Optimal dietary carbohydrate to lipid ratio in African catfish Clarias gariepinus (Burchell 1822)

An 8-week feeding trial was conducted in a recycling water system at 28±1°C to investigate carbohydrate to lipid ratio (CHO:L ratio) in African catfish Clarias gariepinus (12.32±0.04g). Five isonitrogenous (40% crude protein) and isoenergetic (20kJg^–1 gross energy (GE)) fishmeal based diets with varying carbohydrate to lipid (CHO:L g/g) ratios of 0.74, 1.13, 1.66, 2.47 and 3.42 for diets 1–5, were tested, respectively. The diets containing a fixed protein to energy ratio (P:E ratio) of 20-mg proteinkJ^–1 GE were fed to triplicate groups of 20 fish (per 30-L tank). Fish were fed 5% of their body weight per day adjusted fortnightly. Diet 1, containing 14% carbohydrate and 21% lipids with a CHO:L ratio of 0.74 produced the poorest (P<0.05) growth rates, feed and protein efficiency. Increasing carbohydrate content in the diets to 27% concomitant with a reduction in lipid content to 16% with a CHO:L ration of 1.66 of diet 3 significantly improved (P<0.05) growth rates, feed and protein efficiency. A further increase in dietary carbohydrate up to 38% and a decrease in lipids levels to 11% with a CHO:L ratio ranging from 1.66 to 3.42 (diet 3 – 5) did not significantly improve the fish performance. Apparent net protein utilisation (ANPU) of fish fed diet 4 was higher (P<0.05) than for diets 1–3 but did not differ from diet 5. Higher lipid deposition (P<0.05) in whole body and liver were observed with decreasing dietary CHO:L ratios as increasing lipid levels. Whole body protein and liver glycogen content, digestive enzyme activities (protease and lipase) and histological examination of intestine and liver of fish fed varying CHO:L diets did not show any discernible changes among the dietary treatments. However intestinal -amylase activity increased (P<0.05) with increasing dietary carbohydrate levels. This study revealed that African catfish can perform equally well on diets containing carbohydrate ranging from 27 to 38% of the diet, with lipid content ranging from 16 to 11% or at CHO:Lg/g ratio of 1.7–3.4.     

Aspects of mineral composition and growth rate of the hybrid African catfish fry fed inorganic phosphorus-supplemented diets

Hybrid African catfish fry were acclimated for 14 days. A 70‐day feeding experiment involving sixteen 38% crude protein diet treatments of four inorganic phosphorus (P) sources (monosodium phosphate, monopotassium phosphate, monocalcium phosphate (MCP), dicalcium phosphate (DCP)), four levels of P (0.04%, 0.06%, 0.08%, 1.2%) and three replicates of each diet followed. A non‐P‐supplemented diet and a purified diet (controls) were additionally fed. Gross efficiency of food conversion (GEFC), daily rate of growth (DRG), tissue ash, tissue phosphorus (TP), tissue calcium (Ca) and Ca:P ratio of the fish were measured weekly. These parameters varied significantly (P<0.01) among the (a) 18 test diets, (b) inorganic P sources and (c) duration. Monocalcium phosphate‐supplemented diets resulted in better response to GEFC, DRG, TP and Ca than other P‐supplemented diet while the Ca:P ratio was best exhibited by fish fed the DCP diet. The fish fed the control diets had better GEFC, DRG, TP and Ca than the P‐supplemented diets probably because of nearer to optimum available P in these diets. In conclusion, supplementation with 0.6% MCP produced comparatively better growth, feed conversion and mineral deposition in the fry than other inorganic P sources.     

云和梯田的形成及传统农耕习俗探究

位于浙江省南部山区的云和县崇头镇,有着"中国最美梯田"之称的云和梯田,以其层层叠叠、高低错落、云山雾海、千姿百媚的自然与人文景观享誉天下。然而,究竟是谁开辟了这片神奇的梯田,并孕育了独具特色的农耕文化,学术界未有定论。从畲汉农耕历史、生态环境、农业生产方式以及农耕习俗等方面探求云和梯田和传统农耕文化的形成与发展轨迹,可为挖掘云和梯田独特的农业文化遗产价值提供参考。     

No Effect of Social Competition on Sham Dustbathing in Furnished Cages for Laying Hens

The wire-mesh netting used as the floor material in cages is often claimed to cause walking problems for foxes. The validity of this claim was tested in 96 15-year-old secondary school pupils. They were shown five separate 2 min fragments of videotapes showing the cage pairs with randomized floor material (solid or wire mesh) but with an obstructed view of the floor. The pupils were asked to evaluate the flooring material based on what they actually saw. The mean proportion of correct answers out of 5 for individuals were slightly more than half correct (0.54), but this did not differ significantly from the random value (0.5). When the pairs of foxes had different flooring material, the pupils answered correctly (0.58, P <0.05). Thus, the pupils were not able to identify a specific floor type (wire-mesh or solid floor) but were able to differentiate between two different types of floor based solely on the behaviour of the foxes.     

Preparation of inorganic silica nanofibers containing silver nanoparticles

Silica nanofibers containing silver nanoparticles were successfully prepared using sol-gel chemistry and electro-spinning technique. Solution of tetraethly orthosilicate in ethanol containing silver nitrate was aged to have sufficient viscosity and electrospun to form nanofibers. Upon thermal treatment, the gelation reaction between silanols was completed in the prepared silica nanofibers, and at the same time, silver ions in the nanofiber changed to metallic silver or silver oxides. The reduction of silver ions could be also achieved by UV irradiation, and the generated silver nanoparticles were present preferentially on the surface of the silica nanofibers. On testing release behavior of silver ions, it was found that most of silver remained in the silica nanofiber. The silica nanofibers containing silver nanoparticles exhibited excellent antibacterial and deodorant properties.     

斑点叉尾嗜麦芽寡养单胞菌的分离鉴定及系统发育分析

从发生在四川、重庆等省市的斑点叉尾急性流行性传染病病鱼的肝脏、肾脏内分离到1株高致病性菌株(CCF00024),人工感染健康鱼表现出与自然病鱼相同的症状,并从中分离获得同种细菌,证实其为斑点叉尾急性流行性传染病的病原菌。形态、生理生化检测表明,该菌为非发酵型直杆菌,严格需氧,革兰氏阴性,极生多鞭毛,对除麦芽糖和甘露糖以外的多种糖类不利用产酸,氧化酶阴性,DNA酶、蛋白酶、脲酶、赖氨酸脱羧酶阳性,MR、VP阴性。在以该菌16S rDNA序列(GenBank登录号AY970826)和GenBank及RDP数据库内同源性较高的细菌16S rDNA序列构建的系统发育树中,分离菌CCF00024与嗜麦芽寡养单胞菌(Stenotrophomonas maltophilia)聚在一簇,特别是与S.maltophilia M5-1的同源性最高,序列相似性达99.6%,结合形态和生理生化特点将其鉴定为嗜麦芽寡养单胞菌(Stenotrop homonas maltophilia)。药敏试验结果表明,对磺胺甲口恶唑、磺胺异口恶唑、阿齐霉素、洛美沙星高度敏感,而对新霉素、卡那霉素、氨苄青霉素、头孢唑啉、先锋霉素和链霉素不敏感。     

Influence of native catfish mucus on Flavobacterium columnare growth and proteolytic activity

Flavobacterium columnare causes columnaris disease of farmed and wild freshwater fish. Skin mucus is an important factor in early stages of columnaris pathogenesis, albeit little studied. Our objectives were to (a) characterize the terminal glycosylation pattern (TGP) of catfish mucus, (b) determine the growth of F. columnare in formulated water (FW)‐containing channel catfish (Ictalurus punctatus) or hybrid catfish (Ictalurus punctatus X Ictalurus furcatus) mucus and (c) examine extracellular protease activity of two F. columnare isolates differing in virulence. The TGP of catfish mucus by lectin binding was as follows: alpha‐D‐mannose/alpha‐D‐glucose >N‐acetyl‐beta‐D‐glucosamine >N‐acetyl‐beta‐D‐glucosamine/N‐acetylneuraminic acid >N‐acetyl‐D‐galactosamine >alpha‐D‐galactose/N‐acetyl‐alpha‐D‐galactosamine >beta‐D‐galactose = alpha‐L‐fucose. Virulence studies demonstrated isolate AL‐02‐36 was highly virulent in channel catfish fry (0.1 g) with cumulative mortality of 90%‐100% versus 60% for isolate ALG‐00‐530 at equivalent doses (~3 × 10⁶ CFU/ml); a similar result was observed in larger (0.7 g) catfish. In multiple experiments, F. columnare replicated (2‐3 logs) and survived (28 days) in formulated water‐containing catfish mucus. Highly virulent isolate AL‐02‐36 possessed at least 2.5‐ to fivefold higher protease activity following growth in mucus than the less virulent ALG‐00‐530. Flavobacterium columnare utilized catfish mucus as a nutrient source and mucus presence modulated extracellular protease production.     

3种黄颡鱼SOCSs基因分子特性及致病菌胁迫下的表达模式

细胞因子信号传导抑制因子(SOCS)是JAK/STAT信号通路中细胞因子信号受体的重要抑制因子。为探究SOCS在鱼类免疫应答过程中的作用，本研究以杂交黄颡鱼“黄优1号”及其母本黄颡鱼和父本瓦氏黄颡鱼为研究对象，克隆了杂交黄颡鱼“黄优1号”3个免疫相关基因(SOCS1、SOCS2和SOCS3)，并对其生物信息学进行了比较分析；采用qRT-PCR技术研究了SOCS1、SOCS2和SOCS3基因分别在3种黄颡鱼感染嗜水气单胞菌和鮰爱德华氏菌后的表达模式。结果显示，杂交黄颡鱼“黄优1号”SOCS1、SOCS2和SOCS3基因的全长分别为561、735和672 bp，分别编码186、244和223个氨基酸，其预测的蛋白结构均含有保守的SH2结构域和SOCS盒。黄颡鱼、瓦氏黄颡鱼和杂交黄颡鱼“黄优1号”SOCS1、SOCS2和SOCS3基因的表达在被检的8个不同组织中呈现组织特异性。在两种致病菌感染后，杂交黄颡鱼“黄优1号”及其双亲的SOCS1、SOCS2和SOCS3基因在肝、鳃和头肾组织的表达量均在前24 h显著升高，随后逐渐恢复至正常水平。此外，鮰爱德华氏菌感染后，杂交黄颡鱼“黄优1号” SOCS1、SOCS2和SOCS3基因的表达量显著高于双亲，表现出较双亲更强的免疫调节能力且具有病原特异性。该结果为进一步解析黄颡鱼SOCS家族免疫防御调控机制提供了参考依据。