An Fgf-Shh positive feedback loop drives growth in developing unpaired fins.

The origin and diversification of appendage types is a central question in vertebrate evolution. Understanding the genetic mechanisms that underlie fin and limb development can reveal relationships between different appendages. Here we demonstrate, using chemical genetics, a mutually agonistic interaction between Fgf and Shh genes in the developing dorsal fin of the channel catfish, Ictalurus punctatus. We also find that Fgf8 and Shh orthologs are expressed in the apical ectodermal ridge and zone of polarizing activity, respectively, in the median fins of representatives from other major vertebrate lineages. These findings demonstrate the importance of this feedback loop in median fins and offer developmental evidence for a median fin-first scenario for vertebrate paired appendage origins.

Identification of Langerhans-like cells in the immunocompetent tissues of channel catfish, Ictalurus punctatus.

Dendritic cells (DCs) are the most powerful antigen presenting cells (APCs) that have a critical role in bridging innate and adaptive immune responses in vertebrates. Dendritic cells have been characterized morphologically and functionally in the teleost fish models such as rainbow trout, salmonids, medaka, and zebrafish. The presence of DCs with remarkable similarities to human Langerhans cells (LCs) has been described in the spleen and anterior kidney of salmonids and rainbow trout. However, there is no evidence of the presence of DCs and their role in channel catfish immunity. In this study, we assessed DC-like cells in the immunocompetent tissues of channel catfish by immunohistochemistry (IHC), flow cytometry and transmission electron microscopy (TEM). We identified Langerin/CD207+ (L/CD207+) cells in the channel catfish anterior kidney, spleen and gill by IHC. Moreover, we described the cells that resembled mammal LC DCs containing Birbeck-like (BL) granules in channel catfish spleen, anterior and posterior kidneys and gill by TEM. Our data suggest that cells with DC-like morphology in the immune related organs of catfish may share morphological and functional properties with previously reported DCs in teleost fish and mammals. More detailed knowledge of the phenotype and the function of catfish DCs will not only help gain insight into the evolution of the vertebrate adaptive immune system but will also provide valuable information for development and optimization of immunotherapies and vaccination protocols for aquaculture use.

Histological and computed tomographic evaluation of a parasitic conjoined twin in hybrid catfish (Ictalurus punctatus [Rafinesque] X Ictalurus furcatus [Lesueur]).

There is growing use of hybrid catfish (Ictalurus punctatus ♀ X Ictalurus furcatus ♂) in commercial aquaculture to utilize hybrid vigour to improve production A conjoined twin specimen found during the course of production studies by the United States Department of Agriculture Catfish Genetic Research Unit (USDA-CGRU) was submitted to the Aquatic Research and Diagnostic Laboratory (ARDL). After preliminary inspection, it was transported to Mississippi State University, College of Veterinary Medicine for further evaluation. The specimen was examined using both computed radiography and computed tomography antemortem. Following humane euthanasia, the specimen was examined both grossly and histologically. Tissues from both fish were also submitted for genetic analysis to determine whether twins were derived from the same egg. This report records the presentation and examination of a pair of conjoined hybrid catfish (I. punctatus X Ictalurus furcatus).

Timing of clade divergence and discordant estimates of genetic and morphological diversity in the Slender Madtom, Noturus exilis (Ictaluridae).

Phylogeographic relationships, the timing of clade diversification, and the potential for cryptic diversity in the Slender Madtom, Noturus exilis, was investigated using mitochondrial Cyt b, nuclear RAG2, shape analysis, and meristic and pigmentation data. Three well-supported and deeply divergent clades were recovered from analyses of genetic data: Little Red River (White River drainage) clade, Arkansas+Red River (Mississippi River) clade, and a large clade of populations from the rest of the range of the species. Recovered clades showed little to no diagnostic morphological differences, supporting previous hypotheses of morphological conservatism in catfishes, and indicating morphology may commonly underestimate diversity in this group of fishes. The Little Red River clade is the most distinct lineage of N. exilis with 11 POM pores (vs. 10 in other populations) and unique Cyt b haplotypes and RAG 2 alleles. However, treating it as a species separate from N. exilis would imply that the other major clades of N. exilis are more closely related to one another than they are to the Little Red River clade, which was not supported. The UCLN age estimate for Noturus was 23.9mya (95% HPD: 13.49, 35.43), indicating a late Oligocene to early Miocene origin. The age of N. exilis was estimated as late Miocene at 9.7mya (95% HPD: 5.32, 14.93). Diversification within the species spanned the late Miocene to mid-Pleistocene. The largest clade of N. exilis, which dates to the late Miocene, includes populations from the unglaciated Eastern and Interior Highlands as well as the previously glaciated Central Lowlands. Diversification of this clade coincides with a drastic drop in sea-level and diversification of other groups of Central Highlands fishes (Centrarchidae and Cyprinidae). Sub-clades dating to the Pleistocene show that northern populations occurring in previously glaciated regions resulted from dispersal from populations in the Ozarks up the Mississippi River following retreat of the Pleistocene glaciers. Pre-Pleistocene vicariance, such as drainage pattern changes of the Mississippi River, also played a prominent role in the history of the species. The incorporation of a temporal estimate of clade diversification revealed that in some instances, phylogeographic breaks shared with other aquatic species were best explained by different or persistent vicariant events through time, rather than a single shared event.

Morphological variability of black bullhead Ameiurus melas in four non-native European populations.

External morphology in black bullhead Ameiurus melas, a fish species considered to have high invasive potential, was studied in its four non-native European populations (British, French, Italian and Slovak). The aim of this study was to examine this species' variability in external morphology, including ontogenetic context, and to evaluate its invasive potential. Specimens from all non-native populations reached smaller body size compared to individuals from native populations. Juvenile A. melas were found to have a relatively uniform body shape regardless of the population's origin, whereas adults developed different phenotypes depending upon location. Specimens from the U.K., Slovak and French populations appeared to be rather similar to each other, whereas the Italian population showed the most distant phenotype. This probably results from the different thermal regime in the Italian habitat. Ameiurus melas from non-native European populations examined in this study showed some potential to alter the body shape both within and between populations. The phenotypic plasticity of A. melas, however, was not found to be as significant as in other invasive fish species. The results suggest that morphological variability itself is not necessarily essential for invasive success. The invasiveness of A. melas is therefore probably favoured by variations in its life-history traits and reproduction variables, together with some behavioural traits (e.g. voracious feeding and parental care) rather than by phenotypic plasticity expressed in external morphology.

Adaptive significance of venom glands in the tadpole madtom Noturus gyrinus (Siluriformes: Ictaluridae).

Piscine venom glands have implicitly been assumed to be anti-predatory adaptations, but direct examinations of the potential fitness benefits provided by these structures are relatively sparse. In previous experiments examining this question, alternative phenotypes have not been presented to ecologically relevant predators, and the results are thus potentially confounded by the presence of sharp, bony fin spines in these species, which may also represent significant deterrents to predation. Here, I present the results of experiments exposing Micropterus salmoides (largemouth bass) to tadpole madtoms (Noturus gyrinus) with one of several fin spine phenotypes (intact, stripped, absent), which indicate that the venom glands of this species do provide a significant fitness benefit, relative to individuals having fin spines without venom glands or no spines at all. Intact madtoms were repeatedly rejected by the bass and were almost never consumed, while alternative phenotypes were always consumed. Madtoms with stripped fin spines showed increases in predator rejections relative to spineless madtoms and control minnows, but non-significant increases in handling time, contrasting with previous results and predictions regarding the adaptive benefit of these structures. Comparisons with a less venomous catfish species (Ameiurus natalis) indicate that a single protein present in the venom of N. gyrinus may be responsible for providing the significant selective advantage observed in this species. These results, considered in conjunction with other studies of ictalurid biology, suggest that venom evolution in these species is subject to a complex interplay between predator behavior, phylogenetic history, life history strategy and adaptive responses to different predatory regimes.

Effect of yeast polysaccharide on some hematologic parameter and gut morphology in channel catfish (Ictalurus punctatus).

A study was conducted to investigate the effect of dietary yeast polysaccharides on some hematologic parameters and intestinal morphology of channel catfish. Channel catfish were fed diets containing yeast polysaccharides at 0 (control), 0.1, 0.2, or 0.3 % for 7 weeks. Each diet was provided to 10 channel catfish specimens (5.82 ± 0.13 g initial weight) replicated 3 times in individual 250 L fiberglass tanks. Some hematologic parameters, leukocyte phagocytic activity, and intestinal morphology were monitored. After 7 weeks of trial, 0.2 % yeast polysaccharides resulted in significantly higher (P < 0.05) monocyte numbers. Furthermore, fish fed 0.2 % yeast polysaccharide diet had higher (P < 0.05) phagocytic rate of leukocyte. And 0.3 % yeast polysaccharide enhanced (P < 0.05) phagocytic index of leukocyte. Histological evaluation showed yeast polysaccharide supplementation increased the height of intestine fold (0.1, 0.2 and 0.3 %) and the thick of muscular layers (0.2 %) in intestine (P < 0.05). In addition, 0.1 and 0.3 % yeast polysaccharide supplementation improved the number of goblet cells (P < 0.05). The results of this trial indicate that yeast polysaccharides supplementation could affect blood monocytes, improve leukocytes phagocytic activity, and the development of intestine in channel catfish.

Adhesion dynamics of Flavobacterium columnare to channel catfish Ictalurus punctatus and zebrafish Danio rerio after immersion challenge.

The adhesion dynamics of Flavobacterium columnare to fish tissues were evaluated in vivo by immersion challenge followed by bacterial plate count and confirmatory observations of gill-adhered bacterial cells using scanning electron microscopy. Adhesion of F. columnare genomovar I (ARS-1) and II (BGFS-27) strains to skin and gill of channel catfish Ictalurus punctactus and gill of zebrafish Danio rerio was compared. At 0.5 h post-challenge, both strains adhered to gill of channel catfish at comparable levels (10(6) colony forming units [CFU] g(-1)), but significant differences in adhesion were found later in the time course. Channel catfish was able to effectively reduce ARS-1 cells on gill, whereas BGFS-27 persisted in gill beyond the first 24 h post-challenge. No significant difference was found between both strains when adhered to skin, but adhered cell numbers were lower (10(3) CFU g(-1)) than those found in gill and were not detectable at 6 h post-challenge. Adhesion of BGFS-27 cells to gill of zebrafish also occurred at high numbers (> 10(6) CFU g(-1)), while only < 10(2) CFU g(-1) of ARS-1 cells were detected in this fish. The results of the present study show that particular strains of F. columnare exhibit different levels of specificity to their fish hosts and that adhesion to fish tissues is not sufficient to cause columnaris disease.

First record of the black bullhead Ameiurus melas (Teleostei: Ictaluridae) in Poland.

The North American catfish, the black bullhead Ameiurus melas, is recorded for the first time in Poland. The origin of these fish is not clear, but their presence may be associated with unregulated introductions by anglers.

Exposure of fish to high-intensity sonar does not induce acute pathology.

This study investigated immediate effects of intense sound exposure associated with low-frequency (170-320 Hz) or with mid-frequency (2.8-3.8 kHz) sonars on caged rainbow trout Oncorhynchus mykiss, channel catfish Ictalurus punctatus and hybrid sunfish Lepomis sp. in Seneca Lake, New York, U.S.A. This study focused on potential effects on inner ear tissues using scanning electron microscopy and on non-auditory tissues using gross and histopathology. Fishes were exposed to low-frequency sounds for 324 or 628 s with a received peak signal level of 193 dB re 1 microPa (root mean square, rms) or to mid-frequency sounds for 15 s with a received peak signal level of 210 dB re 1 microPa (rms). Although a variety of clinical observations from various tissues and organ systems were described, no exposure-related pathologies were observed. This study represents the first investigation of the effects of high-intensity sonar on fish tissues in vivo. Data from this study indicate that exposure to low and midfrequency sonars, as described in this report, might not have acute effects on fish tissues.

Growth, health aspects and histopathology of brown bullhead (Ameiurus nebulosus L.): replacing fishmeal with soybean meal and brewer's yeast.

A ten-week feeding trial was carried out to investigate the effects of replacing fishmeal (FM) with soybean meal (SBM) and brewer's yeast (BY) on growth performance, blood parameters, oxidative stress and micromorphology of liver and intestines in brown bullhead (Ameiurus nebulosus L.). Fish were fed nine feeds in which FM was replaced with 25%, 50%, 75% and 100% SBM (K1, K2, K3 and K4) and 17% + 8%, 42% + 8%, 67% + 8% and 92% + 8% of SBM/BY combination (K5, K6, K7, K8). Growth indices showed greater outcomes for the K2 group in comparison to all other groups. A decrease in plasma cholesterol and triglycerides concentrations was found after FM replacement. Activity of SOD was higher in groups K4, K7 and K8. The early inflammatory indications with abnormal vacuolization of lamina propria and basal epithelium were present in diets K4 and K8. Hepatocytes were irregular in shape with signs of inflammatory reaction in diet K8. A decreased perimeter of hepatocyte nuclei was detected in all experimental diets when compared with the control. This study demonstrates that the optimal replacement of FM with SBM/BY in brown bullhead diets contains up to 50% of FM replaced with SBM in order to obtain advantageous growth performance and adequate health condition.

Amplitude modulation patterns of local field potentials reveal asynchronous neuronal populations.

Neural oscillations, which appear in several areas of the nervous system and cover a wide frequency range, are a prominent issue in current neuroscience. Extracellularly recorded oscillations are generally thought to be a manifestation of a neural population with synchronized electrical activity resulting from coupling mechanisms. The vertebrate olfactory neuroepithelium exhibits beta-band oscillations, termed peripheral waves (PWs), in their population response to odor stimulation. Here, we examine PWs in the channel catfish and propose that their properties could be explained as the superposition of asynchronous oscillators. Our model shows that the intriguing random pattern of amplitude-modulated PWs could be explained by Rayleigh fading, an interference phenomenon well known in physics and recognizable using statistical methods and signal analysis. We are proposing a mathematical fingerprint to characterize neural signals generated by the addition of random phase oscillators. Our interpretation of PWs as arising from asynchronous oscillators could be generalized to other neuronal populations, because it suggests that neural oscillations, detected in local field potential recordings within a narrow frequency band, do not necessarily originate from synchronization events.

The taste system of the channel catfish: from biophysics to behavior.

Catfish, described as 'swimming tongues', are unique experimental models for studies of taste reception because of the extensive distribution of taste buds over their external body surface and within their oropharyngeal cavity. Both the extraordinary numbers of taste buds and their high sensitivity to amino acids have made it possible to perform in the same species: biochemical and biophysical studies of stimulus recognition and signal transduction; electrophysiological recordings of taste activity from receptor cells, afferent nerve fibers and CNS relays; and behavioral studies of taste-controlled food search, biting and mastication. The close correspondence of results obtained with these diverse experimental approaches has provided critical information concerning vertebrate gustation.

Isolation and characterization of putative O2 chemoreceptor cells from the gills of channel catfish (Ictalurus punctatus).

Little is known about the cells or mechanisms of O2 chemoreception in vertebrates other than mammals. The purpose of this study, therefore, was to identify O2-sensitive chemoreceptors in a fish. Putative O2-sensitive chemoreceptors were dissociated from the gills of channel catfish, Ictalurus punctatus, and cultured. A population of cells was identified with morphology and a histochemical profile similar to mammalian carotid body Type I (glomus) cells and pulmonary neuroepithelial cells. These cells stain with neutral red and appear to be the branchial neuroepithelial cells. Immunocytochemical staining showed that these cells contain neuron-specific enolase (NSE), tyrosine hydroxylase (TH) and 5-hydroxytryptamine (5HT). Patch-clamp experiments showed that these cells have a O2-sensitive, voltage-dependent outward K+ current like mammalian O2 sensors. Two kinds of electrophysiological responses to hypoxia (P(O2) < 10 Torr) were observed. Some cells showed inhibition of outward current in response to hypoxia, whereas other cells showed potentiation. Neurochemical content and electrophysiological responses to hypoxia indicate that these cells are piscine O2-sensitive chemoreceptors.

Morphological and biochemical heterogeneity in facial and vagal nerve innervated taste buds of the channel catfish, Ictalurus punctatus.

In catfish, the facial nerve innervates taste buds distributed over the entire body including the barbels, while the glossopharyngeal and vagal nerves innervate oropharyngeal taste buds. Facial nerve innervated taste buds (FITBs) are thought to be involved in food detection and localization, while glossopharyngeal and vagal nerve innervated taste buds (VITBs) evaluate the palatability of food prior to ingestion. Physiological studies indicate that both oral and extra-oral taste buds detect sapid substances such as amino acids and nucleotides, but the facial taste system is more sensitive to some of these substances. The anatomical, molecular, and/or physiological mechanisms underlying the functional differences in these two gustatory pathways remain to be identified. In the current investigation we compare the basic morphological features of FITBs and VITBs and the distribution of the following metabolites: gamma-aminobutyric acid (GABA), glutamate, aspartate, alanine, taurine, and glutathione. Vagal innervated taste buds are significantly longer and narrower than FITBs, with fewer taste cells and a smaller nerve plexus. Each of the metabolites examined was heterogeneously distributed in taste cells with notably more GABA positive cells present in the VITBs. Patterns of metabolite colocalization suggest the presence of several taste cell subtypes. The morphological and metabolite differences noted between FITBs and VITBs provide a potential anatomical basis for the previously noted differences in physiological sensitivity.

Visual system of the channel catfish (Ictalurus punctatus): II. The morphology associated with the multiple optic papillae and retinal ganglion cell distribution.

The retinal organization associated with the multiple optic papillae of the catfish Ictalurus punctatus was examined. In each retina from ten to 17 papillae form an oval ring (which is wider dorsoventrally than mediolaterally). The dorsalmost papilla in this ring lies at the center of the retina. In addition, up to seven small papillae lie within the ring. Bundles of fibers leave the neural retina via the papillae. These bundles remain separate as they pass through the distal portions of the neural retina and then merge before passing through the choroid. Bundles running through dorsal papillae receive fibers from a roughly wedge-shaped retinal area; bundles running through ventral papillae receive fibers from a small area of central retina and a disproportionately large area of peripheral retina. A band of high ganglion cell density was observed extending between the nasal and temporal poles of the retina. No correlation was found between the retinal areas contributing fibers to the bundles of axons emerging from individual papillae and the areas of high cell density. Furthermore, no correlation was found between the average area of the retinal ganglion cells and the ganglion cell density. From HRP preparations and axon counts we estimate that each retina of 95-mm catfish contains about 50,000 ganglion cells.

Transcellular labeling of taste bud cells by carbocyanine dye (DiI) applied to peripheral nerves in the barbels of the catfish, Ictalurus punctatus.

In order to study the pattern of innervation of taste buds and the surrounding epithelium, the carbocyanine dye diI was applied to the nerve stump in isolated, paraformaldehyde-fixed barbels obtained from channel catfish, Ictalurus punctatus. After a diffusion period of 7-41 days, the barbels were sectioned on a vibratome and examined with epifluorescence. Labeled axons were observed up to 1 cm from the site of application. Frequently, a fascicle of labeled axons turned outward toward the epithelium to innervate taste buds or to end apparently as free endings within the epithelium. Within 2-3 mm of the dye-application site, many taste buds contained one or at most 5-10, labeled spindle-shaped, presumed receptor, cells. In taste buds containing multiple labeled cells, the cells usually were arranged as intertwined pairs or triplets rather than being homogeneously distributed within the taste bud. In a few cases, labeled basal cells could be discerned among the labeled axons of the basal plexus. The cells of the taste bud apparently were labeled by transcellular passage of the dye from the nerve fibers into the cells. The limited number of labeled cells within each taste bud may indicate a special relationship between these cells and the nerve fibers innervating them.

Postlarval growth of the peripheral gustatory system in the channel catfish, Ictalurus punctatus.

The phenomenon of postlarval cell addition to the peripheral nervous system of fish has been reported for some sensory systems, but has yet to be characterized for the gustatory system. Many fishes, such as catfish, possess taste buds scattered across their body surface, and presumably, the number of taste buds increases during growth of the animal. The present study was undertaken in order to examine the process of growth in the peripheral gustatory system and to determine whether the degree of convergence of receptors onto primary sensory afferents changes during growth. The recurrent facial nerve of channel catfish was used for these studies since this nerve contains no general cutaneous components and innervates taste buds along the fish's body surface. Electron micrographs were made of cross sections of this nerve taken from individuals ranging in size from 5.1 to 39.5 cm standard length. In addition, estimates were made of the number of taste buds innervated by this nerve by determining taste bud density along selected regions of the flank and fins in large and small fish. As catfish get larger, the number of both myelinated and unmyelinated axon profiles in the recurrent facial nerve increases, but at a slower rate than the number of taste buds innervated by this nerve. Thus, on average, the number of taste buds innervated by each fiber increases as the fish enlarges; on average there are 2 taste buds per axons profile in small fish and nearly 14 taste buds per axon profile in large fish. The rate of addition of new axon profiles to the nerve is estimated at roughly 70 per day over the range of sizes studied. Although generation of new ganglion cells and axons may contribute to this increase, several lines of evidence indicate that axonal branching occurs. In addition, the mean axon diameter for both myelinated and unmyelinated axons increases during postlarval growth. The finest myelinated fibers (0.2 micron) in small animals were significantly smaller than the finest myelinated fibers (0.7 micron) in larger animals.

Visceral afferent and efferent columns in the spinal cord of the teleost, Ictalurus punctatus.

In tetrapod vertebrates, neural circuitries subserving visceral and somatic reflexes are each represented in distinct columns of cells within the gray area of the spinal cord. To determine the location of visceral elements of the spinal cord of a teleost fish, crystals of the carbocyanine dye 1,1'dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (DiI), were placed on either the abdominal sympathetic (mesenteric) nerves, the coeliac ganglia, or on the rostral three somatic spinal nerves, in fixed specimens of the channel catfish, Ictalurus punctatus. In fish in which DiI had been placed on the mesenteric nerves, labeled fibers coursed along the lateral margin of the dorsal horn within the first and second spinal segments, and appeared to terminate in a region at the base of the dorsal horn. In contrast, when DiI crystals were placed on the somatic spinal nerves, labeled primary afferents terminated in the dorsalmost two thirds of the dorsal horn, as well as in ventral and ventromedial areas of the medial funicular nuclear complex. Labeled somata (motor neurons) were situated in the ventral horn. When DiI crystals were placed bilaterally on the coeliac ganglia, labeled piriform and fusiform preganglionic neurons occurred in intermediate positions adjacent to the central canal, corresponding to the paracentral nucleus of Herrick, and in the lateral funiculus. These results demonstrate that somatic and visceral afferent and efferent functional columns are distinct in a teleost fish as they are in amniote vertebrates.

Axonal projection patterns of neurons in the secondary gustatory nucleus of channel catfish.

The second gustatory nucleus of teleost fishes receives ascending fibers from the primary gustatory center in the medulla and sends efferent fibers to several nuclei in the inferior lobe of the diencephalon. Similar to the corresponding parabrachial nucleus in birds and mammals, the secondary gustatory nucleus of catfish consists of several cytoarchitectonically distinct subnuclei which receive input from different portions of the primary gustatory nuclei. However, it is unclear how the subnuclear organization relates to the processing of gustatory information in the hindbrain and the subsequent transmission of that information to the forebrain. To determine whether cells within different subnuclei of the secondary gustatory nucleus of channel catfish project to different diencephalic targets, single cells were intracellularly labeled with biocytin. Three subnuclei have been identified in the secondary gustatory nucleus: a medial subnucleus spanning most of the rostrocaudal extent of the nucleus, a central subnucleus and a dorsal subnucleus, the latter two located in the rostrolateral portion of the complex. Cells throughout the secondary gustatory nucleus typically possessed similar collateral projections to several nuclei in the inferior lobe, although four of the six cells filled in the medial subnucleus projected only to nucleus centralis. The only apparent subnucleus-specific projection pattern involved cells at the rostral edge of the secondary gustatory nucleus and in the secondary visceral nucleus. Axons of these cells terminated only in restricted portions of nucleus lobobulbaris. These results suggest that efferents from different subnuclei of the secondary gustatory nucleus of catfish, like those of the parabrachial nucleus of birds and mammals, do not possess simple, topographical projections to target nuclei in the diencephalon.