Crustacean zooplankton size structure in aquaculture lakes: is larger size structure always associated with higher grazing pressure?

Crustacean zooplankton size structure in 27 aquaculture lakes was studied to test the hypothesis that larger size structure is associated with higher grazing pressure. Mean body length of crustaceans was positively correlated with increasing Chl a (r(2) = 0.40, P = 0.000) and TP (r(2) = 0.38, P = 0.000), contrary to the empirical studies. However, the ratio of zooplankton to phytoplankton biomass decreased significantly with increasing TP (r(2) = 0.27, P = 0.005) and mean body length (r(2) = 0.46, P = 0.000). Meanwhile, size structure showed no significant effect in explaining residual variations of phosphorus-chlorophyll relationship (P = 0.231). These results indicate that larger size structure was not always associated with higher zooplankton grazing pressure. It is likely that in aquaculture lakes crustacean zooplankton size structure was of minor importance in control of phytoplankton biomass, and it was mainly regulated by fish predation. The results showed in our study and the empirical studies might be a reflection of two different stages of lake eutrophication and fish predation intensity.

Changes in the concentrations of size-fractioned iron and related environmental factors in the northeastern part of lake Dianchi (China)

To observe changes in the concentrations of size-fractionated iron and related environmental factors, experiments were conducted in the northeastern part of the shallow eutrophic lake Dianchi (China) from March 2003 to February 2004. Iron concentrations were measured for three size fractions: particulate iron (phi >0.22 mu m), colloidal iron (phi = 0.025-0.22 mu m) and soluble iron (phi < 0.025 mu m), and environmental factors (physicochemical and biological factors) were synchronously analyzed. Results showed that size-fractionated iron and the related environmental factors all varied with season. Colloidal iron accounted for only 5-9% of total iron, while particulate and soluble iron each accounted for 40-50% of total iron. The results suggested that size-fractionated iron can transform into each other, especially the highly reactive colloidal iron. Significant linear correlations were found between iron in different size fractions, and significant correlations were also obtained between chlorophyll a and environmental factors, such as TN, TP and secchi depth. No significant correlation between iron and chlorophyll a was found in this study.

Experimental study of the effects of temperature variation on droplet size and wetness fraction in a low-pressure model steam turbine

The three-stage low-pressure model steam turbine at the Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM) was used to study the impact of three different steam inlet temperatures on the homogeneous condensation process and the resulting wetness topology. The droplet spectrum as well as the particle number concentration were measured in front of the last stage using an optical-pneumatic probe. At design load, condensation starts inside the stator of the second stage. A change in the steam inlet temperature is able to shift the location of condensation onset within the blade row up- or downstream and even into adjoining blade passages, which leads to significantly different local droplet sizes and wetness fractions due to different local expansion rates. The measured results are compared to steady three-dimensional computational fluid dynamics calculations. The predicted nucleation zones could be largely confirmed by the measurements. Although the trend of measured and calculated droplet size across the span is satisfactory, there are considerable differences between the measured and computed droplet spectrum and wetness fractions. © IMechE 2013 Reprints and permissions: sagepub.co.uk/ journalsPermissions.nav.

A passive acoustic monitoring method applied to observation and group size estimation of finless porpoises

The present study aimed at determining the detection capabilities of an acoustic observation system to recognize porpoises under local riverine conditions and compare the results with sighting observations. Arrays of three to five acoustic data loggers were stationed across the main channel of the Tian-e-zhou Oxbow of China's Yangtze River at intervals of 100-150 m to record sonar. signals of free-ranging finless porpoises (Neophocaena phocaenoides). Acoustic observations, concurrent with visual observations, were conducted at two occasions on 20-22 October 2003 and 17-19 October 2004. During a total of 42 h of observation, 316 finless porpoises were sighted and 7041 sonar signals were recorded by loggers. The acoustic data loggers recorded ultrasonic signals of porpoises clearly, and detected the presence of porpoises with a correct detection level of 77.6% and a false alarm level of 5.8% within an effective distance of 150 m. Results indicated that the stationed passive acoustic observation method was effective in detecting the presence of porpoises and showed potential in estimating the group size. A positive linear correlation between the number of recorded signals and the group size of sighted porpoises was indicated, although it is faced with some uncertainty and requires further investigation. (C) 2005 Acoustical Society of America.

Photosynthetic physiology and growth as a function of colony size in the cyanobacterium Nostoc sphaeroides

Algal size can affect the rate of metabolism and of growth. Different sized colonies of Nostoc sphaeroides were used with the aim of determining the effects of colony size on photosynthetic physiology and growth. Small colonies showed higher maximum photosynthetic rates per unit chlorophyll, higher light saturation point, and higher photosynthetic efficiency (a) than large colonies. Furthermore, small colonies had a higher affinity for DIC and higher DIC-saturated photosynthetic rates. In addition, small colonies showed higher photosynthetic rates from 5-45degreesC than large colonies. There was a greater decrease in Fv/Fm after exposure to high irradiance and less recovery in darkness for large colonies than for small colonies. Relative growth rate decreased with increasing colony size. Small colonies had less chl a and mass per unit surface area. The results indicate that small colonies can harvest light and acquire DIC more efficiently and have higher maximum photosynthetic rates and growth rates than large colonies.

Effect of feeding frequency on growth, feed utilization, and size variation of juvenile gibel carp (Carassius auratus gibelio)

Juvenile (3.0 +/- 0.2 g) gibel carp (Carassius auratus gibelio ) were fed to satiation for 8 weeks to investigate the effect of feeding frequency on growth, feed utilization and size variation. Five feeding frequencies were tested: two meals per day (M2), three meals per day (M3), four meals per day (M4), 12 meals per day (M12) and 24 meals per day (M24). The results showed that daily food intake increased significantly with the increase in feeding frequency and there was no significant difference between daily food intakes in M12 and M24 treatments. Growth rate, feed efficiency increased significantly with increasing feeding frequencies. Size variation was not affected by feeding frequency. Apparent digestibility of dry matter was not influenced by feeding frequency, while apparent digestibility of protein and energy increased significantly at high feeding frequencies. The feeding frequency had no significant effect on the moisture, lipid, protein, or energy contents of gibel carp, while the ash content decreased with increased feeding frequency. It was recommended that 24 meals per day was the optimal feeding frequency for juvenile gibel carp.

Effects of the stocking density and body size of the mitten crab (Eriocheir sinensis) on aquatic plant biomass

Experiments in tanks and cages were conducted to examine the effects of stocking density and body size of the Mitten crab (Eriocheir sinensis) on transplanted submersed macrophyte biomass. The early juvenile crab with 7.0 +/-0.6 mm. carapace width (CW) had little effect on plant biomass, regardless of the stocking densities. However, larger crabs (CW: 18.0 +/-2.2,35.0 +/-3.6, and 60.0 +/-5.7 mm) significantly influenced plant biomass, especially at large stocking densities. Predictive models, using crab body size and stocking density, were generated to demonstrate effect of the mitten crab on the changes Of plant biomass. The results indicate that dense mitten crab populations may adversely affect aquatic plant communities, particularly when its animal food resources are scarce.

Spontaneous activity was unaffected by ration size in Nile tilapia and gibel carp

Two growth trials using a range of ration sizes from starvation to maximum feeding suggested that linear relationships existed between specific growth rate and ration size for Nile tilapia and givel carp, Continuous measurement of activity showed that activity level, in terms of distance swum per day, was not affected significantly by ration size in both Nile tilapia and gibel carp. (C) 2001 The Fisheries Society of the British Isles.

Effect of body size on growth and energy budget of Nile tilapia, Oreochromis niloticus

A growth trial was conducted at 30 degrees C to investigate the effect of body size on growth and energy budget of Nile tilapia. The average initial body weights of the four size groups tested were 9.3, 34.1, 80.3 and 172.4 g, respectively. Fish were fed to satiation twice a day with a diet containing 35.6% crude protein. Food consumption (C-max: kJ/day) increased with body size (W: g) according to the relationship: Ln C-max = 1.45 + 0.42 LnW. The final body contents of dry matter, crude protein and ash per unit body weight increased with increasing body size while contents of fat and energy were independent of body size. Specific growth rates of wet weight, dry weight, protein and energy decreased as the fish increased in size. Feed efficiencies in wet weigh, dry weight and crude protein decreased with increasing body size, while that of energy remained unchanged. The proportions of energy intake allocated to the various components (faecal energy, excretory energy, heat production and recovered energy) of the energy budget were not significantly affected by body size, and the average budget was: 100IE-18.5(+/- 1.33)FE + 5.9 (+/- 3.09)(ZE + UE) + 49.3(+/- 3.77)HE + 26.3(+/- 6.23)RE, where IE, FE, (ZE + UE), HE and RE represent gross energy intake, faecal energy, excretory (non-faecal) energy loss, heat production and recovered energy (growth), respectively. It is suggested that the decrease in growth rate in larger fish is mainly due to the decrease in relative food intake. (C) 1997 Elsevier Science B.V.

Energy budget of Nile tilapia (Oreochromis niloticus) in relation to ration size

Nile tilapia weighing 8.29-11.02 g were fed a practical diet at seven ration levels (starvation, 0.5, 1, 2, 3, 4% body weight per day and satiation) twice a day at 30 degrees C. Feed consumption, apparent digestibility, nitrogenous excretion and growth were determined directly, and heat production was calculated by difference of energy budget. The relationship between specific growth rate in wet weight (SGR(w), percentage per day) and ration size (RL, percentage per day) was a decelerating curve described as SGR(w) = 2.98 (1 - e(-0.61(RL-0.43))). The apparent digestibility coefficients for dry matter and protein showed a decreasing pattern with increasing ration while the apparent digestibility coefficient of energy was not significantly affected by ration size. The proportion of gross energy intake lost in nitrogenous excretion tended to decrease with increasing ration. Feed efficiency was highest, and the proportion of gross energy intake channelled to heat production was lowest, at an intermediate ration level (2% per day). The energy budget at the satiation level was: 100IE = 16.9FE + 1.2(ZE + UE) + 62.3HE + 19.6RE, where IE, FE, (ZE + UE), HE and RE represent gross energy intake, faecal energy, excretory (non-faecal) energy loss, heat production and recovered energy (growth), respectively. (C) 1997 Elsevier Science B.V.

Changes in culture growth dynamics and cell size in a Scenedesmus quadricauda upon action of potassium dichromate

The effect of potassium dichromate in concentrations of 0.5 to 10 mg/l on a laboratory culture of Sc. quadricauda algae was studied in standard conditions. The total cell numbers decreased at potassium dichromate concentrations over 1 mg/l, and the proportion of living cells decreased at all studied concentrations. A positive correlation was found between changes in cell size and their numbers at toxin concentrations of 1 and 3 mg/l, and a negative correlation was found between the relative size and the cell numbers at 3 and 10 mg/l. This may be due to different intensity of growth inhibition and cell division under the influence of the toxin. The culture sensitivity to the toxin increased in autumn and decreased in the spring.

PCDD/F-s, PCBs, HCHs and HCB in sediments and soils of Ya-Er lake area in China: Results on residual levels and correlation to the organic carbon and particle size

Sediments and soils collected from the Ya-Er Lake area in China were analysed for the polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyl (PCBs), hexachlorocyclohexane (HCHs) and hexachlorobenzene (HCB). The results indicated the main pollution problems in the Ya-Er Lake area, which was heavily polluted by HCHs and chlorobenzenes, now is dominantly polluted by PCDD/Fs, PCBs and HCB. The occurrence of PCDD/Fs and PCBs with relatively high levels of HpCDDs, OCDD and low chlorinated-substituted PCBs, is attributed to the discharge of waste water and biodegradation. The vertical distributions of HCH-residues are related with the content of organic carbon and particle size. Copyright (C) 1996 Elsevier Science Ltd

Effect of ration and body size on the energy budget of juvenile white sturgeon

Growth and energy budget were measured for three sizes(2.4, 11.1 and 22.5 g) of juvenile white sturgeon Acipenser transmontanus held at 18.5 degrees C and fed tubificid worms at different levels ranging from starvation to ad libitum. For each size-class, specific growth rate increased linearly with increasing ration, and conversion efficiency was highest at the maximum ration. Growth rate decreased with increasing fish size at the maximum ration, but increased with size al each restricted ration. Conversion efficiency increased with increasing ration for each size-class and was usually highest at the maximum ration. Faecal production accounted for 3.2-5.2% of food energy. The proportion of food energy lost in nitrogenous excretion decreased with increasing ration. With increases in ration, the allocation of metabolizable energy to metabolism decreased, while that to growth increased. Fish size had no significant effect on the allocation of metabolizable energy to metabolism or growth. Al the maximum ration, on average 64.9% of metabolizable energy was spent on metabolism, and 35.1% on growth. (C) 1996 The Fisheries Society of the British Isles

KINETICS OF SIZE-FRACTIONATED AND DISSOLVED ALKALINE-PHOSPHATASE IN A FARM POND

Nutrient addition bioassays were conducted in 10 L carboys with water from a eutrophic farm pond. The four bioassay treatments each conducted in triplicate were control (no nutrients added), +N (160 mu mol L(-1) NH4Cl), +P (10 mu mol L(-1) KH2PO4), and N+P (160 mu mol L(-1) NH4Cl and 10 mu mol L(-1) KH2PO4). The size fractionated (0.2-0.8, 0.8-3, > 3 mu m) contents of the carboys were analyzed after 7 d for alkaline phosphatase activity (APA) and chlorophyll-a content. Chlorophyll data suggested P deficiency in ammonium and control mesocosms and no P deficiency with phosphate additions. Pond water also was collected in June, August, October, and March for measurement of APA. In water from the pond, the greatest V-max of APA usually was associated with microorganisms in the size classes between 0.8-3 mu m. In mesocosm experiments, the N+P treatment increased V-max of dissolved and particulate associated APA in the 0.2-0.8 mu m size range and in dissolved form. The V-max of APA in the largest size-fraction (> 3 mu m) increased markedly with P deficiency (+N treatment) and decreased in the P-enrichment treatment. The patterns of APA and chlorophyll associated with different size fractions often varied independently among different treatments and seasons and not always as a function of P deficiency, indicating the difficulty of attempting to normalize APA to phytoplankton biomass or chlorophyll. The Michaelis half saturation constant of APA in the pond water showed no strong trends with varied seasons or size fraction.

HYDROGRAPHIC VARIATIONS IN SIZE STRUCTURE OF PLANKTON BIOMASS IN A CHANGJIANG FLOODPLAIN LAKE

The size structure of the planktonic community in a Changjiang floodplain lake (Lake Chenhu, Hubei, P. R. China) was described for the inundation period of May through September 1983. The modality of the Sheldon-type size distributions changed hydrographically with the spectral profiles being bimodal during low, rising, mid-high and falling water phases, and trimodal soon after filling and shortly before falling. The modal peaks corresponded respectively to the dominant organisms of chlorophytes and nauplii, while the troughs centered on the bacteria and macrocrustacean size classes in the lake. The slope of the normalized biomass spectrum (an index of plankton size distribution) was less than -1.0 for the filling and falling phases or close to -1.0 for the high water period, indicating that the planktonic biomass tended to decrease or evenly distributes across logarithmically ordered size classes, respectively. This observed variation in the size distribution of the plankton community mainly resulted from changes in water levels and contents of particulate inorganic matter (PIM) in the lake.