The niche of Salsuginus thalkeni, a gill parasite of Fundulus zebrinus

Distribution of a monogenean parasitic helminth Salsuginus thalkeni on the gills of the fish Fundulus zebrinus is described by calculation of mean positions and niche breadths on the linear spatial resource gradients gill filament length, gill arch length and arch number. All distributions are given for parasites in the presence and absence of various combinations of potential competitors, namely the 6 other parasite species that occupy the same host species. Filament niche breadth was narrowest in the absence of potential competitors; breadth on arch was widest in the presence of potential competitors. Breadth on both resources was correlated positively with mean number of parasites per individual. Arch breadth exhibited cyclic seasonal changes, being lowest in early to mid-summer. Mean position exhibited no repeated pattern of variation on either resource. The results are considered consistent with predictions about the niche structures of species in unsaturated noninteractive specialist communities.     

Intraspecific variation in gill morphology of juvenile Nile perch, Lates niloticus, in Lake Nabugabo, Uganda

Several studies have demonstrated intraspecific variation in fish gill size that relates to variation in dissolved oxygen (DO) availability across habitats. In Lake Nabugabo, East Africa, ecological change over the past 12 years has coincided with a shift in the distribution of introduced Nile perch such that a larger proportion of the population now inhabits waters in or near wetland ecotones where DO is lower than in open waters of the lake. In this study, we compared gill size of juvenile Nile perch between wetland and exposed (open-water) habitats of Lake Nabugabo in 2007, as well as between Nile perch collected in 1996 and 2007. For Nile perch of Lake Nabugabo [<20 cm total length (TL)], there was a significant habitat effect on some gill traits. In general, fish from wetland habitats were characterized by a longer total gill filament length and average gill filament length than conspecifics from exposed habitats. Nile perch collected from wetland areas in 2007 had significantly larger gills (total gill filament length) than Nile perch collected in 1996, but there was no difference detected between Nile perch collected from exposed sites in 2007 and conspecifics collected in 1996.     

Site preference of fish myxosporeans in the gill

In addition to the morphological and size characteristics of the spores, indicating the exact location and tissue specificity is also essential for differentiation of the large number of species belonging to the group of gill-parasitic fish, the myxosporeans. According to the observations of the present author, Myxobolus, Henneguya and Thelohanellus species are characterised by strict tissue specificity, and species showing affinity to the epithelium, connective tissue, cartilage or vascular tissue usually occur in a strictly defined location within the gill apparatus. Some of the species typically form plasmodia in the lamellae of the gill and others in the gill filaments. Yet other species develop their plasmodia at the base of the gill filament or in the gill arch. Instead of the generally accepted but misleading terms 'intra-' and 'interlamellar', the present author distinguishes interlamellar-epithelial and intralamellar-vascular types in the case of plasmodia developing in the gill lamellae, and intrafilamental-epithelial, intrafilamental-vascular and intrafilamental-chondroidal types in the case of plasmodia developing in the gill filaments. Regarding site of development within the gill, the location of basifilamental plasmodia and that of plasmodia developing in the cartilaginous matrix, connective tissue or blood vessels of the gill arch are well distinguishable from the above types. The different types and their variations are shown in histological illustrations.     

The source of lamellar mitochondria-rich cells in the air-breathing fish, Trichogaster leeri

Pavement cells and the mitochondria-rich cells (MRCs) are two of the main types of cells in fish gill epithelia. The pavement cells are generally responsible for gas exchange and MRCs for ion regulation. MRCs are found especially in the trailing edge and the interlamellar region of gill filament. In some species, MRCs are also observed in the gill lamellae. A previous study reported the likelihood of having lamellar MRCs in air-breathing fishes. Nevertheless, the source of lamellar MRCs is unclear. We used the air-breathing fish, Trichogaster leeri, to investigate the source of proliferated cells on the lamellae when 5-bromo-2-deoxyuridine (BrdU) was injected at different times before fish were sampled from deionized water. There were two major findings in this study. First, undifferentiated cells were found in the lamellae, as well as in the filaments. And, within 12-24 hr, a proliferated cell, identified as BrdU cell, could differentiate to an MRC in the gill lamellae. Second, the filaments and the lamellae in T. leeri responded to ionic stress differently but the proportion of the proliferated MRCs to the BrdU cells remained constant. Our results suggested that the lamellar MRCs were mainly differentiated from the cells that proliferated earlier from the lamellae.     

Developmental and environmental regulation of chloride cells in young American shad, Alosa sapidissima

Location, abundance, and morphology of gill chloride cells were quantified during changes in osmoregulatory physiology accompanying early development in American shad, Alosa sapidissima. During the larval-juvenile transition of shad, gill chloride cells increased 3.5-fold in abundance coincident with gill formation, increased seawater tolerance, and increased Na(+),K(+)-ATPase activity. Chloride cells were found on both the primary filament and secondary lamellae in pre-migratory juveniles. Chloride cells on both the primary filament and secondary lamellae increased in abundance (1.5- to 2-fold) and size (2- to 2.5-fold) in juveniles held in fresh water from August 31 to December 1 (the period of downstream migration) under declining temperature. This proliferation of chloride cells was correlated with physiological changes associated with migration (decreased hyperosmoregulatory ability and increased gill Na(+),K(+)-ATPase activity). Increases in chloride cell size and number of fish in fresh water were delayed and of a lower magnitude when shad were maintained at constant temperature (24 degrees C). When juveniles were acclimated to seawater, chloride cell abundance on the primary filament did not (though size increased 1.5- to 2-fold), but cells on the secondary lamellae disappeared. Na(+),K(+)-ATPase was immunolocalized to chloride cells in both fresh water and seawater acclimated fish. The disappearance of chloride cells on the secondary lamellae upon seawater acclimation is evidence that their role is confined to fresh water. The proliferation of chloride cells in fresh water during the migratory-associated loss of hyperosmoregulatory ability is likely to be a compensatory mechanism for increasing ion uptake. J. Exp. Zool. 290:73-87, 2001.     

Sieving functional morphology of the gill raker feeding apparatus of atlantic menhaden

Menhaden occupy an important position in estuarine food webs, thus the rate processes associated with their feeding are critical to the ecosystem management of fishery and ecological resources. Atlantic menhaden feed on a wide range of plankton, the size and food quality of which change ontogenetically. We analyzed the functional morphology of the menhaden feeding apparatus in a size series of menhaden representative of juveniles and the adult migratory stock. The physical dimensions of gill arches and rakers increased isometrically with fish length; however, branchiospinule spacing, the dimension that forms the sieve apertures of the branchial basket, scaled allometrically with fish length. Juvenile menhaden from North Carolina have branchiospinule spacings that averaged 12 microm, with three arch subsections of average spacing < 10 microm. Spacings did not increase with juvenile growth until the first allometric inflection point at approximately 100 mm fork length (FL). Spacing data for juveniles from other locations suggests spacing increases with latitude. Spacings increase with fish length in adults until a second inflection at 200 mm FL, after which spacing averages 37 microm. These data suggest menhaden juveniles filter smaller plankton with higher filtration efficiency than previously considered and that regional recruitment may affect adult distribution through foraging preferences.     

Morphometrics of gills during growth and development of the air-breathing habit in Colisa fasciatus (Bloch and Schneider)

Gill area and other component parameters of Colisa fasciatus during early life were measured for fish larvae divided into two groups (a) exclusively aquatic and (b) bimodal breathers. Statistical analyses of the data in relation to body size yielded two significantly different straight lines (one for aquatic and other for bimodal breathers) for each parameter. Morphological examinations of gill arches indicated that an increase in the gill area was brought about mainly by an increase in the filament length. The higher slope value (2.41) of gill area in the aquatic phase than that in the bimodal phase ( b = 0.80) is suggestive of a higher weight-specific metabolism in the younger larvae. A heterogenous growth pattern during early ontogenesis of the fish results in intraspecific variation in the gill dimensions which might have been influenced by the acquisition of the air-breathing mechanism in the post-larval stage, besides ecological factors.     

Environmental transmission of a sulfur-oxidizing bacterial gill endosymbiont in the tropical lucinid bivalve Codakia orbicularis.

Codakia orbicularis is a large tropical member of the bivalve mollusk family Lucinidae which inhabits shallow-water sea-grass beds (Thalassia testudinum environment) and harbors sulfur-oxidixing endosymbiotic bacteria within bacteriocytes of its gill filaments. When a C. orbicularis-specific 16S rDNA (DNA encoding rRNA) primer is used with a bacterium-specific 16S rDNA reverse primer in amplifications by PCR, the primer set was unsuccessful in amplifying symbiont DNA targets from ovaries, eggs, veligers, and metamorphosed juveniles (600 microns to 1 mm in shell length) cultivated in sterile sand, whereas successful amplifications were obtained from gill tissue of adult specimens and from metamorphosed juveniles (600 microns to 1 mm in shell length) cultivated in unsterilized sea-grass bed sand. To ascertain the presence of the symbiont target in juveniles, restriction fragment length polymorphism analysis, Southern blotting, and transmission electron microscopy were used. Specific hybridizations and observation of endosymbiotic bacteria in the gills of numerous juveniles cultivated in unsterilized sea-grass bed sand showed that the sulfur-oxidizing endosymbionts of C. orbicularis are environmentally transmitted to the new generation after larval metamorphosis.     

Studies on the extent of gill surface in a fresh water cat-fish Bagarius bagarius (Ham.).

The total gill area of the fish ranges from 37,537 to 56,551 lamellae. The number of lamellae per mm of the gill filament and area of lamellae knowing the respiratory gill area, the gill area per g of body weight and per cm3 of body volume were calculated to correlate the variation in gill surface area per unit weight and volume of the fish. The fish can survive for quite long out of water as the lamallae are spaced wide apart and do not adhere together.     

Gill area and dimensions of gilthead sea bream Sparus aurata L.

Detailed measurements of gill area and constituent variables (total filament length, lamellar frequency and bilateral area) were performed on both hemibranchs of all eight arches in six specimens of gilthead sea bream Sparus aurata (mean ±s.e . 49·9 ± 0·2 g). Shrinkage was also quantified and results were corrected accordingly. Filament number decreased from the first to the fourth gill arch, and average bilateral area of secondary lamellae was higher in the second and third arches. Total and mean filament length, total number of secondary lamellae and total gill area (A_TG) were lower in posterior than in anterior hemibranchs of the second, third and fourth gill arches; while the opposite was observed for the first arch. Lamellar frequency was increased in posterior hemibranchs of all arches compared to that in anterior hemibranchs, especially at the fourth arch. Comparison of the actually measured A_TG and constituent variables with estimates revealed that the third gill arch is the most representative for appropriate measurements and that any of its components (even one hemibranch) approximates the best A_TG (within the range of 0·2–4·3%, P > 0·05) and related dimensions. Consequently, necessary measurements were restricted to the posterior hemibranch of the third gill arch, and A_TG and dimensions (y) were estimated in 21 specimens (23·5–217·6 g) and correlated to body mass (M) according to the allometric equation y = aM^b. As fish increased in size, A_TG (b= 0·664), total (b= 0·425) and mean (b= 0·323) filament length, total number of filaments (b= 0·103) and secondary lamellae (b= 0·377), as well as average lamellar bilateral area (b= 0·288), increased, while the opposite was observed for lamellar frequency (b=?0·049) and mass‐specific area (b=?0·336). Data obtained are discussed in relation to S. aurata activity and living ethology.     

Mast cell responses to Ergasilus (Copepoda), a gill ectoparasite of sea bream

Immunocytochemical, light microscopy and ultrastructural studies were conducted on gill of sea bream, Sparus aurata L., naturally parasitized with the important parasitic copepod Ergasilus sp. to assess pathology and cellular responses. Thirty-seven S. aurata were examined from a fish farm; 26 (70%) were parasitized, with infection intensity ranging from 3 to 55 parasites per fish. Hosts were divided into two groups, lightly infected fish (<15 parasites per fish) and heavily infected fish (>15 parasites per fish). In histological sections, the copepod encircled gill lamellae with its second antennae, compressed the epithelium, provoked hyperplasia and hemorrhage, occluded arteries and often caused lamellar disruption. Fusion of the secondary lamellae due to epithelial hyperplasia was common in all infected fish; heavily infected fish showed more intense branchial inflammation. In both healthy and infected fish, mast cells (MCs) were free within the connective tissue inside and outside the blood vessels of the primary lamellae and made close contact with vascular endothelial cells, mucous cells and rodlet cells (RCs). MCs were irregular in shape with a cytoplasm filled by numerous electron-dense, membrane-bound granules. Immunostaining of primary and secondary gill filaments with an antibody against the antimicrobial peptide (AMP) piscidin 3 (anti-piscidin 3 antibody, anti-HAGR) revealed a subpopulation of MCs that were positive. These MCs were more abundant in gills of heavily infected fish than in either lightly infected or uninfected fish (ANOVA, P<0.05). Our report documents the response of gill to ectoparasite infection and provides further evidence that mast cells and their AMPs may play a role in responding to branchial ectoparasite infections.     

Gill filament differentiation and experimental colonization by symbiotic bacteria in aposymbiotic juveniles of Codakia orbicularis (Bivalvia: Lucinidae)

Summary

Codakia orbicularis is a tropical lucinid harboring gill endosymbionts which are environmentally transmitted from a free living-symbiont form to the new host generation after metamorphosis. Structural changes occurring in the cellular organization from incomplete gill filaments in young aposymbiotic juveniles to full differentiated gill filaments containing bacterial endosymbionts in reared symbiotic juveniles, were analyzed for juveniles from 250 μm to 2 μm shell-length. Aposymbiotic juveniles possess differentiated gill filaments with ciliated, intermediary, and lateral zones similar to those described in wild juveniles, except for the bacteriocytes which are lacking. Granule cells, which progressively differentiate during the morphogenesis of the gill filament, do not appear as a consequence of symbiosis. Experimental colonization of aposymbiotic juveniles by the free-living symbiont form has been obtained through the addition of unsterilized sand collected from the natural habitat of C. orbicularis. Two days after exposure to crude sand, symbiosis-competent bacteria enter by endocytosis at the apical pole of undifferentiated cells which progressively differentiate into classical bacteriocytes similar to those found in the adult gill filaments. Undifferentiated cells of aposymbiotic gill filaments remain receptive to bacteria several months after metamorphosis, and become bacteriocytes when aposymbiotic juveniles get contact with the symbiont free-living form. Therefore, the environmental transmission of symbionts does not appear to be restrained to a defined period of time during post-larval development in C. orbicularis.     

Morphology of central compartment and vasculature of the gills of Lepidosiren paradoxa (Fitzinger)

The four paired gill arches of the South American lungfish Lepidosiren paradoxa contain single branchial arteries directly connecting dorsal and ventral arteries. In gill arches 3 and 4 the branchial arteries also supply looped arlerioles and capillaries to much-reduced gill filaments. Regulation of blood between these routes is thought to be by alteration of vascular resistance. Within the filaments, extensive subepithelial capillary networks and numerous small pumps connect lymphatic vessels in the central connective tissue compartment with venules which, in turn, drain to paired branchial veins.
The features of the endothelium of many of the filament blood vessels suggest extensive transporting, haematolytic and granulopoeitic functions. Large numbers of macrophages pack the connective tissue. Many contain extensive quantities of haemosiderin.     

Gill ectoparasites of Barbus martorelli (Teleostean: Cyprinidae) from a tropical watercourse (Cameroon,Africa): conflict or coexistence?

The structure and stability of parasite communities have been mainly explained by high diversity and strong interactions among parasite species. During 16 months, 558 Barbus martorelli gill infracommunities were studied in a tropical zone to determine whether parasite infrapopulations interact. Three levels were retained: the infracommunity level, the gill filament level, and the filament fraction level. Single species infections in Barbus martorelli were very rare and only concerned the core species: Dactylogyrus bopeleti, D. insolitus, D. simplex and Myxobolus barbi. Mixed infections appeared as a general rule in this fish species. Interspecific interactions at all three levels were statistically non significant. Our results suggest that Barbus martorelli gill parasites are non interactive (isolationist).     

Habitat utilization by coral reef fish: implications for specialists vs. generalists in a changing environment

1. The impact of environmental disturbance and habitat loss on associated species is expected to be dependent on a species' level of specialization. We examined habitat use and specialization of coral reef fish from the diverse and ecologically important family Pomacentridae, and determined which species are susceptible to declines in coral cover due to disturbance induced by crown-of-thorns seastar (COTS, Acanthaster planci L.). 2. A high proportion of pomacentrid species live in association with live coral as adults (40%) or juveniles (53%). Adults of many species had strong affiliations with branching corals, while juveniles favoured plating growth forms, reflecting the sizes of refuge provided by coral types. 3. Juveniles of species that associated with coral had narrower niche breadths than adult conspecifics, due to associations with specific coral types. The especially high coral association and narrower niche breadth of juveniles suggest that the presence of live coral is crucial for many species during early life history, and that disturbance-induced coral loss may have serious flow-on effects on adult abundance. 4. Microhabitat availability was a poor predictor of fish species abundance. Significant correlations between coverage of coral types and abundance of five adults and two juvenile species were detected; however, these relationships explained <35% and <10% of the variation in abundance of adult and juvenile species, respectively. 5. Niche breadth explained 74% of the variation in species' mean response to coral decline and it is clear that disturbance has a greater impact on resource specialists, suggesting that increasing frequency and intensity of coral loss will cause reef fish communities to become dominated by habitat generalists at the expense of coral-dwelling specialists.     

Vascular anatomy of the fish gill

The fish gill is the most physiologically diversified vertebrate organ, and its vasculature the most intricate. Application of vascular corrosion techniques that couple high-fidelity resins, such as methyl methacrylate, with scanning electron microscopy yields three-dimensional replicas of the microcirculation that have fostered a better appreciate gill perfusion pathways. This is the focus of the present review. Three vascular networks can be identified within the gill filament. The arterioarterial (respiratory) pathway consists of the lamellae and afferent and efferent segments of the branchial and filamental arteries and lamellar arterioles. The body of the filament contains two post-lamellar pathways: the interlamellar and nutrient. The interlamellar system is an extensive ladder-like network of thin-walled, highly distensible vessels that traverses the filament between, and parallel to, the lamellae and continues around the afferent and efferent borders of the filament. Interlamellar vessels are supplied by short, narrow-bore feeder vessels from the medial wall of the efferent filamental artery. A myriad of narrow-bore, tortuous arterioles arise from the basal efferent filamental artery and efferent branchial artery and anastomose to form the nutrient circulation of the arch and filament. In the filament body, nutrient capillaries and interlamellar vessels are often closely associated, and the former may ultimately drain into the latter. Many of the anatomical characteristics of interlamellar vessels are strikingly similar to those of mammalian lymphatic capillaries, with the exception that interlamellar vessels are directly fed by arteriovenous-like anastomoses. It is likely that gill interlamellar and mammalian lymphatics are physiologically, if not embryologically, equivalent.     

Morphometric examination of the gills of walleye, Stizostedion vitreum vitreum (Mitchill) and rainbow trout, Salmo gairdneri Richardson

Observations on the gill morphology of individual gill arches of walleye, Stizostedion vitreum vitreum and rainbow trout, Salmo gairdneri suggest that the first two arches account for the highest proportion of gill filament number, secondary lamellae number, lamellae area, and gill surface area. Interspecific comparisons suggest walleye contain a larger number of gill filaments, with a lower secondary lamellae count, but a larger gill surface area than a trout of the same weight. This is partially attributed to the larger surface area of each lamella in a walleye than in a trout.
A detailed examination suggests the surface area of a lamella is dependent on its position on the gill filament, and the position of the gill filament on the gill arch.     

褶纹冠蚌钩介幼虫非寄生变态发育观察及早期稚蚌的生长

为揭示褶纹冠蚌钩介幼虫变态发育特征及过程,采用体外培养方法实现了褶纹冠蚌钩介幼虫的非寄生变态发育。运用光学显微镜和扫描电子显微镜对变态发育过程中幼虫外部形态、内部器官发育进行了系列观察,对非寄生变态发育的稚蚌后期生长发育进行跟踪研究,并分析了底泥和光照两种环境因子对稚蚌存活及生长的影响。结果显示:在整个培养过程中,钩介幼虫的外部形态及大小未出现显著性变化,而斧足、鳃丝、外套膜及内脏团等组织器官逐步形成;在培养第3天,幼虫可见斧足雏形,鳃丝、外套膜纤毛尚未发现;在培养第6天,斧足成形,可见斧足侧沟,外套膜纤毛稀疏,鳃丝出现;培养第9天,斧足纤毛、外套膜纤毛增多,鳃丝密集。稚蚌投喂30d后,鳃丝基本成形。养殖试验结果表明:底泥对稚蚌存活和生长具有显著影响（P < 0.01）,而光照无显著性影响（P>0.05）。该结果为蚌科钩介幼虫变态发育生物学研究积累了基础资料,也通过对稚蚌生长的评估证实了体外培养是蚌类人工繁育及保护的有效技术途径。     

The structure of the gill of the trout,Salmo gairdneri (Richardson)

Summary A light and electron microscopic study was made of the structure of the gill arch, filament and secondary lamella of Salmo gairdneri R. Blood pathways through the gill were traced from serial histological sections, and from the examination of ink perfused tissue and perspex casts formed following resin injection of the circulatory system.The epithelium covering the gill consists of unspecialized, dark, chloride and mucous cells. The distribution of specialized cells appears to be related to gill function. The basement membrane underlying the epithelium consists of three layers, the inner collagen layer being continuous with the connective tissue core of the gills.Blood supply to the secondary lamellar respiratory surface is via branchial, filament and secondary lamellar arteries. Blood spaces of the secondary lamellae are delimited by pillar cells containing what appears to be contractile material. The marginal channel of each lamella is bounded distally by cells of endothelial origin. A network of lymph spaces within the filaments connects with efferent branchial arteries. Nutritionary capillaries within the filaments connect with afferent branchial arteries. No shunts between afferent and efferent filament arteries were found.Data from this study and previous physiological and histopathological studies suggest a mechanism for the control of blood flow to suit the respiratory requirements of the fish. This mechanism involves a system of recruitment of additional respiratory units and changes in overall blood flow patterns.This work formed part of a thesis submitted for the degree of Doctor of Philosophy in 1971 and for which M. M. was in receipt of a studentship from the Natural Environmental Research Council. The authors are grateful for the support given by research grants from the M.R.C (P.T.) and the N.E.R.C. (M.M.), and to Prof. G. M. Hughes in whose department the work was carried out.     

Dietary-morphological relationships of fishes in Liangzi Lake, China

Species in Liangzi Lake were clustered into four trophic groups: Hemiramphus kurumeus and Hemiculter bleekeri bleekeri fed predominantly on terrestrial insects; Carassius auratus auratus and Abbottina rivularis on non-animal food; Hypseleotris swinhonis, Ctenogobius giurinus, Pseudorasbora parva and Toxabramis swinhonis on cladocerans or copepods; Culterichthys erythropterus on decapod shrimps. Gut length, mouth width, mouth height, gill raker length and gill raker spacing, varied widely among species. With the exception of three species pairs ( H. swinhonis, C. giurinus; C. erythropterus, H. kurumeus; T. swinhonis, H. bleekeri bleekeri ), principal components analysis of morphological variables revealed over-dispersion of species. Canonical correspondence analysis of dietary and morphological data revealed five significant dietary-morphological correlations. The first three roots explained > 85% of the total variance. The first root reflected mainly the relationship of gut length to non-animal food, with an increase in gut length associated with an increase in non-animal food. The second root was influenced strongly by the relationship of the gill raker spacing to consumption of copepods, with an increase in gill raker spacing associated positively with copepods in the diet. The third root was influenced by the relationship of mouth gape to consumption of fish and decapod shrimps, with an increase in mouth gape associated with more fish and decapod shrimps in the diet. These significant dietary-morphological relationships supported the eco-morphological hypotheses that fish morphology influence food use, and morphological variation is important in determining ecological segregation of co-existing fish species.