Presence and development of populations of the introduced brown alga Sargassum muticum in the southwest Netherlands

Of the three Brachionus species used in aquaculture, Brachionus rubens, B. calycilorus and B. plicatilis, the latter is most widely used in raising marine fish and shrimp larvae due to its tolerance to the marine environment. In freshwater aquaculture the use of B. rubens and B. calycilorus is limited, probably because inert food products are readily available as feed for freshwater larvae.The rotifer Brachionus plicatilis is used in large numbers as the first food organism in intensive cultures of marine fish and shrimp larvae. An adequate supply of these rotifers relies on mass cultures. The reproductive rate of rotifers in these cultures depends on food quality and quantity, salinity, temperature and pH of the medium. Removal of waste products from culture tanks leads to higher and more efficient production of rotifers over extended periods of time. Rotifers have to be enriched with polyunsaturated fatty acids, which are essential for proper development and survival of marine fish and shrimp larvae.The future use of preserved rotifers and their resting eggs may help to overcome unforeseen failures of live cultures and may lead to more efficient use of these organisms in raising freshwater and marine fish and shrimp larvae.     

Effect of rainstorms on heterotrophic bacterial activity in a hypertrophic African lake

Hartbeespoort Dam is a hypertrophic man-made lake which is located in the Transvaal Province of South Africa. This region has recently experienced its most severe drought of the century. However, on three occasions in the summer rainy seasons of 1984 and 1985, major rainfalls (> 50 mm) occurred which caused large inflows to the lake. Inflowing river water entered as a density current causing marked silting of the water. Within the epilimnion (0–10 m) prior to these rainfalls there was usually no variation of bacterial numbers with depth, but heterotrophic bacterial activity (glucose uptake) decreased with depth concomitant with primary production. With the increased river inflow bacterial numbers did not increase but bacterial activity at the bottom of the epilimnion (10 m) increased to as high as 2.7 µg C l^–1 h^–1 in January 1985, reversing the depth profile of bacterial activity within the epilimnion. This resulted in decreased glucose concentrations (K_t + S_n) and turnover times. Heterotrophic activity per cell increased by between 2.5 and 5 times. These data demonstrate that storm events are important phenomena causing short-term changes in the metabolic activity of planktonic heterotrophic bacteria in lakes.     

Antiprogestagen RU486 prevents the LH-dependent decrease in the serum concentrations of inhibin in the rat

Summary 1. In the rat, the LH-dependent ovarian progesterone rise mediates several actions of the primary surge of LH on the ovary. This experiment was aimed at elucidating the effects of the antiprogestagen RU486 on the LH-dependent decrease in both the serum concentrations and the ovarian content of inhibin.2. All rats in this experiment were treated with an antagonist of LHRH (1 mg/200 µl saline at 0800 h in proestrus) to supress the endogenous release of LH. One group of rats received 32 µg LH/250 µl saline at 1200 h in proestrus. Other group was given 4 mg RU486/200 µl oil at 0800 h in proestrus. The third group was injected with both RU486 and LH. Rats from the control group were injected with 250 µl saline and 200 µl oil. Animals were decapitated at 1700 h in proestrus and trunk blood and ovaries collected to determine the serum concentrations of LH, FSH, progesterone, 17ß-estradiol and inhibin as well as the ovarian content of inhibin.3. The ovulatory dose of LH in LHRHa-treated rats decreased both the serum concentrations and the ovarian content of inhibin and increased the serum concentrations of FSH. The administration of RU486 blocked the effect of LH on the serum concentrations of inhibin but not that on the ovarian content of inhibin.4. Since the antiprogestagen RU486 blocked the effect of LH on the serum concentrations of inhibin, we conclude that ovarian progesterone, besides mediating the effects of the primary LH surge on the ovulatory process and luteinization, participates in the LH-dependent drop in the serum concentrations of inhibin in proestrous afternoon.     

（强）热带风暴条件下农田林网对防止棉花倒伏及减产的效应

研究结果表明 ,林带背风面 2 7H范围内 ,林网具有不同程度减轻棉株倒伏及产量损失的功能 ,有效防护范围为 0 .42～ 2 3H ,最大籽棉产量和衣分率效果区为 1 0～ 1 3H .与受灾区相比 ,保护区的籽棉产量增加 45.0 1 % ,皮棉产量增加 52 .69% .整个林网内的籽棉产量增加 2 9 94% ,皮棉产量增加 35 0 6% .     

Regulation of phytoplankton dynamics in a Laurentian Great Lakes estuary

The composition and dynamics of phytoplankton populations were examined in Old Woman Creek estuary, Lake Erie (USA). The centric bacillariophytes,Cyclotella atomus Hust.,Cyclotella meneghiniana Kütz., andAulacoseira alpigena (Grun.) Krammer, and the cryptophytes,Cryptomonas erosa Ehren. andRhodomonas minuta var. nannoplanctonica Skuja, dominated the phytoplankton most of the year. Chlorophytes, euglenophytes, and cyanophytes were observed less frequently. Estuarine and Lake Erie phytoplankton were considered distinct populations; lake taxa were largely confined to the estuary mouth and present only in low biomass. Maxima and minima of estuarine phytoplankton coincided with meteorological and hydrological forcing in the form of rainfall and subsequent storm-water inflows, respectively. Distinct population dynamics between the upper and lower estuary following storm events were attributed to the presence/absence of refugia serving as a source for repopulation by opportunistic taxa, fluctuating light conditions in the water column resulting from influx of particulate matter and resuspension of bottom sediments, and nutrient inputs associated with surface runoff and sub-surface interflow. Additionally, agricultural herbicides introduced by storm-water inflows potentially may affect and/or control the growth and physiological responses of individual taxa.     

Assessing the effects of repeated handling on the physiology and condition of semi‐precocial nestlings

Repeated exposure to elevated levels of glucocorticoids during development can have long‐term detrimental effects on survival and fitness, potentially associated with increased telomere attrition. Nestling birds are regularly handled for ecological research, yet few authors have considered the potential for handling‐induced stress to influence hormonally mediated phenotypic development or bias interpretations of subsequent focal measurements. We experimentally manipulated the handling experience of the semi‐precocial nestlings of European Storm Petrel Hydrobates pelagicus to simulate handling in a typical field study and examined cumulative effects on physiology and condition in late postnatal development. Neither baseline corticosterone (the primary glucocorticoid in birds), telomere length nor body condition varied with the number of handling episodes. The absence of a response could be explained if Storm Petrels did not perceive handling to be stressful or if there is dissociation of the hypothalamic–pituitary–adrenal axis from stressful stimuli in early life. Eliciting a response to a stressor may be maladaptive for cavity‐dwelling young that are unable to escape or defend themselves. Furthermore, avoiding elevated overall glucocorticoid exposure may be particularly important in a long‐lived species, in which accelerated early‐life telomere erosion could impact negatively upon longevity. We propose that the level of colony‐wide disturbance induced by investigator handling of young could be important in underlining species‐specific responses. Storm Petrel nestlings appear unresponsive to investigator handling within the limits of handling in a typical field study and handling at this level should not bias physiological and morphological measurements.     

Multiple matings modify the estrous length,the moment of ovulation,and the estradiol and LH patterns in ewes

In several species, mating reduces the estrous length and advances ovulation. The aim of this study was to determine if multiple matings reduces the estrous length and modifies the moment of ovulation, as well as the estradiol and LH patterns in ewes. The estrous cycle of Corriedale ewes was synchronized, and the onset of receptivity was monitored every 3 h with rams, avoiding mating. At the estrous onset, ewes were assigned to two experimental groups (n=10 each): 1) estrous was monitored every 3 h with a ram avoiding mating (group CON), and 2) a ram was allowed to mate and ejaculate once every 3 h (group MAT). The ovaries were scanned with transrectal ultrasonography and blood samples were collected for measuring 17β-estradiol and LH concentrations every 3 h until ovulation. Estrus was shorter in MAT than CON ewes (24.7 ± 1.5 h vs. 30.4 ± 1.5 h, respectively; P=0.02); the proportion of animals that ovulated before the end of estrus was greater in CON ewes: (9/10 vs. 3/10, P=0.009). The area under the LH curve (AUC) was greater in MAT than CON ewes (36.1 ± 3.5 ng.h^-1.mL^-1 vs 24.9 ± 3.5 ng.h^-1.mL^-1 P=0.03). However, MAT ewes had a lower 17β-estradiol AUC than CON ewes (41.0 ± 4.9 pg.h^-1.mL^-1 vs 59.4 ± 4.9 pg.h^-1.mL^-1 P=0.01). Mating reduced the estrous length, induced a greater secretion of LH but less total 17β-estradiol secreted and, additionally, ovulation occurred more frequently after the end of estrus in mated ewes.     

Minor FSH surge,minor follicular wave,and resurgence of preovulatory follicle several days before ovulation in heifers

Blood samples were collected and follicle diameters were determined daily beginning on Day 12 (Day 0 = ovulation) in 35 interovulatory intervals (IOIs) in heifers. A minor follicular wave with maximal diameter (6.0 ± 0.3 mm) on Day −4 was detected in six of seven IOIs that were scanned for follicles 4 mm or greater. The number of IOIs with a CV-identified minor FSH surge toward the end of the IOI was greater (P < 0.03) in two-wave IOIs (10/17) than in three-wave IOIs (4/18). The 17 two-wave IOIs were used for study of the temporal relationships among preovulatory follicle, FSH, LH, and estradiol. Daily growth rate of the preovulatory follicle was maximum on Days −11 to −7, minimum (P < 0.05) on Days −7 to −4, and increased (resurged, P < 0.05) on Days −4 to −3. A transient increase in FSH was maximum on mean Day −4, and the peak of a minor FSH surge occurred on Day −4.5 ± 0.2. Concentration of LH and estradiol increased between Days −5 and −4. Results demonstrated resurgence of the preovulatory follicle apparently for the first time in any species. Resurgence seemed more related temporally to the minor FSH surge than to the LH increase, but further study is needed. Results supported the novel hypotheses that a minor FSH surge near the end of the IOI is temporally associated with (1) the emergence of a minor follicular wave and (2) the resurgence in growth rate of the preovulatory follicle.