Endosymbiotic communities of two herbivorous labroid fishes,Odax cyanomelas andO. pullus

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.     

Food habits, gut morphology and pH, and assimilation efficiency of the zebraperch Hermosilla azurea, an herbivorous kyphosid fish of temperate marine waters

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     

Symbiontic bacteria in the gut of the blood-sucking Antarctic fish parasite Gnathia calva (Crustacea: Isopoda)

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.     

Isotopic shifts with size, culture habitat, and enrichment between the diet and tissues of the Japanese scallop Mizuhopecten yessoensis (Jay, 1857)

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.     

Sponge-specific bacterial symbionts in the Caribbean sponge, Chondrilla nucula (Demospongiae, Chondrosida)

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.     

Characterisation of cysteine proteinase activities in the digestive tract of juvenile <Emphasis Type="Italic">Paragnathia formica</Emphasis> isopods,ectoparasites of estuarine fish

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.     

The trophic status of herbivorous fishes on coral reefs

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     

Cyclical contributions of the digestive epithelium to faecal pellet formation by the copepod Calanus helgolandicus

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.     

A test for space limitation with an application to recently settled lobsters

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).     

Comparison of larval fish assemblages in three large estuarine systems, KwaZulu-Natal, South Africa

 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, ρ_w = 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     

Primary co-culture as a complementary approach to explore the diversity of bacterial associations in marine invertebrates: the example of <Emphasis Type="Italic">Nautilus macromphalus</Emphasis> (Cephalopoda: Nautiloidea)

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.     

Clostridia dominate 16S rRNA gene libraries prepared from the hindgut of temperate marine herbivorous fishes

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.     

Domoic acid in benthic flatfish on the continental shelf of Monterey Bay,California, USA

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.     

Temporal and spatial occurrence of UV-absorbing mycosporine-like amino acids in tissues of the antarctic sea urchin Sterechinusneumayeri during springtime ozone-depletion

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     

Prey selection by the hogchoker, Trinectes maculatus (Pisces: Soleidae), along summer salinity gradients in Chesapeake Bay, USA

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     

Structural and functional peculiarities of the digestive system of Cucumaria frondosa (Echinodermata: Holothuroidea)

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.     

Recurrent disease outbreaks in corneous demosponges of the genus Ircinia: epidemic incidence and defense mechanisms

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.     

Spatio-temporal variations in the diet and stable isotope composition of the Argentine hake <Emphasis Type="Italic">Merluccius hubbsi</Emphasis> Marini, 1933 of the continental shelf of southeastern Brazil

The feeding ecology of Merluccius hubbsi was investigated in 2 regions of SE Brazil. The major food sources for the hakes were fish, crustaceans, and squid. In the upwelling system of Cabo Frio, the diet was very similar in the summers of 2001/2002 and spring 2002; fish were the most important prey followed by crustaceans. In Ubatuba, euphausiids were an important prey during the winter 2001 (100 m), while in the summer 2002, fish and amphipods predominated in the diet in the shallower site (40 m) and squid in the deeper site (100 m). The hakes showed temporal differences in stable isotope signatures in both regions, while C:N ratios varied only in Cabo Frio. δ¹⁵N and δ¹³C (bulk and corrected for lipid content) increased with fish length, which seems to be related to the increasing importance of fish and decreasing importance of euphausiids and amphipods in the diet of larger hakes. The mean trophic level of 3.7 for M. hubbsi was estimated using δ¹⁵N of bivalves as baseline and the fractionation of 3.4‰ between trophic levels.     

Tissular localization of the digestive proteases in the sedentary polychaetous annelid Sabellaria alveolata

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.     

Diel variability of feeding activity in haddock (Melanogrammus aeglifinus) larvae in the East Shetland area, North Sea

Investigations of factors affecting feeding success in fish larvae require knowledge of the scales of variability of the feeding process itself and the indices used to assess this variability. In this study, we measured short-term (diel) variability in feeding rates of wild haddock (Melanogrammus aeglifinus) larvae four times per day during a 10-d cruise in the northern North Sea. Feeding activity was evaluated using indices of gut fullness, prey digestive state and biochemical measurements (tryptic enzyme activity). The gut fullness and the enzyme activity indices indicated moderate to high rates of food consumption throughout the cruise. Time series analysis of the three indices showed significant diel variability in all indices and enabled identification of significant lags between food uptake and peak digestive enzyme activity. The typical pattern of food consumption and digestion was characterized by maximal ingestion of prey early in the evening (19:00 hrs) and peak digestive enzyme activity at 01:00  hrs. The time scale over which enzyme activities reacted to prey ingestion was ca. 6 h, and is consistent with expectations from controlled laboratory experiments with other larval fish species. Significant diel variability in tryptic enzyme activity suggests that attempts to relate this measure of feeding success to other variables (e.g. food concentrations) should take care to accommodate natural cycles in feeding activity before making statistical comparisons. Received: 29 October 1998 / Accepted: 18 June 1999