温度对施氏鲟幼鱼摄食、生长和肠道消化酶活性的影响

研究不同养殖温度(15℃、18℃、21℃、24℃、27℃)对施氏鲟(Acipenser schrenckii)幼鱼摄食、生长和肠道消化酶活性的影响。结果表明,在15～24℃范围内,幼鱼的特定生长率(SGR)和相对增重率(RWG)随温度的升高而显著增加(P<0.05),均在24℃时达到最高值;随着温度升高,其饵料系数(FC)先降低后升高(P<0.05),且在24℃时达到最小值;此外,摄食率(FR)随着温度的升高而显著升高(P<0.05),其不同温度组的生长速度由高到低依次为24℃、21℃、27℃、18℃、15℃组。温度对幼鱼前肠蛋白酶活性影响显著,24℃组和27℃组前肠的蛋白酶活性显著低于15℃组(P<0.05),而温度对中肠和后肠蛋白酶活性则无显著性影响(P>0.05);温度对幼鱼肠道脂肪酶活性无显著性影响(P>0.05),各温度组前肠脂肪酶活性均高于中肠和后肠;温度对幼鱼肠道淀粉酶活性无显著性影响(P>0.05)。综合以上结果认为,施氏鲟幼鱼快速生长的适宜温度范围为21～24℃,在此温度范围内施氏鲟幼鱼可获得最大生长率和存活率。     

Ontogenetic development of digestive enzymes and effect of starvation in miiuy croaker <Emphasis Type="Italic">Miichthys miiuy</Emphasis> larvae

The ontogenetic development of the digestive enzymes amylase, lipase, trypsin, and alkaline phosphatase and the effect of starvation in miiuy croaker Miichthys miiuy larvae were studied. The activities of these enzymes were detected prior to exogenous feeding, but their developmental patterns differed remarkably. Trypsin activity continuously increased from 2 days after hatching (dah), peaked on 20 dah, and decreased to 25 dah at weaning. Alkaline phosphatase activity oscillated at low levels within a small range after the first feeding on 3 dah. In contrast, amylase and lipase activities followed the general developmental pattern that has been characterized in fish larvae, with a succession of increases or decreases. Amylase, lipase, and trypsin activities generally started to increase or decrease at transitions from endogenous to exogenous feeding or diet changes, suggesting that these enzymatic activities can be modulated by feeding modes. The activities of all the enzymes remained stable from 25 dah onwards, coinciding with the formation of gastric glands and pyloric caecum. These results imply that specific activities of these enzymes underwent changes due to morphological and physiological modifications or diet shift during larval development but that they became stable after the development of the digestive organs and associated glands was fully completed and the organs/glands functioned. Trypsin and alkaline phosphatase were more sensitive to starvation than amylase and lipase because delayed feeding up to 2 days after mouth opening was able to adversely affect their activities. Enzyme activities did not significantly differ among feeding groups during endogenous feeding; however, all activities were remarkably reduced when delayed feeding was within 3 days after mouth opening. Initiation of larvae feeding should occur within 2 days after mouth opening so that good growth and survival can be obtained in the culture.     

密度和饲料种类对凡纳滨对虾Litopenaeus vannamei争胜行为和生长的影响

在水温(23.0±1.0)℃和盐度(26±1.0)‰下,将体长(46.1±3.2)mm的凡纳滨对虾Litopenaeus vannamei饲养在0.54m×0.36m×0.28m的塑料水槽中,密度为40尾/m~2(LLD)、80尾/m~2(MLD)、120尾/m~2(MHD),和160尾/m~2(HHD),投喂人工配合饲料;同时在密度50尾/m2下分别投喂人工配合饲料(ACF)、菲律宾蛤仔肉(RPF)和冰鲜杂鱼(FFF),测定投喂前1h、投喂时、投喂后1h对虾间的争斗数量、争斗时间、争斗发起方、胜利次数等指标,以探讨密度和饲料种类对凡纳滨对虾争胜行为和生长性能的影响。61d的饲养结果表明:凡纳滨对虾个体间的争斗次数和胜利次数随密度的升高而增加;不同密度间平均优势指数差异不显著(P0.05);饱食情况下凡纳滨对虾对三种饲料的选择无倾向性。     

农户农地流转行为及影响因素实证研究——以山西农村固定跟踪观察户为例

本文运用山西农村固定跟踪观察户的资料,对农户农地流转行为及影响因素进行研究。研究结果表明：营地户减地行为总体强于增地行为,与此对应,营地户呈现强化包出行为而弱化包入行为的趋势,但现阶段包出力度仍低于包入力度;家庭拥有耕地的规模与零碎度、家庭收入水平、家庭劳动者接受培训的比率、家庭经营非农化程度、家庭人口数量等是影响农户农地流转的主导因素;农户在农地流转中表现出了较高的经济理性,尤其表现在高收入户、高文化户、受培训户和有声望户。     

毛蚶在不同底质与撒播方式下潜沙行为的观测与分析

为了探究不同底质与撒播方式对毛蚶(Scapharca subcrenata)潜沙行为的影响,在实验室条件下,观察了壳长(10.0±0.9)mm毛蚶的潜沙过程,并研究了沙质(粒径251~500μm)和泥沙质(粒径120μm)两种底质和播散方式(集中和分散)对毛蚶潜沙时间和潜沙率的影响。结果显示,毛蚶潜沙过程分为准备、潜沙及结束3个阶段。在两种底质条件下,集中播撒方式的毛蚶潜沙时间均短于分散播撒方式,但同种底质不同播撒方式下的毛蚶潜沙时间差异不显著(P0.05)。无论是集中播撒还是分散播撒,沙质条件下毛蚶的潜沙时间均短于泥沙质的潜沙时间,并且在分散播撒方式下,两种底质的差异达到显著水平(P0.05);两种底质条件下,毛蚶的潜沙率均表现为集中播撒高于分散播撒。研究表明,与泥沙质底质相比,毛蚶在沙质条件下更易于快速潜底;与分散播散方式相比,集中播撒更利于毛蚶快速潜底。     

Nutrient digestibility studies in Heteropneustes fossilis (Bloch), Clarias batrachus (Linnaeus) and C. gariepinus (Burchell)

The apparent digestibility coefficient (ADC %) for protein in catfishes, Clarias batrachus (Linnaeus) (16–18 cm; 45–50 g), C. gariepinus (Burchell) (21–22 cm; 60–65 g) and Heteropneustes fossilis (Bloch) (10–12 cm; 10–15 g) was estimated for nine feedstuffs of plant and animal origin. Fat digestibility was tested for C. batrachus and C. gariepinus, wherein the influence of feeding frequency on protein digestibility was also examined. The digestibility trials were conducted with triplicate groups of 25 fish each in 70‐L polyvinyl indoor flow‐through (1–1.5 L min^?1) circular tanks (water volume=55 L). Fish were fed to satiation daily, at 08:00 and 18:00 hours, and faecal matter was collected through slow siphoning. For studying the effect of feeding frequency, fish were fed the experimental diets at 08:00, 11:00, 14:00 and 17:00 hours. The protein digestibility of the feedstuffs varied significantly within each test species. However, the protein digestibility values for most of the ingredients tested were comparable between the three catfish species. The most efficient utilization of protein in these fishes was noted for soybean meal followed by lab‐prepared fishmeal. The lowest protein digestibility was recorded for rice bran. Similarly, the utilization of fat from the feedstuffs was also significantly different within each of the two species, C. batrachus and C. gariepinus. Fat digestibility of feed ingredients was similar between the two species. With respect to the fat, soybean meal, lab‐prepared fishmeal, full‐fat soybean meal and dried fish were more efficiently utilized, while the lowest fat digestibility was obtained for rice bran. A marked decline in protein utilization was observed in the two species where the feeding frequency was increased from two to four times a day.     

Changes in fox squirrel anti-predator behaviors across the urban–rural gradient

Predator stimuli created by humans in the urban environment may alter animals’ anti-predator behaviors. I hypothesized that habituation would cause anti-predator behaviors to decrease in urban settings in response to humans. Additionally, I hypothesized that populations habituated to humans would show reduced responses to other predator stimuli. I observed three populations of squirrels (urban, suburban and rural) responses to human approaches, red-tailed hawk vocalizations (Buteo jamaicensis) and coyote (Canis latrans) vocalizations. Mahalanobis distances of anti-predator behaviors in response to human approaches were consistent with the urban–rural gradient. Flight initiation distances (X ² = 26.33, df = 2, P < 0.001) and amount of time dedicated to anti-predator behavior (X ² = 10.94, df = 2, P = 0.004) in response to human approaches were also consistent with the urban–rural gradient. Supporting the habituation hypothesis, naive juvenile squirrels increased flight initiation distances (X ² = 35.89, df = 1, P < 0.001) and time dedicated to anti-predator behaviors (X ² = 9.46, df = 1, P = 0.002) relative to adult squirrels in the same urban environment. Time dedicated to anti-predator behaviors differed among all three sites in response to both coyote (X ² = 9.83, df = 2, P = 0.007) and hawk (X ² = 6.50, df = 2, P = 0.035) vocalizations. Responses to both vocalizations on rural sites (coyote = 45%, hawk = 55%) greater than twice that found on the urban sites (coyote = 11%, hawk = 20%). This is possibly the first case of a transfer of habituation demonstrated under field conditions.     

水稻土中Cd、Cr、Hg、Pb污染元素的研究进展

本文主要阐述了水稻土中Cd、Cr、Hg、Pb污染元素的形态、土壤化学行为、生物效应及被污染土壤修复的研究进展。     

农业转移人口市民化过程中的企业行为研究——基于博弈论的视角

以企业行为为研究对象,梳理了农业转移人口市民化过程中企业成本的概念、内涵、类型,并构建博弈论模型,分析了农业转移人口市民化过程中的企业承担意愿及行为选择,针对性地提出了促进企业主动参与农业转移人口市民化进程的建议。     

水产颗粒饲料投饵装置的原理与应用

本文分析了离心抛撒式投饵机、气力输送式投饵机和水力输送式投饵机等三种型式投饵机的技术原理与应用,指出水力输送式投饵机适合水产湿颗粒饲料自动投饵,但应解决好湿颗粒饲料机生产能力与水力输送式投饵机投饵能力的衔接配套、降低湿颗粒饲料在输送过程中的饵料溃散技术,以及根据养殖品种不同,分别进行抛投技术处理等问题。