Dermal morphogenesis controls lateral line patterning during postembryonic development of teleost fish

The lateral line system displays highly divergent patterns in adult teleost fish. The mechanisms underlying this variability are poorly understood. Here, we demonstrate that the lateral line mechanoreceptor, the neuromast, gives rise to a series of accessory neuromasts by a serial budding process during postembryonic development in zebrafish. We also show that accessory neuromast formation is highly correlated to the development of underlying dermal structures such as bones and scales. Abnormalities in opercular bone morphogenesis, in endothelin 1-knockdown embryos, are accompanied by stereotypic errors in neuromast budding and positioning, further demonstrating the tight correlation between the patterning of neuromasts and of the underlying dermal bones. In medaka, where scales form between peridermis and opercular bones, the lateral line displays a scale-specific pattern which is never observed in zebrafish. These results strongly suggest a control of postembryonic neuromast patterns by underlying dermal structures. This dermal control may explain some aspects of the evolution of lateral line patterns.     

VISION AND SENSORY PHYSIOLOGY The lateral line systems of three deep-sea fish

The distribution and ultrastructure of the lateral line systems in three taxonomically dispersed deep-sea fish are described: Poromitra capito, Melanonus zugmayeri and Phrynichthys wedli. They are meso- to bathpelagic and are thought to feed on small crustaceans and fish. All possess highly developed lateral line systems, a feature associated with life in the deep sea. Poromitra capito and M. zugmayeri exhibit widened head canals which are connected to the outside by large pores and which contain around 60 large neuromasts. Each neuromast consists of a cupula, shield-shaped mantle and a sensory plate containing hundreds to thousands of hair cells. Direction of sensitivity is in the long axis of the canal (perpendicular to the long axis of the mantle). Depending on their position on the sensory plate, the hair cells have different morphologies. They fall into three basic classes which, from comparison with past work, may be tuned to different frequencies. Alternatively, the various hair cell morphologies could be interpreted as being members of a developmental or growth sequence. Phrynichthys wedli has no canal organs, these being replaced secondarily by many superficial neuromasts placed on prominent papillae in rows which cover much of the 'head' and body. Direction of sensitivity is along the axis of the neuromast row. An extreme proliferation of superficial neuromasts are also found on the heads of P. capito and M. zugmayeri and these are of a type not described before. They consist of stitches, raised on papillae in M. zugmayeri and several mm long in P. capito , in which continuous lines of hair cells, two to three cells wide, are embedded. Direction of sensitivity is perpendicular to the long axis of the stitch. Based on the structure and direction of sensitivity, possible functional implications of all the neuromast types described are compared and discussed.     

Effects of development and altered gravity conditions on cytochrome oxidase activity in a vestibular nucleus of the larval teleost brain: A quantitative electronmicroscopical study

The mitochondrial enzyme, cytochrome oxidase, was localized cytochemically in the nucleus magnocellularis, a primary relay nucleus of vestibular information within the area octavolateralis in the fish brain. Larvae of the cichlid fish Oreochromis mossambicus were analyzed at different developmental stages (4, 10, and 35 days posthatching) and after long-term exposure (8 days) to increased gravity (2–4 g). Quantification of highly reactive, moderately reactive, and nonreactive mitochondria reveals differences in the cytochrome oxidase activity of various cellular structures, for example, perikarya of neurons, presynaptic terminals, and myelinated and nonmyelinated cell profiles. Cytochrome oxidase activity in the mitochondria of neuronal perikarya increases during development which parallels the differentiation of the area octavolateralis. This possibly reflects the increasing energy demand during maturation and innervation of the magnocellular nucleus. Hyper-g-exposure of the larvae for 8 days (centrifuge) caused a further augmentation of cytochrome oxidase activity in the perikarya within the nucleus magnocellularis. This may reflect an increased oxidative metabolism resulting from the need for compensation of altered inputs from gravity-sensitive epithelia in the inner ear. Another possibility is that acceleration within a centrifuge causes physiological stress for the animals and, therefore, influences the cytochrome oxidase activity in neurons. © 1993 John Wiley & Sons, Inc.     

Organization of the superficial neuromast system in goldfish, Carassius auratus

Distribution, morphology, and orientation of superficial neuromasts and polarization of the hair cells within superficial neuromasts of the goldfish (Carassius auratus) were examined using fluorescence labeling and scanning electron microscopy. On each body side, goldfish have 1,800-2,000 superficial neuromasts distributed across the head, trunk and tail fin. Each superficial neuromast had about 14-32 hair cells that were arranged in the sensory epithelium with the axis of best sensitivity aligned perpendicular to the long axis of the neuromast. Hair cell polarization was rostro-caudal in most superficial neuromasts on trunk scales (with the exception of those on the lateral line scales), or on the tail fin. On lateral line scales, the most frequent hair cell polarization was dorso-ventral in 45% and rostro-caudal in 20% of the superficial neuromasts. On individual trunk scales, superficial neuromasts were organized in rows which in most scales showed similar orientations with angle deviations smaller than 45 degrees . In about 16% of all trunk scales, groups of superficial neuromasts in the dorsal and ventral half of the scale were oriented orthogonal to each other. On the head, most superficial neuromasts were arranged in rows or groups of similar orientation with angle deviations smaller than 45 degrees . Neighboring groups of superficial neuromasts could differ with respect to their orientation. The most frequent hair cell polarization was dorso-ventral in front of the eyes and on the ventral mandible and rostro-caudal below the eye and on the operculum.     

Comparison of the lateral line and ampullary systems of two species of shovelnose ray

The anatomical characteristics of the mechanoreceptive lateral line system and electrosensory ampullae of Lorenzini of Rhinobatos typus and Aptychotrema rostrata are compared. The spatial distribution of somatic pores of both sensory systems is quite similar, as lateral line canals are bordered by electrosensory pore fields. Lateral line canals form a sub-epidermal, bilaterally symmetrical net on the dorsal and ventral surfaces; canals contain a nearly continuous row of sensory neuromasts along their length and are either non-pored or pored. Pored canals are connected to the surface through a single terminal pore or additionally possess numerous tubules along their length. On the dorsal surface of R. typus, all canals of the lateral line occur in the same locations as those of A. rostrata. Tubules branching off the lateral line canals of R. typus are ramified, which contrasts with the straight tubules of A. rostrata. The ventral prenasal lateral line canals of R. typus are pored and possess branched tubules in contrast to the non-pored straight canals in A. rostrata. Pores of the ampullae of Lorenzini are restricted to the cephalic region of the disk, extending only slightly onto the pectoral fins in both species. Ampullary canals penetrate subdermally and are detached from the dermis. Ampullae occur clustered together, and can be surrounded by capsules of connective tissue. We divided the somatic pores of the ampullae of Lorenzini of R. typus into 12 pore fields (10 in A. rostrata), corresponding to innervation and cluster formation. The total number of ampullary pores found on the ventral skin surface of R. typus is approximately six times higher (four times higher in A. rostrata) than dorsally. Pores are concentrated around the mouth, in the abdominal area between the gills and along the rostral cartilage. The ampullae of both species of shovelnose ray are multi-alveolate macroampullae, sensu Andres and von Düring (1988). Both the pore patterns and the distribution of the ampullary clusters in R. typus differ from A. rostrata, although a basic pore distribution pattern is conserved.     

Capillary distribution and metabolic histochemistry of the lateral propulsive musculature of pelagic teleost fish

Metabolic and vascular adaptation of teleost lateral propulsive musculature to an active mode of life was investigated in four pelagic teleosts (mackerel, yellowtail scad, pilchard and Australian salmon). Histochemical profiles and capillarisation data of the red and white muscle were compared to those of less active demersal species. Pelagic white muscle stained positively for the aerobic enzymes succinate dehydrogenase and NADH diaphorase, and had both subsarcolemmal and intermyofibrillar mitochondria which corresponded to the loci of the histochemical stain. Subsarcolemmal mitochondria tended to be localised close to capillaries. In contrast, white muscle from demersal species was unstained for the same enzymes and was devoid of mitochondria. Red muscle of all species had abundant mitochondria and stained intensely for aerobic enzymes. Capillarisation was quantified by determining the percentage of fibres surrounded by a given number of peripheral capillaries, mean fibre diameter, mean number of peripheral capillaries, capillary: fibre ratio and sharing factor where appropriate. Red muscle of mackerel, Australian salmon, pilchard and scad are better vascularised than red muscle of the flathead having 153, 200, 242, 291 and 309 microns 2 of cross-sectional fibre area per peripheral capillary, respectively. White muscle of mackerel, pilchard and scad are better vascularised than white muscle of the Australian salmon and flathead having 2040, 3367, 4992, 9893 and 10,469 microns 2 of cross-sectional fibre area per peripheral capillary, respectively. Red muscle of Australian salmon had distinct regional variation. Deep red muscle was found to be more highly vascularised (4.2 peripheral capillaries per muscle fibre) than lateral red muscle (1.9 peripheral capillaries per muscle fibre). Red muscle of the other species was less heterogeneous. White muscle capillarisation was slightly variable in all species. It is concluded that the white muscle of the pelagic species studied is functionally and structurally adapted for sustained aerobic activity with relatively abundant mitochondria being preferentially situated close to the source of gas and metabolite exchange.     

Distant wave-mediated interactions in early embryonic development of the loachMisgurnus fossilis L.

Groups of loach (Misgurnus fossilis L.) embryos of different ages were kept in different quartz cuvettes for 20–24 h so that only optic contact between the groups was, possible. Subsequent observations showed that parameters of their development deviated from those in the control groups. Wave-mediated biocorrection proved to have both positive and negative effects, depending on the developmental stages of the interacting groups. Changes in spectral characteristics and polarization of biological radiation affected the results of the experiments. Various developmental abnormalities, caused by distant wave-mediated interactions of embryos and specific to each combination of developmental stages and conditions of optic communication are described.     

Sex-change and gonadal steroids in sequentially-hermaphroditic teleost fish

Sex-change is an intriguing phenomenon that is common among certain groups of teleost fishes. The process itself has a number of independent origins, although in each case it is initiated and (or) regulated by gonadal steroids. Despite the commercial importance of sex-change technology to fish culturists, our understanding of the relationship between steroids and sex-change is, at best, rudimentary. In this paper I review the current state of knowledge concerning (a) which steroids are involved, (b) how such steroids mediate sex-change, and (c) how steroidogenesis is regulated during gonadal transition. I conclude that the steroidal endocrinology of sex-change is multifarious and species specific – a result which challenges the relative stability of vertebrate endocrine axes, but one which probably reflects the independent evolution of this adaptation.     

Cephalic lateral line systems in the Far Eastern species of the genus Phoxinus (Cyprinidae)

The cephalic lateral line systems of seven Far Eastern Phoxinus species (P. phoxinus, P. kumgangensis, P. semotilus, P. lagowskii, P. oxycephalus, P. perenurus, and P. czekanowskii) were investigated. In this genus, the infraorbital canal is not connected with either the supraorbital canal or the preoperculomandibular canal. Phoxinus phoxinus is unique for having an underdeveloped condition, such as canal formation or remaining as uncovered. A unified supraorbital canal was observed in all species, but the infraorbital canal of both P. perenurus and P. czekanowskii was not unified into a single canal throughout their development. Unification between both sides of the supratemporal canal occurred in larger individuals of P. lagowskii, P. oxycephalus, and P. czekanowskii. The preoperculomandibular canal of P. kumgangensis, large P. lagowskii, and large P. oxycephalus was unified. The pore number of each part of the canal system also varied depending on the species. Intraspecific variations were observed between Korean and Japanese specimens of P. lagowskii in the unification of the supratemporal canal and the preoperculomandibular canal, and the number of pores of the supratemporal canal. It was inferred that the specific characteristic patterns of their cephalic lateral line systems reflected the following two factors: different environmental requirement for their microhabitat and different maximum body size.     

Trace metals in vertebral columns of deep-sea teleost fish

Deep-sea teleost fish were collected from the Sagami Bay near a deep fissure in the Pacific Ocean. Fish were identified as Chlorophthalmis albatrosis, Engyprosopan xystrias, Satyrichthys hians, Ventrifossa garmani, and Halieutaea stellata. The Etmopterus lucifer is not a teleost, but a deepsea shark. Just after being caught and fixed in neutral 20% formol, the vertebral column was resected and prepared for measurement by inductively coupled plasma-atomic emission spectrometry. Trace elements were found to be Al, Si, Ti, Fe, Cu, Cd, Zn, and Hg at micrograms per gram levels. Major elements were Mg, Ca, P, and S at the milligram per gram level. Some of trace elements, Zn and Hg, were also usually found at this level.     

Paired development of hair cells in neuromasts of the teleost lateral line.

Lateral line neuromasts of the bullseye Parapriacanthus ransonetti and the cardinal fish Apogon cyanosoma were examined by scanning electron microscopy. Neuromasts showed large numbers of degenerating hair cells and immature hair cells, suggesting a high degree of hair cell turnover. New hair cells were mainly produced in pairs (fewer than 5% appear singly), the two cells of a pair having opposite but parallel orientations of their mechanosensitive axes. It is suggested that each pair results, directly or indirectly, from a single mitosis. The results further suggest that the axis of mitosis is one of the factors which determine the direction of the hair cell axis of mechanosensitivity.     

Organization and physiology of posterior lateral line afferent neurons in larval zebrafish

The lateral line system of larval zebrafish can translate hydrodynamic signals from the environment to guide body movements. Here, I demonstrate a spatial relationship between the organization of afferent neurons in the lateral line ganglion and the innervation of neuromasts along the body. I developed a whole cell patch clamp recording technique to show that afferents innervate multiple direction-sensitive neuromasts, which are sensitive to low fluid velocities. This work lays the foundation to integrate sensory neuroscience and the hydrodynamics of locomotion in a model genetic system.     

Lateral line nerve fibers do not code bulk water flow direction in turbulent flow

The discharges of anterior and posterior lateral line nerve afferents were recorded while stimulating goldfish, Carassius auratus, with bulk water flow. With increasing flow velocity lateral line afferents increased their discharge rates. However, an increased response to flow rates occurred even if flow direction was reversed. Thus, individual lateral line afferents did not encode the direction of running water. Frequency spectra of the water motions quantified with particle image velocimetry revealed flow fluctuations that increased with increasing flow velocity. Maximal spectral amplitudes of the flow fluctuations were below 5 Hz (bulk flow velocity 4–15 cm s⁻¹). The frequency spectra of the firing rates of lateral line afferents also showed an increase in amplitude when fish were exposed to running water. The maximal spectral amplitudes of the recorded data were in the frequency range 3–8 Hz. This suggests that the lateral line afferents mainly responded to the higher frequency fluctuations that developed under flow conditions, but not to the direct current flow or the lower frequency fluctuations. Although individual lateral line afferents encoded neither flow velocity nor flow direction we suggest that higher order lateral line neurons can do so by monitoring flow fluctuations as they move across the surface of the fish.     

Coding of lateral line stimuli in the goldfish midbrain in still and running water

We investigated in goldfish, Carassius auratus, how running water affects the responses of toral lateral line units to a stationary vibrating sphere or to a non-vibrating sphere that moves along the side of the fish. Experiments were conducted in the presence of running water (hydrodynamic noise) to further explore the sensory capabilities of the lateral line with special focus on the morphological sub-modalities. Previous recordings from lateral line nerve fibres in various fish species and the first nucleus of the ascending lateral line pathway in goldfish revealed flow-sensitive and flow-insensitive units. These physiological differences represent, at least in part, the differences in morphology of the lateral line, superficial and canal neuromasts. Following up on these findings we recorded flow-sensitive and flow-insensitive units in the Torus semicircularis of goldfish. In still water, both types of units responded to a vibrating or moving sphere. In running water, neural responses were weaker when the sphere was moved with the flow but were comparable or slightly stronger when the sphere was moved against the flow. In running water, responses of flow-sensitive fibres to the vibrating sphere were masked. In contrast, the responses of units insensitive to water flow were not masked. Our data confirm previous findings but also indicate differences when compared to previous reports. We discuss these differences with respect to lateral line morphology, sub-modalities and convergence of different channels of information at higher brain stations.     

Morphological basis of the interactions between endocrine cell types in the pancreatic islets of the teleost, Blennius gattoruggine

The endocrine pancreas of the teleost fish Blennius gattoruggine was studied by immunochemistry using both light and electron microscopy. Generally, one large Brockmann body, along with intermediate and small islets, was found. Cells immunoreactive (IR) to anti-insulin (B), anti-glucagon (A) anti-somatostatin (D) anti-pancreatic polypeptide and anti-PYY sera were detected with B cells located at the center of the islet and the other cell types forming a peripheral mantle. The B-cell cytoplasm showed rows of microtubules close to the secretory granules and perpendicular to the plasmalemma. The ultrathin section images revealed exocytotic and endocytotic features, and the presence of intercellular gap junctions between the plasmalemma of contiguous cells, suggesting intercellular routes of communication, e.g. via autocrine and/or paracrine mechanism. These features were observed in all of the cell types, and were abundant in D cells. D cells were particularly numerous in the islets and were disposed close to A and B cells, as observed in other teleost species. The most peripheral B cells, in closer contact with D cells than the central ones, appeared strongly immunolabeled, perhaps owing to the inhibitory action of somatostatin. Some D cells exhibited a long protrusion directed towards the center of the islet. In view of their cytological characteristics and their secretion, D cells might have an important role in the modulation of A and B-cell secretion in an endocrine and/or paracrine fashion.     

Daily spawning and development of sensitivity to gonadotropin and maturation-inducing steroid in the oocytes of the bambooleaf wrasse, Pseudolabrus japonicus

The cycle of oocyte development of the bambooleaf wrasse, Pseudolabrus japonicus, was studied to elucidate the endocrinological mechanism of oocyte maturation in a marine teleost. A single female reared with two males spawned every day for 17 days in captivity, indicating that this species is a daily spawner. Ovarian histology revealed that germinal vesicle migration of the largest oocytes progressed from 12:00 to 3:00 h, and germinal vesicle breakdown (GVBD) was completed at 6:00 h. Ovulation and spawning occurred between 6:00 and 9:00 h. The effectiveness of human chorionic gonadotropin (HCG) and 17,20-dihydroxy-4-pregnen-3-one (17,20-P), which is one of the most potent steroidal inducers of GVBD in bambooleaf wrasse oocytes, in inducing final oocyte maturation was examined at eight different times of the day. The responsiveness of the oocyte to HCG and steroid differed at different times of the day. The GVBD could be induced by HCG but not 17,20-P at 9:00 h. Between 12:00 and 18:00 h, not only HCG but also 17,20-P induced GVBD. Both GVBD and ovulation spontaneously occurred between 0:00 and 6:00 h without any hormonal treatment. These results clearly showed that the oocyte of the bambooleaf wrasse possessed a diurnal maturation cycle. Responsiveness of oocytes to HCG appeared earlier than responsiveness to 17,20-P. This suggests that sensitivity to 17,20 -P is induced by gonadotropic hormone (GTH).     

Diversity of the structure of lateral line scales in Pleuronectiformes

Scales of the lateral line (Sll) in representatives of the order Pleuronectiformes were studied, and its large morphological diversity was revealed. It was shown that Sll early in ontogenesis reach a definitive structure and have an insignificant individual variation. In some cases, features of Sll are species specific, but the main distinctions in its structure are typical of taxa of the supraspecies rank. Types of structure of Sll, as well as tendencies in its specialization, are distinguished.     

Isolation, culture and characterization of a primary fibroblast cell line from channel catfish

A primary cell line (designated as CCf) derived from caudal fin tissue of channel catfish, Ictalurus punctatus, was developed using explant techniques. The cell line grew fastest in media supplied with FBS and channel catfish serum. The duplication time of the cell line under optimal conditions was ∼56 h at a plating density of 1.1 × 10⁵ cells/ml. The cell line has been propagated continuously for 25 passages (1:4 dilution per passage), cryopreserved, and recovered successfully at different passages. The cultured cells had fibroblastic morphology, and synthesized fibronectin and Type I and III collagens in the cytoplasm. The cell line maintained the normal diploid chromosome number (58) of channel catfish throughout the experiment. Nucleolus organizer regions were located on the short arms of a pair of medium-sized submetacentrics, which is typical for channel catfish. This study provides a method for acquiring a cell line from juvenile catfish without sacrifice, and is especially useful for early screening of valuable fishes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Trk-neurotrophin receptor-like immunoreactivity in the gut of teleost species

Neurotrophins, acting through their high-affinity signal-transducing Trk receptors, are involved in the development, differentiation and maintenance of discrete neuron populations in the higher vertebrates. Furthermore, the presence of Trk receptors in some non-neuronal tissues, including the endocrine cells of the gut, could indicate an involvement of neurotrophins also in these tissues. Recently, neurotrophins and neurotrophin receptor proteins have been identified in the lower vertebrates and invertebrates, whose amino acid sequences are highly homologous with those found in mammals. The present study investigates the occurrence and distribution of Trk-like proteins in the neurons and gut endocrine cells in five species of teleost. Single and double immunolabeling was carried out on fresh and paraffin-embedded tissue using commercially available antibodies against sequences of the intracytoplasmic domain of the mammalian Trk. Western-blot analysis, carried out on samples of stomach and intestine of bass, identified proteins whose estimated molecular masses (140 kDa, 145 kDa and 143–145 kDa) were similar to those reported for full-length TrkA, TrkB and TrkC in the higher vertebrates. TrkA-like immunoreactivity was found in the enteric nervous system plexuses of three fish species. Trk-like immunoreactivity was observed in the endocrine cells as follows: sparse TrkA-like immunoreactive endocrine cells were detected only in the intestine; TrkB-like immunoreactive cells were detected only in the stomach; and TrkC-like immunoreactive cells were found both in the intestine of the carp and in the stomach of the bass, where they also showed TrkB-like immunoreactivity. These findings confirm the occurrence and distribution of Trk-like proteins in teleosts. These proteins are closely related to the Trk neurotrophin receptors of mammals. The functional significance of Trk-like proteins in both neuronal and non-neuronal cells of teleosts is still not clear. Received: 3 August 1998 / Accepted: 2 October 1998