Size-dependent predation on marine fish larvae by Ctenophores, Scyphomedusae, and Planktivorous fish   总被引：3，自引：0，他引：3  

JAMES H. COWAN JR.  EDWARD D. HOUDE 《Fisheries Oceanography》1992,1(2):113-126

Size-dependent predation rates on marine fish larvae by the ctenophore Mnemiopsis leidyi , scyphomedusa Chrysaora quinquecirrha , and planktivorous fish Anchoa mitchilli were estimated via experiments in 3.2 m³ me-socosms. Predation rates on larvae of the goby Gobio-soma bosci were estimated in relation to 1) length of larval prey, 2) presence or absence of alternative < 1 mm zooplankton prey, and 3) a predator-prey interaction between the scyphomedusa and ctenophore. The consumption rate of larvae by the three predators generally declined as larval length increased. The ctenophore ate fewer (1.0 d^-1 per predator) larvae than did the medusa (7.8 d ^-1 per predator) or bay anchovy (4.0 d ^-1 per predator), but it consumed larvae in all size classes tested (3.0–9.5 mm SL). Predation by bay anchovy and the medusa was more size-dependent: 3.0–5.0 mm larvae were most vulnerable. Fewer larvae were eaten by the ctenophore and bay anchovy when zooplankton alternative prey was available, but predation on larvae by the medusa was not influenced by alternative zooplankton prey. Consumption rate of fish larvae by the medusa was reduced 20–25% when the ctenophore was present as its alternative prey. An encounter-rate model was developed and its parameters estimated from the experimental results. Model simulations indicated that the relationship between larval size and vulnerability is dependent on size, swimming speed, and behavior of both predators and larvae, and that bigger or faster-growing fish larvae are not always less vulnerable to predation.  相似文献   

Lesions of a rock beauty, Holacanthus tricolor (Bloch), from Puerto Rico     

J. M. GRIZZLE  E. H. WILLIAMS JR 《Journal of fish diseases》1985,8(1):129-134

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A myopathy in North Dakota walleye, Stizostedion vitreum (Mitchill)     

H.L. HOLLOWAY  JR  C. E. SMITH 《Journal of fish diseases》1982,5(6):527-530

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The Solar Acoustic Spectrum and Eigenmode Parameters     

F Hill  PB Stark  RT Stebbins  ER Anderson  HM Antia  TM Brown  TL Duvall  DA Haber  JW Harvey  DH Hathaway  R Howe  RP Hubbard  HP Jones  JR Kennedy  SG Korzennik  AG Kosovichev  JW Leibacher  KG Libbrecht  JA Pintar  EJ Rhodes  J Schou  MJ Thompson  S Tomczyk  CG Toner  R Toussaint  WE Williams 《Science (New York, N.Y.)》1996,272(5266):1292-1296

The Global Oscillation Network Group (GONG) project estimates the frequencies, amplitudes, and linewidths of more than 250,000 acoustic resonances of the sun from data sets lasting 36 days. The frequency resolution of a single data set is 0.321 microhertz. For frequencies averaged over the azimuthal order m, the median formal error is 0.044 microhertz, and the associated median fractional error is 1.6 x 10(-5). For a 3-year data set, the fractional error is expected to be 3 x 10(-6). The GONG m-averaged frequency measurements differ from other helioseismic data sets by 0.03 to 0.08 microhertz. The differences arise from a combination of systematic errors, random errors, and possible changes in solar structure.  相似文献   

Orchardgrass and perennial ryegrass with applied nitrogen and in mixtures with legumes     

L. E. SOLLENBERGER †  W. C. TEMPLETON JR  R. R. HILL JR 《Grass and Forage Science》1984,39(3):263-270

High-yielding grass-legume mixtures play an important role in forage-animal systems but finding compatible and adapted species can sometimes be difficult. The objective of this study was to examine productivity of perennial ryegrass and orchardgrass in pure stands with N and in mixtures with legumes.
Broadcast sowings were made on conventionally prepared seedbeds in August 1979 and May 1980 on a Hagerstown silt loam soil (fine, mixed mesic Typic Hapludalf). When sown alone orchardgrass cv. Pennlate and perennial ryegrass cv. Reveille received rates of N ranging from 0 to 448 kg ha⁻¹ a⁻¹. The grasses were also grown in mixtures with alfalfa cv. Arc, red clover cv. Arlington, or birds foot trefoil cv. Viking. The same legumes were sown alone. Four legume seed rates were used in both the pure legume and mixed stands.
Orchardgrass-N swards were more productive than ryegrass-N swards over 3 years. More dry matter (DM) was harvested from pure stands of  相似文献   

不同温度对甜菜种子吸胀过程中线粒体CCO和MDH活性的影响     

宋松泉  陈玲 《种子》1999,(4):6-8

吸胀温度显著地影响甜菜种子的萌发速率。吸胀温度为３０℃和２０℃时,５０％萌发所需要的时间分别为３６ｈ和５６ｈ;在７℃中吸胀１２０ｈ,仍未见萌发。在种子吸胀过程中,粗线粒体蛋白的含量,细胞色素Ｃ氧化酶和苹果酸脱氢酶的活性增加,且它们在３０℃和２０℃中的活性较高,在７℃下较低。  相似文献   

Transmission of virulent footrot between sheep and goats     

SC GHIMIRE  JR EGERTON  OP DHUNGYEL 《Australian veterinary journal》1999,77(7):450-453

OBJECTIVE: To determine the infectivity of ovine and caprine strains of Dichelobacter nodosus for both sheep and goats. DESIGN: Pen experiments in which 20 sheep and 19 goats were challenged directly with the two strains, and transmission experiments on pasture, using donors infected by experimental challenge. RESULTS: Sheep and goat strains of D nodosus infected both animal species in experimental challenges. Animals so infected transmitted footrot to both sheep and goats on pasture plots. A significantly smaller proportion of goats than sheep was infected when challenged with either strain. The interval between exposure and development of footrot in goats was longer than in sheep when recipient animals were exposed to infected donors on pasture. The disease was less invasive in goats than in sheep. CONCLUSIONS: With the strains of D nodosus used there was no evidence of host specificity. Direct transmission of footrot can occur between sheep and goats in the same environment. There is a need to include goats in ovine footrot eradication programs and vice versa.  相似文献   

Digestive proteinases and peptidases in the hepatopancreas of the southern brown shrimp (Farfantepenaeus subtilis) in two sub‐adult stages     

D.S. BUARQUE  P.F. CASTRO  F.M.S. SANTOS  I.P.G. AMARAL  S.M. OLIVEIRA  K.B. ALVES  L.B. CARVALHO JR  R.S. BEZERRA 《Aquaculture Nutrition》2010,16(4):359-369

The aim of this study was to examine proteinases and peptidases from the hepatopancreas of two sub‐adult stages of Farfantepenaeus subtilis: SAS₆ (5.93 ± 0.69 g wet weight) and SAS₁₃ (13.26 ± 0.60 g wet weight). Trypsin and chymotrypsin activity was higher in the extract from the SAS₆ individuals (P < 0.05). The highest activity among aminoacyl‐β‐naphthylamide substrates was found using alanine‐, arginine‐, leucine‐ and lysine‐β‐naphthylamide. There was a positive correlation between the recommended concentration of essential amino acids in penaeid shrimp feed and aminopeptidase activity in both sub‐adult stages. Proteolytic activity of F. subtilis was strongly inhibited by specific trypsin inhibitors. The optimal temperature for trypsin, chymotrypsin and leucine aminopeptidase activity was between 45 and 55 °C. Six and seven bands were found in caseinolytic zymograms for SAS₆ and SAS₁₃ respectively. All bands were inhibited by phenylmethylsulfonyl fluoride in both sub‐adult stages. The use of tosyl‐lysine‐chloromethyl‐ketone and benzamidine caused strong inhibition of the proteolytic bands. Trypsin and chymotrypsin activity was the main difference observed between the protease pattern of SAS₆ and SAS₁₃F. subtilis.  相似文献