Inhibition of DNA replication by fish oil-treated cytoplasm is counteracted by fish oil-treated nuclear extract

We have recentlynoted that cells treated with fish oil and n-3-fatty acids showslower DNA replication rates than cells treated with a control emulsionor corn oil only. However, it is not clearly understood howsuch an effect is induced. Fish oil and its metabolites are known tohave several modulating effects on signal transduction pathways.Alternatively, they may influence DNA replication by interactingdirectly with nuclear components. To investigate this problem ingreater detail, we have studied the kinetics of DNA synthesis in acell-free system derived from HeLa cells. Nuclei and cytosolic extractwere isolated from cells synchronized in early S phase after treatmentwith control emulsion, corn oil, or fish oil, respectively. The nucleiwere reconstituted with cytosolic extract and a reaction mixturecontaining bromodeoxyuridine (BrdU) triphosphate to label newlysynthesized DNA. The rate of DNA synthesis was measured by bivariateDNA/BrdU analysis and flow cytometry. We show that fish oil-treatedcytosol inhibits the elongation of newly synthesized DNA by ~80% incontrol nuclei. However, nuclei treated with fish oil escape thisinhibitory effect. We also show that addition of nuclear extract fromfish oil-treated cells reverses the inhibitory effect seen in thereconstitution system of control nuclei and fish oil-treated cytosol.These results indicate that polyunsaturated fatty acids can modulateDNA synthesis through cytosolic as well as soluble nuclear factors.

     

Eyespots divert attacks by fish

Eyespots (colour patterns consisting of concentric rings) are found in a wide range of animal taxa and are often assumed to have an anti-predator function. Previous experiments have found strong evidence for an intimidating effect of eyespots against passerine birds. Some eyespots have been suggested to increase prey survival by diverting attacks towards less vital body parts or a direction that would facilitate escape. While eyespots in aquatic environments are widespread, their function is extremely understudied. Therefore, we investigated the protective function of eyespots against attacking fish. We used artificial prey and predator-naive three-spined sticklebacks (Gasterosteus aculeatus) as predators to test both the diversion (deflection) and the intimidation hypothesis. Interestingly, our results showed that eyespots smaller than the fish’ own eye very effectively draw the attacks of the fish towards them. Furthermore, our experiment also showed that this was not due to the conspicuousness of the eyespot, because attack latency did not differ between prey items with and without eyespots. We found little support for an intimidating effect by larger eyespots. Even though also other markings might misdirect attacks, we can conclude that the misdirecting function may have played an important role in the evolution of eyespots in aquatic environments.     

Iron acquisition by teleost fish

Iron is a vital micronutrient for teleost fish, being an integral component of proteins involved in cellular respiration and oxygen transfer. However, in excess iron is toxic, and fish need to balance uptake to prevent deficiency vs. potential toxicity. This review assesses the current physiological and molecular knowledge of the mechanisms of iron acquisition in the teleost fish. It focuses on freshwater teleost fish when assessing the gill as a possible site for iron acquisition, and includes a summary of geochemical processes that govern aquatic iron bioavailability. It focuses on marine teleost fish for assessing the mechanism of intestinal iron uptake. Physiological evidence indicates that iron preferentially crosses the apical membrane of both the gills and intestine in the ferrous (Fe2+) state. Molecular evidence supports this, demonstrating the presence of homologues in fish to the large Slc 11a family of evolutionary conserved proteins linked to Fe2+ transport. This symporter is probably linked to a reductase, which reduces either ferric (Fe3+) or organic complexed iron to Fe2+ prior to uptake.     

Metabolic aspects of temperature adaptation by fish

During 8-hour acclimation to changes in the water temperature by 10 degrees within the range of 20-30 degrees C the metabolic compensation of the temperature effects in the carp liver mitochondria is manifested at the level of thermogenesis, activity of succinate dehydrogenase and rate of oxidative phosphorylation. No temperature compensation is found for the activity of cytochromoxidase, ATPase, rate of nonphosphorylating oxidation, content of ATP, phosphorus and calcium in the mentioned organelles.     

Directional encoding by fish auditory systems

This paper reviews and discusses several investigations of the peripheral neural code for the directional axis of acoustical particle motion in the saccule of two fishes: goldfish (Carassius auratus) and toadfish (Opsanus tau). Most saccular afferents are directional in the manner of hair cells, having a cosine-shaped directional response pattern. The saccular sensory epithelia are orientated almost vertically in a parasagittal plane. In the horizontal plane, these epithelia are orientated obliquely with respect to the midline. Hair-cell stereocilia project perpendicularly. Thus, directional response patterns of saccular afferents tend to be orientated in azimuth parallel to the orientation of the epithelia in the head. The oblique angle of the toadfish saccule is greater than that of the goldfish, and the range of best directions in the horizontal plane for each species reflects those differing orientations. The azimuth of acoustical particle motion could be computed by comparing the relative activation of the two saccules, as is the case for the ears of most terrestrial vertebrates. The spatial patterns of saccular hair-cell orientation of most fishes thus appear to have little function in azimuthal source location, but for toadfish are probably most important for determining the elevation of monopole sources.     

Comparative effects of fish oil given by gavage and fish oil-enriched diet on leukocytes

The comparative effects of fish oil given by gavage and fish oil enriched diet on metabolism and function of lymphocytes and macrophages were investigated. For this purpose, the following parameters were examined: 1) phagocytosis capacity, production of superoxide (O2*-) and hydrogen peroxide (H2O2) by macrophages, 2) lymphocytes proliferation capacity, 3) antioxidant enzyme activities in the mesenteric lymph nodes (MEN) and liver, 4) Thiobarbituric Acid Reactive Substances (TBARS) content in MLN, liver, and plasma, 5) total antioxidant capacity of the plasma, and 6) fatty acid composition of macrophages, MLN, liver and plasma. Both FO treatments did not affect phagocytosis capacity but increased hydrogen peroxide production by macrophages in the presence of PMA. FO given by gavage markedly increased lymphocytes proliferation both in the absence (5.8-fold) and in the presence (16.7-fold) of Con A, whereas FO-rich diet showed an increase in the presence of Con A only (53.3%). FO given by gavage raised the proliferation index by 2.9-fold and FO-rich diet increased by 29% only as compared to controls. Concomitantly, FO given by gavage was more effective to increase TBARS content in plasma. The proportion of some fatty acids in the tissues and cells was also differently changed depending on the way FO was administered to rats: in particular: myristic, arachidonic, and eicosapentaenoic acids. This fact may partially explain the differences between both FO treatments.     

Hormone metabolism by the fish gill

The fish gill, like the mammalian lung, is ideally situated to process circulating biomolecules because: 1) the gill is the only organ perfused by the entire cardiac output, 2) the in-series positioning of branchial and systemic circulations permits "conditioning" of blood immediately before systemic perfusion and 3) gill microcirculation is extensive, providing substantial endothelial/pillar cell surface in contact with plasma. In addition, two or three distinct circulatory pathways within the gill may differentially affect plasma substrates, raising the possibility of vasoactive control of hormone titers. Hormones may be activated or inactivated by the gill, the latter involving extraction (uptake) from the plasma, metabolism by enzymes on the endothelial surface without uptake or uptake plus intracellular metabolism. Over 60% of angiotensin I (ANG I) is activated to angiotensin II (ANG II) in a single transit through the gill lamellae by pillar cell angiotensin-converting enzyme, whereas both ANG I and II are inactivated by the non-lamellar filamental vasculature. Gills may accumulate and store (uptake 1) or degrade (uptake 2) catecholamines via intracellular monoamine oxidase and catechol-O-methyl transferase enzymes, and they show substrate preference for norepinephrine over epinephrine. Similar processes may exist for serotonin. Atrial natriuretic peptides are efficiently (60-90%) extracted from plasma in vivo by C-type clearance receptors. Fifty percent of an endothelin-1 bolus is removed in a single transit through the gill circulation, arginine vasotocin extraction is modest and bradykinin is virtually unaffected. Arachidonic acid is completely extracted by the gill, whereas extraction of prostaglandins I2 and E2 is only 13 and 5%, respectively. Intense cytochrome P450 immunofluorescence in the pillar cells suggests that the gill vasculature may be an important site of detoxification and production of biologically active epoxides. Thus, gills appear to be potent and selective effectors of hormonal signals.     

Signal transduction by xenobiotics in fish

Signal transduction by xenobiotics in fish has recently gained much attention. The better known transduction mechanisms are those elicited by organochlorines, organophosphates, carbamates and heavy metals. Organochlorines specifically bind to the membrane bound ouabain sensitive Na+-K+-ATPase affecting neural transmission while the organophosphates and carbamates bind specifically to the membrane bound enzyme acetylcholinesterase again affecting neural transmission. Since the nervous system is one of the important integrative and interactive physiological systems in animals, hypofunction of the nervous system leads to secondary effects in the endocrine system including thyroidal, gonadal, interrenal, pituitary and hypothalamic functions. Even low levels of xenobiotics are efficient enough to bring about remarkable changes in the functional physiology of the non target animals. Heavy metals such as cadmium or mercury belonging to the same group II B in the periodic table probably have a similar mechanism of action. Avidity of these metals to SH-radicals allow them to bind indiscriminately to SH groups in proteins. One pathway of interaction by inorganic mercury with the membrane bound ouabain sensitive Na+-K+-ATPase has been clearly established in fish liver and ovary. Binding of inorganic mercury to the membrane bound enzyme is through sulfhydryl group which inactivates the sodium pump leading to accumulation of the cation in the cytosol. The inorganic mercury is next conjugated by the cytosolar nucleophile, glutathione, and is transported to the nucleus where dissociation occurs and the free metal binds to the metal regulatory element to initiate gene expression. The inducible proteins are 3beta-hydroxysteroid dehydrogenase in the oocyte and metallothionein and C-reactive protein in the liver. The present review deals with the role of xenobiotic as a stress factor.     

Cleaner fish Labroides dimidiatus manipulate client reef fish by providing tactile stimulation.

The cleaner wrasse Labroides dimidiatus often touches 'client' reef fish dorsal fin areas with its pelvic and pectoral fins. The relative spatial positions of cleaner and client remain constant and the cleaner's head points away from the client's body. Therefore, this behaviour is not compatible with foraging and the removal of client ectoparasites. As clients seek such 'tactile stimulation', it can be classified as an interspecific socio-positive behaviour. Our field observations on 12 cleaners (observation time of 112h) suggest that cleaners use tactile stimulation in order to successfully (i) alter client decisions over how long to stay for an inspection, and (ii) stop clients from fleeing or aggressive chasing of the cleaner in response to a cleaner fish bite that made them jolt. Finally, predatory clients receive tactile stimulation more often than non-predatory clients, which might be interpreted as an extra service that cleaners give to specific partners as pre-conflict management, as these partners would be particularly dangerous if they started a conflict. We therefore propose that cleaner fish use interspecific social strategies, which have so far been reported only from mammals, particularly primates.     

Peripheral electrosensory imaging by weakly electric fish

Different species have developed different solutions to the problem of constructing a representation of the environment from sensory images projected onto sensory surfaces. Comprehension of how these images are formed is an essential first step in understanding the representation of external reality by a given sensory system. Modeling of the electrical sensory images of objects began with the discovery of electroreception and continues to provide general insights into the mechanisms of imaging. Progress in electric image research has made it possible to establish the physical basis of electric imaging, as well as methods to accurately predict the electric images of objects alone and as a part of a natural electric scene. In this review, we show the following. (1) The internal low resistance of the fish’s body shapes the image in two different ways: by funneling the current generated by the electric organ to the sensory surface, it increases the fields rostrally, thus enhancing the perturbation produced by nearby objects; and by increasing the projected image. (2) The electric fish’s self-generated currents are modified by capacitive objects in a distinctive manner. These modulations can be detected by different receptor types, yielding the possibility of “electric color.” (3) The effects of different objects in a scene interact with each other, generating an image that is different from the simple addition of the images of individual objects, thus causing strong contextual effects.     

Dynamics of nest defense by male centrarchid fish

Field observations were conducted on four species of nesting male centrarchids to determine if guarding males discriminate intruders with respect to their potential threat to the brood, their size or position in the water column, or by the stage of the nest. Results demonstrated that bluegill (Lepomis macrochirus) and pumpkinseed (L. gibbosus) sunfish were the most frequent intruders and were attacked the most often. Nest guarding male largemouth bass (Micropterus salmoides) attacked intruders further from the nest and had the highest probability of attack of the four species studied. Rock bass (Ambloplites rupestris) males had the shortest distance of attack and one of the lowest probabilities of attack. Male black crappie (Pomoxis nigromaculatus) and pumpkinseed were intermediate in both responses. For all species, the size of intruder did not influence attack distance but larger males had a greater attack distance than smaller males. The distance of attack was greatest during the period immediately after hatch. These findings indicate species-specific differences in nest defense and males did discriminate intruders, possibly on their potential threat to the brood. The defense of the nest was related to nest stage, a finding which supports current theory of parental care.     

Cryostabilization mechanism of fish muscle proteins by maltodextrins

Maltodextrins of varying mean molecular weights (MW) were evaluated for cryoprotective ability in Alaska pollock surimi (leached mince) versus sucrose or a sucrose-sorbitol mixture. Treatments were stored either isothermally at -8, -14, or -20 degrees C for 3 months or freeze-thaw (F/T) cycled six times to induce freeze-related protein denaturation, measured as a decrease in myosin Ca+2 ATPase activity and change in heat-induced gel-forming ability. Results indicated good cryoprotection by all maltodextrins at -20 degrees C isothermal storage irrespective of MW, but poor cryoprotection by higher MW maltodextrins at higher isothermal storage temperatures or after F/T cycling. These observations, and surface tension measurements of maltodextrin solutions, indicated that lower MW maltodextrins likely cryoprotect by a preferential solute exclusion mechanism, similar to sucrose and sorbitol. Higher MW maltodextrins presumably cryoprotect at lower storage temperatures via a reduced water mobility mechanism. As the MW of maltodextrins increased the gelling ability of the surimi was increasingly impaired, such that evidence of cryoprotection from gelation data was obscured. Copyright 1999 Academic Press.     

Detection of fish nocardiosis by loop-mediated isothermal amplification

AIMS: Loop-mediated isothermal amplification (LAMP) is a novel method that amplifies DNA with high specificity and rapidity under isothermal conditions. In this study, using the LAMP method, a protocol for detecting Nocardia seriolae which is a causative agent of fish nocardiosis, was designed. METHODS AND RESULTS: A set of four primers, two inner and two outer, were designed based on the sequence of the 16S-23S ribosomal RNA internal transcribed spacer region of N. seriolae. Time and temperature conditions for detection of N. seriolae were optimized for 60 min at 65 degrees C. Other fish pathogen was not amplified by this LAMP system. The detection of N. seriola using LAMP was found to be more sensitive than that by polymerase chain reaction. CONCLUSIONS: LAMP is a highly sensitive and rapid diagnostic procedure for detection of N. seriolae. SIGNIFICANCE AND IMPACT OF THE STUDY: LAMP is a useful diagnostic method for fish nocardiosis.     

Temperature adaptation by the myotomal muscle of fish

Fish living within a fluctuating thermal environment (eurythermal) are able to adapt their contractile proteins to suit a particular temperature. In goldfish, this adaptive capability has limits, which correspond to their preferred temperature (10°C - 30°C), but fish are able to tolerate extremes (0°C - 40°C). Adaptations in catalytic efficiency and thermostability of the myofibrillar ATPase are controlled by the regulatory proteins. Fish living in a limited temperature range have evolved contractile proteins designed specifically to function at that temperature. A fish living at a constant temperature (stenothermal) was also examined to see if it could adapt its contractile apparatus. Myofibrillar ATPase from trout kept at 5°C and at 20°C showved no differences in either specific activity or thermostability. Furthermore, when placed in a temperature gradient trout have been reported to select the same temperature, regardless of thermal history. It is unknown whether trout, as it is a primitive fish, has never had the ability to adapt its contractile apparatus, or, as it lives in a relatively unchanging temperature it has never needed to.     

Prey behaviour and size-selective predation by fish

SUMMARY 1. We investigate the role of differential activity of chiro-nomids as an explanation for the size selection of small larvae by fish.
2. In the laboratory, pumpkinseed sunfish (Lepomis gibbosus L.) selectively consumed large larvae of Chironomus tentans Fab. when no tube-building materials were available. Small larvae were selectively consumed when a mud substrate was provided but there was no difference in predation rates on large and small larvae in sand.
3. Small larvae spent more time out of their tubes than large larvae in the presence of fish, which may explain the selection for small larvae in mud. Large larvae apparently compensated for decreased foraging activity in the presence of fish by increasing activity when fish were absent. Visibility of large larvae inside tubes may account for their increased mortality in sand.
4. Our results suggest that differential activity is important in explaining the size-selective mortality observed in the field.     

Feeding by fish visiting inundated subtropical saltmarsh

Australian saltmarshes are inundated less frequently and for shorter periods than most northern hemisphere marshes, and when inundated provide transient fish a diverse prey assemblage. We determined the extent of feeding on saltmarsh by examining stomach contents of a common marsh transient, glassfish (Ambassis jacksoniensis), in the Coombabah estuary in subtropical Queensland. We tested the hypotheses that fish caught after visiting the marsh (after (M)) would have similar quantities of food (stomach fullness index, SFI) but different prey composition (abundance, weight) both to fish collected before (Before) saltmarsh inundation and to fish that had not visited the marsh but were caught after marsh inundation (After (NM)). Sampling was done on multiple nights over 3 months in winter, when the marsh is inundated on spring tides at night only. SFI values of After (M) fish were significantly higher (SFI ≈ 12%) than those of Before and After (NM) fish (SFI ≈ 0-1%). After (M) fish also had very different prey composition, eating more crab zoea (> 100 zoea fish^− 1) than Before fish (10) and After (NM) fish (0). After (M) fish showed a consistent pattern in zoea abundances among sampling nights, in all months, with lower zoea abundances on the first night that the marsh was inundated than on subsequent nights. This is attributed to the synchronized spawning of crabs resident on the marsh, releasing their zoea on the ebb of the second inundating tide of the month. Fish stomach contents did not differ before and after smaller high tides not inundating the marsh (SFI ≈ 0-1%). Experimental evidence showed that glassfish evacuate their stomach contents in about an hour under starvation conditions, further strengthening our contention that the stomach contents of After (M) fish represent prey ingested on the marsh. The demonstration of intensive feeding by fish visiting this marsh points to a potentially important role of saltmarsh in the trophodynamics of subtropical Australian estuaries.