Non-teleost Fishes Research Articles

Development of testis and digestive tract in longnose gar (Lepisosteus osseus) at the onset of exogenous feeding of larvae and in juveniles

The aim of this study was to describe the ontogenetic development of the testis and the alimentary tract in longnose gar (Lepisosteus osseus) related to fish size and age at the onset of exogenous feeding and late ontogenesis. Using light microscopy, testes were first detected histologically by the appearance of primordial germ cells 9 days after the first exogenous feeding [31-31.5 mm total body length(TL)] and presumptive seminiferous tubules (maleness characteristic) in fish of 107 mm TL. The present histological studies indicated that the alimentary tract of lepisosteids is completely functional at the beginning of exogenous feeding, several days before the completion of yolk absorption. Based on these results, we have concluded that garfish larvae/juveniles can be effectively trained to consume formulated diets at early stages, after an initial feeding of live food for 2-3 days (23.5 mm TL). Our findings provide evidence of the first controlled rearing of longnose gar using live and formulated diets, providing the possibility of experimental work with this non-teleost fish.

Calcium-Activated Potassium (BK) Channels Are Encoded by Duplicate slo1 Genes in Teleost Fishes

Calcium-activated, large conductance potassium (BK) channels in tetrapods are encoded by a single slo1 gene, which undergoes extensive alternative splicing. Alternative splicing generates a high level of functional diversity in BK channels that contributes to the wide range of frequencies electrically tuned by the inner ear hair cells of many tetrapods. To date, the role of BK channels in hearing among teleost fishes has not been investigated at the molecular level, although teleosts account for approximately half of all extant vertebrate species. We identified slo1 genes in teleost and nonteleost fishes using polymerase chain reaction and genetic sequence databases. In contrast to tetrapods, all teleosts examined were found to express duplicate slo1 genes in the central nervous system, whereas nonteleosts that diverged prior to the teleost whole-genome duplication event express a single slo1 gene. Phylogenetic analyses further revealed that whereas other slo1 duplicates were the result of a single duplication event, an independent duplication occurred in a basal teleost (Anguilla rostrata) following the slo1 duplication in teleosts. A third, independent slo1 duplication (autotetraploidization) occurred in salmonids. Comparison of teleost slo1 genomic sequences to their tetrapod orthologue revealed a reduced number of alternative splice sites in both slo1 co-orthologues. For the teleost Porichthys notatus, a focal study species that vocalizes with maximal spectral energy in the range electrically tuned by BK channels in the inner ear, peripheral tissues show the expression of either one (e.g., vocal muscle) or both (e.g., inner ear) slo1 paralogues with important implications for both auditory and vocal physiology. Additional loss of expression of one slo1 paralogue in nonneural tissues in P. notatus suggests that slo1 duplicates were retained via subfunctionalization. Together, the results predict that teleost fish achieve a diversity of BK channel subfunction via gene duplication, rather than increased alternative splicing as witnessed for the tetrapod and invertebrate orthologue.

Phylogeny of nucleus medianus of the posterior tubercle in rayfinned fishes

The brains of ray-finned fishes form a morphocline of increasing complexity, from cladistians through teleosts. This is particularly apparent in the posterior tubercle of the diencephalon. In cladistians, the posterior tubercle consists of a periventricular nucleus and a migrated nucleus medianus that is fused across the midline. In more advanced ray-finned fishes, such as gars and bowfins, the posterior tubercle comprises numerous additional migrated nuclei, termed the preglomerular complex, in addition to a more well developed nucleus medianus. In teleosts, the most derived ray-finned fishes, there is an even more elaborate preglomerular complex, but there is no recognizable nucleus medianus. In an attempt to explain the variation in the posterior tubercle of the diencephalon in ray-finned fishes, the immunohistochemistry and connections of nucleus medianus were examined in cladistians, gars and bowfins. In each of these taxa, nucleus medianus exhibits large numbers of calretinin-positive neurons and has ascending projections that terminate in several divisions of the pallium. Although teleosts, such as goldfish, also exhibit numerous cell groups in the posterior tubercle that are rich in calretinin, none of these cell groups has connections that are comparable to those of nucleus medianus in non-teleost ray-finned fishes. It is possible, therefore, that nucleus medianus was lost with the origin of teleosts.

The relationship between temperature and standard rate of metabolism in African lungfish, Protopterus aethiopicus, from Uganda

The relationship between temperature and metabolism among ancient (non-teleost) fishes, while largely unknown, is essential to an understanding of the effects of temperature on fish energetics. This study quantifies the effect of temperature on the standard rate of metabolism in the African lungfish, Protopterus aethiopicus. We present a Q10 value of 3.3 for individuals ranging in body mass from 42–222g across an ecologically-relevant 10°C temperature range. Protopterus aethiopicus showed a positive bilogarithmic (log-log) relationship between the rate of oxygen consumption and body mass (range = 44–222g) at three water temperatures (20, 25, 30°C). However, adjusted mean rates of oxygen consumption differed among all three temperatures. A Q10 value derived as the means of Q10 values calculated for each individual lungfish averaged 3.3 ± 0.4 (SE) for 20–30°C. A comparison of literature-derived Q10 values for both tropical and temperate fishes suggests a higher Q10 in tropical species (n = 3) than in temperate species (n = 10) across an ecologically-relevant thermal range.

Chloride inhibition of nitrite uptake for non-teleost Actinopterygiian fishes

Fish that transport environmental chloride with a gill uptake mechanism (gill epithelial Cl(-)/HCO(3)(-)cotransport exchange system), also transport nitrite into plasma through the same mechanism. Because of the relationship between nitrite uptake and the gill chloride uptake mechanism, nitrite uptake can provide insight regarding the method of chloride uptake for fish. This study was designed to determine if non-teleost fishes concentrate nitrite in their plasma, and to determine if chloride inhibits nitrite uptake in non-teleost fish. To determine if bowfin Amia calva, spotted gar Lepisosteus oculatus, alligator gar Atractosteus spatula, and paddlefish Polyodon spathula concentrate environmental nitrite in their plasma, individuals were exposed to concentrations of 0, 1, 10, or 100 mg/L nitrite-N. After exposure, all species had plasma nitrite-N concentrations greater than environmental levels. To determine if chloride inhibits nitrite uptake for spotted gar, alligator gar, and paddlefish, fish were exposed to 1 mg/L nitrite-N and 20 mg/L chloride as calcium chloride, or to 1 mg/L nitrite-N only. Chloride effectively prevented nitrite from being concentrated in the plasma of all species. It appears that non-teleost fish concentrate nitrite in their plasma via their chloride uptake mechanism and that this is an ancestral characteristic for teleost.

The functional roles of passive electroreception in non-electric fishes

Abstract Passive electroreception is a complex and specialised sense found in a large range of aquatic vertebrates primarily designed for the detection of weak bioelectric fields. Particular attention has traditionally focused on cartilaginous fishes, but a range of teleost and non-teleost fishes from a diversity of habitats have also been examined. As more species are investigated, it has become apparent that the role of electroreception in fishes is not restricted to locating prey, but is utilised in other complex behaviours. This paper presents the various functional roles of passive electroreception in non-electric fishes, by reviewing much of the recent research on the detection of prey in the context of differences in species' habitat (shallow water, deep-sea, freshwater and saltwater). A special case study on the distribution and neural groupings of ampullary organs in the omnihaline bull shark, Carcharhinus leucas, is also presented and reveals that prey-capture, rather than navigation, may be an important determinant of pore distribution. The discrimination between potential predators and conspecifics and the role of bioelectric stimuli in social behaviour is discussed, as is the ability to migrate over short or long distances in order to locate environmentally favourable conditions. The various theories proposed regarding the importance and mediation of geomagnetic orientation by either an electroreceptive and/or a magnetite-based sensory system receives particular attention. The importance of electroreception to many species is emphasised by highlighting what still remains to be investigated, especially with respect to the physical, biochemical and neural properties of the ampullary organs and the signals that give rise to the large range of observed behaviours.

Ascorbic acid biosynthesis in Amazonian fishes

The incapacity to synthesize ascorbic acid (AA) is due to the lack of activity of l-gulonolactone oxidase (GLO), which catalyzes the last step of AA biosynthesis. It was postulated that vertebrates unable to synthesize AA had sufficient amounts of this nutrient in their diet and consequently did not need to preserve synthetic capability. In the present study, we analyzed the GLO activity in kidney and liver of 13 fish species, including 11 teleosts, namely: freshwater stingray, Potamotrygon sp.; South American lungfish, Lepidosiren paradoxa; “sardinhão,” Pelona sp.; arowana, Osteoglossum bicirrhosum; arapaima, Arapaima gigas; “piranha caju,” Pygocentrus nattereri; “piranha mucura,” Serrasalmus elongatus; “aracu,” Schizodon fasciatus; “tambaqui,” Colossoma macropomum; “acari-pedra,” Hypostomus sp.; “sarapó,” Steatogenys elegans; electric eel, Electrophorus electricus; and the peacock bass, Cichla sp. Four representatives of the Characiformes order with distinct feeding habits were included in this study to evaluate the influence of feeding habit on GLO activity. Only two species of non-teleost fishes, the freshwater stingray (Miliobatiformes) and the South American lungfish (Lepidosireniformes), showed GLO activity in their kidneys, corroborating the hypothesis that teleosts are unable to synthesize AA. Additionally, as expected, we observed that the phylogenetic position is more important than feeding habit as a determinant of the biosynthetic ability since none of the Characiformes species analyzed synthesize AA, independent of their distinct feeding habits. Female freshwater stingrays had a significantly higher GLO activity than males ( P<0.05), but there was no difference in the biosynthetic capability regarding the portion of the kidney analyzed ( P>0.05), as previously reported in white sturgeon. This is the first report of the AA biosynthetic ability in South American lungfish and freshwater Elasmobranchs.

Use of electroreception during foraging by the Australian lungfish

A diverse range of animals, including elasmobranchs and nonteleost fish, use passive electroreception to locate hidden prey. The Australian lungfish, Neoceratodus forsteri (Krefft 1870), has ampullary organs analogous in form to the electroreceptors of other nonteleost fish. Afferents from these ampullae project to regions in the brain that are known to process electrosensory information in other species, suggesting that N.forsteri possesses an electric sense that may be used during prey location. To explore this hypothesis directly, we first characterized food-locating behaviour inN.forsteri and then conducted an experiment designed to quantify the effects of manipulating electrical and olfactory stimuli from live prey. A small crayfish, Cherax destructor, was housed in a specially constructed chamber hidden beneath the substrate, which prevented emission of chemical, mechanical and visual cues, but allowed transmission of bioelectric fields. Control treatments included presentation of electrically shielded prey, a dead crayfish and an empty chamber. In some treatments, a competing olfactory signal was presented simultaneously at the other end of the test tank to assess the relative salience of this sensory modality. The lungfish responded to the crayfish in the unshielded chamber with accurate and sustained feeding movements, even with a competing olfactory signal. By contrast, the abolition of electrical cues in the three control treatments reduced the accuracy and frequency of feeding movements in the vicinity of the target chamber. These results show that N.forsteri is capable of perceiving the weak electric fields surrounding living animals, and suggest that it uses this information when foraging to locate prey hidden from view.

A Comparative Analysis of Somatolactin-Related Immunoreactivity in the Pituitaries of Four Neopterygian Fishes and One Chondrostean Fish: An Immunohistochemical Study

An antiserum to cod somatolactin (SL) was used for immunohistochemical screening of the pars intermedia of two teleosts (Oreochromis mossambicusandGymothorax meleagris), two holostean fishes (Lepisosteus osseusandAmia calva), and a chondrostean fish (Acipenser fulvescens) for SL-immunopositive (SL-IR) cells. As expected, a subset of the epithelial cells in the pars intermedia ofO. mossambicus(tilapia) was immunopositive for SL, and the remainder of the epithelial cells was immunopositive for α-MSH-specific antiserum (α-MSH-IR). SL-IR was not detected in any of the epithelial cells in the pars intermedia of the moray eelG. meleagris.To determine whether SL-IR could be detected in nonteleost fishes, immunohistochemical analyses were done on the pituitaries of two holostean fishes and one chondrostean fish. In the pars intermedia of the gar,L. osseus,a subset of cells was immunopositive for both SL and α-MSH. The majority of the pars intermedia cells was immunopositive for α-MSH only. However, in the pars intermedia of the bowfin,A. calva,all of the epithelial cells indicated the presence of both SL and α-MSH. Finally, no SL-positive cells were detected in the pars intermedia of the sturgeon,A. fulvescens.

Sequence and regulation of European eel prolactin mRNA

cDNA clones encoding the European eel ( Anguilla anguilla L.) prolactin were isolated from a pituitary cDNA library constructed in γτ 10, using a rainbow trout Prl cDNA fragment as a probe. Four different inserts were subcloned into the pGEM 3Z plasmid after PCR amplification. The 1082 bp-long nucleotide sequence revealed an open reading frame of 627 bp encoding a 24 amino acid-long signal peptide followed by a 185 amino acid-long mature protein. Comparison studies showed 60–70% homology with other known teleost fish prolactins and 30–45% with non-teleost fish, amphibian, reptilian, avian and mammalian prolactins. In situ hybridization studies using labelled prolactin RNA probe showed a strong signal in the rostral pars distalis of the pituitary gland. We next examined the physiological regulation of this prolactin synthesis in vivo using Northern blot analysis and prolactin cDNA probe labelled by random priming. The pituitary prolactin mRNA level was markedly decreased 3 weeks after transfer of eels from freshwater to sea water. Implants of thyroid hormones left for up to three weeks were ineffective on prolactin mRNA. Estradiol administered as implant, alone or in combination with 500 μg testosterone, was also unable to significantly alter the pituitary mRNA level for prolactin in the freshwater silver eels whatever the dose used (20–500 μg) and whatever the duration of treatment (from 4 days to 10 weeks).

Ampullary sense organs, peripheral, central and behavioral electroreception in chimeras (Hydrolagus, Holocephali, Chondrichthyes).

Ampullary sense organs are distributed in groups over the head of Hydrolagus colliei with their pores in clusters and innervated by the buccal, hyomandibular and superficial ophthalmic branches of the anterior lateral line nerve. The ampullae contain ciliated sense cells in an alveolate-shaped epithelium, which communicates to the surface through a jelly-filled tube. The sense cells synapse at their bases with the afferent nerve fibers that terminate in the dorsal nucleus of the anterior lateral line lobe of the medulla. The anatomy and ultrastructure support the homology with the ampullae of Lorenzini of elasmobranchs. Single units recorded from the buccal branch of the anterior lateral line nerve are either lateral line or ampullary in character, the former being sensitive only to mechanical stimuli, the latter to both mechanical and to weak electric stimuli. They are also distinguished by the positions of their receptive fields. The electroreceptive units are spontaneously active and are excited by a cathode placed near the opening of their pore and inhibited by an anode. Compound evoked potentials are recorded from beneath the lateral aspect of the tectum in response to weak electric fields in the bath. Each recording locus has a best position and orientation of the electric field. The electric fields are effective if their duration is longer than ca. 2 ms; longer than 10 ms makes no difference until an OFF effect becomes distinct at ca. 50 ms. The reception is tuned to low frequencies but is not sensitive to maintained current (DC). Evoked potentials summating moderate numbers of responses are clear at < 1 microV/cm. Ratfish were conditioned in a ring-shaped tank to reverse the direction of swimming when an electric field was switched ON. The stimulus was a 5 Hz square wave or the onset of a DC of 1-10 microA between a pair of electrodes on the floor of the tank. The fish responded to fields as weak as 0.2 microV/cm. A specialized sense modality for electroreception, similar to that in elasmobranchs and most other groups of nonteleost fishes, except for Myxini and Neopterygii (holosteans), is present in the subclass Holocephali. The notion is supported that this modality and its central as well as peripheral apparatus arose early in the evolution of vertebrates. Only two losses of the whole system need be hypothesized, on this idea, once in the ancestors of the hagfishes and once in the ancestors of the neopterygians, which include the teleosts. Some orders of teleosts then evolved a new system of electroreception independently. The ciliary receptor cells are probably primitive; microvillar sense cells evolved independently.

Retinal projections in the bowfin, Amia calva: cytoarchitectonic and experimental analysis.

The retinofugal projections in the bowfin, a non-teleost actinopterygian, were studied by autoradiographic and horseradish peroxidase methods, and the cytoarchitecture of retinorecipient regions of the diencephalon was analyzed with serially sectioned, Bodian stained material. Nuclei were identified in the thalamus, the periventricular portion of the posterior tuberculum, synencephalon, and pretectum which are homologous to like-named nuclei in teleosts and other non-teleost actinopterygian fishes. Of particular note, a posterior pretectal nucleus and, possibly, a homologue of nucleus corticalis were found to be present in the pretectum. These nuclei have previously been identified only in teleosts. The posterior pretectal nucleus is relatively small in the bowfin, and the distribution of a small, versus a large, posterior pretectal nucleus in Teleostei and Halecomorphi suggests that this nucleus was small plesiomorphically. The pattern of retinofugal projections in the bowfin is similar to that in other non-teleost actinopterygian fishes and in teleosts in most regards. Contralaterally, the retina projects to nuclei in the dorsal and ventral thalamus, superficial and central pretectum, dorsal and ventral accessory optic nuclei, and to the optic tectum. Additionally, there are sparse projections to the suprachiasmatic nucleus in the preoptic area, the periventricular nucleus of the posterior tuberculum, and the dorsal and ventral periventricular pretectal nuclei. Ipsilateral projections are sparse and are derived from fibers which do not decussate in the optic chiasm. Undecussated ipsilateral retinal projections, as present in the bowfin, are a widely distributed character in vertebrates and appear to be plesiomorphic for vertebrates.

Ciliated Sensory Cells in the Rostral Organ of the CoelacanthLatimeria chalumnae(Smith 1939)

The rostral organ of the coelacanth Latimeria chalumnae contains a sensory epithelium with luminated ciliated sensory cells, which very much resemble electroreceptors from other non-teleost fish. This, as well as the innervation and a dorsal nucleus, indicate that this interesting species is electroreceptive.

Glutamine metabolism in a holostean (Amia calva) and teleost fish (Salvelinus namaycush).

Amino acid metabolism was examined in mitochondria from the lateral red muscle of a teleost (lake char, Salvelinus namaycush) and a nonteleost fish (bowfin, Amia calva). Isolated mitochondria oxidize a wide variety of substrates and have high respiratory control ratios. In both species, glutamine is oxidized more rapidly than any other amino acid. The rate of glutamine oxidation by bowfin mitochondria exceeds that of lake char mitochondria, and the bowfin displays correspondingly higher levels of mitochondrial phosphate-dependent glutaminase. It is suggested that amino acids in general, and glutamine in particular, are important oxidative substrates for nonteleost red muscle. The teleost red muscle, however, may rely on both glutamine and fatty acids as oxidative substrates. It appears that glutamate derived from glutamine is oxidized primarily via glutamate dehydrogenase, whereas exogenous glutamate is oxidized primarily via aspartate aminotransferase. Complete oxidation of glutamine may be accomplished in the absence of other substrates by conversion of glutamine-derived malate to pyruvate via malic enzyme. To assess the relative abilities of various tissues to synthesize and oxidize glutamine, the activities of glutamine synthetase and glutaminase were measured. The results of these studies indicate that the organization of glutamine metabolism of fish differs markedly from that in mammals.

The origin of the mammalian form of GnRH in primitive fishes

The presence of neuroendocrine hormones in extant agnathan fishes suggests that a method of control involving these hormones was operating 500-600 million years ago in emerging vertebrates. Data on a limited number of species show that several members of the GnRH family of peptides may have arisen in non-teleost fishes. Lamprey (Petromyzon marinus) GnRH has a unique composition and has not been detected in other vertebrates. It is not yet clear whether the chicken II GnRH-like molecule arose in cartilaginous fishes, but a chromatographically and immunologically similar molecule is found in dogfish (Squalus acanthias) and ratfish (Hydrolagus colliei). Finally, a mammalian GnRH-like molecule is detected in three primitive bony fish: sturgeon (Acipenser transmontanus), reed fish (Calamoichthys calabaricus), and alligator gar (Lepidosteus spatula). Minor forms are also present, but are not yet characterized. Clearly, the basic structure of GnRH peptides was established in primitive fish. In contrast, at least three other identified forms of GnRH have been detected in teleosts or tetrapods: Salmon I, catfish I, and chicken I GnRH. Evidence for the presence of members of the GnRH family and the neurohypophysial hormone family in primitive fishes argues for the importance of neuroendocrine control throughout the history of vertebrates.

Chapter 14 Comparative anatomy of vertebrate electroreceptors

Publisher Summary This chapter focuses on the comparative anatomy of vertebrate electroreceptors. Electrosensitivity plays an important role in the biological activities of fish and amphibia for prey detection, feeding behaviour and social communication and its significance is reflected in the number of sensory cells and the amount of nerve supply that ranks in the order of other sensory systems. Two types of electroreceptors are characteristic in teleost as well as non-teleost fishes and in some amphibia: the ampullary and the tuberous receptor organs. Three types of ampullae can be distinguished in chondrichthyes with regard to the length of the canal and the size and differentiation of the alveolus: (1) macro-ampullae, (2) micro-ampullae, and (3) mini-ampullae. The macro-ampullae (known as the ampullae of Lorenzini) are macroscopically identified by large pores in the skin surface. Micro-ampullae occur in restricted areas of the maxillary and the mandibular processes of Holocephali and Hexanchidae. The mini-ampullae of freshwater rays, however, exhibit very short canals of about 300–500 μm length.

End buds: non-ampullary electroreceptors in adult lampreys.

Shared anatomical and physiological characters indicate that the low-frequency sensitive electrosensory system of lampreys is homologous with those of non-teleost fishes and amphibians. However, the ampullary electroreceptor organs which characterize all of these gnathostomes are not found in lampreys. Experimental anatomical and physiological studies reported here demonstrate that the epidermal end buds are the electroreceptors of adult lampreys. End buds, consisting of both sensory and supporting cells, are goblet-shaped with the top (25-60 microns diameter) at the epidermal surface and the stem directed toward the dermis (Fig. 1A). Short lines or clusters of 2-8 end buds (Fig. 1B) are distributed over both trunk and head. Injections of horseradish peroxidase (HRP) into vitally-stained end buds labeled anterior lateral line afferents terminating in the ipsilateral dorsal nucleus (Fig. 2A) - the primary electrosensory nucleus of the lamprey medulla. Conversely, after HRP injection into the dorsal nucleus HRP-filled fibers and terminals were present on ipsilateral end buds (Fig. 2B). End buds are usually not visible without staining. However, in adult sea lampreys the presence of end buds was histologically confirmed in skin patches containing the receptive fields of electroreceptor fibers recorded in the anterior lateral line nerve. Additionally, in the rare instance of two silver lampreys in which end buds were visible without staining, electrosensory activity indistinguishable from that of the primary electroreceptor afferents was recorded from the end bud surface (Figs. 3, 4). End buds were initially characterized as chemoreceptors (Johnston 1902) but were later correctly advanced as lateralis receptors based on the presence of presynaptic dense bodies in the receptor cells (Whitear and Lane 1981).(ABSTRACT TRUNCATED AT 250 WORDS)

The phylogenetic distribution of electroreception: Evidence for convergent evolution of a primitive vertebrate sense modality

Specializations for electroreception in sense organs and brain centers are found in a wide variety of fishes and amphibians, though probably in a small minority of teleost taxa. No other group of vertebrates or invertebrates is presently suspected to have adaptations for electroreception in the definition given here. The distribution among fishes is unlike any other sense modality in that it has apparently been invented, lost completely and reinvented several times independently, using distinct receptors and central nuclei in the medulla. There are so far no clearly borderline or transitional fishes, either physiologically or anatomically. We rather expect a few new electroreceptive taxa to be found. The evoked potential method and the newly validated central anatomical criteria provide two useful tools for searching. Although Myxiniformes probably lack electroreception, it is well developed in Petromyzoniformes and in all other non-teleost fishes except Holostei. Thus Elasmobranchia, Holocephala, Dipneusti, Crossopterygii, Polypteriformes and Chondrostei have the physiological and anatomical specializations in a common form consistent with a single origin in primitive vertebrates. Amphibian ancestors probably inherited the system from a stem similar to one of these and passed it on at least to the ambystomatoid and salamandroid urodeles, apparently after losing the kinocilium of the sense cell. The suggestion of electroreception in ichthyophid apodans from skin histology has not been confirmed physiologically, behaviorally or by brain anatomy. With respect to more advanced fishes the most parsimonious interpretation is that the entire system, peripheral and central was lost in ancestors of holostean and teleostean fishes and new systems reinvented in Siluriformes, in Gymnotiformes, in Xenomystinae and in Mormyriformes. These 4 taxa must represent at least two, and probably 3 or 4 independent inventions, presumably from mechanoreceptive lateral line organs and brain centers.

Central connection of the octavolateralis nerves in the pike cichlid, Crenicichla lepidota

The primary projections of the lateral line and eight (octavolateralis) nerves in the teleost, Crenicichla lepidota were found to conform to the pattern of projections of these nerves in non-teleost fishes. The lateral line nerves terminate in the dorsal portion of the octavolateralis area of the medulla, the eight nerve terminates in the ventral portion of this area, and overlap is restricted to nucleus, is composed of posterior lateral line nerve fibers which enter the medulla with the eight nerve but terminate with lateral branchlet, is composed of posterior lateral line nerve fibers which enter tthe medulla with the eigth nerve bur terminate with lateral line inputs.

Physiological characterization of electroreceptors in the lampreysIchthyomyzon unicuspis andPetromyzon marinus

1. We examined the physiological properties and distribution of electroreceptors in the skin of adult lampreys (vertebrates, class: Agnatha) by recording electroreceptor afferent fiber activity in the anterior lateral line nerve. Stimulation was with uniform or local electric fields in the water around the fish. 2. Lampreys possess ampullary electroreceptors widely distributed over the head and trunk (Fig. 1) that are sensitive to weak, low-frequency electric fields. The response thresholds to uniform fields are 1–10 μV/cm and the dynamic range of the receptors includes 4 log units of intensity (Fig. 3). Maximum sensitivity with sinusoidal currents is to frequencies ≦ 1 Hz (Fig. 4). 3. Like the ampullary receptors of elasmobranchs and other non-teleost fishes, lamprey electroreceptors are excited by weak cathodal fields (i.e. negative at the receptor opening relative to a distant reference) and inhibited by anodal fields. With very intense stimuli (1–10 mV/cm) the responses reverse so that strong cathodal fields are inhibitory and anodal fields are excitatory (Fig. 3). These results indicate that similar transduction mechanisms exist in the electroreceptors of lampreys and non-teleost jawed fishes. Likewise, as in other non-teleosts, all electroreceptors in lampreys including those on the trunk are innervated by the anterior lateral line nerve. 4. The similarities in receptor physiology and innervation taken in conjunction with known similarities in medullary organization indicate that electrosensory systems of lampreys and non-teleost gnathostome fishes are homologous.