Free amino acids and energy metabolism in eggs and larvae of seabass, Lates calcarifer

Contents of free amino acids (FAA), protein and ammonium ions together with rates of ammonia excretion and oxygen consumption were measured in order to study the role of FAA as an energy substrate in developing eggs and larvae of seabass (Lates calcarifer) maintained in seawater (30 ppt) at 28 °C without feeding. Initially eggs contained 25.3 nmol ind⁻¹ of FAA of which 21.5 nmol was rapidly utilised by the developing eggs and larvae during the period up to 40 h post spawning (PS) when nearly all the yolk had been resorbed. During the same period, a net increase in protein content of 1.7 μg ind⁻¹ was observed, indicating that the major part of the amino acids lost from the free pool had been polymerised into body proteins. Assuming that the balance of the FAA after protein synthesis was used entirely for energy metabolism, FAA appeared to be an important energy substrate during the embryonic stages (2 to 16 h PS); after hatching, the contribution of FAA to energy metabolism was less significant. From 50 h PS until the end of the study period at 100 h PS, amino acids derived from somatic protein were used for energy metabolism. For the overall period from just after spawning up to 100 h PS, the data indicate that ca. 14% of the total aerobic energy metabolism was derived from amino acid catabolism. Received: 26 September 1997 / Accepted: 1 April 1998     

Major osmolyte changes during oocyte hydration of a clupeocephalan marine benthophil: Atlantic herring (<Emphasis Type="Italic">Clupea harengus</Emphasis>)

The major inorganic and organic osmolytes responsible for hydrating the oocytes during pre-ovulatory meiotic maturation in autumn- and spring-spawning stocks of Atlantic herring are examined. Despite the ovulated eggs of spring-spawning herring being 1.6- to 2-fold larger than the autumn-spawning stock, the GSI (27 ± 3%) and degree of oocyte hydration (70–72% water) were similar. Normalising the data with respect to dry mass revealed that the physiological mechanisms underlying the maturational influx of water were the same for both classes of egg. Cl⁻, K⁺ and P_i together with a small pool of free amino acids (FAA) represented the driving forces for oocyte hydration. K⁺ (autumn and spring) and P_i (spring) maintained their concentrations in the ovulated eggs, while all other ions, including Cl⁻, Na⁺, NH₄ ⁺ and Mg²⁺ were significantly diluted. In contrast the FAA concentration increased during the hydration process. Amongst the inorganic ions, Cl⁻ showed the greatest increase in the ovulated eggs. The FAA content doubled from 1.5 to 3.3% of dry mass during oocyte hydration and accounted for 29% of the calculated ovoplasmic osmolality in the ovulated eggs from both autumn- and spring-spawners. This significant osmotic effect of the small pool of FAA was due to the low water content of the benthic eggs. The differential movement of the inorganic and organic osmolytes that underly oocyte hydration in Atlantic herring are discussed in relation to current models of transmembrane ion flux.     

Influence du niveau sonore de bruit ambiant sur le métabolisme de Crangon crangon (Decapoda: Natantia) en élevage

The influence of ambient noise on the metabolism of the sand-shrimp Crangon crangon L. was estimated from NH₄ excretion and O₂ consumption rates. Two ambient noise levels were compared: the first (+32 dB bar⁺¹) was that present under usual rearing conditions, the second (+5 to 0 dB bar⁺¹) was the level in a soundproof rearing tank. Over a 24 h period, NH₄ excretion and O₂ consumption rates were higher by 1.4 times and 1.2 to 1.4 times, respectively, under the noisy conditions than in the sound-proof tank. The influence of ambient noise level on the shrimp's metabolic level appears to be long-lasting(>1 month). When the acoustic pressure of the environment was increased abruptly, the excretion rate was strongly enhanced but oxygen consumption was reduced; these stress-effects usually disappeared within 3 h. The influence of ambient noise on the metabolic level of this shrimp should be taken into consideration during physiological studies as well as rearing experiments in the laboratory.     

Free amino acid and protein contents of start-feeding larvae of turbot (Scophthalmus maximus) at three temperatures

The contents of free amino acids (FAA) and total protein, together with growth and gut-content, of turbot (Scophthalmus maximus L.) larvae reared at 14, 18 and 22 °C were studied from first-feeding to approximately 140 effective day-degrees post hatch (D_eff ^∘). Artemia franciscana nauplii and two species of rotifers were used as prey. Protein content accounted for about 42 and 26% of dry body mass in the A. franciscana nauplii and the rotifers, respectively. The FAA pool constituted 5.6 and 4.8% of the total amino acids in the same animals. The dry body mass of turbot larvae was exponentially related to D_eff ^∘. Protein and FAA contents were linearly related to dry body mass, and were independent of rearing temperature between 14 and 18 °C. At the end of the experiment, however, turbot larvae at 22 °C had lower gut content values, retarded growth rates, and decreased FAA contents and concentrations. Thus, at this high temperature, turbot larvae seem unable to catch and ingest sufficient prey, or to sustain an amino acid assimilation rate from the intestine sufficient to meet metabolic demands. Received: 2 January 1997 / Accepted: 25 September 1998     

The influence of macrofauna on estuarine benthic community metabolism: a microcosm study

Effects of benthic macrofauna (Corophium volutator, Hydrobia sp., Nereis virens) on benthic community metabolism were studied over a 65-d period in microcosms kept in either light/dark cycle (L/D-system) or in continuous darkness (D-system). Sediment and animals were collected in January 1986 in the shallow mesohaline estuary, Norsminde Fjord, Denmark. The primary production in the L/D-system after 10 d acted as a stabilizing agent on the O₂ and CO₂ flux rates, whereas the D-system showed decreasing O₂ and CO₂ flux throughout the period. Mean O₂ uptake over the experimental period ranged from 0.38 to 1.24 mmol m^–2 h^–1 and CO₂ release varied from 0.80 to 1.63 mmol m^–2 h^–1 in both systems. The presence of macrofauna stimulated community respiration rates measured in darknes, 1.4 to 3.0 and 0.9 to 2.0 times for O₂ and CO₂, respectively. In contrast, macrofauna lowered primary production. Gross primary production varied from 1.06 to 2.26 mmol O₂ m^–2 h^–1 and from 1.26 to 2.62 mmol CO₂ m^–2 h^–1. The community respiratory quotient (CRQ, CO₂/O₂) was generally higher in the begining of the experiment (0–20 d, mean 1.89) than in the period from Days 20 to 65 (mean 1.38). The L/D-system exhibited lower CRQ (ca. 1) than the D-system. The community photosynthetic quotient varied for both net and gross primary production from 0.64 to 1.03, mean 0.81. The heterotrophic D-system revealed a sharp decrease in the sediment content of chlorophyll a as compared to the initial content. In the autotrophic L/D-system, a significant increase in chlorophyll a concentration was observed in cores lacking animals and cores with C. volutator (The latter species died during the experiment). Due to grazing and other macrofauna activities other cores of the L/D-system exhibited no significant change in chlorophyll a concentration. Community primary production was linearly correlated to the chlorophyll a content in the 0 to 0.5 cm layer. Fluxes of DIN (NH₄ ⁺+NO₂ ^–+NO₃ ^–) did not reveal significant temporal changes during the experiment. Highest rates were found for the cores containing animals, mainly because of an increased NH₄ ⁺ flux. The release of DIN decreased significantly due to uptake by benthic microalgae in the L/D-system. No effects of the added macrofauna were found on particulate organic carbon (POC), particulate organic nitrogen (PON), total carbon dioxide (TCO₂) and NH₄ ⁺ in the sediment. The ratio between POC and PON was nearly constant (9.69) in all sediment dephts. The relationship between TCO₂ and NH₄ ⁺ was more complex, with ratios below 2 cm depth similar to those for POC/PON, but with low ratios (3.46) at the sediment surface.     

Effect of nutrient enrichment on growth of the eelgrass Zostera marina in the Chesapeake Bay,Virginia, USA

The addition of two commerical fertilizers, one 5% NH₄NO₃, 10% P₂O₅, 10% K₂O, and the other 10% NH₄NO₃, 10% P₂O₅, 10% K₂O, ahd a dramatic effect on the growth of Zostera marina in the Chesapeake Bay. There was a significant increase in the length, biomass and total number of turions of fertilized plots compared with controls during a 2 to 3 month period. Data from this short-term field experiment suggest that Z. marina beds in the Chesapeake Bay are nutrient-limited, that the grwoth form of Z. marina may be related to the sediment nutrient supply, and that Z. marina may competitively exclude Ruppia maritima by light-shading.     

Effects of starvation,season, and diet on the free amino acid and protein content of<Emphasis Type="Italic"> Calanus finmarchicus</Emphasis> females

Effects of food availability and season on the free amino acid (FAA) and total protein content of the copepod Calanus finmarchicus females were investigated in two mesocosm experiments on the Norwegian west coast in spring and autumn. Starved C. finmarchicus females showed no change in total FAA content, but the FAA pool composition changed drastically. During the first 10 days of starvation the protein content showed a moderate decline (<2 µg ind ^-1); however, during the following 21 days the total content was drastically reduced, from 63 to 9 µg ind ^-1. This supports the notion of a sequential catabolism of endogenous nutrients during starvation. In females at high food concentrations, the body protein content increased during spring, but decreased during autumn. The FAA pool composition of females differed between spring and autumn in 14 of the 18 FAA investigated. Reduced body protein content and increased proportion of essential free amino acid were observed during starvation. Similar changes were observed in females sampled at the end of the mesocosm experiments in the autumn. The results suggest that mature C. finmarchicus females are in a negative protein balance during autumn, despite high food concentrations, contributing to a lower fitness than in females maturing during the spring.     

Respiratory physiology in summer diapause embryos of the neustonic copepodAnomalocera patersoni

The respiratory physiology of summer diapausing eggs of the neustonic copepodAnomalocera patersoni, maintained under constant temperature (13 °C) and light (12 h light:12 h dark) conditions, was characterized by a bell-shaped curve, with low O₂ uptake levels at the beginning of dormancy. This was followed by a steady rise in O₂ consumption with maximum levels of 0.002 l O₂ embryo^–1 h^–1 70 d after spawning. A slow diminution in O₂ uptake then occurred until Day 150 when minimum values of 0.0003 l O₂ embryo^–1 h^–1 were recorded, coinciding with the hatching of the first embryos. Embryos continued to hatch asynchronously up to 360 d from the moment of egg laying. When eggs were subjected to 20 °C, the respiratory activity was almost three times higher than at 13 °C, even though both respiratory curves were similar. The elevated metabolism in eggs kept at 20 °C led to death of the embryos possibly due to a total depletion of metabolic reserves. ATP content also differed at the two temperatures. Diapause eggs kept at 20 °C showed no rapid rise in ATP content as opposed to those kept at 13 °C. The results of temperature shock experiments, in which eggs were first kept at winter temperatures for several weeks, after which the temperature was raised to 20 °C for another number of weeks prior to a second period of chilling at 13 °C, showed that as long as embryos were kept at 20 °C no hatching occurred. By contrast, hatching was observed after 10 d following the resumption of winter temperatures, suggesting that low environmental temperatures are an essential prerequisite for hatching of these eggs. The type of diapause inA. patersoni differs considerably from the one described in insects and in another neustonic copepod,Pontella mediterrana. In this case, there is a U-shaped respiratory curve with greatest O₂ consumption prior to the onset or upon breaking of diapause. Differences in the two types of diapause seem to involve not only differences in O₂ consumption levels but also in the sequence of metabolic changes with time and the metabolic requirements during sommer and winter dormancy.     

NO conversion by positive streamer discharge—effects of gas compositions and reaction conditions

The effects of gas compositions and reaction conditions on NO conversion by positive streamer discharge were experimentally investigated by using a link tooth wheel-cylinder reactor. The results showed that NO conversion increased with increasing O₂ concentration and NH₃ concentration, but decreased with increasing inlet NO concentration and gas flow rate. The addition of CO₂ or H₂O to the feed gas promoted NO conversion by increasing the maximum discharge voltage, and NH₄NO₃ was formed in the presence of NH₃. There was a most suitable range interval between discharge tooth wheels if both NO conversion and energy consumption were considered. Increasing applied voltage resulted in the increase in the amount of O₃ generated by streamer discharge.     

Modulation of the free amino acid pool and protein content in populations of the brine shrimp Artemia spp.

 Free amino acid (FAA) and protein content were measured in various developmental stages of Artemia franciscana, from cysts to Instar III metanauplii. In addition, decapsulated cysts of 15 Artemia populations from different localities were compared with respect to their FAA and protein content. Furthermore, the content and composition of the FAA pool were modulated by hatching the cysts at various salinities, and by enriching the nauplii with algae or a lipid-enrichment emulsion. The FAA content increased threefold from cysts to nauplii, and Instar III metanauplii contained nearly 50% taurine of total FAA. Cysts of A. franciscana were found to contain one-third the amount of FAA compared to the other Artemia species investigated. The content and pool composition of FAA was successfully modulated in 11 of 13 populations, where by the content of FAA was significantly increased when hatched at high salinity. Finally, enrichment elevated the content of FAA and changed the pool composition, thereby showing a dietary effect. Algal enrichment also increased the protein content. Received: 27 September 1999 / Accepted: 17 July 2000     

Transport and Diffusion of Ozone in the Nocturnal and Morning Planetary Boundary Layer of the Phoenix Valley

The evolution of ozone (O ₃) in the nocturnal and morning-transitional planetary boundary layer (PBL) of the Phoenix valley was measured as a part of the `Phoenix Sunrise Experiment 2001' of the U.S. Department of Energy conducted in June 2001. The goal of the field program was to study the transport, distribution and storage of ozone and its precursors in the urban boundary layer over a diurnal cycle. The ground level O <sub>3</sub> as well as mean meteorological variables and turbulence were measured over the entire period, and vertical profiling (using a tethered balloon) was made during the morning transition period. Approximately half of the observational days showed the usual diurnal cycle of high O <sub>3</sub> during the day and low O <sub>3</sub> at night, with nitrogen oxides (NO <sub>x</sub> = NO <sub>2</sub> + NO) showing an out of phase relationship with O <sub>3</sub>. The rest of the days were signified by an anomalous increase of O <sub>3</sub> in the late evening ( 2200 LST), concomitant with a sudden drop of temperature, an enhancement of wind speed and Reynolds stresses, a positive heat flux and a change of wind direction. NO <sub>x</sub> measurements indicated the simultaneous arrival of an `aged' air mass, which was corroborated by the wind predictions of a mesoscale numerical model. In all, the results indicate that the recirculation of O ₃ rich air masses is responsible for the said high-O ₃ events. Such air masses are produced during the transport of O ₃ precursors by the upslope flow toward mountainous suburbs during the day, and they return back to the city at night via downslope winds (i.e. mountain breeze). The corresponding flow patterns, and hence the high-O ₃ events, are determined by background meteorological conditions. The vertical profiling of O ₃ and flow variables during the morning transition points to a myriad of transport, mixing and chemical processes that determine the fate of tropospheric O ₃. How well such processes are incorporated and resolved in predictive O ₃ models should determine the accuracy of their predictions.     

Changes in phospholipase A2 activity and lipid content during early development of Atlantic halibut (Hippoglossus hippoglossus)

During early development in fish, phospholipase A₂ (EC 3.1.1.4) regulates membrane lipid modifications, which relates to changes in environmental conditions and provision of fatty acids required for metabolic energy substrates and prostaglandin biosynthesis. A method to analyze phospholipase A₂ in rat tissues has been modified to measure its activity in embryonic Atlantic halibut (Hippoglossus hippoglossus L.). Egg and embryo samples were collected during the 1994 spawning season. Enzyme activity was undetectable at fertilization but in 10-d embryos was 230 pmol mg⁻¹ h⁻¹ (at 20 °C) and increased by ∼120% at hatch (17-d). Significant alterations in the fatty acid composition of important phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), were also observed. The content of some critical polyunsaturated fatty acids, and the ratio of unsaturated/saturated fatty acids, declined significantly over development. Acyl-chain restructuring mediated through the activity of phospholipase A₂, coupled with other observed lipid changes (significant increases in the PC/PE ratio and cholesterol content), would produce a decreased fluidity of membranes during embryonic development, coinciding with the predicted upward movement of larvae in the water column. Arachidonic acid (20:4n-6) removed from PE could serve as a precursor for biosynthesis of 2-series prostaglandins, and eicosapentaenoic acid (20:5n-3) from PC is a likely source for other prostaglandin types. Despite removal of polyunsaturated fatty acids, there was an overall increase in lipid and fatty acid concentration, which can be attributed to amino acid catabolism during early developmental stages. Received: 9 September 1996 / Accepted: 8 September 1997     

镉胁迫对脊尾白虾的毒性效应研究

为揭示重金属镉对脊尾白虾的毒性效应,采用急性毒性实验方法,研究了不同浓度镉(Cd~(2+))对脊尾白虾(Exopalaemon carinicauda)血清氧化应激相关生理指标的活性以及肌肉组织中腺苷酸转移酶基因(ANT)和热激蛋白70基因(HSC70)表达水平的影响。共设置4个Cd2+浓度胁迫(0、0.0002、0.001、0.005 mmol·L~(-1)),分别在0、3、6、9、12、24、36、48、72和96 h共10个时间点对相关指标进行测定。结果显示:不同浓度镉胁迫下,脊尾白虾血清中H_2O_2含量、MDA含量和GSH含量均表现为先升高后降低的趋势,H2O2含量在胁迫3 h时即出现明显的升高,而MDA和GSH则均在9 h时出现升高趋势,表现为一定的滞后性。H2O2含量在0.005 mmol·L~(-1)胁迫3 h时出现峰值,MDA含量在0.005 mmol·L~(-1)胁迫9 h时出现峰值,GSH含量在0.001mmol·L~(-1)胁迫48 h时出现峰值,且均与对照组存在显著性差异(P0.05)。HSC70基因的表达量在不同浓度胁迫下均表现为先升高后降低的趋势,且均在24 h时达到峰值,具体表达量水平的顺序为:0.0002 mmol·L~(-1)0.001 mmol·L~(-1)0.005 mmol·L~(-1)。ANT基因的表达量在不同浓度下则均表现为明显的下调趋势。由此可见,急性Cd~(2+)胁迫不仅影响脊尾白虾的氧化应激相关生理指标,还影响机体内组成型HSC70及与能量传递有关的ANT基因的表达水平。     

Seasonal changes in nucleic acids,amino acids and protein content in juvenile Norway lobster (<Emphasis Type="Italic">Nephrops norvegicus</Emphasis>)

The objective of this study was to describe the seasonal variations in nucleic acid contents and amino acid profiles in the muscle of juvenile Nephrops norvegicus. RNA and protein contents, and RNA:protein and RNA:DNA ratios varied significantly between seasons, being highest in spring and lowest in autumn/winter ( P<0.05). Though DNA content increased significantly from autumn to summer ( P<0.05), protein:DNA ratio did not show significant seasonal variations ( P=0.05). In respect to protein-bound amino acid content (BAA), a significant increase was observed from winter to summer ( P<0.05). Both essential (EAA) and non-essential amino acids (NEAA) increased significantly (27.6% and 27.8%, respectively; P<0.05), mainly due to the considerable increase in arginine and proline (59.1% and 225.2%, respectively; P<0.05). A significant decrease was observed in the free amino acid content (FAA) from winter to summer ( P<0.05); and a higher percentage decrease occurred in free non-essential (FNEAA; 27.9%) in comparison to free essential amino acids (FEAA; 21.8%). The significant increase in RNA and BAA contents from winter to spring may be related to protein synthesis. On the other hand, the lowest values obtained in winter may be due to a reduction in feeding activity; in this period the muscle protein must be progressively hydrolysed, which is evident with the higher FAA content. The liberated amino acids enter the FAA pool and become available for energy production.     

Effect of temperature fluctuations and food supply on the growth and metabolism of juvenile sea scallops (Placopecten magellanicus)

On the eastern shore of Nova Scotia late summer atmospheric systems cause upwelling of shelf water; the associated temperature variations of 10 °C with a 6 to 8 d period are comparable in magnitude to the seasonal variation. A laboratory study was undertaken to assess the effects of these temperature fluctuations on sea scallop (Placopecten magellanicus) growth and metabolism. In a factorial design, scallops were subjected to constant (10 °C) or a variable (6 to 15 °C) 8 d temperature cycle, and either a low (seston in filtered seawater) or high (seston supplemented with cultured phytoplankton) food diet. During the 48 d experiment scallop mortality was low and growth positive in all treatments. Shell and total tissue growth rate did not differ between temperature treatments, but growth in the high food treatments was 40 to 50% higher than in the low food treatments. However, soft tissue (excluding adductor) growth did show a temperature treatment effect; growth rates were significantly higher in the fluctuating temperature treatment, due in part to greater gonad development. Weight-standardized rates of scallop oxygen consumption (V _sO₂ , μmol O₂ g⁻¹ h⁻¹) were 20 to 25% higher in high food than in low food treatments, consistent with the expected increase in respiration due to the higher growth rates. Scallop metabolism did not acclimate to the fluctuating temperature cycle; V _sO₂ and ammonium excretion (V _sNH⁺ ₄, μmol O₂ g⁻¹ h⁻¹) remained dependent on ambient temperature throughout the experiment. V _sNH⁺ ₄ Q₁₀ (2.77) was higher than V _sO₂ Q₁₀ (2.01) which was reflected in a decrease in the O:N ratio at 15 °C, indicating a shift toward increased protein catabolism and a stressed state. At 10 °C, V _sO₂ and V _sNH⁺ ₄ in the variable temperature treatments were 15 to 18% lower than in the constant temperature treatments, a difference that was not detected in growth measurements. Results demonstrate that the metabolism of Placopecten magellanicus, unlike some bivalve species, is tightly coupled to fluctuations in ambient temperature. Although an absence of compensatory acclimation had a minimal effect on growth in this study, if high temperatures were combined with low food conditions a reduction in scallop production could result. Received: 23 June 1998 / Accepted: 8 February 1999     

Investigation of fluorescence characterization and electrochemical behavior on the catalysts of nanosized Pt-Rh/γ-Al2O3 to oxidize gaseous ammonia

This work describes the environmentally friendly technology for oxidation of ammonia (NH₃) to form nitrogen at temperatures range from 423K to 673K by selective catalytic oxidation (SCO) over a nanosized Pt-Rh/γ-Al₂O₃ catalyst prepared by the incipient wetness impregnation method of hexachloroplatinic acid (H₂PtCl₆) and rhodium (III) nitrate (Rh(NO₃)₃) with γ-Al₂O₃ in a tubular fixed-bed flow quartz reactor (TFBR). The characterization of catalysts were thoroughly measured using transmission electron microscopy (TEM), threedimensional excitation-emission fluorescent matrix (EEFM) spectroscopy, UV-Vis absorption, dynamic lightscattering (DLS), zeta potential meter, and cyclic voltammetry (CV). The results demonstrated that at a temperature of 673K and an oxygen content of 4%, approximately 99% of the NH₃ was removed by catalytic oxidation over the nanosized Pt-Rh/γ-Al₂O₃ catalyst. N₂ was the main product in NH₃-SCO process. Further, it reveals that the oxidation of NH₃ was proceeds by the over-oxidation of NH₃ into NO, which was conversely reacted with the NH₃ to yield N₂. Therefore, the application of nanosized Pt-Rh/γ-Al₂O₃ catalyst can significantly enhance the catalytic activity toward NH₃ oxidation. One fluorescent peak for fresh catalyst was different with that of exhausted catalyst. It indicates that EEFM spectroscopy was proven to be an appropriate and effective method to characterize the Pt clusters in intrinsic emission from nanosized Pt-Rh/γ-Al₂O₃ catalyst. Results obtained from the CV may explain the significant catalytic activity of the catalysts.     

Free amino acids as energy substrate in developing eggs and larvae of the cod Gadus morhua

The content of free amino acids (FAA) in the cod (Gadus morhua L.) egg is about 200 nmol at spawning, decreasing by about 100 nmol/egg during the egg stage and about 75 nmol/larva during the yolksac larval stage. Together, alanine, leucine, serine, isoleucine, lysine, and valine account for about 75% of the decrease. Ammonium accumulates gradually during the egg stage and is quickly excreted after hatching. The body protein content is maintained during the egg and yolksac larval stages. The measured oxygen uptake of the cod embryo during the egg and yolksac larval stages accounts for about 85% of the oxygen necessary to catabolize the FAA disappearing during this period. Ammonia excretion of the cod embryo, as taken from literature data, is similar to the expected ammonia production from catabolism of the FAA. Our data suggest that FAA are a major substrate for aerobic energy production in cod eggs and yolksac larvae. The implication of this finding for the production of a favourable first-feed for cod and other cultivated marine fish larvae, and for the selection of high quality eggs of marine fishes, is stressed.     

Growth,condition and specific dynamic action in the mussel Mytilus edulis recovering from starvation

Juvenile Mytilus edulis were grown individually in plastic racks in a tidal salt marsh for 72 d in 1984, starved in the laboratory for 130 d, and then fed the alga Isochrysis galbana daily for 64 d. Oxygen consumption was measured at various times during the course of starvation and recovery. The effects of both size (tissue dry weight) and condition (tissue size relative to shell size) on the rate of oxygen consumption during the course of starvation and recovery were analyzed by multiple regression. Weight-specific preprandial rate was inversely correlated with both size and condition. Weight-specific active rate (measured shortly after feeding) was correlated with size but not condition. Relative Scope for Activity was inversely correlated with size and positively correlated with condition. Relative Specific Dynamic Action (RSDA; the integrated physiological and mechanical response to a meal) was initially correlated negatively with size and subsequently positively with condition. Glycogen content was shown to be positively correlated with condition in mussels before starvation and during recovery. During recovery, experimental mussels returned to 90% of their estimated dry weight prior to starvation, and from 53% after starvation. At weekly intervals during recovery, oxygen consumption was measured following a meal until it returned to the preprandial rate. Both pre- and postprandial volumes (l at STP) of oxygen consumed per hour ( O _2pre and O _2post , respectively) increased significantly during recovery. The postprandial rise in oxygen consumption increased significantly from 15% to 23% of O _2pre . At the end of the recovery period, RSDA [( O _2post – O _2pre )/ O _2pre ] was independent of final dry weight, but was significantly correlated with percent dry weight recovered (r ²=0.44; df=10; P<0.02). The increase in RSDA may reflect increased utilization of food and its conversion to soma during recovery from starvation, as distinct from mechanical energy expenditure (feeding activity) following a meal.     

Bioturbation effects of the amphipod Corophium volutator on microbial nitrogen transformations in marine sediments

Microcosms containing different densities of Corophium volutator, ranging from 0 to 6000 ind m^-2, were incubated in a flow-through system. Benthic fluxes of CO₂, O₂, NO₃ ^- and NH₄ ⁺ were measured regularly. Thirteen days after setup the microcosms were sacrificed and sediment characteristics, pore water NO₃ ^-, NH₄ ⁺ and exchangeable NH₄ ⁺ concentrations, and potential nitrification activity were measured. The presence of C. volutator increased overall mineralization processes due to burrow construction and irrigation. The amphipods increased the ratio CO₂/O₂ fluxes from 0.73 to 0.86 in microcosms inhabited by 0 and 6000 ind m^-2, respectively. Burrow ventilation removed NH₄ ⁺ from the sediment, which was nitrified in the oxic layer and transported NO₃ ^- to the burrow sediment, where denitrification potential was enhanced. Nitrification and total denitrification rates (denitrification of NO₃ ^- coming from the overlying water and of NO₃ ^- generated within the sediment) were calculated and discussed. Bioturbation by C. volutator increased both nitrification and denitrification, but denitrification was stimulated more than nitrification. Denitrification of NO₃ ^- coming from the overlying water was stimulated 1.2- and 1.7-fold in microcosms containing 3000 and 6000 ind m^-2 relative to control microcosms. The presence of C. volutator (6000 ind m^-2) stimulated nitrogen removal from the system, as dinitrogen, 1.5-fold relative to non-bioturbated microcosms. C. volutator individuals used in our study were collected from Norsminde Fjord, Denmark, in 1990.     

Effect of sexual maturation on the tissue biochemical composition of<Emphasis Type="Italic"> Octopus vulgaris</Emphasis> and<Emphasis Type="Italic"> O</Emphasis>.<Emphasis Type="Italic"> defilippi</Emphasis> (Mollusca: Cephalopoda)

Changes in the protein, lipid, glycogen, cholesterol and energy contents, total amino acid and fatty acid profiles of Octopus vulgaris and O. defilippi tissues (gonad, digestive gland and muscle) during sexual maturation (spermatogenesis and oogenesis) were investigated. Both species showed an increase of amino acids and protein content in the gonad throughout sexual maturation (namely in oogenesis), but allocation of these nitrogen compounds from the digestive gland and muscle was not evident. The major essential amino acids in the three tissues were leucine, lysine and arginine. The major non-essential amino acids were glutamic acid, aspartic acid and alanine. With respect to carbon compounds, a significant increasing trend (P<0.05) in the lipid and fatty acid contents in the three tissues was observed, and, consequently, there was also little evidence of accumulated lipid storage reserves being used for egg production. It seems that for egg production both Octopus species use energy directly from food, rather than from stored products. This direct acquisition model contrasts with the previous model for Octopus vulgaris proposed by ODor and Wells (1978: J Exp Biol 77:15–31). Most of saturated fatty acid content of the three tissues was presented as 16:0 and 18:0, monounsaturated fatty acid content as 18:1 and 20:1 and polyunsaturated fatty acid content as arachidonic acid (20:4n-6), eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3). Though cholesterol is an important precursor of steroid hormones, this sterol content exhibited variations that do not seem to be related with the maturation process. Moreover, significant differences (P<0.05) were obtained between genders, suggesting that perhaps there is a greater physiological demand for cholesterol during spermatogenesis than oogenesis. If the component sterols of octopus are of a dietary origin, considerable variation in the cholesterol content between species might be expected on the basis of the sterol composition of their prey. The glycogen reserves increased significantly in the gonad and decreased significantly (P<0.05) in the digestive gland and muscle of O. vulgaris (these trends were not evident in O. defilippi). Glycogen may play an important role in the maturation process and embryogenesis of these organisms, because carbohydrates are precursors of metabolic intermediates in the production of energy. It was evident that sexual maturation had a significant effect upon the gonad energy content, but the non-significant energy variation (P>0.05) in the digestive gland and muscle revealed no evidence that storage reserves are transferred from tissue to tissue. The biochemical composition of digestive gland and muscle may not be influenced by sexual maturation, but rather by other biotic factors, such as feeding activity, food availability, spawning and brooding.Communicated by S.A. Poulet, Roscoff