A description of rodlet cells from the alimentary canal of Anguilla anguilla and their relationship with parasitic helminths

Rodlet cells in intestinal epithelia of infected and uninfected European eels Anguilla anguilla from brackish and fresh water were studied by light and electron microscopy. Deropristis inflata (Trematoda) was found in eels from brackish water, whereas eels from fresh water were infected with Acanthocephalus clavula (Acanthocephala). In a comparison between uninfected and infected eels from brackish water, a higher number of rodlet cells was recorded in the intestinal epithelia of infected fish. Evidence is presented that rodlet cells secrete their contents in a holocrine manner into the lumen of the eel intestine. The occurrence of organelles within the mature rodlet cell was rare. ? 1998 The Fisheries Society of the British Isles     

Rodlet cells in epidermal explant cultures of Lepomis Macrochirus

Sunfish rodlet cells were examined in vitro using a novel tissue explant system. Outgrowth of epidermal cell layers from explanted fish scales enabled both live cell videomicroscopy and immunocytochemical analysis of rodlet cells within the cell layer. Cells stained with fluorescent phallotoxin and antibody to tubulin showed that F‐actin is a component of the fibrous capsule that envelopes the cell and a microtubule network extends from the basal to apical ends of the cell interior. The fibrous capsule is also enriched for phosphotyrosine suggesting a potential signal‐transducing capability is present in this structure. Videomicroscopy analysis of live explant cultures demonstrated that rodlet cells are immobile and that interior structures are highly dynamic. Rodlet sacs can undergo extension and retraction, while intracellular particles can move rapidly within these cells. Fish scale tissue explants provide a useful system for analyzing the molecular composition and dynamic behavior of rodlet cells.     

Observations on rodlet cells found in the vascular system and extravascular space of angelfish (Pterophyllum scalare scalare)

In the angelfish ( Pterophyllum scalare scalare ) numerous rodlet cells were found in the large post-orbital blood vessel caudal to the eye and in the surrounding extravascular space. Within the vessel the rodlet cells formed striking regular arrays, along the inner aspect of the wall. The rodlets within the cells were positive to PAS but negative to Sudan Black B, Masson's, and the Fuelgen stain. The capsule around the cells was negative for all these stains. These rodlet cells appeared to be traversing the vessel endothelium, and to be pushing the endothelium aside without damaging it. Some discharged their contents into the vessel, but we never observed the release of intact rodlets. The nuclei of rodlet cells in actual contact with the vessel were at the end of the cell more distant from the endothelial wall. Cell-to-cell adhesion structures or communications junctions between rodlet cells and the endothelium were not evident. A putative rodlet cell precursor in the extravascular space contained large electron-dense granules, and extended pseudopodia that contacted nearby rodlet cells. Based on their morphology, tissue distribution, and their behaviour, we conclude that the rodlet cell is an endogeneous teleost cell type, and possibly represents a form of matured granulocyte.     

Inflammatory cells of teleostean fish: a review focusing on mast cells/eosinophilic granule cells and rodlet cells

In contrast to the roles played by monocytes/macrophages, neutrophils and lymphocytes, the presence and functions of basophils, mast cells/eosinophilic granule cells, eosinophils and rodlet cells in teleosts are areas of controversy. The tissue distribution of mast cells/eosinophilic granule cells in species from a certain genus shows a characteristic pattern, and this pattern is usually also present at the family level. Functionally, the mast cells/eosinophilic granule cells of teleosts show close similarity to the mast cells of mammals. Acute tissue damage is causing mast cell/eosinophilic granule cell degranulation and release of mediators of inflammation, whereas an increase in the number of these cells is often found in chronically inflamed tissues. The mast cells/eosinophilic granule cells of teleosts show marked diversity in their staining properties, with both basophilic and acidophilic components in their granules. In some fish families, e.g. the labrids, the eosinophilic component is dominating, whereas in the pike the granules are strongly basophilic and show the metachromatic staining characteristics found in the granules of mast cells, but being more akin to the granules of the mucosal than to those of the connective tissue type of mast cells of mammals. With respect to rodlet cells, a cell type hitherto clearly demonstrated only in teleosts, a characteristic distribution pattern seems to be established in certain families. In other families rodlet cells are absent in some individuals and present in different tissues in others. However, there is a close relation between the presence of helminths or other noxious agents and the presence of rodlet cells. Massive aggregations of such cells can be seen in affected epithelia of gills or the intestinal tract, and in individuals of species from some fish families they also occur in association with mesothelial and endothelial tissues. The rodlet cell may represent a type of eosinophilic granulocyte that populates the tissues at its immature stage and mature in response to the appropriate stimuli, in a way similar to that of mast cell precursors. Present evidence points to a functional role for the rodlet cells of teleosts in host defence against parasites.     

Intraspecific variability in the “vowel”‐like sounds of beluga whales (Delphinapterus leucas): Intra‐ and interpopulation comparisons

The beluga whale (Delphinapterus leucas) has a rich and complicated vocal repertoire. However, different populations use similar and common types of signals. We studied physical features of one of these types, “vowels,” in three Russian populations: the White Sea population (European North), the Chukotka population (the Bering Sea, Chukotka), and the Okhotsk Sea population (Russian Far East) as well as in four summer aggregations of the White Sea belugas over several years in duration. The pulse repetition rate (PRR) at half of the duration of the signal was measured. We found that the PRR of “vowels” collected in the same summer aggregation during different years is stable in time but varies between locations. The degree of variation corresponds with the geographic distance between different locations. Significant differences were discovered between populations separated by thousands of kilometers, and to a lesser extent, between summer aggregations inhabiting different bays of the White Sea. The variation in PRR between the locations can be caused by the divergence of signals owing to the accumulation of random errors during transmission of these signals from generation to generation, which progressed independently in different summer aggregations and populations.     

Development of rodlet cells in the gut of turbot (Psetta maxima L.): Relationship between their morphology and S100 protein immunoreactivity

Rodlet cells are an enigmatic cell type described in tissues of both marine and freshwater teleosts. Although their structure is well established, up to date their function remains subject of debate. However, there is consensus among the majority of researchers that rodlet cells play an important role within immune system, and this function is probably related with the release of rodlets due to contractile capability of their fibrous layer. Regulation of the contraction mechanism would require proteins that modulate Ca⁺⁺ intracellular concentration to be expressed in rodlet cells. We performed a morphological and immunohistochemical study at light and electron microscopy levels to assess S100 protein immunoreactivity in developing rodlet cells. Immature stages did not exhibit immunoreactive signal; however, immunoreactivity was observed in the fibrous layer of both transitional and mature rodlet cells. The latter stage also showed immunosignal within the rodlets. These findings suggest a clear association between S100 protein expression and rodlet cell development that could be linked to the regulation of rodlet activity and contractile property of their fibrous layer. Furthermore, S100 protein antibody constitutes a novel marker for rodlet cells that could be used in future studies of this particular cell type.     

Reappraisal of nuclear DNA content of rodlet cells compared to several cell types from some freshwater teleosts, using two methods of microdensitometry

Nuclear DNA contents of rodlet cells from Catostomus commersoni, Semotilus atromaculatus and Cyprinus carpio were compared with nuclear DNA of erythrocytes and larger cells of the same species, using scanning microdensitometry and averaging microdensitometry. This study reappraises the work of Barber & Westermann (1983), which employed averaging microdensitometry only, and compared rodlet cell nuclear DNA only with erythrocyte DNA. In addition, this work considers sources of error in both methods of microdensitometry, and comments upon the use of microdensitometry of either method as a mechanism for making distinctions among the DNA contents of cells of different types. The results of the present work consistently indiate no significant differences within species between nuclear DNA content of rodlet cells and larger teleost cells, using either method of microdensitometry. Because of the lack of statistically significant difference in DNA content between nuclei of rodlet cells and those of known teleost cells, it has been concluded that the rodlet cell itself is probably of teleost origin. However, the method indicates nothing about the origin of the rodlets, which have also been shown to contain DNA, but are Feulgen-negative.     

Prediction and verification of possible reef‐fish spawning aggregation sites in Los Roques Archipelago National Park,Venezuela

This study attempts to predict and verify possible spawning aggregation sites and times in the Los Roques Archipelago National Park, Venezuela, based on physical reef characteristics and the knowledge of experienced local fishermen. Three possible aggregation sites were selected for monitoring based on satellite images, low‐cost bathymetric mapping and interviews with experienced local fishermen. Abundances and sizes of 18 species that are known to form reproductive aggregations were monitored at these sites using underwater visual census for 7 days after each full moon from February to August, 2007. While spawning events were not observed, possible indirect evidence of spawning aggregations was found for Lutjanus analis at Cayo Sal and Boca de Sebastopol, Lutjanus apodus at Cayo Sal, Lutjanus cyanopterus at Cayo Sal and Piedra La Guasa and Epinephelus guttatus at Bajo California and Cayo de Agua. Additionally, indirect evidence was identified for the past existence of a spawning aggregation of Epinephelus striatus in the northern part of the archipelago, which may have been eliminated by overfishing c.15 years ago. Bathymetric mapping showed that the shelf edge at sites monitored in this study was shallower than at spawning aggregation sites in other parts of the Caribbean, and that sites were not proximal to deep water. While this study does not prove the existence or locations of spawning aggregations of reef fishes in the archipelago, it does add insight to a growing understanding of generalities in the relationship between seafloor characteristics and the locations of transient reef‐fish spawning aggregations in the Caribbean.     

Density and maturation of rodlet cells in brain tissue of fathead minnows (Pimephales promelas) exposed to trematode cercariae

Evidence for the presumed linkage between the enigmatic rodlet cells of fish and exposure to helminths is anecdotal and indirect. We evaluated the proliferation and development of rodlet cells in the optic lobes of fathead minnows exposed to cercariae of Ornithodiplostomum ptychocheilus. Mean rodlet cell densities (ca. 10/mm²) in the optic lobes were similar between unexposed controls and minnows with 1- and 2-week old infections. Rodlet cell densities increased at 4 weeks p.i., reaching maxima (ca. 200/mm²) at 6 weeks p.i., followed by a decline at 9 weeks. This temporal pattern of proliferation and maturation paralleled the development of metacercariae within the optic lobes. Unencysted metacercariae develop rapidly within tissues of the optic lobes for approximately 4 weeks after penetration by cercariae, then shift to the adjacent meninges to encyst. The former stage is associated with tissue damage, the latter with massive inflammation of the meninges. Thus, peak densities and maturation of rodlet cells correspond to the period when inflammation of the meninges caused by the large metacercarial cysts is at a maximum. Our results support recent contentions that rodlet cells comprise part of the host inflammatory defence response.     

Introduced ants reduce interaction diversity in a multi‐species,ant–aphid mutualism

Mutualisms contribute in fundamental ways to the origin, maintenance and organization of biological diversity. Introduced species commonly participate in mutualisms, but how this phenomenon affects patterns of interactions among native mutualists remains incompletely understood. Here we examine how networks of interactions among aphid‐tending ants, ant‐tended aphids, and aphid‐attacking parasitoid wasps differ between 12 spatially paired riparian study sites with and without the introduced Argentine ant Linepithema humile in southern California. To resolve challenges in species identification, we used DNA barcoding to identify aphids and screen for parasitoid wasps (developing inside their aphid hosts) from 170 aphid aggregations sampled on arroyo willow Salix lasiolepis. Compared to uninvaded sites, invaded sites supported significantly fewer species of aphid‐tending ants and ant‐tended aphids. At invaded sites, for example, we found only two species of ant‐tended aphids, which were exclusively tended by L. humile, whereas at uninvaded sites we found 20 unique ant–aphid interactions involving eight species of ant‐tended aphids and nine species of aphid‐tending ants. Ant–aphid linkage density was thus significantly lower at invaded sites compared to uninvaded sites. We detected aphid parasitoids in 14% (28/198) of all aphid aggregations. Although the level of parasitism did not differ between invaded and uninvaded sites, more species of wasps were detected within uninvaded sites compared to invaded sites. These results provide a striking example of how the assimilation of introduced species into multi‐species mutualisms can reduce interaction diversity with potential consequences for species persistence.     

Spatial Nest‐Settlement Decisions in Digger Wasps: Conspecifics Matter more than Heterospecifics and Previous Experience

Research into the driving forces behind spatial arrangement of wasp nests has considered abiotic environmental factors, but seldom investigated attraction or repulsion towards conspecifics or heterospecifics. Solitary female digger wasps (Hymenoptera) often nest in dense aggregations, making these insects good models to study this topic. Here, we analysed the nesting patterns in an area shared by three species of the genus Bembix, in a novel study to discover whether female wasps are attracted to or repulsed by conspecific nests, heterospecific nests or their own previously established nests when choosing nest‐digging locations. Early in the season, each species showed a clumping pattern of nests, but later in the season, a random distribution of nests was more common, suggesting an early conspecific attraction. Such behaviour was confirmed by the fact that females started building their nests more frequently where other females of their species were simultaneously digging. The distances between subsequent nests dug by individual females were shorter than those obtained by random simulations. However, this pattern seemed to depend on the tendency to dig close to conspecifics rather than remain in the vicinity of previous nests, suggesting that females' experience matters to future decisions only on a large scale. Nesting patches within nest aggregations largely overlapped between species, but the nests of each species were generally not closer to heterospecific nests than expected by chance, suggesting that females are neither repulsed by, nor attracted to, congenerics within nest aggregations. A role of the spatial distribution of natural enemies on the observed nesting patterns seemed unlikely. Bembix digger wasp nest aggregations seem thus to be primarily the result of female–female attraction during nest‐settlement decisions, in accordance with the ‘copying’ mechanisms suggested for nesting vertebrates.     

Fine structure and cytochemistry of the endothelial cells and rodlet cells in the bulbus arteriosus in species of Cichlidae (Teleostei)

The ultrastructure of endothelial cells and rodlet cells in the bulbus arteriosus of specimens representing six genera of Cichlidae is described. The former are very closely packed by membrane–bound and mainly electron–dense inclusion bodies (0.3–0.7μm).
In Apistogramma ramirezi I observed numerous subendothelial rodlet cells throughout the entire length of the bulbus arteriosus. These cells penetrate the endothelium and connect to the latter by desmosomes and tight junctions. The luminal part of the cell contains numerous vesicles and tubules (width 50–100 nm), whereas the basal part is occupied by a number of membrane–bound, club–like inclusions (length ≤ 5 μm). Between these two layers there occurs a layer of small, elongated mitochondria. Peripherally, these cells consist of a filamentous wall, except in the apical area.
The endothelial and rodlet cell inclusion bodies do not react with phosphotungstic acid (pH 1) or Sudan black B stain. The endothelial cells react strongly with periodic acid–Schiff (PAS) stain, whereas the rodlet cells are only moderately coloured by this stain.
The present results are discussed and compared with those reported previously for endothelial/ endocardial cells and rodlet cells in bony fish.     

State of gonads in juvenile triploid trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> under conditions of South Vietnam after artificial sex inversion

Gonad morphology and structure of sex cells in juvenile triploid trout Oncorhynchus mykiss of the Donaldson breed incubated and reared at a trout plant under climatic conditions of South Vietnam have been studied. Anomalies in the structure of sex gonads and oocyte structure were found, and partial resorption of sex cells was detected. It was shown that sex inversion in triploid (unisexual) fingerlings of rainbow trout passed successfully on the whole since many sex gonads of these fish simultaneously had both female and male sex cells and sometimes were sterile. The connection of anomalies found in the structure of sex system of trout with species rearing under unusual for it climatic conditions and artificial sex inversion is discussed.     

The rodlet cells of teleostean fish: their potential role in host defence in relation to the role of mast cells/eosinophilic granule cells

The distribution and potential function of the rodlet cells of teleosts were studied by microscopic observations on tissue samples from the digestive tract and adjacent tissues, including the bulbus arteriosus. Fish representing 3-5 genera from each of the families Salmonidae, Cyprinidae, Gadidae and Labridae were included in the study. Great individual variations in the distribution of rodlet cells were found in all species of salmonids, gadids and labrids. The cells seemed to be absent in some individuals of a species and were associated with different epithelial tissues in others, but were not found in vascular endothelia. Their occurrence was common in all salmonids caught in their natural environment, whereas those in aquaculture, kept under controlled conditions with respect to water quality, showed extremely few rodlet cells. In species of the cyprinid family, the picture was different. Rodlet cells were consistently present under the endothelium of the bulbus arteriosus, and were very numerous at this location in individuals infected with blood flukes. In other epithelial tissues of cyprinids, rodlet cells were encountered in fairly high numbers, but in some tissues of individuals from all species they were occasionally absent. In all of the studied families rodlet cells seemed to be recruited when helminths affected epithelial tissues. Mast cells/eosinophilic granule cells were consistently very numerous in tissues of the intestine of cyprinids and labrids. In gadids, mast cells/eosinophilic granule cells seemed to be absent. Present evidence points to a role for the rodlet cells in defence functions, e.g. in combating helminths, and the suggestion earlier made for mast cells/eosinophilic granule cells, that evolution has created a "standing force" in particular tissues of teleosts consistently exposed to pathogens, whereas an efficient "mobilization force" has been an advantage in those living in more pathogen-free environments, may also be applied to rodlet cells, explaining the differences between teleostean families with respect to their distribution pattern.     

New observations on the rodlet cell (Rhabdospora thelohani) in the white sucker Catostomus commersoni (Lacépède): LM and EM studies

Light and electron microscopic studies of the morphological features of immature and mature rodlet cells in Catostomus commersoni are presented emphasizing the cells' association with epithelial tissues. The peripheral fibrillar layer is lacking from the apex and from the base of the cell. A cytoplasmic extension from the base may be a feeding mechanism whereby the rodlet cell obtains nutrient at the expense of adjacent cells leaving intercellular spaces often containing myelin figures. RNAase digestion studies demonstrate the presence of RNA in the electron dense rodlet core.
The structure and histochemistry of the rodlets which do not appear to disintegrate upon expulsion from the cell are compared to the cytoplasmic inclusions of both normal fish cells and protozoan parasites. The possible association of the rodlet cell with various pathological conditions is briefly reviewed and the authors conclude that it is premature to disregard the possibility that this cell could be a parasite or infective agent.     

The state of gonads of resident sockeye salmon <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis> from the Tolmachev Reservoir

Morphology of gonads and structure of sex cells in females and males of the resident sockeye salmon Oncorhynchus nerka—kokanee—from Tolmachevskoe Reservoir are investigated. Anomalies in structure of sex cells and structure of oocytes are found. Partial or mass resorpbion of cells in the ovaries of males and testes of males is found, leading to sterility of gonads. The relationship between anomalies found in structure of the sex system of kokanee, changes in biological parameters of fish and the increase of the population abundance is discussed.     

Alteration of rodlet cells in chub caused by the herbicide Stam® M-4 (Propanil)

Handling stress and exposure to the herbicide Stam® M-4 (Propanil) were associated with an exponential depletion of the rodlet cells (RC) in the bulbus arteriosus of chub Leuciscus cephalus . Structural changes of the RC in herbicide-exposed fish were encountered, including the occurrence of myeloid bodies in the cytoplasm of the RC of the intestine, various degrees of rodlet degeneration and high vacuolization in the cytoplasm of RC in almost all examined organs of exposed chub.     

Morphological and immunohistochemical characterisation of the thymus in juvenile turbot (<Emphasis Type="Italic">Psetta maxima,</Emphasis> L.)

We performed structural and immunohistochemical studies on the thymus of juvenile turbot (Psetta maxima L.) in order to define its cellular composition. The thymic stroma was mainly composed of two subpopulations of reticulo-epithelial cells (RECs). RECs immunoreactive to anti-actin antibody were distributed through the organ, while RECs that were cytokeratin-immunopositive were located in the outer zone of the thymus. The parenchyma of the thymus was composed of several cell types such as lymphocytes/thymocytes, lymphoblasts, melano-macrophages and to a lesser extent of nurse-like cells, immunoglobulin positive (Ig+) cells, mucous cells, rodlet cells and neuroendocrine cells. CD3ε+ lymphocytes were mainly located in the outer zone. On the other hand, Ig+ cells were observed in the transitional region between the inner and outer zones of the thymus. The neuroendocrine cells were large and exhibited immunoreactivity to neuropeptide Y and vasoactive intestinal polypeptide. They were located in the inner zone of the thymus in close association with lymphoblasts and lymphocytes/thymocytes. This work provides useful information on the structure and cellular composition of the thymus of turbot, identifying several immunomarkers that allow the identification of different cell types, providing the basis for further studies on the immune response of turbot against diseases.     

Density‐dependent effects on initial growth of a branching coral under restoration

Coral reef restoration aims to help threatened coral ecosystems recover from recent severe declines. Here we address whether coral fragments should be out‐planted individually or in larger aggregations. Theory suggests alternative possible outcomes: whereas out‐plants within aggregations might suffer from heightened negative interactions with neighbors (e.g. competition for space), they may alternatively benefit from positive interactions with neighbors (e.g. buffering wave disturbances). On a degraded reef in the Caribbean (St. Croix, USVI), using out‐plants of the critically endangered staghorn coral Acropora cervicornis, we experimentally tested how aggregation density (1–20 out‐planted coral fragments spaced at approximately 5 cm) influenced initial coral growth (over 3 months). Coral growth declined as a function of aggregation size, and out‐plants within larger aggregations had fewer and shorter secondary branches on average, indicative of horizontal competition for space. Our results therefore suggest that wide spacing of individuals will maximize the initial growth of out‐planted branching corals.     

Aggregations of <Emphasis Type="Italic">Plectropomus areolatus</Emphasis> and <Emphasis Type="Italic">Epinephelus fuscoguttatus</Emphasis> (groupers,Serranidae) in the Komodo National Park,Indonesia: Monitoring and Implications for Management

Synopsis We identify fishery management implications from a long-term monitoring program focusing on spawning aggregations of high valued reef fish in Komodo National Park (KNP), Eastern Indonesia. Management objectives of KNP are not only to protect biodiversity, but also to conserve spawning stocks of high-valued commercial species for the replenishment of surrounding fishing grounds. We monitored two sites twice monthly over five years for two species of grouper, Epinephelus fuscoguttatus and Plectropomus areolatus. One site had an aggregation of both E. fuscoguttatus and P. areolatus, whereas the other site contained an aggregation of P. areolatus only. Over the five years monitoring period, aggregations typically formed during each full moon between September and February. Additionally, P. areolatus occasionally aggregated during new moons between April and July. We observed spawning only once, but because formation of aggregations were correlated to a higher incidence of behavior and signs indicative of reproduction and because most fish present were adults, it is likely that the formation of aggregations was associated with spawning. Over the five years monitoring period there was a reduction in mean fish size of up to 8 cm for P. areolatus, and a reduction in numbers of aggregating E. fuscoguttatus. Despite limited protection initiated in 2001, both sites are still heavily fished by local artisanal fishers. Because the observed reductions in size and in numbers could be caused by fishing pressure, managers should follow the precautionary principle by putting additional protective management in place. Since both species are relatively long-lived, at least five years of continued monitoring may be necessary to determine the outcome of management intervention. The variability in timing of aggregation in respect to season and moon phase in P. areolatus indicates that long-term monitoring must cover the entire year and both moon phases.