, 0–2°C; North Sea and Atlantic, 8–10°C; Indo-West Pacific, 23–25°C). P₀ values at physiological temperatures (200–300 kN·m^–2) were similar for Antarctic, temperate, and tropical species. A temperature induced tension hysteresis was observed in muscle fibres from some species. Exposure to <0°C in Antarctic and <2°C in temperate fish resulted in the temporary depression of tension over the whole experimental range, an effect reversed by incubation at higher temperatures. At normal body temperatures the half-times for activation and relaxation of twitch and tetanic tension increased in the order Antarctic>temperate>tropical species. Relaxation was generally much slower at temperatures <10°C in fibres from tropical than temperate fish. Q₁₀ values for these parameters at NBTs were 1.3 2.1 for tropical species, 1.7–2.6 for temperate species, and 1.6–3.5 for Antarctic species. The forcevelocity (P-V) relationship was studied in selected species using iso-velocity releases and the data below 0.8 P₀ iteratively fitted to Hill's equation. The P-V relation at NBT was found to be significantly less curved in Antarctic than temperate species. The unloaded contraction velocity (V_max) of fibres was positively correlated with NBT increasing from about 1 muscle fibre length·s^–;1 in an Antarctic fish (Trematomus lepidorhinus) at 1°C to around 16 muscle fibre lengths·s^–1 in a tropical species (Thalassoma duperreyi) at 24°C. It is concluded that although muscle contraction in Antarctic fish shows adaptations for low temperature function, the degree of compensation achieved in shortening speed and twitch kinetics is relatively modest.Abbreviations ET environmental temperature - m. add. p major adductor profundis - m. add. s. major adductor superficialis - NBT normal body temperature - P ₀ maximum isometric tension - P-V force velocity - SR sarcoplasmic reticulum - T 1/2 a half activation time - T 1/2 r half relaxation time - V _max unloaded contraction     

Opposite effects of nonapeptide antagonists on paternal behavior in the teleost fish Amphiprion ocellaris

The nonapeptides isotocin (IT) and arginine vasotocin (AVT), along with their mammalian homologs oxytocin and arginine vasopressin, are well known regulators of social behaviors across vertebrate taxa. However, little is known about their involvement in paternal care. Here, we measured the effect of an IT and an AVT V1a receptor antagonist on paternal behaviors in the primarily paternal teleost Amphiprion ocellaris. We also measured the effect of the IT receptor antagonist on aggression in dyadic contests between two non-reproductive fish to assess specificity of the effect on paternal behaviors. Individual differences in levels of paternal behaviors (nips, fanning the eggs, and proportion of the time in the nest) were consistent across spawning cycles when no treatments were administered. The IT receptor antagonist severely reduced paternal behaviors but had no effect on aggression, whereas the AVT V1a receptor antagonist increased paternal behaviors. These results support the idea that IT signaling is crucial for the expression of paternal behavior in A. ocellaris. Based on a previous study showing that the AVT V1a antagonist decreases aggression in dyadic contests, we hypothesize that the antagonist enhances paternal behavior indirectly by reducing vigilance and aggression, thereby alleviating effort directed towards other competing behaviors and allowing for the increased expression of paternal behaviors.     

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.     

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.     

Sexual dimorphism in a trophically polymorphic cichlid fish?

Sexual dimorphism in ecologically relevant traits is ubiquitous in animals. However, other types of intraspecific phenotypic divergence, such as trophic polymorphism, are less common. Because linkage to sex should often lead to balancing selection, understanding the association between sex and phenotypic divergence could help explain why particular species show high morphological variability. To determine if sexual dimorphism could be helping to maintain ecomorphological variation in a classic case of intraspecific trophic polymorphism, we examined the association between sex and morphological divergence in the cichlid Herichthys minckleyi. Although H. minckleyi with enlarged molariform teeth on their pharyngeal jaws have been reported to more commonly be male, we did not find an association between sex and pharyngeal morphotype. Sex was associated with divergence in body size (as measured through standard length). But, sex was not associated with any of the other trophic traits examined. However, pharyngeal morphotype did show an association with gut length, gape, and tooth number. Sexual dimorphism is not playing a central role in enhancing trophic diversity within H. minckleyi. J. Morphol. 276:1448–1454, 2015. © 2015 Wiley Periodicals, Inc.