Field observations on the lepidophagous teleost Terapon jarbua (Forsk»l)

Synopsis Foraging behaviour of the lepidophagous Indo-Pacific teleost Terapon jarbua in the Bulolo and Mtumbane estuaries of southern Africa is described. These observations suggest that scale removal from large fish and the complete ingestion of fish fry represents a modified form of predation. Prey reaction to T. jarbua shoals is also discussed.     

Intestinal bicarbonate secretion by marine teleost fish--why and how?

Intestinal fluids of most marine teleosts are alkaline (pH 8.4-9.0) and contain high levels of HCO(3)(-) equivalents (40-130 mM) which are excreted at a significant rate (>100 microEq kg(-1) h(-1)). Recent research reveals the following about this substantial HCO(3)(-) secretion: (1) It is not involved in acid-base regulation or neutralisation of stomach acid, but increases in parallel with drinking rate at elevated ambient salinities suggesting a role in osmoregulation; (2) In species examined so far, all sections of the intestine can secrete bicarbonate; (3) The secretion is dependent on mucosal Cl(-), sensitive to mucosal DIDS, and immuno-histochemistry indicates involvement of an apical Cl(-)/HCO(3)(-) exchanger. In addition, hydration of CO(2) via carbonic anhydrase in combination with proton extrusion appears to be essential for bicarbonate secretion. The mode of proton extrusion is currently unknown but potential mechanisms are discussed. One consequence of the luminal alkalinity and high bicarbonate concentrations is precipitation of calcium and magnesium as carbonate complexes. This precipitation is hypothesised to reduce the osmolality of intestinal fluids and thus play a potential role in water absorption and osmoregulation. The present studies on European flounder reveal that elevated luminal calcium (but not magnesium) concentrations stimulate intestinal bicarbonate secretion both acutely and chronically, in vitro and in vivo. At the whole animal level, the result of this elevated bicarbonate secretion was increased calcium precipitation with an associated reduction in the osmolality of rectal fluids and plasma. These observations suggest direct functional links between intestinal bicarbonate secretion, divalent cation precipitation and osmoregulation in marine teleost fish.     

Hematological responses of the Neotropical teleost matrinxã (Brycon cephalus) to environmental nitrite

Environmental increase in nitrite impairs the function of several aquatic species, including fishes. Nitrite reacts with hemoglobin yielding the non-functional methemoglobin (metHb), and many physiological disturbances can arise. The physiological mechanisms to cope with nitrite are still unclear in fish. Hematological parameters, the role of NADH-methemoglobin reductase system and the electrolytic balance were studied in the freshwater teleost Brycon cephalus (matrinx?) exposed to 0.2, 0.4 and 0.6 mg/L of nitrite N-NO(2) for 24 and 96 h. Hematocrit, total hemoglobin and the red blood cell (RBC) number decreased. Methemoglobin content increased from 1% to 69% for 24 h of exposure and drastically from 5-6% to 90% for 96 h. The activity of NADH-methemoglobin reductase system displayed a tendency of increase in response to nitrite concentration or time of exposure. In the plasma, nitrite was accumulated to values 30-fold higher than the environmental concentration. The plasma K(+) concentration increased only in fish exposed to NO(2) for 24 h. No changes in plasma protein and Na(+) were observed during nitrite exposure but Cl-presented a punctual increase at 0.2 mg/L N-NO(2)-96 h. The hematological data suggest that nitrite caused functional and hemolytic anemia. Furthermore, the electrolytic balance was relatively undisturbed, and the nitrite clearance in matrinx? is likely depending on other factors than NADH-methemoglobin reductase system.     

Do habitat shifts drive diversification in teleost fishes? An example from the pufferfishes (Tetraodontidae)

Habitat shifts are implicated as the cause of many vertebrate radiations, yet relatively few empirical studies quantify patterns of diversification following colonization of new habitats in fishes. The pufferfishes (family Tetraodon‐tidae) occur in several habitats, including coral reefs and freshwater, which are thought to provide ecological opportunity for adaptive radiation, and thus provide a unique system for testing the hypothesis that shifts to new habitats alter diversification rates. To test this hypothesis, we sequenced eight genes for 96 species of pufferfishes and closely related porcupine fishes, and added 19 species from sequences available in GenBank. We time‐calibrated the molecular phylogeny using three fossils, and performed several comparative analyses to test whether colonization of novel habitats led to shifts in the rate of speciation and body size evolution, central predictions of clades experiencing ecological adaptive radiation. Colonization of freshwater is associated with lower rates of cladogenesis in pufferfishes, although these lineages also exhibit accelerated rates of body size evolution. Increased rates of cladogenesis are associated with transitions to coral reefs, but reef lineages surprisingly exhibit significantly lower rates of body size evolution. These results suggest that ecological opportunity afforded by novel habitats may be limited for pufferfishes due to competition with other species, constraints relating to pufferfish life history and trophic ecology, and other factors.     

Characterization of the long-wavelength opsin from Mecoptera and Siphonaptera: does a flea see?

Mecoptera and Siphonaptera represent two insect orders that have largely been overlooked in the study of insect vision. Recent phylogenetic evidence demonstrates that Mecoptera (scorpionflies) is paraphyletic, with the order Siphonaptera (fleas) nesting as sister to the family Boreidae (snow fleas), showing an evolutionary trend towards reduction in gross eye morphology within fleas. We provide the first molecular characterization of long-wavelength opsins from these three lineages (opsin gene from fleas [FL-Opsin], the Boreidae [B-Opsin], and a mecopteran family [M-Opsin]) and assess the effects of loss of visual acuity on the structure and function of the opsin gene. Phylogenetic analysis implies a physiological sensitivity in the red-green spectrum for these opsins. Analysis of intron splice sites reveals a high degree of similarity between FL-Opsin and B-Opsin as well as conserved splice sites across insect blue-green and long-wavelength opsins. Calculated rates of evolution and tests for destabilizing selection indicate that FL-Opsin, B-Opsin, and M-Opsin are evolving at similar rates with no radical selective pressures, implying conservative evolution and functional constraint across all three lineages.     

Disposition and cellular binding of 3H-benzo(a)pyrene at subzero temperatures: studies in an aglomerular arctic teleost fish – the polar cod (Boreogadus saida)

Autoradiography at different levels of resolution was used to study the disposition of the polycyclic aromatic hydrocarbon benzo(a)pyrene (³H-BaP) in juvenile and sexually mature polar cod (Boreogadus saida). Exposure took place via the water or after intragastric administration at subzero temperatures. In water-exposed fish, high total tissue levels were found in the gills, olfactory organ, anterior kidney, liver, skin and intestinal wall. Only traces of radioactivity were present in the muscle, brain and gonads. No major differences in tissue levels or in general distribution pattern between males, females or juvenile fish were observed. The gills appeared to be the absorption site for exposure via water. After oral administration, tissue levels of ³H-BaP-derived radioactivity were negligible. Following both administration routes, levels of radioactivity were highest in the bile and intestinal contents while only traces were observed in the urine, indicating biliary excretion as the major excretory pathway in this aglomerular species. Tape-section autoradiography of fish exposed via water revealed tissue-bound residues of ³H-BaP in the olfactory organs, gills, kidney, liver, skin and intestinal mucosa. Light-microscopy autoradiography demonstrated that the bound residues in the olfactory organ, gills and anterior kidney were localized in epithelial cells, while those in liver and intestinal mucosa were evenly distributed. In conclusion, the present study shows that BaP is absorbed from the water via the gills at subzero temperatures, that tissue levels are considerably higher after water exposure than after dietary exposure, that biliary excretion is predominant and, finally, that site-specific tissue binding in the olfactory organs, gills and anterior kidney is confined to epithelial cells. Accepted: 3 January 2000     

Acid–base regulation in the plainfin midshipman (Porichthys notatus): an aglomerular marine teleost

The plainfin midshipman (Porichthys notatus) possesses an aglomerular kidney and like other marine teleosts, secretes base into the intestine to aid water absorption. Each of these features could potentially influence acid–base regulation during respiratory acidosis either by facilitating or constraining HCO₃ ⁻ accumulation, respectively. Thus, in the present study, we evaluated the capacity of P. notatus to regulate blood acid–base status during exposure to increasing levels of hypercapnia (nominally 1–5% CO₂). Fish exhibited a well-developed ability to increase plasma HCO₃ ⁻ levels with values of 39.8 ± 2.8 mmol l⁻¹ being achieved at the most severe stage of hypercapnic exposure (arterial blood PCO₂ = 21.9 ± 1.7 mmHg). Consequently, blood pH, while lowered by 0.15 units (pH = 7.63 ± 0.06) during the final step of hypercapnia, was regulated far above values predicted by chemical buffering (predicted pH = 7.0). The accumulation of plasma HCO₃ ⁻ during hypercapnia was associated with marked increases in branchial net acid excretion (J _NETH⁺) owing exclusively to increases in the titratable alkalinity component; total ammonia excretion was actually reduced during hypercapnia. The increase in J _NETH⁺ was accompanied by increases in branchial carbonic anhydrase (CA) enzymatic activity (2.8×) and CA protein levels (1.6×); branchial Na⁺/K⁺-ATPase activity was unaffected. Rectal fluids sampled from control fish contained on average HCO₃ ⁻ concentrations of 92.2 ± 4.8 mmol l⁻¹. At the highest level of hypercapnia, rectal fluid HCO₃ ⁻ levels were increased significantly to 141.8 ± 7.4 mmol l⁻¹ but returned to control levels during post-hypercapnia recovery (96.0 ± 13.2 mmol l⁻¹). Thus, the impressive accumulation of plasma HCO₃ ⁻ to compensate for hypercapnic acidosis occurred against a backdrop of increasing intestinal HCO₃ ⁻ excretion. Based on in vitro measurements of intestinal base secretion in Ussing chambers, it would appear that P. notatus did not respond by minimizing base loss during hypercapnia; the increases in base flux across the intestinal epithelium in response to alterations in serosal HCO₃ ⁻ concentration were similar in preparations obtained from control or hypercapnic fish. Fish returned to normocapnia developed profound metabolic alkalosis owing to unusually slow clearance of the accumulated plasma HCO₃ ⁻. The apparent inability of P. notatus to effectively excrete HCO₃ ⁻ following hypercapnia may reflect its aglomerular (i.e., non-filtering) kidney coupled with the normally low rates of urine production in marine teleosts.     

Synthesis and characterization of tris(β-diketonato)technetium(III) and -(IV) complexes

The preparations and properties of tris(dipivaloylmethanato)technetium(III), tris(trifluoroacetylacetonato)technetium(III), and tris(hexafluoroacetonato)technetium(III) are described. The oxidation of the dipivaloyl derivative to tris(dipivaloyl)technetium(IV) hexafluorophosphate was shown to take place readily. Voltammetric studies and magnetic resonance results on the new complexes are reported. The large shifts observed for the complexes seem to be due to a contact interaction.     

Non-laminar cerebral cortex in teleost fishes?

A large skull is disadvantageous to animals that move quickly in three-dimensional space, such as fishes and birds in water or air. A cerebral neocortex with a six-layered sheet has not evolved, most likely due to the limited cranial space. Instead of the laminar cortex, telencephalic nuclear masses seem to have evolved as the pallium in teleost fishes. We consider that the nuclear masses contain rather simple neural circuits sharing a skeleton of simple circuits in the mammalian cortex, which have been elaborated by additional circuits in mammals. Such basic similarities at the connectional level shared by nuclear and cortical pallium might underlie similar or equivalent functions.     

Syntheses of (±)-Epoformin (Desoxyepoxydon) and (±)-Epiepoformin (Desoxyepiepoxydon)

Boron is an essential nutrient for plants, but it is toxic in excess. Transgenic rice plants expressing an Arabidopsis thaliana borate efflux transporter gene, AtBOR4, at a low level exhibited increased tolerance to excess boron. Those lines with high levels of expression exhibited reduced growth. These findings suggest a potential of the borate transporter BOR4 for the generation of high-boron tolerant rice.     

Reproducible and sustained regulation of Gαs signalling using a metazoan opsin as an optogenetic tool

Originally developed to regulate neuronal excitability, optogenetics is increasingly also used to control other cellular processes with unprecedented spatiotemporal resolution. Optogenetic modulation of all major G-protein signalling pathways (Gq, Gi and Gs) has been achieved using variants of mammalian rod opsin. We show here that the light response driven by such rod opsin-based tools dissipates under repeated exposure, consistent with the known bleaching characteristics of this photopigment. We continue to show that replacing rod opsin with a bleach resistant opsin from Carybdea rastonii, the box jellyfish, (JellyOp) overcomes this limitation. Visible light induced high amplitude, reversible, and reproducible increases in cAMP in mammalian cells expressing JellyOp. While single flashes produced a brief cAMP spike, repeated stimulation could sustain elevated levels for 10s of minutes. JellyOp was more photosensitive than currently available optogenetic tools, responding to white light at irradiances ≥1 μW/cm(2). We conclude that JellyOp is a promising new tool for mimicking the activity of Gs-coupled G protein coupled receptors with fine spatiotemporal resolution.     

Does melatonin have a time-dependent effect on brain and gill ionic metabolism in a teleost, Anabas testudineus (Bloch)?

Exogenous administration of 0.20, 0.40 and 0.60 microg/g body weight melatonin over a 24 hr cycle caused an inhibition of Na+, K+ ATPase activity in both brain and gills of A. testudineus. However, Ca2+ ATPase activity in the brain was significantly inhibited by the highest dose, and that in the gill at all the doses of melatonin. Evening injection of melatonin had an inhibitory effect on both brain and gill Na+ K+ and Ca2+ ATPase activity. Melatonin treatment in the morning for 12 hrs did not have an effect on brain Na+, K+ ATPase, while Ca2+ ATPase was inhibited. Similar treatment stimulated Na+, K+ and Ca2+ ATPase activity in the gills. Sodium, potassium and calcium ions in the gill were significantly reduced in the evening treated group while no change was observed in the morning melatonin injected group. The results suggest that melatonin elicits a time-dependent effect on the enzymes and ionic content in the brain and gills of A. testudineus.     

Synthesis of (±)-Homosarkomycin and (±)-Rosaprostol

(±)-Homosarkomycin (2) and (±)-rosaprostol (3) were synthesized from (±)-methyl 2-oxo-bicyclo[3.1.0]hexane-1-carboxylate (1) by using the nucleophilic ring opening reaction on the double-activated cyclopropane ring as the key step.     

Synthesis of (±)-Lamprolobine and (±)-Epilamprolobine

(±)-Lamprolobine, the (+)-enatiomer of which was isolated from the leaves of Lamprolobium fruticosum, and (±)-epilamprolobine were synthesized from δ-valerolactam.     

A comparison of myocardial β-adrenoreceptor density and ligand binding affinity among selected teleost fishes

This study quantified the cell surface β-adrenoreceptor density and ligand binding affinity in the ventricular tissue of seven teleost species; skipjack tuna (Katsowonus pelamis), yellowfin tuna (Thunnus albacares), Pacific mackerel (Scomber japonicus), mahimahi (dolphin fish; Coryphaena hippurus), sockeye salmon (Oncorhynchus nerka), rainbow trout (Oncorhynchus mykiss) and an Antarctic nototheniid (Trematomus bernacchii). β-Adrenoreceptor density varied by almost fourfold among these species, being highest for the athletic fish: sockeye salmon among the salmonids and skipjack tuna among the scombrids. β-Adrenoreceptor density was lowest for the Antarctic icefish. β-Adrenoreceptor binding affinity varied by almost threefold. We conclude that there is a significant species-specific variability in myocardial β-adrenoreceptor density and binding affinity and these interspecific differences cannot be attributed to temperature even though intraspecifically cold temperature can stimulate an increase in myocardial β-adrenoreceptor density. Instead, we suggest that interspecifically myocardial β-adrenoreceptor density is highest in fish that inhabit tropical water. Accepted: 12 July 2000     

Synthesis and characterization of β-diketiminate germanium(II) and tin(II) bromides

The equimolar reaction of a β-diketiminate lithium salt LLi(OEt₂) [L = HC(CMeNAr)₂; Ar = 2,6-iPr₂C₆H₃] with either GeBr₂ or SnBr₂ in diethyl ether affords the synthetically useful monomeric β-diketiminate-element halides LGeBr (1) and LSnBr (2), respectively. Both are soluble in hydrocarbon solvents, stable in inert atmosphere, and have been characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction analysis.     

Are Stannius corpuscles the parathyroid glands of teleost fishes? Ultrastructural, cytologic and immunocytochemical arguments

Parathyrin of Stannius corpuscles (PCS), glands which are restricted to Holostei and Teleostei, is closely related to mammalian parathyrin (PTH) secreted by the parathyroids [( 6] to [9]). In unstimulated and stimulated CS we have shown the same structure and cellular types that are described in mammalian parathyroids. We observed three types of cells; the two sorts of cells already described [14] present such a difference of density (Fig. 1) that type I may be compared to chief dark cells and type II to chief light cells. The difference between these two forms was particularly marked in activated CS; a similar observation has been reported concerning PT [15]. Furthermore, we have detected a third type of cell present either singly in unactivated CS or in small groups between chief cells in activated CS. They showed all the characteristics of oxyphil cells [17]; they present an extremely dense cytoplasm with numerous mitochondria and a typical stellate form with cytoplasmic processes extending between chief cells (Figs. 2, 3). In CS of untreated eels, we have shown by means of indirect immunocytology (using an immunserum raised against the active fragment 1-34 bPTH) that the immunostained reaction product was limited to dilated cisternae and ribosomes of the rough endoplasmic reticulum and to most of the granules in all the chief cells (Figs. 4, 5). No immunoreaction was observed in Golgi area. Oxyphil cells did not present an immune localization of PCS. CS are structurally and cytologically similar to mammalian PT; furthermore their chief cells synthesize, stock and secrete a substance immunologically similar to mammalian PTH; the exact function of oxyphil cells has to be demonstrated.     

Characterization and anions inhibition studies of an α-carbonic anhydrase from the teleost fish Dicentrarchus labrax

Carbonic anhydrase (CA; EC 4.2.1.1) was purified from the gill of the teleost fish Dicentrarchus labrax (European seabass). The purification procedure consisted of a single step affinity chromatography on Sepharose 4B-tyrosine-sulfanilamide. The enzyme was purified 84.9-fold with a yield of 58%, and a specific activity of 838.9 U/mg proteins. It has an optimum pH at 8.0; an optimum temperature at 10°C. The kinetic parameters of this enzyme were determined for its esterase activity, with 4-nitrophenyl acetate (NPA) as substrate. The following anions, H?NSO??, I?, SCN?, NO??, NO??, N??, Br?, Cl?, SO?2?, and F? showed inhibitory effects on the enzyme. Sulfamic acid, iodide, and thiocyanate exhibited the strongest inhibitory action, in the micromolar range (K(i)s of 87-187 μM). NO??, NO?? and N?? were moderate inhibitors, whereas other anions showed only weak actions. All tested anions inhibited the enzyme in a competitive manner. Our findings indicate that these anions inhibit the fish enzyme in a similar manner to other α-CAs from mammals investigated earlier, but the susceptibility to various anions differs significantly between the fish and mammalian CAs.     

Schistosomicidal and trypanocidal structure-activity relationships for (±)-licarin A and its (-)- and (+)-enantiomers

(±)-Licarin A (1) was obtained by oxidative coupling, and its enantiomers, (?)-licarin A (2) and (+)-licarin A (3), were resolved by chiral HPLC. Schistosomicidal and trypanocidal activities of these compounds were evaluated in vitro against Schistosoma mansoni adult worms and trypomastigote forms of Trypanosoma cruzi. The racemic mixture (1) displayed significant schistosomicidal activity with an LC₅₀ value of 53.57 μM and moderate trypanocidal activity with an IC₅₀ value of 127.17 μM. On the other hand, the (?)-enantiomer (2), displaying a LC₅₀ value of 91.71 μM, was more active against S. mansoni than the (+)-enantiomer (3), which did not show activity. For the trypanocidal assay, enantiomer 2 showed more significant activity (IC₅₀ of 23.46 μM) than enantiomer 3, which showed an IC₅₀ value of 87.73 μM. Therefore, these results suggest that (±)-licarin A (1) and (?)-licarin A (2) are promising compounds that could be used for the development of schistosomicidal and trypanocidal agents.