Lipid content and fatty acid composition of target tissues in wild Perca fluviatilis females in relation to hepatic status and gonad maturation

Variation in liver ultra‐structure and composition in relation to energy mobilization was investigated in female perch Perca fluviatilis from the Meuse River between August 2001 and June 2002. In April, just before spawning, the lipo‐somatic index ( I _F) was 0·3%, the gonado‐somatic index ( I _G) was 28% and the total lipid content of the liver was 2·53%. The average areas of lipid droplets and mitochondria were 0·05 and 0·06 μm², respectively. Glycogen supply reached 7·9% of the total area of the hepatocyte. During the sexual resting period, females accumulated energy in perivisceral fat and in the liver to reach 1·6% I _F and 4·85% of liver lipid content in August with lipid droplets average size of 0·09 μm² and glycogen average area of 15%. Liver cells contained a weakly developed rough endoplasmic reticulum (RER) and a great number of small mitochondria (average size 0·02 μm²). The I _G was 0·6% at this time. During the whole annual cycle, the average lipid content of female liver never exceeded 3·9 ± 1·9%. The concentration of docosahexaenoic (DHA), linolenic and linoleic acids increased in mature gonads while linolenic and linoleic acids decreased in the liver during the same period. Fatty acid composition of muscles of perch was characterized by a high content of DHA.     

Presence of xyloglucan-like polysaccharide in Spirogyra and possible involvement in cell–cell attachment

By methylation analysis, it was found that the cell walls of Spirogyra contained 4,6-linked glucose, 4-linked glucose and terminal xylose, which could be components of xyloglucan. Immunocytochemical analysis was carried out using an anti-serum against xyloglucan. After removal of pectic substances, the cell walls of both rhizoid cells and inner cells were stained. Crude protein extract from Spirogyra had a hydrolase activity for xyloglucans. In addition, the exogenously applied xyloglucan prevented the detachment of the cell wall of the severed cell. Involvement of xyloglucan-like polysaccharide in cell–cell attachment was discussed.     

黑龙江省双星藻科新种

三江水绵图1 Spirogyra sanjingensis sp. nov. Celluis vegetativis 104-133μlatis, 142—295μlongis; dissepimentis planis; chromatophoris 9-10(11), anfractibus 1-1.5; conjugations scalari, tubo ex utroque cellula mascula et feminca emisso; cellulis fructiferis cylindricis, levi-     

河鲈胚胎及卵黄囊期仔鱼发育

为探究河鲈(Perca fluviatilis)早期生活史和发育生物学,采用体视解剖镜、显微镜仔细观察、测量、描述、绘图的方法,连续观察了6个批次河鲈胚胎及卵黄囊期仔鱼发育状况,进行比较分析。结果显示:(1)在水温8~13℃时,胚胎期约需265h,有效积温2540~2880℃.h;水温11~13℃时,卵黄囊期约需6d,有效积温1750~2120℃.h;(2)辐射状次级卵膜将受精卵连成长带形单层网片状,每个胚胎周围有6个胚胎,排列很有规则。胚胎卵黄囊表面有一个大圆形油球。出膜前期可见眼球色素、胸鳍突起;(3)胚胎出膜的不同步主要是由于出膜前期长短不一和孵化水温较低所致。     

DISTRIBUTION,MORPHOLOGICAL DIVERSITY AND EVIDENCE FOR POLYPLOIDY IN NORTH AMERICAN ZYGNEMATACEAE (CHLOROPHYTA)1

Large-scale collections of Zygnemataceae in the continental United States of America were made between March and August in 1982, 1983, and 1984. Collections were made on a 31000-km transect through 35 states. Zygnemataceae were found at 318 sites was inspected. Temperature average 19°C and p^H averaged 6.1 over all sites. Algal strains in collections were identified to genus, characterized for filament width, chloroplast number, and end wall type, then photographed and isolated into unialgal culture. Spirogyra was the most common genus collected(632 strains), followed in abundance by Zygnema (174 Strains) and Mougeotia (135 strains). These three genera contained 95% of the strains collected and were equally widely distributed. Strains of the three genera frequently occurred together; no genus displayed evidence of habitat specialization among the three habitat types: flowing water, permanent ponds or lakes, and temporary pools. In Spirogyra, strains with plane (flat) end walls were four times more abundant than those with replicate (interlocking) end walls. Spirogyra with plane end walls showed more variation in filament width than Zygnema, Mougeotia, or Spirogyra with replicate end walls. In Spirogyra with plane end walls, filament width was correlted with nuclear DNA content and number of strains found per collection site was twice that of other genera or Spirogyra, with replicate end walls. Spirogyra strains wider than 70 μm were more frequent on the northern part of the transect. It is proposed that polyploidy may be of widespread occurrence in Spirogyra with plane end walls and that associated morphological plasticity may account for the high apparent specied diversity and survival of the genus in a wider variety of microhabitats than occupied by other Zygnemataceae.     

Effects of two chitin synthesis inhibitors on Thalassiosira fluviatilis and Cyclotella cryptica

Abstract The effects of two commercial chitin synthesis inhibitors, dimilin and polyoxin D, on chitin fiber formation and cell sedimentation for the diatoms Thalassiosira fluviatilis and Cyclotella cryptica (Bacillariophyceae) were investigated. Dimilin treatments for both diatom species were indistinguishable from controls in terms of chitin fiber productions, cell density and sedimentation. Polyoxin D-treated cells of both diatom species completely lacked the characteristic chitin fibers. Polyoxin D cultures were also characterized by a significant decrease in population density, increased sedimentation rates and a strong tendency to clump in comparison with control and dimilin treatments. It was concluded that (1) dimilin does not directly inhibit chitin synthesis in diatoms; (2) polyoxin-D inhibits β-chitin fibril formation, and (3) chitin fibers play an important role in cell separation and cell buoyancy.     

Effects of temperature on allocation of metabolic energy in perch (Perca fluviatilis) fed submaximal rations

Growth and long-term trends of oxygen consumption were monitored at 15 and 20° C in spontaneously swimming juvenile perch fed a fixed daily submaximal ration. The average rate as well as the efficiency of assimilation were the same at the two temperatures but a much higher proportion of food energy was allocated to activity and maintenance, and a correspondingly lower proportion to growth, at 20 than at 15° C. By computing average specific rates of oxygen consumption separately for all light and dark periods, it was found that at 20, but not at 15° C, the' scope for spontaneous activity' of two consecutive (dark and light) phases of a diurnal cycle was indirectly proportional to the average rate of oxygen consumption in the dark phase. This indicates that at 20° C the perch displayed partial compensation for a high metabolic rate in the dark by reducing swimming activity in the following light phase. However, the overall effect of this behaviour was probably too small to make a noticeable impact on the low conversion efficiency in the juvenile perch at 20 as compared to 15° C.     

Predation of perch on vendace larvae: diet composition in an oligotrophic lake and digestion time of the larvae

The diet of perch Perca fluviatilis was studied to reveal possible predation on vendace Coregonus albula larvae in an oligotrophic lake. Perch diet changed with the size of the fish: small perch ate mainly zooplankton and the diet shifted more to benthic invertebrates and fishes in larger perch. There were also annual and spatial differences in the diet, probably reflecting differences in the availability of prey animals. Perch predation on vendace larvae was only observed in the area with high availability of the larvae. The result suggested strengthened predation when the density of the larvae increases. According to bioenergetics modelling, the perch population increased natural mortality of vendace larvae only marginally. Food intake of spawning female perch was slightly reduced, whereas spawning males fed similarly to non-spawning males. Hence, the spawning period of perch was only a minor refuge for vendace larvae. Laboratory experiments of perch digestion rate demonstrated that, due to rapid digestion of the small fish larvae, diet sampling interval should not be >2 h in the field.     

Delayed spawning of perch, Perca fluviatilis L., in acidified lakes

The timing of spawning of perch was examined in four acidified lakes (pH 4.4–4.8) and in one circum-neutral lake (pH 6.3) in southern Finland in spring 1987. In three of the lakes, perch started to spawn soon after the ice melt (4–14 degree days > 5° C) and had spawned by the end of May at about 100 degree days > 5° C. In the two most acidified lakes, fish started to spawn later, at 35 and 60 degree days > 5° C, and had spawned in early June, at about 200 degree days > 5° C. The maturing of gonad products was delayed in both males and females.