施肥和密度对春小麦群体质量及产量的影响

以强筋春小麦品种龙麦26为试验材料,研究了施肥和密度处理对群体质量指标、产量的影响。结果表明,产量在施肥(氮磷钾纯量)180 kg/hm2,密度600万株/hm2条件下达最大值,为5 716.5 kg/hm2,其关键群体调控指标为孕穗期叶面积指数6.0,地上部干物质积累量和花后干物质积累量分别为16 899 kg/hm2和9 211.5 kg/hm2;在此施肥和密度条件下,叶面积指数在整个生育期维持在较高水平,并且后期下降较慢。     

Cage culture of the Pacific white shrimp Litopenaeus vannamei (Boone, 1931) at different stocking densities in a shallow eutrophic lake

Postlarvae of Litopenaeus vannamei were acclimated and stocked in lake-based cages at the following stocking densities: 10, 20, 30 and 40 shrimp m⁻². Another set of shrimp was stocked in concrete tanks as reference samples at 30 shrimp m⁻². Significant differences were observed among stocking densities throughout the 95-day culture. The final weight at harvest decreased with increasing stocking density: mean weights of 23.3, 15.8, 13.0, 10.9 and 14.6 g for the 10, 20, 30, 40 shrimp m⁻² and reference tanks were observed respectively. There were no significant differences in survival throughout the culture period, ranging between 69% and 77%. Daily growth rates (range: 0.11–0.24 g day⁻¹) and specific growth rates (range: 3.54–4.34%) also differed significantly among stocking densities, both increasing with decreasing stocking density. The feed conversion ratio in the cages did not differ among the stocking densities, ranging from 1.53 to 1.65. The relationship between stocking density and mean individual weight at harvest followed the equation y =81.06 x ^−0.54 ( R ²=0.938) and that of stocking density and production (in g m⁻²) is y =58.01 x ^−0.46 ( R ²=0.834).     

Effects of stocking density on the survival, growth, size variation and condition index of juvenile rabbitfish Siganus rivulatus

Spinefoot rabbitfish, Siganus rivulatus, is an economically important species of herbivorous fish that is relatively easy to rear and thus considered to be suitable for aquaculture. Juveniles are generally reared in nursery systems before being stocked into growout cages or ponds. We report here our evaluation of the effects of stocking density on the survival, growth, feed efficiency and condition index of S. rivulatus juveniles in nursery tanks. The experiment was conducted in a recirculating system of twelve 52-l aquaria connected to a biological filter and a sand filter. Juvenile fish (average weight 6.5 g) were stocked into aquaria at four stocking densities (10, 20, 30, and 40 fish/aquarium) with three replicate aquaria per treatment. Diet was provided at 3% body weight daily divided into two feedings. Fish were weighed weekly for 8 weeks and the diet increased accordingly. Survival was greater than 95% in all treatments, with no significant differences observed among treatments. There were also no differences in specific growth rate (SGR 2.12–2.27) of the fish among treatments. Growth rate was linear during the 8 weeks in all treatments, and harvested biomass increased proportionally to stocking density (198, 401, 600 and 785 g per increasing stocking density, respectively). Feed efficiency (FE 0.67–0.71) of the fish did not vary significantly among treatments. The coefficient of variation was high (35–41%) among the harvested fish, but it also did not differ significantly among treatments. The final condition indices of the fish in all treatments were similar to each other but significantly greater than the initial values (P < 0.05). The results suggest that there is no apparent effect of stocking density at the levels tested on the survival and growth of juvenile rabbitfish.     

大亚湾杨梅坑人工鱼礁区渔业资源变动初步研究

杨梅坑人工鱼礁区位于大亚湾西北部,2007年12月25日完成投礁9．51×10^4m^3,礁区面积2．75km^2。分别于2007年、2008年和2009年春季,采用拖网和刺网相结合的方法,进行了1次建礁前的本底调查和2次建礁后的跟踪调查。结果表明,礁区2次拖网跟踪调查的游泳生物平均渔获种数分别为建礁前调查的2．13倍和2．50倍,平均资源密度分别为建礁前调查的3．38倍和8．19倍,平均尾数资源密度分别为建礁前调查的11．57倍和23．39倍。礁区2次刺网跟踪调查礁区游泳生物平均渔获种数分别为建礁前的2．29倍和3．14倍,平均渔获率分别为建礁前的5．51倍和9．49倍,平均尾数渔获率分别为建礁前的11．33倍和10．06倍。渔业资源生物多样性指数呈上升趋势。     

The density dilemma: limitations on juvenile production in threatened salmon populations

Density‐dependent processes have repeatedly been shown to have a central role in salmonid population dynamics, but are often assumed to be negligible for populations at low abundances relative to historical records. Density dependence has been observed in overall spring/summer Snake River Chinook salmon Oncorhynchus tshawytscha production, but it is not clear how patterns observed at the aggregate level relate to individual populations within the basin. We used a Bayesian hierarchical modelling approach to explore the degree of density dependence in juvenile production for nine Idaho populations. Our results indicate that density dependence is ubiquitous, although its strength varies between populations. We also investigated the processes driving the population‐level pattern and found density‐dependent growth and mortality present for both common life‐history strategies, but no evidence of density‐dependent movement. Overwinter mortality, spatial clustering of redds and limited resource availability were identified as potentially important limiting factors contributing to density dependence. The ubiquity of density dependence for these threatened populations is alarming as stability at present low abundance levels suggests recovery may be difficult without major changes. We conclude that density dependence at the population level is common and must be considered in demographic analysis and management.     

Effects of stocking density on haematological parameters,growth and fin erosion of great sturgeon (Huso huso) juveniles

The influence of stocking density (1, 2, 4, 6 and 8 kg m^?2) was investigated on haematological parameters, growth and fin erosion of great sturgeon (Huso huso) juveniles for a period of 8 weeks. The mean weight of fish at the start of trial was 93.13±1.04 g. After 8 weeks of rearing, the mean weight was 362.4, 319.7, 267, 242.1 and 211.1 in densities 1–8 kg m^?2 respectively. The results of this study showed that growth parameters, including condition factor, weight, weight gain, feed conversion ratio, specific growth rate and body weight increase, had a statistically significant difference among treatments (P<0.05). A significant difference (P<0.05) was observed in haematocrit, but the other haematological parameters, including red blood cells, white blood cells (WBC), haemoglobin concentration, mean corpuscular haemoglobin, mean corpuscular volume, mean corpuscular haemoglobin concentration and differential WBC count, showed no significant effect with stocking density (P>0.05). At the end of the experiment, stocking density had no significant effect on plasma cortisol and glucose concentration. The fin length (dorsal, anal, ventral, pectoral and caudal) of fish was measured to calculate the fin index. According to this index, dorsal, anal, ventral and pectoral fins showed no significant difference among treatments (P>0.05), but the erosion of the caudal fin was significantly different between fish held on 6 and 8 kg m^?2 (P<0.05). These results showed that rearing density has a major effect on the growth indices of H. huso. Unlike many other fish, great sturgeon exhibited lower stress responses to high stocking density. This indicates that they are more tolerable to rearing conditions in high stocking densities. With respect to the various effects that density causes on growth, fin erosion and physiological and haematological parameters, better understanding of these phenomena considering different levels of density could have a beneficial impact on many rearing steps of this species.     

Development of nursery culture techniques for the mud crab Scylla paramamosain (Estampador)

Cannibalism is one of the main causes of mortality in the culture of the mud crab Scylla paramamosain, particularly in the early post‐larval and juvenile stages when the densities of hatchery‐reared crabs may be very high before stocking into ponds or release into the wild for stock enhancement. In a series of experiments investigating cannibalism mitigation, the influence of stocking density, the effectiveness of sand substrate, brick and shell shelters and feed type were compared in culture of crabs from instar 1 for short nursery periods of 15–30 days. Inclusion of brick and shell shelters significantly increased survival over sand substrate alone. However, inclusion of shelters did not affect growth rates. In scaled‐up nursery production in lined‐ponds, with shelters, live Artemia biomass and fresh chopped shrimp or tilapia were found to be equally effective feeds for juvenile crabs stocked at a density of 70 m⁻² from instar 1 and grown for 30 days [52–66% survival, 21.6–24.6 mm carapace width (CW)]. In an extended nursery period for a further 30 days, crabs of 22 mm CW, stocked at 30 m⁻² in the same ponds, attained a final size of 34.5–36.2 mm CW with a survival of 64.3–67.0% using the same feeds.     

气升式光生物反应器培养微藻溶氧和pH值变化规律研究

为了解决在光生物反应器养殖微藻过程中,溶解氧和pH值2个培养工艺参数的控制问题,分别在80 L、350 L和900 L的3种规格气升式光生物反应器中培养湛江等鞭金藻(lsochrysis zhanjiangensis),高藻细胞浓度分别达到900×104,700×104,500×104cell/mL,测定其中溶氧和pH值的日变化。结果显示,在光照度4 000 lx以上时,湛江等鞭金藻光合作用强,表现为反应器中藻液溶氧较高,日最高溶氧分别可达17.91 mg/L、15.84 mg/L和12.7 mg/L。所测定的藻液日pH值均在7.00~9.16变化。     

Long-term changes in the smolt size and age of Atlantic salmon, Salmo salar L., in a northern Baltic river related to parr density, growth opportunity and postsmolt survival

Abstract –  The size of wild Atlantic salmon ( Salmo salar L.) smolts in 1972–2004 was studied in relation to parr density, smolt age, growth opportunity and postsmolt survival in the Simojoki River. There was a significant negative regression between the annual mean smolt size and the density of wild >1 year parr in the previous autumn, but not between the annual mean smolt size and age. The density of reared parr released into the river or the growth opportunity, based on the day length and air temperature during the previous summer, did not affect the size of wild smolts. The data on postsmolt survival based on recaptures of Carlin-tagged smolts showed a significant positive relationship ( P  < 0.01) between the survival of postsmolts and the annual size of wild smolts. It is hypothesised that the increased density of wild >1 year parr could have contributed to the decreased smolt size since the 1990s, and the reduced size of wild smolts could be included among the factors resulting in their declined postsmolt survival in the Baltic Sea.     

黔北地区主要竹种竹材气干密度与力学性质的关系研究

对黔北地区几种主要竹种的气干密度与力学性质的关系研究表明:各竹种的气千密度与力学性质除部分竹种外均存在一定的曲线或直线关系,其中在气干密度与抗剪强度关系中,除慈竹、花吊丝、毛脚龙竹、金佛山方竹等竹种外,其他竹种均可利用回归方程T12=ap12b,T12=ap12+b进行估测.在气干密度与顺纹抗拉强度关系中除硬头黄、花吊...