Possible factors responsible for the toxicity of Cochlodinium polykrikoides,a red tide phytoplankton

Cochlodinium polykrikoides, a harmful red tide dinoflagellate, is highly toxic to fish, but the toxic mechanism is still unknown. Recent study has suggested that C. polykrikoides generates reactive oxygen species (ROS) such as superoxide anion (O(2)(-)) and hydrogen peroxide (H(2)O(2)), and the ROS-mediated ichthyotoxicity has been proposed. In this study, we found that the levels of O(2)(-) and H(2)O(2) detected in C. polykrikoides were trace levels as compared with those of Chattonella marina which is well-known to produce ROS. Furthermore, no significant increase in O(2)(-) generation by C. polykrikoides was observed in the presence of lectins such as concanavalin A (Con A) and wheat germ agglutinin (WGA) or fish mucus prepared from skin and gill of yellowtail, whereas C. marina generated increased level of O(2)(-) responding to these stimuli. Interestingly, the cell-free aqueous extract prepared from C. polykrikoides showed toxic effect on the HeLa cells, but the extract of C. marina had no significant effect. Furthermore, gradual accumulation of polysaccharides in the medium was observed during the growth of C. polykrikoides, and the medium gradually became viscous, but no such changes were observed in the medium of C. marina. These results suggest that multiple factors may be responsible for the toxic mechanism of C. polykrikoides.     

Presence of Cochlodinium catenatum (Gymnodiniales: Gymnodiniaceae) in red tides of Bahía de Banderas, Mexican Pacific

The evolution of an ichthiotoxic algal bloom caused by the dinoflagellate Cochlodinium catenatum was studied from July to December 2000. The abnormal multiplication of this dinoflagellate occurred in the form of a discoloration spreading between a temperature and salinity interval of 25-32 degrees C and 33-35 ups, respectively. The density of C. catenatum reached 10 841 cells ml(-1). The event was observed in large areas of Banderas Bay affecting 13 fish species, whose massive killing was due to suffocation (gill obstruction and excessive mucus production). The human population around the area did not present respiratory affections or skin irritation. The C. catenatum measurements suggest a hologamic and heterothalic reproduction. Their morphological characteristics suggest that C. polykrikoides, C. heterolobatum and C. catenatum are the same species. It is estimated that the species could be a recent introduction in the Mexican Pacific.     

Distribution patterns of fishes in a canyon-shaped reservoir

In August 2004 and 2005, an extensive study of the fish community was carried out in the largest water supply reservoir in the Czech Republic and Central Europe, the canyon‐shaped ?elivka Reservoir, using a fleet of Nordic multimesh gillnets. Fishes were sampled at eight locations along the longitudinal profile of the reservoir and at five benthic depth layers covering depths from the surface down to 18 m (benthic gillnet 1·5 m high), and at three pelagic depth layers down to the depth of 5 m above the bottom (pelagic gillnets 4·5 m high). Catches of both juvenile (age 0+ year) and adult (fishes >1 year) fishes were highest in the upper layers of the water column (i.e. in the epilimnion down to 5 m, and down to 10 m in the benthic habitats). Along the tributary–dam axis in the pelagic habitats, both juvenile and adult fishes preferred the upper part of the reservoir, where the maximum number of species and also the greatest abundance of zooplankton were found. In the benthic habitats, fishes selected location according to factors other than trophic status. More juvenile fishes were recorded in the benthic habitats than in the pelagic habitats. Depth had the largest explanatory power for predicting fish community composition, followed by the affiliation with benthic and pelagic habitats, and location on the longitudinal axis of the reservoir. The fish community was represented mainly by cyprinids and consisted of two distinct groups of species, with bleak Alburnus alburnus, rudd Scardinius erythrophthalmus and asp Aspius aspius dominating the offshore group while perch Perca fluviatilis and ruffe Gymnocephalus cernuus were affiliated with the inshore group of the adult fish community. Roach Rutilus rutilus, bream Abramis brama and pikeperch Sander lucioperca occurred in important proportions in both the inshore and the offshore zones. All species, with the exceptions of adult perch (1+ year and older), 0+ year perch and 0+ year roach, preferred the most eutrophic tributary part of the reservoir. The fish community was relatively stable between the 2 years sampled.     

An investigation of carbonic anhydrase activity in the gills and blood plasma of brown bullhead (Ameiurus nebulosus), longnose skate (Raja rhina), and spotted ratfish (Hydrolagus colliei)

Separated plasma and whole blood non-bicarbonate buffering capacities, together with plasma and gill carbonic anhydrase activities and endogenous plasma carbonic anhydrase inhibitor activity were investigated in three species of fish: the brown bullhead (Ameirus nebulosus), a teleost; the longnose skate (Raja rhina), an elasmobranch; and the spotted ratfish (Hydrolagus colliei), a chimaeran. The objective was to test the hypothesis that species possessing gill membrane-bound carbonic anhydrase and/or plasma carbonic anhydrase activity would also exhibit high plasma nonbicarbonate buffering capacity relative to whole blood non-bicarbonate buffering capacity and would lack an endogenous plasma carbonic anhydrase inhibitor. Separated plasma non-bicarbonate buffering capacity constituted > or = 40% of whole-blood buffering in all three species. In addition, all species lacked an endogenous plasma carbonic anhydrase inhibitor. Separated plasma from skate and ratfish contained carbonic anhydrase activity, whereas bullhead plasma did not. Examination of the subcellular distribution and characteristics of branchial carbonic anhydrase activity revealed that the majority of branchial carbonic anhydrase activity originated from the cytoplasmic fraction in all species, with only 3-5% being associated with a microsomal fraction. The microsomal carbonic anhydrase activity of bullhead and ratfish was significantly reduced by washing, indicating the presence of carbonic anhydrase activity that was not integrally associated with the membrane pellet, microsomal carbonic anhydrase activity in skate was unaffected by washing. In addition, microsomal carbonic anhydrase activity from skate and ratfish but not bullhead gills was released to a significant extent from its membrane association by treatment with phosphatidylinositol-specific phospholipase C. The results obtained for skate are consistent with published data for dogfish, suggesting that the possession of branchial membrane-bound carbonic anhydrase activity may be a generalised elasmobranch characteristic. Ratfish, which also belong to the class Chondrichthyes, exhibited a similar pattern. Unlike skate and ratfish, bullhead exhibited high plasma non-bicarbonate buffering capacity and lacked an endogenous carbonic anhydrase inhibitor in the absence of plasma and gill membrane-bound carbonic anhydrase activities.     

Biochemical Characterization of a S-glutathionylated Carbonic Anhydrase Isolated from Gills of the Antarctic Icefish <Emphasis Type="Italic">Chionodraco hamatus</Emphasis>

Gill cytoplasmic carbonic anhydrase of the haemoglobinless Antarctic icefish Chionodraco hamatus (Ice-CA) was directly sequenced and consists in 259 residues with an acetylated N-terminus. The molecular mass, deduced from the sequence, was 28.45 kDa, while mass spectrometry analysis of the native protein gave higher values. Treatment with dithiothreitol abolished this difference, indicating possible post-translational modifications. Isoelectric focusing analysis of Ice-CA suggested S-thiolation, which was identified as S-glutathionylation by immunostaining. Deglutathionylated Ice-CA maintained the anhydrase activity but showed higher susceptibility to hydrogen peroxide, suggesting that glutathione binding to Cys residues may have a role in the defence against oxidative damage. Ice-CA is characterized by lower thermal stability, higher activity and lower activation energy than its homologue gill CA of the temperate European eel, confirming the adaptation of the catalytic capacity to low temperatures. Alignment of Ice-CA with homologous enzymes from other fish shows high identity; the enzyme is grouped with a previously described fish CA monophyletic clade although Ice-CA shows several characteristics that can increase protein-solvent interaction and structural flexibility. Sequence data submission and accession numbers: the icefish carbonic anhydrase (Ice-CA) amino acid sequence is available in the SWISS-PROT Protein Data Bank under the accession number P83299.     

Isoenzymes of carbonic anhydrase of an euryhaline fish. Variations related to the osmoregulation]

A chemical study of carbonic anhydrase (EC 4.2.1.1) from the red blood cells and the gills of an euryhaline fish (Anguilla anguilla) is presented. Animals adapted to fresh water were compared to those adapted to sea water. The physiochemical constants of the various molecular formsisolated by chromatography and isoelectric focusing were determined; isoelectric pH, molecular weight, and the Km and V/E of the enzyme dehydration activity were compared. In both red cells and gills of fish adapted in either media various forms were isolated, characterized by different enzymatic kinetics (high- and low- activity forms) but having the same molecular weight (27 250). Some isoenzymes isolated from the gills differed significantly from those isolated from the red cells. Adaptation to fresh water or sea water is accompanied by modifications in the distribution of the isoenzymes in both red cells and gills: adaptation to sea water is characterized by a shift of the molecular forms towards an isoelectric pH higher than pH equals 6. The role of these enzymes is discussed under both a physiological and biochemical point of view in relation to the electrolyte exchange across fish gill. The origin of the different molecular forms of the carbonic anhydrase is discussed in relation to the prevailing theories on this subject.     

Cl- uptake mechanism in freshwater-adapted tilapia (Oreochromis mossambicus)

In this study, the correlation between Cl(-) influx in freshwater tilapia and various transporters or enzymes, the Cl(-)/HCO(3)(-) exchanger, Na(+),K(+)-ATPase, V-type H(+)-ATPase, and carbonic anhydrase were examined. The inhibitors 2x10(-4) M ouabain (a Na(+),K(+)-ATPase inhibitor), 10(-5) M NEM (a V-type H(+)-ATPase inhibitor), 10(-2) M ACTZ (acetazolamide, a carbonic anhydrase inhibitor), and 6x10(-4) M DIDS (a Cl(-)/HCO(3)(-) exchanger inhibitor) caused 40%, 60%-80%, 40%-60%, and 40%-60% reduction in Cl(-) influx of freshwater tilapia, respectively. The inhibitor 2x10(-4) M ouabain also caused 50%-65% inhibition in gill Na(+),K(+)-ATPase activity. Western blot results showed that protein levels of gill Na(+),K(+)-ATPase, V-type H(+)-ATPase, and carbonic anhydrase in tilapia acclimated in low-Cl(-) freshwater were significantly higher than those acclimated to high-Cl(-) freshwater. Based on these data, we conclude that Na(+),K(+)-ATPase, V-H(+)-ATPase, the Cl(-)/HCO(3)(-) exchanger, and carbonic anhydrase may be involved in the active Cl(-) uptake mechanism in gills of freshwater-adapted tilapia.     

Involvement of host recognition by oncomiracidia and post-larval survivability in the host specificity of Heterobothrium okamotoi (Monogenea: Diclidophoridae)

Heterobothrium okamotoi, a monogenean gill parasite, shows high host specificity for tiger puffer, Takifugu rubripes. In the present study, in vivo and in vitro experimental infections were conducted using various fish species, including T. rubripes, to understand the mechanisms of specificity. In in vivo experiments, T. rubripes, grass puffer, Takifugu niphobles, olive flounder, Paralichthys olivaceus, and red sea bream, Pagrus major, were exposed to oncomiracidia of H. okamotoi labelled with a fluorescent dye, 5- (and -6) carboxyfluorescein diacetate succinimidyl ester, and the numbers of parasites on the gills and skin were recorded at intervals. Oncomiracidia were attached to gills and skin of all the experimental fish species immediately after exposure, and the infection intensity on T. rubripes was higher than that on T. niphobles and much higher than those on the other two species. After 2 days, the attached parasites remained on the gills of T. rubripes, but disappeared from the other hosts. During in vitro experiments, gill filaments excised from seven different fish species (four fish species used in the in vivo experiments and panther puffer, Takifugu pardalis, southern flounder, Paralichthys lethostigma and spotted halibut, Verasper variegates) were exposed to oncomiracidia and the attachment to each fish species and subsequent larval behaviour was observed. The percentage of post-larvae that attached to T. rubripes was slightly higher than those which attached to congeneric fish species and much higher than those of non-tetraodontid fish species. In vivo and in vitro experiments demonstrated that oncomiracidia of H. okamotoi have an affinity for their natural host, T. rubripes, and congeneric fish species. The disappearance of attached post-larvae from 'alien' hosts within 2 days during in vivo experiments suggested that host recognition by oncomiracidia and subsequent post-larval survivability are involved in the host specificity of H. okamotoi.     

Light and nutrients regulate energy transfer through benthic and pelagic food chains

The amount of energy flowing to top trophic levels depends on primary production and the efficiency at which it is converted to production at each trophic level. In aquatic systems, algal production is often limited by light and nutrients, and the nutritional quality of algae depends on the relative balance of these two resources. In this study, we used a mesocosm experiment to examine how light and nutrient variation affected food chain efficiency (FCE, defined as the proportion of primary production converted to top trophic level production), using a food web with benthic and pelagic food chains. We also related variation in benthic and pelagic efficiencies to the nutritional quality of primary producers, i.e. carbon:nitrogen:phosphorus stoichiometry. As predicted, pelagic and benthic FCEs were highest under low light/high nutrient conditions, the treatment with the best algal food quality, i.e. the lowest C:nutrient ratios. Pelagic FCE and pelagic herbivore efficiency (HE_P) were more responsive than benthic FCE to variation in light and nutrients. Furthermore, pelagic FCE and HE_P were highly correlated with algal C:P, suggesting ‘carryover effects’ of algal food quality on carnivores (larval fish) via effects on herbivore (zooplankton) quality. Benthic (tadpole) production was primarily explained by primary production rate, suggesting food quantity rather than quality drives their production. However, benthic FCE was also highest at low light/high nutrients and was significantly correlated with food quality. The stronger effect of food quality in mediating pelagic compared to benthic efficiencies, is consistent with differences in the stoichiometric mismatches between algae and consumers. Pelagic FCE and HE_P were more likely to be P‐limited, whereas benthic FCE was more likely N‐limited. This study is the first to examine both pelagic and benthic FCE within the same system, and highlights the importance of differential consumer needs in determining how food quality affects energy transfer efficiency.     

Bottom‐up and top‐down effects of browning and warming on shallow lake food webs

Productivity and trophic structure of aquatic ecosystems result from a complex interplay of bottom‐up and top‐down forces that operate across benthic and pelagic food web compartments. Projected global changes urge the question how this interplay will be affected by browning (increasing input of terrestrial dissolved organic matter), nutrient enrichment and warming. We explored this with a process‐based model of a shallow lake food web consisting of benthic and pelagic components (abiotic resources, primary producers, grazers, carnivores), and compared model expectations with the results of a browning and warming experiment in nutrient‐poor ponds harboring a boreal lake community. Under low nutrient conditions, the model makes three major predictions. (a) Browning reduces light and increases nutrient supply; this decreases benthic and increases pelagic production, gradually shifting productivity from the benthic to the pelagic habitat. (b) Because of active habitat choice, fish exert top‐down control on grazers and benefit primary producers primarily in the more productive of the two habitats. (c) Warming relaxes top‐down control of grazers by fish and decreases primary producer biomass, but effects of warming are generally small compared to effects of browning and nutrient supply. Experimental results were consistent with most model predictions for browning: light penetration, benthic algal production, and zoobenthos biomass decreased, and pelagic nutrients and pelagic algal production increased with browning. Also consistent with expectations, warming had negative effects on benthic and pelagic algal biomass and weak effects on algal production and zoobenthos and zooplankton biomass. Inconsistent with expectations, browning had no effect on zooplankton and warming effects on fish depended on browning. The model is applicable also to nutrient‐rich systems, and we propose that it is a useful tool for the exploration of the consequences of different climate change scenarios for productivity and food web dynamics in shallow lakes, the worldwide most common lake type.     

Discrete foraging niches promote ecological, phenotypic, and genetic divergence in sympatric whitefish (Coregonus lavaretus)

Natural populations often vary in their degree of ecological, morphological and genetic divergence. This variation can be arranged along an ecological speciation continuum of increasingly discrete variation, with high inter-individual variation at one end and well defined species in the other. In postglacial fishes, evolutionary divergence has commonly resulted in the co-occurrence of a pelagic and a benthic specialist. We studied three replicate lakes supporting sympatric pelagic and benthic European whitefish (Coregonus lavaretus (L.)) morphs in search for early signs of possible further divergence into more specialized niches. Using stomach content data (recent diet) and stable isotope analyses (time-integrated measure of trophic niche use), we observed a split in the trophic niche within the benthic whitefish morph, with individuals specializing on either littoral or profundal resources. This divergence in resource use was accompanied by small but significant differences in an adaptive morphological trait (gill raker number) and significant genetic differences between fish exploiting littoral and profundal habitats and foraging resources. The same pattern of parallel divergence was found in all three lakes, suggesting similar natural selection pressures driving and/or maintaining the divergence. The two levels of divergence (a clear and robust benthic – pelagic and a more subtle littoral – profundal divergence) observed in this study apparently represent different stages in the process of ecological speciation.     

Biochemical changes as enzymatic defense system of phenanthrene exposure in olive flounder, Paralichthys olivaceus

The objective of this study was to investigate early biological response in olive flounder exposed to sub-lethal concentrations of waterborne phenanthrene (0.5, 1 or 2 microM). The fish were exposed for 4 weeks and we analyzed their enzymatic defense system, antioxidant and phase II enzyme activities, to evaluate the chronic exposure toxicity of phenanthrene. Waterborne phenanthrene affected antioxidant enzymes and glutathione-mediated detoxification as enzyme defense system. Hepatic, gill and kidney glutathione reductase as well as glutathione S-transferase, and catalase activities were markedly elevated after two or four weeks of exposure. These enzymes activities of olive flounder, Paralichthys olivaceus seem to be a convenient tool for monitoring pollution in coastal areas against PAHs pollution including phenanthrene.     

Morphological and biochemical variations in the gills of 12 aquatic air-breathing anabantoid fish

All fish species in the Anabantoidei suborder are aquatic air-breathing fish. These species have an accessory air-breathing organ, called the labyrinth organ, in the branchial cavity and can engulf air at the surface of the water to assist in gas exchange. It is therefore necessary to examine the extent of gill modification among anabantoid fish species and the potential trade-offs in their function. The experimental hypothesis that we aimed to test is whether anabantoid fishes have both morphological and functional variations in the gills among different species. We examined the gills of 12 species from three families and nine genera of Anabantoidei. Though the sizes of the fourth gill arch in three species of Trichogaster were reduced significantly, not all anabantoid species had morphological and functional variations in the gills. In these three species, the specific enzyme activity and relative protein abundance of Na(+)/K(+)-ATPase were significantly higher in the anterior gills as compared with the posterior gills and the labyrinth organ. The relative abundance of cytosolic carbonic anhydrase, an indicator of gas exchange, was found to be highest in the labyrinth organ. The phylogenetic distribution of the fourth gill's morphological differentiation suggests that these variations are lineage specific, which may imply a phylogenetic influence on gill morphology in anabantoid species.     

Community structure of fishes attracted to shallow water fish aggregation devices off South Carolina,U.S.A.

Synopsis Twenty-two fish aggregation devices were deployed in 14 m of water off South Carolina. Species composition and abundance were determined by diver visual census on eight occasions from May through November, 1985. A total of 21 families and 36 species of fishes was observed at 121 stations. Pelagic fishes dominated the fauna with a 99.3% relative abundance, and Decapterus punctatus accounted for 97.6% of the individuals. Caranx crysos, Diplectrum formosum, Decapterus punctatus, Centropristis striata and Monacanthus hispidus were the most frequent species. Total fish abundance, number of species and abundance of four of the six most common species were significantly affected by season. Hurricane activity may have caused a significant drop in pelagic fish abundance at the FADs in July. No significant correlations among species abundances were found after removal of season and FAD type effects. Spatial zonation and seasonal occurrence patterns suggest some competition among pelagic fishes. Several factors that regulate FAD faunal abundance and composition are hypothesized, including: juvenile fish availability, availability of shelter, availability of adequate food resources, interspecific and intraspecific competition, severe sea conditions, and sporadic intrusions of large predatory fishes. It is hypothesized that the abundances of benthic and pelagic FAD fishes are correlated and that there is a direct or indirect energetic link between shallow water pelagic and benthic fish assemblages near FADs.     

River of the dammed: longitudinal changes in fish assemblages in response to dams

Although dams are a common feature on rivers throughout the world, their effects on diversity, composition, and structure of fish assemblages are often unclear. We used electrified benthic trawls and stable isotope analysis of δ¹³C and δ¹⁵N to determine the complex relationships between taxonomic diversity and food web structure of fish assemblages among sites in the free-flowing and impounded reaches of the Allegheny River, Pennsylvania, USA. We found higher gamma and beta fish diversity in the free-flowing section, where Brillouin diversity increased in a downstream direction; however, in the impounded section, we found decreasing diversity downstream. Analysis of similarity and non-metric multi-dimensional scaling revealed longitudinal differences in Bray–Curtis similarity between assemblages from impounded and those from free-flowing sites. Finally, using stable isotope analysis, we showed that fishes in the free-flowing section derived nutrients primarily from benthic sources while fishes in the impounded section had a stronger reliance on pelagic nutrients. Our findings reveal that dams can reduce fish taxonomic diversity, driven primarily by decreases in lotic taxa, while shifting resource use from benthic toward pelagic nutrients. A multi-faceted approach to assess the cumulative effects of dams on aquatic communities is, therefore, recommended.     

Cloning and characterization of cytoplasmic carbonic anhydrase from gills of four Antarctic fish: insights into the evolution of fish carbonic anhydrase and cold adaptation

Although carbonic anhydrase is a ubiquitous enzyme involved in a variety of physiological processes, the information on its evolution and cold adaptation among Antarctic fish is still limited: the only Antarctic fish carbonic anhydrase characterized up-to-date is from Chionodraco hamatus, a member of the Channichthyidae family. In this work, we characterized orthologous genes within two other fish families: Nototheniidae (Trematomus eulepidotus, Trematomus lepidorhinus, Trematomus bernacchii) and Bathydraconidae (Cygnodraco mawsoni). The cDNAs of epithelial gill carbonic anhydrases were cloned and sequenced. Both coding and deduced amino acid sequences were used in phylogenetic analyses. The group of enzymes preferentially expressed in fish erythrocytes (CAIIb) represented the most conserved variant. This result suggests that, although the two variants derived from the same ancestor, CAIIc genes have a more complex evolutionary history than CAIIb. The peculiar distribution of Antarctic CAs among fish CAIIcs suggests that the CAIIc gene appeared at different times through independent duplication events, even after the speciation that led to the differentiation of Antarctic fish families. Using the new CA sequences, we built homology models to trace the expected consequences of sequence variability at the protein structure level. From these analyses, we inferred that sequence variability in Antarctic fish CAs affect important physicochemical properties of these proteins and consequentially influence their reactivity. Furthermore, we searched and tested the validity of various potential molecular trademarks for cold adaptation: significant features that can be related to cold adaptation in fish CAs include reduction of positively charged solvent accessible surfaces and an increased flexibility of N-terminal and C-terminal regions.     

Piscivore diet response to a collapse in pelagic prey populations

Pelagic fish populations in the upper San Francisco Estuary have experienced significant declines since the turn of the century; a pattern known as the pelagic organism decline (POD). This study investigated food habits of piscivorous fishes over two consecutive fall seasons following the decline of pelagic fish prey. Specifically, this study addressed the contribution of pelagic versus benthic prey to piscivorous fish diets, including the frequency of predation on special-status pelagic species, and the spatial variability in prey consumption. The piscivore community was dominated by Striped Bass and also included small numbers of Sacramento Pikeminnow and Largemouth Bass. Overall, pelagic prey items contributed less than 10% of the diet by weight in both years, whereas pre-POD studies gleaned from the literature found contributions of 39–100%, suggesting a major switch from pelagic to benthic prey resources. Between-year variation in piscivore diets reflected differences in environmental conditions associated with variation in freshwater outflow. No special status fish species were detected in any of the piscivore stomachs examined. The consequences of this pelagic to benthic diet shift warrants further investigation to understand its ecological relevance.     

Biochemical characterization of isolated branchial mitochondria-rich cells of Oreochromis mossambicus acclimated to fresh water or hyperhaline sea water

Mitochondria-rich cells have been separated from other epithelial cells of tilapia (Oreochromis mossambicus) gills by density gradient centrifugation on Percoll. During centrifugation two main bands of cells formed. The viability of the cells in both bands was high (>90%). In one band, 45–47% of the total cell number was mitochondria-rich cells. The other band contained at least 80% pavement cells, representing the majority of other gill epithelial cell types. A comparison of the activities of four enzymes involved in major metabolic and ion regulatory functions was made between these two different fractions of cells. Furthermore, the separation of gill epithelial cells and determination of enzymatic activity was carried out in tilapia after the fish were acclimated to fresh water or hyperhaline sea water (60 mg·ml^-1 S) to gain an indication of the relative contribution of mitochondria-rich cells and pavement cells to both NaCl excretion and absorption. Regardless of acclimation salinity, the activities of Na⁺/K⁺-ATPase, glutamate dehydrogenase and glucose-6-phosphate dehydrogenase were significantly higher in mitochondria-rich cells than in pavement cells. However, tilapia acclimated to hyperhaline sea water possessed significantly lower carbonic anhydrase activity in mitochondria-rich cells than in pavement cells. In contrast, no significant difference of carbonic anhydrase activity was observed between the two cell fractions in tilapia acclimated to fresh water.Abbreviations ATPase adenosine triphosphatase - CA carbonic anhydrase - DASPMI dimethylaminostyrylmethylpyridinium iodine - FW fresh-water - GIDH glutamate dehydrogenase - G6PDH glucose-6-phosphate dehydrogenase - HSW hyperhaline sea water (60 mg·ml^-1) - MR cells, mitochondria-rich cells - S salinity     

Isoenzymes de l'anhydrase carbonique d'un poisson euryhalin: Variations en relation avec l'osmoregulation

A chemical study of carbonic anhydrase (EC 4.2.1.1) from the red blood cells and the gills of an euryhaline fish (Anguilla anguilla) is presented. Animals adapted to fresh water were compared to those adapted to sea water.The physicochemical constants of the various molecular forms isolated by chromatograhy and isoelectric focusing were determined; isoeleletric pH, molecular weight, and the K_m and V/E of the enzyme dehydration activity were compared.In both red cells and gills of fish adapted in either media various forms were isolated, characterized by different enzymatic kinetics (high- and low-activity forms) but having the same molecular weight (27 250). Some isoenzymes isolated from the gills differed significantly from those isolated from the red cells.Adaptation to fresh water or sea water is accompanied by modifications in the distribution of yhe isoenzymes in both red cells and gills: adaptation to sea water is characterized by a shift of the molecular forms towards an isoelectric pH higher than pH = 6.The role of these enzymes is discussed under both a physiological and biochemical point of view in relation to the electrolyte exchange across fish gill. The origin of the different molecular forms of the carbonic anhydrase is discussed in relation to the prevailing theories on this subject.     

Enzymes released from Lepeophtheirus salmonis in response to mucus from different salmonids

Adult and mobile preadult sea lice Lepophtheirus salmonis were incubated with mucus samples from rainbow trout (Oncorhynchus mykiss), coho salmon (O. kisutch), Atlantic salmon (Salmo salar), and winter flounder (Pseudopleuronectes americanus) to determine the response of L. salmonis to fish skin mucus as assessed by the release of proteases and alkaline phosphatase. There was variation in the release of respective enzymes by sea lice in response to different fish. As well, sealice collected from British Columbia responded differently than New Brunswick sea lice to coho salmon mucus. Fish mucus and seawater samples were also analyzed using protease gel zymography to observe changes in the presence of low molecular weight (LMW) proteases after L. salmonis incubation. Significantly higher proportions of sea lice secreted multiple bands of L. salmonis-derived LMW proteases after incubation with rainbow trout or Atlantic salmon mucus in comparison with seawater, coho salmon, or winter flounder mucus. Susceptibility to L. salmonis infections may be related to the stimulation of LMW proteases from L. salmonis by fish mucus. The resistance of coho salmon to L. salmonis infection may be due to agents in their mucus that block the secretion of these LMW proteases or factors may exist in the mucus of susceptible species that stimulate their release.