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1.
K. D. Clements 《Marine Biology》1991,109(2):223-229
Two herbivorous species of the temperate labroid fish family Odacidae were examined for the presence of gut endosymbionts.Odax cyanomelas (Richardson) from southern Australia andO. pullus Schneider from New Zealand both feed on macroalgae, yet appear to lack obvious morphological specializations for herbivory. Specimens ofO. cyanomelas andO. pullus were collected in 1989 from Sydney, Australia, and Leigh, New Zealand, respectively. Both species were found to harbour dense concentrations of prokaryotic and eukaryotic microbes in their lower intestines. The various cell types present were examined by light microscopy, transmission electron microscopy and scanning electron microscopy. Epifluorescence microscope counts were used to quantify the distribution and abundance of the microbiota along the gut ofO. cyanomelas. Major differences were observed in the composition of microbiota between the two species.O. cyanomelas contained spirilla, large rod-shaped bacteria, filamentous bacteria and two forms of trichomonad flagellates.O. pullus also harboured dense, large, rod-shaped bacterial populations, but lacked the other two large prokaryote categories found inO. cyanomelas, and contained diplomonad flagellates. The large rod-shaped bacteria found in both species resembled prokaryotes described from other herbivorous fish and termites. 相似文献
2.
Adult zebraperch, Hermosilla azurea, were found to be functional herbivores in that animal matter constituted <0.01% of the total dry weight of stomach contents
of fish collected off Santa Catalina Island in southern California waters. The diet of these fish consisted mainly of red
algae (88.2% by dry wt) and also small amounts of brown (7.8%) and green (4.0%) algae. The most important dietary item, the
filamentous red algae Polysiphonia spp., was found in >78% of the stomachs and comprised >60% of the contents by dry weight. The digestive tract was long, on
average 4.0 times the standard length of the fish, and was composed of the stomach, pyloric caeca, intestine, hindgut chamber
with a blind caecum, and rectum. The mean pH of the cardiac stomach was acidic (3.9), whereas that of the intestine was nearly
neutral (6.9) and that of the hindgut and blind caecum slightly acidic (6.3 and 6.6, respectively). Algal foods are apparently
digested by acid lysis in the stomach and by microbial fermentation in the hindgut. Zebraperch assimilated nutritional constituents
from six species of algae with varying degrees of efficiency: carbon (73.7 to 89.7%), nitrogen (72.4 to 84.5%), and protein
(71.9 to 94.9%). The fish assimilated these constituents as efficiently or more efficiently from three species of nondietary
brown algae as from three species of dietary red and green algae. These results show that zebraperch, like their tropical
and subtropical relatives (members of the genus Kyphosus), can digest a wide variety of algae including brown algae containing defensive secondary compounds.
Received: 3 November 1997 / Accepted: 19 June 1998 相似文献
3.
Pinfish, Lagodon rhomboides (Linneaus), undergo a gradual ontogenetic dietary shift during their first year of life, marked by an increase in the consumption of plant material. To determine if this shift in diet was associated with a change in the microbial flora of the intestinal tract that may assist in degradation of plant material, stomach contents were analyzed and microbes in the intestinal tract were isolated from fish ranging from 20 to 139 mm standard length. These fish were collected from Core Sound, North Carolina, USA between March and September 1991. Plant material increased from 16% of dry weight of stomach contents in pinfish under 40 mm standard length (SL) to 65% in pinfish above 120 mm SL, confirming previous observations of a diet-related ontogenetic change in L. rhomboides. Comparison of the total cultivatable facultative and anaerobic microbial flora isolated from the intestinal tract contents of pinfish ranging in size from 26 to 139 mm SL showed a 10-fold increase between fish <40 and fish >40 mm SL, with maximum population densities of approximately 2x107 colony forming units (CFU) g-1 of intestine including contents. The percentage of microbial isolates examined capable of hydrolyzing carboxymethylcellulose (CMC) increased from 12% in fish <40 mm SL to 13 to 50% in fish >40 mm SL, although there was no strict increase with increasing fish size classes. Although the percentage of CMC-hydrolytic microbial isolates varied with respect to fish SL, the percentage of skim-milk hydrolytic (proteolytic) isolates remained relatively constant (4% of total isolates) irrespective of fish SL and dietary composition. Results presented in this study document the first isolation of carboxymethylcellulase producing microbes from the intestinal tract of any fish and demonstrate that the ontogenetic dietary shift in L. rhomboides is paralleled by qualitative and quantitative changes in the intestinal microbial community. The use of strict anaerobic sampling methods in the preparation of intestinal contents from wild-captured fresh specimens was essential in obtaining these isolates. 相似文献
4.
Structure and ultrastructure of the digestive tract of the ectoparasitic stages of the Antarctic isopod Gnathia calva, collected in the Weddell Sea and around the Antarctic Peninsula in the 1984–1985 season, are briefly described. There are only two digestive glands, with an ultrastructure similar to that of other isopods. The gut is divided into six regions: oesophagus, stomach, dilatable reservior for sucked-in blood, sphincter, rectal vesicle with symbiontic bacteria, and rectum. The highly dilatable anterior hindgut (reservoir) takes part in the resorption of nutrients and stores lipids and glycogen. The rectal vesicle has an epithelium with all the features of an organ with high metabolism and the capacity for the transportation of small molecules. The surface is increased by irregular microvilli. A very thin intima and a basal labyrinth are present. The presence of symbiontic bacteria is discussed in correlation with the haematophagous nutrition of G. calva. 相似文献
5.
Use of stable isotope signatures to trace diet patterns in cultured marine bivalves, particularly when changing culture habitat,
requires knowledge of the isotopic shift and enrichment between diet and consumer’s tissues. The aim of this study was to
determine the patterns of isotope change and the variability of enrichment values (∆δ13C and ∆δ15N) in different tissues (muscle, gonad, digestive gland) of the Japanese scallop (Mizuhopecten yessoensis). It was hypothesized that the isotopic signatures of a consumer’s tissues changed during settlement and that the changes
were related to variations in the isotopic signatures of food sources and gut contents. Particular attention was paid to the
isotope enrichment between the diet and a consumer’s tissues using isotope analysis of gut content. Muscle δ15N values decreased significantly 3–5 months post-settlement in a nearshore seabed, concomitant with the ingestion of lower
δ15N food. For juvenile scallops, sinking particles (SP) were considered a more important dietary source than suspended particulate
organic matter (SPOM), based on the correspondence between SP and gut contents δ13C. Enrichment values (∆δ13C and ∆δ15N) varied with tissue and season. ∆δ15N was 2.4‰ in muscle, 1.2‰ in gonad, and 0.7‰ in the digestive gland. ∆δ13C was 3.2‰ in muscle, 2.3‰ in gonad, and −0.5‰ in the digestive gland. ∆δ15N was the lowest in summer (0.3‰), and ∆δ13C was the highest in autumn (2.8‰). ∆δ15N values were significantly influenced by age, but not ∆δ13C. Patterns of isotope ratios and enrichment values may be related to physiological attributes and differences in diet. This
is the first study to demonstrate isotopic shift and enrichment encountered in different tissues of a cultured scallop when
changing culture habitat. 相似文献
6.
Marine sponges harbor dense and highly diverse bacterial communities, and some percentage of the microflora appears to be
specialized for the sponge habitat. Bacterial diversity was examined in Chondrilla nucula Schmidt to test the hypothesis that some subset of sponge symbiont communities is highly similar regardless of the species
of host or habitat requirements of the host. C. nucula was collected from a mangrove channel on Lower Matcumbe Key in the Florida Keys (25°53′N; 80°42′W) in August 1999. Domain-specific
universal bacterial primers were used to amplify the 16S rDNA gene from genomic DNA that had been extracted from sponges and
the surrounding water. An RFLP technique was used to assess diversity of sponge-associated and environmental bacterial communities.
The clone library from C. nucula contained 21 operational taxonomic units (OTUs). None of the 53 OTUs from adjacent water samples were found in the C. nucula library indicating that a distinct community was present in the sponge. Sequence analysis indicated that C. nucula harbors a microbial community as diverse as the microbes from other sponges in different habitats around the world. Phylogenetic
analysis placed several C. nucula clones in clades dominated by bacteria that appear to be sponge specialists (e.g., Acidobacteria, Bacteroidetes, and Cyanobacteria).
Proportional representation of major bacterial taxonomic groups represented in symbiont communities was compared as a function
of geographic location of sponge hosts. This study supports the hypothesis that sponges from different oceans existing in
dissimilar habitats harbor closely related bacteria that are distinct from other bacterial lineages and appear specialized
for residing within sponges. 相似文献
7.
Brigitte M. Manship Anthony J. Walker Lucy A. Jones Angela J. Davies 《Marine Biology》2008,153(3):473-482
Juveniles of Paragnathia formica Hesse (Isopoda; Gnathiidae) are haematophagous ectoparasites, feeding on fish blood which supplies the nutrients for their
development through growth and moulting, and the subsequent survival and reproduction of the free-living adults. Little is
known of the mechanisms of digestion in juvenile gnathiids, and biochemical studies on the digestive tract of these interesting
estuarine isopods have not been undertaken previously. Here, functionally active cathepsin-like cysteine proteinases are identified
in the digestive system of juvenile praniza (fed) and zuphea (unfed) forms. The physiological pH of the digestive tract and
the optimum proteolytic activities detected in praniza 3 homogenates using the cathepsin B/L, cathepsin B, and cathepsin H
fluorogenic substrates, N-Carbobenzoxy-Phe-Arg-4-methoxy-2-naphthylamine (Z-phe-arg-MNA), N-Carbobenzoxy-Arg-Arg-4-methoxy-2-naphthylamine (Z-arg-arg-MNA) and Arg-4-methoxy-2-naphthylamine (H-arg-MNA), respectively, are in the acidic range (pH 5.8–6.7). Inhibition profiles against Z-phe-arg-MNA and Z-arg-arg-MNA using the cathepsin B inactivator urea, and cysteine proteinase inhibitors, support the presence of cathepsin
L- and B-like enzymes. These proteolytic activities are 10–50 times higher in homogenates of praniza 3 compared with zuphea
3 forms. Histochemistry of praniza 3 sections reveals that the predominant enzyme activity towards Z-phe-arg-MNA is limited to the digestive glands during early and mid stages of digestion; later, this activity appears in
the lining of the anterior hindgut. Moreover, activity towards Z-arg-arg-MNA is generally restricted to the digestive glands, and only occasionally present in the anterior hindgut. In conclusion,
the digestive glands are the main site of cathepsin-like cysteine proteinase activities in P. formica juveniles; these enzymes appear to be important to the digestion of host fish blood enabling development through to the free-living
adult. 相似文献
8.
Estimates of feeding rates, alimentary tract structure and temporal patterns of food processing obtained from twelve species of nominally herbivorous fishes on the northern Great Barrier Reef were compared. These included members of the families Acanthuridae, Scaridae and Kyphosidae. Based on an analysis of diet and short-chain fatty acid (SCFA) profiles from a previous study we initially partitioned the twelve species into four dietary categories, as follows: (a) Category 1: herbivores with a diet of macroscopic brown algae and high SCFA profiles in the hindgut region (Naso unicornis, Kyphosus vaigiensis); (b) Category 2: herbivores feeding on turfing and filamentous red and green algae with moderate SCFA profiles in the hindgut region (N. tonganus, K. cinerascens, Zebrasoma scopas, Acanthurus lineatus); (c) Category 3: zooplankton feeders with moderate SCFA profiles (N. vlamingii, N. brevirostris); (d) Category 4: species feeding on detrital and sedimentary materials with low levels of SCFA (Chlorurus microrhinos, Scarus schlegeli, Ctenochaetus striatus, A. olivaceus). The purpose of this comparison was to determine whether measures of feeding activity, alimentary tract structure, and food processing were concordant with diet. A dichotomy in feeding rates was observed. Species with a diet of algae and zooplankton (categories 1–3) had slower feeding rates than those feeding on detrital aggregates and sediment (category 4). The pattern of food processing also followed the same dichotomy with species of categories 1–3 retaining food in the alimentary tract overnight and commencing the feeding day with substantial amounts of food in the intestine and hindgut. Category-4 species commenced the feeding day with empty alimentary tracts suggesting a rapid turnover of gut contents. Within the herbivorous and zooplankton-feeding species neither alimentary tract structure nor food processing mode were predicted by diet or SCFA profiles. A hindgut fermentation chamber was present in K. vaigiensis but not in N. unicornis, a species with high levels of SCFA in the hindgut region and a diet of brown macroscopic algae. In contrast N. vlamingii, with a diet dominated by animal matter, retained large amounts of food material in a hindgut chamber over the entire feeding cycle. In tropical perciform fishes, herbivory and fermentation are not associated with the alimentary tract structures that characterise herbivorous terrestrial vertebrates. Estimates of the abundance of the different groupings of nominally herbivorous fishes indicated that the dominant elements in the reef grazing and browsing fauna were consumers of detrital and sedimentary materials. These could not be classified as herbivores. Members of this group were dominant in all habitats investigated. Explicitly herbivorous taxa were a minority component in all habitats investigated.Communicated by G.F. Humphrey, Sydney 相似文献
9.
Faecal pellet formation within the gut of Stage V and adult females of the copepod Calanus helgolandicus Claus involves (1) cyclical processes of digestion and (2) the contribution of parts of the gut epithelium to the pellets. During an experimental regime in which dim lighting was restricted to day-time and feeding to night-time (17.00 to 09.00 hrs), the copepods responded with cyclical changes in both the quantity of pellets they produced and the fine structure of the contents. During the feeding period, the contents showed changes in the relative amounts of materials originating from disintegrated cells of the digestive epithelium and those derived directly from the ingested food. The vacuolar B-cells of the gut contribute to the content of the pellets and the distal, necrotic N-cells appear to be involved in forming the peritrophic membrane which encloses each pellet. Cells of the gut epithelium which are broken down during feeding are all replaced during the non-feeding period. Other individuals were taken directly from the sea and in these, also, the cells of the gut broke down during feeding and contributed to the faecal pellets. The supply of epithelial cells may limit the duration of the feeding period. 相似文献
10.
Space limitation in larval settlement can play an important role in the population dynamics of marine species. A novel statistical
test for space limitation based on quadrat counts of individuals is described. The test is based on identifying a significant
relationship between the relative dispersion of quadrat counts and overall mean density. An application to a time series of
quadrat counts of recently settled American lobsters Homarus americanus covering the period 1993–2007 in Casco Bay, Maine, USA (43°45′N; 69°58′W), is presented. For this data set, the null hypothesis
that space is not limiting could not be rejected (P = 0.10). 相似文献
11.
The structure of the larval fish assemblages in three large estuarine systems on the KwaZulu-Natal coast of South Africa
was examined using a combination of univariate, distributional and multivariate techniques. The database was comprised of
a full annual set of larval fish samples taken from each estuarine system: Durban Harbour, Richards Bay Harbour and St Lucia
Estuary. The mean monthly densities of each species in each system were used in the species matrix, and the mean monthly values
of salinity, temperature and turbidity were used in the environmental matrix. The mean species diversity and evenness index
were significantly higher in Durban Harbour (H′ = 1.03, J′ = 0.65) than in the other two systems. The cumulative dominance curve showed that St Lucia Estuary has a high dominance
of a few species, with Richards Bay Harbour intermediate and Durban Harbour being the most diverse. Classification and MDS
(multiple-dimensional scaling) analyses of larval fish densities in all three systems grouped together into three main clusters
on the basis of system. The species similarity matrix (inverse analysis) clustered into five groups at the 25% similarity
level. The MDS analysis of the same matrix showed that the groups separated out according to the degree of estuarine association
of a species and hence habitat type. The species most responsible for system groupings were: Glossogobius callidus, Gilchristella aestuaria, Stolephorus holodon, Croilia mossambica and Gobiid 12. The “best fitting” of the environmental variables to explain the larval fish community patterns in each system
was turbidity on its own (weighted Spearman's rank correlation, ρw = 0.55). The relationship of larval densities to environmental conditions was shown to be species-specific with estuarine
species (e.g. G. callidus and G. aestuaria), having a strong positive correlation with temperature and turbidity but negative correlations with salinity. In summary,
much longer term studies with more sites within each system are needed to assess whether the larval fish assemblages are stable
or at an equilibrium (both spatially and temporally) and whether these assemblages are indicative of the relative “health”
and nursery function of the system.
Received: 28 April 1999 / Accepted: 30 May 2000 相似文献
12.
Mathieu Pernice Delphine Pichon Isabelle Domart-Coulon Jocelyne Favet Renata Boucher-Rodoni 《Marine Biology》2007,150(5):749-757
The recent application of molecular tools to address associations between bacteria and marine invertebrates has provided access
to an immense diversity of unidentified microbes resistant to cultivation. However, the role of bacteria as partners in animal
physiology remains unclear and in most cases difficult to investigate in the absence of adequate condition of cell growth
and proliferation. In this work, we studied the reservoir of microbes associated with the excretory organs of Nautilus macromphalus as a model. Using the bacterial 16S RNA gene as a marker, we compared three complementary approaches for bacterial detection:
bacterial DNA extraction from N. macromphalus tissues (“molecular approach”), strain isolation to provide a bacterial culture collection (“microbiological approach”) and
finally, maintenance of N. macromphalus excretory organ cells with associated bacteria (“cellular approach”). Our results stress the potential of the “cellular approach”
as a promising new tool as it promotes the detection of as yet uncultured β-proteobacteria and spirochaetes associated with
N. macromphalus, and serves as a foundation for future studies describing potential roles that these bacteria may play in Nautilus. 相似文献
13.
Kendall D. Clements Isabel B. Y. Pasch Damian Moran Susan J. Turner 《Marine Biology》2007,150(6):1431-1440
Bacterial diversity in the microbial communities of posterior gut sections of three temperate marine herbivorous fish species
from New Zealand was characterised using Amplified Ribosomal DNA Restriction Analysis, and 16S rRNA gene amplification and
sequencing methods. The fish were collected in 1999–2000 in the Hauraki Gulf, New Zealand (35°54’–36°24’S, 174°48’–175°25’E).
The gastrointestinal bacterial communities of Kyphosus sydneyanus (Günther, 1886) (F. Kyphosidae), Odax pullus (Forster in Bloch and Schneider, 1801) (F. Labridae) and Aplodactylus arctidens Richardson, 1839 (F. Aplodactylidae) were dominated by five clades of bacteria, four of which belong to recognized clostridial
clusters. The clone libraries of K. sydneyanus and O. pullus contained sequences from most of these clades, but were dominated by members of clostridial clusters XI and XIVa, respectively.
The clone library of A. arctidens was dominated by members of clostridial cluster XIVb and an unassigned cluster containing Eubacterium desmolans and Papillibacter cinnaminovorans. The finding that strains of Firmicutes dominated the gastrointestinal microbial communities of all three fish species is consistent with the results of similar
studies on terrestrial vertebrate herbivores. This work thus contributes to the view that gastrointestinal symbionts in some
marine herbivorous fishes may play a similar role to those in terrestrial vertebrate herbivores studied to date. 相似文献
14.
Domoic acid in benthic flatfish on the continental shelf of Monterey Bay,California, USA 总被引:1,自引:0,他引:1
Within Monterey Bay, California, USA, the food web transfer of domoic acid (DA), a neurotoxin produced by diatoms of the genus
Pseudo-nitzschia, has led to major mortality events of marine mammals and birds. Less visible, and less well known, is whether invertebrates
and fish associated with the benthos are also affected by blooms of DA-producing Pseudo-nitzschia spp. This study examines the presence of DA in benthic flatfish offshore of Davenport, California, (37°0′36″N, 122°13′12″W)
and within Monterey Bay, California (36°45′0″N, 122°1′48″W), including species that feed primarily in the sediment (benthic-feeding)
and species that feed primarily in the water column (benthopelagic-feeding). Flatfish caught between 10 December 2002 and
17 November 2003 at depths of 30–180 m had concentrations of DA in the viscera ranging from 3 to 26 μg DA g−1 of viscera. Although the DA values reported are relatively low, benthic-feeding flatfish were frequently contaminated with
DA, especially as compared with the frequency of contamination of flatfish species that feed in the water column. Furthermore,
on days in which both benthic-feeding and benthopelagic-feeding flatfish were collected, the former had significantly higher
concentrations of DA in the viscera. Curlfin turbot, Pleuronicthys decurrens, the flatfish with both the highest level and frequency of DA contamination, are reported to feed exclusively on polychaetes,
suggesting that these invertebrates may be an important vector of the toxin in benthic communities and may pose a risk to
other benthic-feeding organisms.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
15.
From September to November 1991, UV-absorbing mycosporine-like amino acids (MAAs) were monitored in a natural population of
the sea urchin Sterechinusneumayeri from a coastal area of Anvers Island (Antarctic Peninsula). MAA concentrations were determined for specific tissues (gonad,
digestive tract and body wall) from adults collected at four depths (intertidal, 8, 15 and 24 m). Four MAAs were identified:
mycosporine-glycine, shinorine, porphyra-334 and paly-thine. Concentrations of MAAs among replicate individuals varied considerably.
Ovaries had high concentrations of MAAs (84 to 1389 μg g−1 dry wt), while testes had non-detectable levels. The relative abundance of specific MAAs in ovaries appeared to be related
to the spawning cycle. Digestive-tract samples had MAA concentrations as high as 3000 μg g−1 dry wt, but the mean MAA content in intertidal individuals decreased by 70% over 3 mo during spring. The body walls of sea
urchins had very low amounts of MAAs (≤ 0.08 μg g−1 dry wt). There were significant depth differences in the␣total MAA content of the ovary ( p <0.001), ( p <0.015), digestive tract ( p <0.001), and body wall with organisms from the intertidal and 8 m depth having the highest concentrations of MAAs. Biological
dosimetry indicated that UV-B (280 to 320 nm) wavelengths penetrated 3 to 7 m below the sea ice during the study period. The
total MAA content in ovaries decreased with depth on all sample dates; however, the MAA content of the digestive tract and
body wall did not exhibit a consistent pattern of change with depth. The MAA content of tissues did not change significantly
with the temporal gradient of light exposure that was established by both ozone depletion and increasing photoperiod, except
in the digestive tract sampled from intertidal specimens. Adult urchins are probably well-protected from UV exposure by the
water column and a calcareous test; however, the results of this study suggest that, even under ice cover, depth of habitation
is a determinant of MAA content in S. neumayeri. Large daily and seasonal fluctuations in the light regime, which are characteristic of Antarctic coastal environments, apparently
do not provide reliable cues to elicit a detectable, temporal, biochemical response.
Received: 19 February 1997 / Accepted: 26 March 1997 相似文献
16.
E. Danulat 《Marine Biology》1986,90(3):335-343
Numbers of aerobic, heterotrophic and chitinolytic bacteria in stomach, pyloric caeca and intestine of eight specimens of freshly caught cod (Gadus morhua L.) were determined by the spread plate method (medium: sea water agar, including 1% chitin). In crude enzyme extracts, chitinase activity was assayed according to the end product measurement. Results revealed no correlation between the number of chitinoclasts and the level of chitinase activity in any part of the digestive tract of cod. In another series of studies, antibiotics (Ampicillin/Sisomicin, or Chloramphenicol) were applied via tank water and feed. In most cases, antibiotic treatment resulted in the complete elimination of bacteria from the digestive tract. In contrast, up to 1.0×109 chitinoclasts per g wet wt were determined in control fish. Chitinase did not reflect the absence or presence of bacteria: no significant difference in enzyme activities of cod treated with Ampicillin/Sisomicin and non-treated fish could be demonstrated. A decrease of chitinase activities of cod exposed to Chloramphenicol is interpreted as a toxic effect of this antibiotic on the fish. It is concluded that chitinase activities measured in the digestive tract of G. morhua primarily originate from fish tissues.Results presented in this paper are part of the author's Ph.D. dissertation. Authorization for pre-publication was given by the Graduation Committee of the Biology Department, University of Hamburg 相似文献
17.
We investigated feeding by the hogchoker, Trinectes maculatus (Bloch and Schneider), in freshwater, oligohaline, mesohaline, and polyhaline regions of Chesapeake Bay, USA, and examined
prey selection in relation to food availability. Otter trawling for fish and Van Veen grab sampling for benthic macrofauna
occurred in July and August 1992 and August and September 1993. Hogchokers exhibited both opportunistic and selective feeding
patterns along the estuarine salinity gradient in four tributaries (Potomac, Rappahannock, York, and James Rivers) and in
the mainstem Chesapeake Bay. Major prey taxa included annelids, arthropods, and tellinid siphons. In polyhaline habitat, polychaetes
dominated both the benthos and gut contents numerically and gravimetrically. On the other hand, oligochaetes were numerically
dominant in freshwater/oligohaline areas but were rarely eaten, perhaps because of their burial depth. Arthropods (mostly
amphipods) occurred at most salinities, were common in gut contents in low-salinity areas, and were replaced as prey by larger
proportions of polychaetes in polyhaline regimes. Although hogchokers ate tellinid siphons, they rarely consumed whole bivalves
or gastropods. These diet patterns (and especially the importance of siphon nipping) are similar to those of juvenile or small
flatfish elsewhere in Europe, Africa, and North America. A size–salinity relationship for hogchokers occurred along the summer
salinity gradient, with smaller fish predominating upstream and larger fish downstream. It was not clear from our data if
variation in diet composition reflected changes in prey composition along the salinity gradient rather than changes in fish
size.
Received: 14 June 1997 / Accepted: 27 June 1997 相似文献
18.
The fine structure of the intestinal epithelium of Cucumaria frondosa has been examined. The digestive cells possessed some specific ultrastructural peculiarities which testify to their participation in the transport of substances and in the processes of intracellular and cavitary digestion. The main units of the intestinal epithelium appear to be multifunctional digestive cells in which the phenomenon of compartmentalization among the organelles' groups, intended to carry out various functions, occurs. The heterogeneity of the structure of populations of the digestive cells is explained. Both primitive and progressive features of the structure of the digestive tract of C. frondosa are indicated. 相似文献
19.
During 2008 and 2009, an epidemic affected sponges of the genus Ircinia in the Western Mediterranean. Investigations at a site on the European coast (6o43′08.80′′N; 3o43′52.20′′W) and another on the African coast (35o10′51.00′′N; 2o25′33.00′′W) revealed healthier African populations. The disease started with small pustules on the sponge surface, which subsequently coalesced forming larger, extensive lesions. An ultrastructural study suggested that a twisted rod is the etiological agent. It infected the sponges from the outside, initially killing the cells below the ectosome and then penetrating deeper into the body. The sponges responded to the bacterial progression by secreting concentric barriers of collagen and concentrating phagocytic cells at the diseased zones. This primitive immune system successfully resisted the disease in many instances, although mortality reached 27% in the studied populations. Epidemic outbreaks recur each year in September through November, arguably favored by abnormally high seawater temperatures in August. 相似文献
20.
C. Michel 《Marine Biology》1977,44(3):265-273
The digestive tract of Sabellaria alveolata (L.) is partitioned into 4 main regions: oesophagus, gizzard, intestine and rectum. Histoenzymologic study of the repartition of the protease activities along the digestive tract has shown that the proteases are secreted in the anterior intestine, where numerous serous gland cells are present. These cells display many histochemical and cytological characteristics similar to those of the gland cells previously described in digestive organs of other polychaetes. The role of the other regions of the digestive tract is discussed. 相似文献