Biomass yields of Chlorella from iron (Y x/Fe) in iron-limited batch cultures

The maximum biomass in iron-limited photosynthetic batch cultures of chlorella increased as the logarithm of the iron concentration. The growth yield from iron (Y _x/Fe) showed a marked inverse relation to the specific growth rate. The maximum biomass yield, g dry biomass/g iron consumed, was 7.5x10³ with specific growth rate 0.108 h^-1; the minimum was 0.79×10³ with specific growth rate 0.145 h^-1. The maximum specific growth rate in the exponential phase of Fe limited cultures varied as the initial Fe concentration. Fe-limited growth made the cells adhere to a glass surface.Abbreviation O.D. optical density     

Variation of ommatidia number as a function of worker size inCamponotus pennsylvanicus (DeGeer) (Hymenoptera: Formicidae)

Summary The relation of worker size to ommatidia number was examined in the polymorphic antCamponotus pennsylvanicus (DeGeer). Linear regression described this relationship as:Y = 260.9 + 113.6×; whereYis ommatidia number andX is head width. A log-log regression described this relationship as:Y = 323.5 + 286.9*logX(r ² = 0.98). This analysis indicated an allometric relation of ommatidia number to head width, where ommatidia numbers increase at a slower rate than head width. This relationship is discussed in terms of ethotypes associated with worker morphotypes, and the possible mechanisms regulating polymorphic development.     

Seasonal Development and Morphological Variability of Cyclotella ocellata (Bacillariophyceae) in the Eutrophic Lake Dagow (Germany)

The development of Cyclotella ocellata Pantocsek was studied systematically in the eutrophic, dimictic hardwater Lake Dagow from March to October, 1994. Cyclotella ocellata was the most important centric diatom in the lake with a maximum cell density of 6 × 10⁶ cells 1⁻¹. The seasonal development, characterized by a spring and a summer maximum, is considered in relation to environmental factors and the succession of the phytoplankton community. The amount of Cyclotella ocellata biomass as a proportion of the total phytoplankton biomass varied from 0.5 to 35%. In addition, seasonal changes in cell size and feature associated with sexual reproduction of Cyclotella ocellata were documented. Light and electron microscopic investigations demonstrate an extremely wide range of morphological variability of this natural population.     

气候变化对鄱阳湖白鹤越冬种群数量变化的影响

分析了1983—2011年鄱阳湖国家级自然保护区越冬白鹤种群数量的年际变化趋势,检验了白鹤种群动态与繁殖地和越冬地气候变化的相关性,气候变量包括月平均气温、月平均最高气温、月平均最低气温和月降水量。研究结果表明,鄱阳湖国家级自然保护区内的白鹤年最大数量平均为(2 130±153)只,呈显著地线性增长趋势(R2=0.454,F=22.441,df=28,P=0.000),但年际波动较大。在越冬地,越冬当年10月、11月、12月的气候变量与白鹤种群数量没有显著的相关性,但越冬初期10月份和越冬后期翌年3月份的气温变量与第4年、第5年、第6年及第7年的白鹤种群数量存在显著的正相关,表明越冬地气候对白鹤种群大小的影响存在时滞效应。越冬初期和末期可能是白鹤补充能量的关键阶段,而且越冬初期的气候可能也与冬季食物的数量或质量相关,因此这两个阶段的适宜气温可能有利于个体尤其是幼鹤的存活,使更多的个体参加繁殖,由于白鹤的性成熟年龄在3—5a,因此其对白鹤种群增长的有利影响会在3a以后表现出来。白鹤种群数量变化与繁殖地繁殖期的降水量没有显著的相关性,而与7月份的气温变量存在显著的正相关。多元线性回归分析结果表明,6a前的10月份平均最低温度、2a前的10月最高温度及5a前的10月平均气温是白鹤种群数量变化的显著预测因子,共同解释了鄱阳湖国家级自然保护区白鹤种群数量变化的74.8%(F=23.807,df=27,P=0.000)。     

An example of a regular inbreeding system with cubic ancestral growth that preserves some genetic variability

A specific regular inbreeding system of quadruple half-second cousin mating is considered. A regular inbreeding system can be thought of as a graph which satisfies certain natural homogeneity properties. Random walks X _n and Y _n are introduced on the nodes of the graph; the event {X _n=Y_n} is a renewal event by the homogeneity properties. In Arzberger (1985) it is shown that 1) graphs associated with left cancellative semigroups are regular, and 2) for regular systems, the population becomes genetically uniform if and only if the event {X _n=Y_n} is recurrent. In Arzberger (1986) the system of quadruple half-second cousin mating is associated with a cancellative semigroup, thus the system is regular. In this paper we show that 1) A_n is asymptotically of the form cn ³, where A _n is the number of ancestors n generations into the past, 2) {X _n=Y_n} is not recurrent (this is shown by associating (X _n, Y _n) with a random walk in Z ³, 3) P[X _3n =Y _3n ] is asymptotically of the form cn ^–3/2. Thus, in this example, genetic heterogeneity is maintained, with a cubic rate of growth for A_n, not by an exponential growth rate, as in all previous examples of regular inbreeding systems in which genetic heterogeneity is maintained.     

Relationship between female body size and demographic parameters inBactrocera Malaysian A (Diptera: Tephritidae)

The effect of body size, as measured by the head width, of the female Bactrocera sp. Malaysian A (kept separately in sexual pairs) on the demographic parameters was investigated in the laboratory under ambient conditions of 28–30°C, 78–85% RH and natural photoperiod. Body size was shown to influence significantly all the demographic parameters. The expectation of life of females at eclosion from pupae was respectively for head widths of 1.6, 1.8, 1.9, 2.0 and 2.1 mm: 76.2, 73.4, 73.8, 102.4 and 115.2 days. The mean number of eggs laid per female in its life time was respectively: 86.4±48.7, 181.8±56.1, 229.7±72.6, 364.3±69.4 and 477.5±109.3 which was significantly different from one another (F=3.73,P<0.05) especially the two smaller sizes from the two larger sizes. The regression line for total eggs laid (Y) against head width (X) was Y=785.2X−1208.7 (R²=0.35,P<0.001). The net reproductive rate (R₀) was respectively 15.8, 34.0, 43.5, 66.9 and 88.8 eggs, while the intrinsic rate of increase (r) was respectivley 0.0435, 0.0538, 0.0670, 0.0665 and 0.0711. The results confirm that for mass rearing purposes, larger females which produce more offspring are to be preferred.     

Distance segregation and compound sex chromosomes in mantispids (Neuroptera: Mantispidae)

The sex chromosomes segregate precociously in prometaphase I of male meiosis, without prior synapsis or any physical connection, in 4 species of American mantispids (Neuroptera: Mantispidae). Segregational movements are interpolar, and are implemented through chromosomal fibers. Univalent autosomes, present from diakinesis on in several species, are capable of a similar distance segregation in prometaphase. The sex chromosomes are XX —XY , as is characteristic of the Order, with the exception of Entanoneura phthisica in which both elements are compound —X¹X²X³Y¹Y²Y³in the male, and X¹X¹X²X²X³X³ in the female. In tetraploid sectors of gonial origin in testes of this species no sex bivalents are formed; a distance segregation of 6 sex univalents to each pole is effected, but — as observed in the one individually identifiable pair — segregation separates complete homologues, Y¹ from Y¹, X¹ from X¹, etc. In all species the male meiotic spindle is formed by the collocation of individual chromosomal spindle units within which bivalents become deformed; the timing and degree of deformation vary with the species. In karyotype the American species conform to a common pattern with the known Japanese and European species; diploid numbers range only from 18 to 22, and each complement carries the family insigné of one pair of disproportionately large autosomes in a set of small and rather uniformly sized chromosomes.     

Response surface methodology for optimization and characterization of limonene-based coenzyme Q10 self-nanoemulsified capsule dosage form

The aim of this study was to systematically obtain a model of factors that would yield an optimized self-nanoemulsified capsule dosage form (SNCDF) of a highly lipophilic model compound, Coenzyme Q10 (CoQ). Independent variables such as amount of R-(+)-limonene (X ₁), surfactant (X ₂), and cosurfactant (X ₃), were optimized using a 3-factor, 3-level Box-Behnken statistical design. The dependent variables selected were cumulative percentage of drug released after 5 minutes (Y ₁) with constraints on drug release in 15 minutes (Y ₂), turbidity (Y ₃), particle size (Y ₄), and zeta potential (Y ₅). A mathematical relationship obtained,Y ₁=78.503+6.058X ₁ +13.738X ₂+5.986X ₃−25.831X ₁ ² +9.12X ₁X₂−26.03X ₁X₃−38.67X ₂ ² +11.02X ₂X₃−15.55X ₃ ³ (r ²=0.97), explained the main and quadratic effects, and the interaction of factors that affected the drug release. Response surface methodology (RSM) predicted the levels of factorsX ₁,X ₂, andX ₃ (0.0344, 0.216, and 0.240, respectively), for a maximized response ofY ₁ with constraints of >90% release onY ₂. The observed and predicted values ofY ₁ were in close agreement. In conclusion, the Box-Behnken experimental design allowed us to obtain SNCDF with rapid (>90%) drug release within 5 minutes with desirable properties of low turbidity and particle size.     

Continuous and biomass recycle fermentations of Clostridium acetobutylicum

Using experimental data from continuous cultures of Clostridium acetobutylicum with and without biomass recycle, relationships between product formation, growth and energetic parameters were explored, developed and tested. For glucose-limited cultures the maintenance models for, the Y _ATP and biomass yield on glucose, and were found valid, as well as the following relationships between the butanol (Y _B/G) or butyrate (Y _BE/G) yields and the ATP ratio (R _ATP, an energetic parameter), Y _B/G =0.82-1.35 R _ATP, Y _BE/G =0.54 + 1.90 R _ATP. For non-glucose-limited cultures the following correlations were developed, Y _B/G =0.57-1.07 , Y _B/G =0.82-1.35 R _ATPATP and similar equations for the ethanol yield. All these expressions are valid with and without biomass recycle, and independently of glucose feed or residual concentrations, biomass and product concentrations. The practical significance of these expressions is also discussed.List of Symbols D h^–1 dilution rate - m _e mol g^–1 h^–1 maintenance energy coefficient - m _G mol g^–1 h^–1 maintenance energy coefficient - R biomass recycle ratio, (dimensionless) - R _ATP ATP ratio (eqs.(5), (10) and (11)), (dimensionless) - X kg/m³ biomass concentration - Y _ATP g biomass per mol ATP biomass yield on ATP - Y _ATP ^max g biomass per mol ATP maximum Y _ATP - Y _A/G mol acetate produced per mol glucose consumed molar yield of acetate - y _an/g mol acetone produced per mol glucose consumed molar yield of acetone - Y _B/G mol butanol produced per mol glucose consumed molar yield of butanol - y _be/g mol butyrate produced per mol glucose consumed molar yield of butyrate - Y _E/G mol ethanol produced per mol glucose consumed molar yield of ethanol - Y _X/G g biomass per mol glucose consumed biomass yield on glucose - Y _ATP ^max g biomass per mol maximum Y _X/G glucose consumed - h^–1 specific growth rate     

新疆干旱区4种柽柳灌丛碳贮量特征

灌丛有机碳贮量对研究干旱区土壤特性及碳循环具有重要意义。以分布于新疆南北疆荒漠区的4种柽柳灌丛(多花柽柳Tamarix hohenackeri、多枝柽柳Tamarix ramosissima、刚毛柽柳Tamarix hispida、沙生柽柳Tamarix taklamakanensis)为研究对象,对其生物量碳和土壤有机碳的分布特征进行了研究。结果表明:1)生物量碳密度从大到小顺序为刚毛多花沙生多枝,生物量碳密度在0.59—2.35 Mg C/hm~2之间,其中,地上生物量碳密度在0.31—0.94 Mg C/hm~2之间,0—100 cm地下植物碳密度在0.28—1.49 Mg C/hm~2之间,根冠比在0.92—1.71之间。2)土壤有机碳密度从大到小的顺序是多花刚毛沙生多枝,多花和沙生柽柳灌丛土壤有机碳密度的最大值出现在表层0—10 cm,多枝和刚毛柽柳灌丛土壤有机碳密度的最高值出现在土层深度为10—20 cm处。4种柽柳灌丛0—10 cm土层土壤有机碳含量在13%—43.7%之间,地下1 m内,0—50 cm土壤有机碳密度所占比例为82.3%—96.4%之间。3)根据分布面积计算,新疆荒漠区4种柽柳灌丛碳贮量在(0.28±0.03)—(56.96±5.36)Tg(1Tg=10~(12)g)之间,总有机碳贮量为(75.00±6.76)Tg。其中,有机碳贮量最多的是刚毛柽柳灌丛,多花柽柳最低。4)4种柽柳灌丛土壤有机碳和生物量碳均表现出了与土壤含水量和土壤有机质的显著相关性,土壤有机碳(C_s)与土壤含水量(X_1)、有机质(X_2)、全N含量(X_3)和电导率(X_4)呈极显著正相关(P0.01),多元线性回归方程为C_s=3.433-10.943X_1+0.378X_2-2.935X_3+0.017X_4;生物量碳(C_p)与土壤含水量、有机质呈显著正相关(P0.05),多元线性回归方程为C_p=2.042-11.930X_1+0.011X_2。说明不同类型的柽柳对水分和有机质的要求不同,碳汇能力和对荒漠生态系统的作用也不同。因此,从物种利用角度来看,选择也应有所侧重。     

An approach to evaluating ecological status of populations in forest-nesting birds (Passeriformes and Piciformes)

A 13-year study of forest-nesting birds (orders Passeriformes and Piciformes) has been conducted at five constant census areas in European Russia, Caucasus, and the mountains of Southern Siberia. The nesting individuals are mapped at each census area for two or more nesting periods. The nesting densities for each species are estimated. Raster maps of spatial allocation (MSA) at the scale of the raster grid of 50 × 50 m are obtained for each species. The degree of spatial conservatism (DSC) for each local population is inferred from the pairwise comparisons of the specific MSAs obtained at the same area in different years with the use of the Gamma rank correlation method. This index characterizes the connection of population with the habitat. Based on 5-year observations at that particular census area, the areas of habitats are estimated (Y) and mean DSC values (X) are obtained for all 18 model species. Using the regression model (Y = 117–103.5X; R = 0.84; p < 0.01), it is demonstrated that, under conditions of almost complete saturation, when a population uses almost the entire area of available habitats and maximum carrying capacity of habitat is almost achieved, the total area occupied by the individual nesting home ranges of the particular species is in an inverse linear relationship with the DSC estimates. Based on this model, it is possible to calculate the maximum carrying capacity of habitat for each species from its DSC value. Maximum nesting density for each species at a particular census area is calculated based on its DSC values and mean size of its nesting home range. The ratio between observed and maximum nesting densities allows estimating the degree of saturation of carrying capacity of habitat and the population status of a particular species under different environmental conditions.     

Performance assessment of malolactic fermenting bacteria Oenococcus oeni and Lactobacillus brevis in continuous culture

The growth performance of malolactic fermenting bacteria Oenococcus oeni NCIMB 11648 and Lactobacillus brevis X₂ was assessed in continuous culture. O. oeni grew at a dilution rate range of 0.007 to 0.052 h⁻¹ in a mixture of 5:6 (g l⁻¹) of glucose/fructose at an optimal pH of 4.5, and L. brevis X₂ grew at 0.010 to 0.089 h⁻¹ in 10 g l⁻¹ glucose at an optimal pH of 5.5 in a simple and safe medium. The cell dry weight, substrate uptake and product formation were monitored, as well as growth kinetics, yield parameters and fermentation balances were also evaluated under pH control conditions. A comparison of growth characteristics of two strains was made, and this showed significantly different performance. O. oeni has lower maximum specific growth rate (μ_max=0.073 h⁻¹), lower maximum cell productivity (Q _x ^max=17.6 mg cell l⁻¹ h⁻¹), lower maximum biomass yield (Y _x/s ^max=7.93 g cell mol⁻¹ sugar) and higher maintenance coefficient (m _s=0.45 mmol⁻¹ sugar g⁻¹ cell h⁻¹) as compared with L. brevis X₂ (μ_max=0.110 h⁻¹; Q _x ^max=93.2 g⁻¹ cell mol⁻¹ glucose; Y _x/s ^max=22.3 g cell mol⁻¹ glucose; m _s=0.21 mmol⁻¹ glucose g⁻¹ cell h⁻¹). These data suggest a possible more productive strategy for their combined use in maturation of cider and wine.     

Optimization of polylactic-co-glycolic acid nanoparticles containing itraconazole using 2<Superscript>3</Superscript> factorial design

This study investigated the utility of a 2³ factorial design and optimization process for polylactic-co-glycolic acid (PLGA) nanoparticles containing itraconazole with 5 replicates at the center of the design. Nanoparticles were prepared by solvent displacement technique with PLGAX ₁ (10, 100 mg/mL), benzyl benzoateX ₂ (5, 20 μg/mL), and itraconazoleX ₃ (200, 1800 μg/mL). Particle size (Y ₁), the amount of itraconazole entrapped in the nanoparticles (Y ₂), and encapsulation efficiency (Y ₃) were used as responses. A validated statistical model having significant coefficient figures (P<.001) for the particle size (Y ₁), the amount of itraconazole entrapped in the nanoparticles (Y ₂), and encapsulation efficiency (Y ₃) as function of the PLGA (X ₁), benzyl benzoate (X ₂), and itraconazole (X ₃) were developed: Y₁=373.75+66.54X₁+52.09X₂+105.06X₃−4.73X₁X₂+46.30X₁X₃; Y₂=472.93+73.45X₁+ 169.06X₂+333.03X₃+62.40X₁X₃+141.49X₂X₃; Y₃= 57.36+6.53X₁+15.52X₂−12.59X₃+1.01X₁X₃+ 1.73X₂X₃.X ₁,X ₂, andX ₃ had a significant effect (P<.001) onY ₁,Y ₂, andY ₃. The particle size, the amount of itraconazole entrapped in the nanoparticles, and the encapsulation efficiency of the 4 formulas were in agreement with the predictions obtained from the models (P<.05). An overlay plot for the 3 responses shows the boundary in whichY ₁ shows the boundary in which a number of combinations of concentration of PLGA, benzyl benzoate, and itraconazole will result in a satisfactory process. Using the desirability approach with the same constraints, the solution composition having the highest overall desirability (D=0.769) was 10 mg/mL of PLGA, 16.94 μg/mL of benzyl benzoate, and 1001.01 μg/mL of itraconazole. This approach allowed the selection of the optimum formulation ingredients for PLGA nanoparticles containing itraconazole of 500 μg/mL.     

A New Method to Estimate the Population Size of Coconut Mite, Aceria Guerreronis, on a Coconut

Studies of the coconut mite, Aceria guerreronis, often require accurate assessment of the population density on individual infested coconuts. Here an efficient and accurate method was developed to estimate its population density on an infested coconut. The coconut mites were removed by washing the bracts and surface of an infested coconut with 30 ml of a detergent solution. Shaking the wash for 5 s allowed the mites to distribute uniformly. The number of mites in the first 1 ml of the first wash (X) yielded a very accurate predictor of the total number of mites on a coconut (Y): Y = 30.1X (R² = 0.99; p <0.0001), also confirming that the wash was indeed homogeneous. The advantages and disadvantages of this method are discussed.     

六盘山南坡华北落叶松人工林冠层LAI的坡面尺度效应

叶面积指数(LAI)是评价森林的生长、结构及众多服务功能的重要参数,受坡面上环境条件变化影响而有坡面变化与尺度效应,对此需要深入理解和精细刻画。在六盘山半湿润区香水河小流域选择了33年生华北落叶松人工林的一个斜坡长480.6m、水平长398.2m的东南坡向的典型坡面,在整个坡面上建立了宽30 m的调查样带,均匀分为空间连续的16个样地,在2014年生长季中期测定了林冠层LAI,并分析其坡面变化规律。结果表明:林冠层LAI存在明显的坡面差异,其坡面平均值为3.11,变化在2.66—3.49,变幅为0.83,变异系数为0.09;LAI总体上随着从坡顶向下的坡长增加呈波动性增大趋势,在坡面中部(水平坡长188.45 m时)达到最大,之后稍微减小。森林冠层LAI存在着坡面空间尺度效应,即冠层LAI的顺坡滑动平均值(Y_1)随水平坡长(X,m)增加而逐渐增大,平均每100 m升高0.12,其回归关系式为:Y_1=-2×10~(-8)X~3+8×10~(-6)X~2+5×10~(-4)X+2.6523,(R~2=0.99);各样地LAI与整个坡面平均值的比值(Y_2,小数)随水平坡长(X_1,m)增加呈现为波动性的非线性变化,其回归关系式为:Y_2=-9×10~(-9)X_1~3+2×10~(-6)X_1~2+1×10~(-3)X1+0.829,(R~2=0.78),可基于此式将特定坡位样地的实测LAI推算整个坡面的估计值。造成研究坡面上LAI坡位变化的主要原因是不同坡位(海拔)样地的气温与土壤含水量的差异。     

Effect of inoculum density, stage of plant growth and dew period on the incidence of black point caused by Alternaria alternata in durum wheat

Glasshouse studies showed that the incidence of black point caused by Alternaria alternata in durum wheat was positively correlated with both the density of the inoculum and the growth stage of the wheat plants at the time of inoculation. A curvilinear relationship of the form Y=a + log X was found between inoculum density and disease incidence. The incidence of black point was linearly related to the stage of plant growth, between anthesis and the late milk stages of development, at the time of inoculation. A better relationship between growth stage and disease incidence was found when plant growth was expressed as days after anthesis than when the Romig scale was used (R²= 0.30 and 0.24 respectively). A threshold dew period of 3–6 h was required for black point symptoms to develop. The incidence of black point increased with increasing duration of the dew period until maximum disease incidence occurred after exposure to a dew period of 48 h.     

Chromosome banding in amphibia

A cytogenetic study performed on a population of the South American leptodactylid frog Eleutherodactylus maussi revealed multiple sex chromosomes of the X₁X₁X₂X₂/X₁X₂Y (=XXAA/XXA^Y) type. The diploid chromosome number is 2n=36 in all females and 2n=35 in most males. The multiple sex chromosomes originated by a centric fusion between the original Y chromosome and a large autosome. In male meiosis the X₁X₂Y (=XXA^Y) multiple sex chromosomes form a classical trivalent configuration. E. maussi is the first species discovered in the class Amphibia that is distinguished by a system of multiple sex chromosomes. Only one single male was found in the population with 2n=36 chromosomes and lacking the Y-autosomal fusion. This karyotype (XYAA) is interpreted as the ancestral condition, preceding the occurrence of the Y-autosome fusion.by H.C. Macgregor     

Seasonal dynamics of aufwuchs Naididae (Oligochaeta) on Phragmites australis in a eutrophic lake

The Oligochaeta and Aphanoneura in the aufwuchs on Phragmites australis in a eutrophic hardwater lake were studied at two sites over a period of one year, in order to elucidate the structure and dynamics of this assemblage. The naidids Chaetogaster diastrophus, Nais spp., and Stylaria lacustris dominated the assemblage at any season. At both sites these taxa showed the same distinct pattern of successive population maxima in spring and summer: Chaetogaster diastrophus reached its peak density first, followed by Nais species, and eventually by Stylaria lacustris. Differences in temporal dynamics between sites were small apart from a second Stylaria maximum which was only observed at one site. Total naidid densities reached peak values of 3.8 individuals per cm² reed stem surface area. With mean individual biomass of 2.2 µg dry mass for Chaetogaster diastrophus, 13.3 µg for Nais, and 86 µg for Stylaria lacustris, respectively, maximum total naidid biomass on reed stems was 44 µg dry mass per cm². The biomass peak occurred later than that of total naidid density because in summer larger naidids dominated the assemblage. The observed succession appears to be consistent with seasonal changes in periphytic algal communities on the reed stems.     

The effects of population density and lake characteristics on growth and size structure of brook trout Salvelinus fontinalis (Mitchill, 1815) in boreal forest lakes in Canada

This paper examines the effect of lake characteristics on population density and how this variation affects growth, mortality and population size structure of brook trout, Salvelinus fontinalis. The study was conducted on 17 recreationally fished, reproductively isolated boreal forest lakes in Newfoundland, Canada from 1993 to 2000. A standardized sampling program, the Fyke Littoral Index Netting program (FLIN) was used to collected data that describes brook trout population parameters and life history attributes. Regression analyses showed significant relationships between fish density and biomass and characteristics of the lakes. Variation in fish density and biomass was explained by lake surface area and littoral habitat area. Significant relationships were found when growth, mortality and size structure were regressed against density. The proportional stock distribution and theoretical maximum size of brook trout were negatively related to density, and natural mortality was positively related to density. The largest maximum length and highest proportional stock densities occurred at brook trout densities of less than 30 fish/ha. In general, the higher the proportion of littoral habitat area the higher the densities of brook trout, which correspondingly had important effects on growth, natural mortality and size structure of the brook trout populations. This information is critical to the development of management strategies aimed at altering size distribution to produce specific fisheries management outcomes.     

CULTIVATION OF ARTHROSPIRA (SPIRULINA) PLATENSIS (CYANOPHYCEAE) BY FED‐BATCH ADDITION OF AMMONIUM CHLORIDE AT EXPONENTIALLY INCREASING FEEDING RATES1

Arthrospira (Spirulina) platensis (Nordstedt) Gomont was cultivated under light‐limited conditions in 5‐L open tanks by daily supplying NH₄Cl as nitrogen source. Exponentially increasing feeding rates were adopted to prevent ammonia toxicity. The total feeding time (T) was varied between 12 and 20 days, and the starting (m₀) and total (m_T) quantities of the nitrogen source per unit reactor volume were varied in the ranges 0.19–1.7 mM and 2.3–23.1 mM, respectively. This intermittent addition of the nitrogen source prevented ammonia from reaching inhibitory levels and ensured final cell concentrations (X_m) and cell productivities (P_x) comparable with those of batch runs with KNO₃. Moreover, the lower nitrogen addition due to the use of NH₄Cl rather than KNO₃ allowed for higher nitrogen‐to‐cell conversions (Y_x/n). These results were evaluated using three‐factor, five‐level, central composite experimental planning, combined with the response surface methodology, selecting T, m₀, and m_T as the independent variables and X_m, P_x, and Y_x/n as the response variables. This approach allowed us to identify, through the simultaneous optimization of the variables, T=16 days, m₀=1.7 mM, and m_T=21.5 mM as the best conditions for A. platensis cultivation at 72 μmol photons·m^?2·s^?1. Under these conditions, a maximum cell concentration of 1239 mg ·L^?1 was obtained, which is a value comparable with that obtained using KNO₃ as nitrogen source and nearly coincident with the theoretical one estimated by the response surface methodology.