Effects of feeding levels on growth performance,feed utilization,body composition and apparent digestibility coefficients of nutrients for juvenile Chinese sucker,Myxocyprinus asiaticus

An experiment was conducted to determine effects of feeding levels on growth performance, feed utilization, nutrient deposition, body composition and apparent digestibility coefficients (ADCs) of nutrients for juvenile Chinese sucker (initial weight, 11.77±0.22 g). Chinese sucker were fed a practical diet from 0% (starvation) to 4.0% (at 0.5% increments) body weight (bw) day^?1 for 8 weeks. The results showed that growth performance, feed utilization, nutrient deposition, body composition and ADCs of dry matter, protein and energy were significantly (P<0.05) affected by feeding levels. Survival was the lowest for the starvation group. Final mean body weight, growth rate, thermal‐unit growth coefficient (TGC) increased with feeding rate from 0% to 3.0% bw day^?1 (P<0.05) and showed no significant differences above the level (P>0.05). Feed conversion rate was significantly lower at a feeding level of 2.5% bw day^?1 than above and below the level (P<0.05). Protein efficiency ratio was markedly highest at the 2.5% bw day^?1 ration level (P<0.05). Fish fed at the feeding level (1.0% bw day^?1), which represented a maintenance ration (energy gain was less than 2.27 kJ fish^?1 day^?1), showed positive protein deposition but negative lipid deposition. This indicates that fish fed a maintenance ration mobilize body lipid reserve to support protein deposition. Lipid contents of whole body, muscle and liver increased with increasing feeding rates from 0.5% to 3.0% bw day^?1 and showed no significant differences above the level (P>0.05). Protein contents of whole‐body composition increased with feeding rate from 0.5 to 3.0% bw day^?1 (P<0.05) and showed no significant differences above the level (P>0.05), whereas muscle and liver remained relatively stable with the different ration amount with the exception of fish fed a ration of 0.5% bw day^?1, at which Chinese sucker possessed significantly lower body protein concentration (P<0.05). The ADCs of dry matter, protein and energy decreased with increasing feeding levels from 0.5% to 3.0% bw day^?1 and then remained relatively constant over the level. Based on the broken‐line regression analysis using WG data, the optimum and maintenance feeding levels for Chinese sucker were 3.10% bw day^?1 and 0.45% bw day^?1 respectively.     

Condition assessment of lamprey populations in the Yorkshire Ouse catchment,north‐east England,and the potential influence of physical migration barriers

• 1. River lamprey (Lampetra fluviatilis) and sea lamprey (Petromyzon marinus) are designated features of the River Derwent Special Area of Conservation (SAC) and the Humber Estuary (a possible SAC). This study determined the condition of lamprey populations in the Yorkshire Ouse catchment by assessing the species composition, distribution, abundance and size‐structure of larval (ammocoete) populations in five major tributary rivers (Derwent, Swale, Ure, Nidd and Wharfe).
• 2. According to EU condition assessment criteria, Lampetra populations (assumed to be mostly river lamprey) are at present in favourable condition, with site mean (±SE) densities ranging from 2.7 (±1.2) to 160.3 (±50.5) individuals m^?2 (all river means >2 individuals m^?2), and at least two size (≈age) classes present in optimal microhabitats. By contrast, no sea lamprey larvae were recorded, suggesting that populations of this species are in unfavourable condition.
• 3. Actions to protect and enhance nationally or internationally important stocks must be implemented from at least a catchment perspective, because many of the issues affecting such species are not localized. With respect to lampreys, particular attention should be given to protecting spawning and nursery habitats, improving water quality, reducing impingement at abstraction points, preventing exploitation at spawning grounds and increasing passage at potential physical obstructions.

Copyright © 2007 John Wiley & Sons, Ltd.     

The pond's shape matters: differential growth,physiological condition and survival of epibenthic Farfantepenaeus aztecus postlarvae

As a function of the water quality provided by square, circular and oval experimental ponds, the growth, survival and oxygen requirements in epibenthic postlarvae of Farfantepenaeus aztecus were analysed in relation to their routine metabolism and apparent heat increment. Temperature, oxygen concentration, pH and salinity were measured daily in two experimental ponds of each shape. The postlarvae oxygen consumption during two 24‐h cycles, their growth, physiological condition and survival and the productivity in the ponds were estimated. Low values of pH, oxygen concentration and phytobenthos productivity, and reduced postlarvae relative growth and survival were observed in the square ponds. We suggest that the latter results from a deficient water circulation related to the effect of the pond's shape on dissolved oxygen levels and, consequently, on growth and survival. The postlarvae routine metabolism, including feeding, varied between 1.91 and 2.25 mg O₂ h^?1 g^?1 wet weight, whereas the minimum oxygen concentration needed in the ponds is approximately 4.25 mg O₂ L^?1. These conditions were achieved in the oval ponds concurrent with higher survival and growth values, in which individuals distributed randomly, for which we suggest that oval‐shaped ponds could be the most adequate for the culture of this and other penaeid species.     

福建海洋渔业产业结构调整对策的探讨

一种产业的高速发展能否得以持续,关键在于是否对该产业结构进行不断调整,使之趋于最合理状态。为再度振兴福建海洋渔业,不失时机地进行渔业结构战略性调整是唯一选择。     

承德地区放线菌物种多样性分布的研究

对采自承德地区南部五县及市区土样共403份,进行了放线菌的分离纯化,并对放线菌的形态、细胞壁化学组分、部分菌株16SrDNA序列进行研究,经初步分析,分离得到的1万余株放线菌,大约95%属于11个已知属。结果表明:承德地区放线菌资源较为丰富,区域地理状况、气候、植被、根系、土壤性质等因素对放线菌的分布有一定的影响,应引起足够重视。     

资源禀赋、收入结构与就业特征对农地承包权退出意愿的影响

为农地承包权的顺利退出提供参考,对苏州市和宿迁市7个村庄391家农户的调查数据,采用二元logistic回归模型分析农户资源禀赋、收入结构和就业特征对农地承包权退出意愿的影响。结果表明:1)资源禀赋方面,承包地面积、承包地块数、实际经营面积、宅基地面积以及是否发生过土地流转对承包权退出意愿影响不显著,而拥有城镇住房的家庭退出意愿更强烈。2)就业特征方面,农民外出务工时间越长、上班地点离农村越远、从事的职业与农业相关性越弱,则农户退出土地承包权的意愿越强烈,同时接受过非农技巧培训的农户更愿意退出土地承包权。3)收入结构方面,工资性收入所占比重越高则农户退出承包权的意愿越强,而家庭经营性收入占比较高的家庭越不愿退出承包地。     

广东省和海南省象耳豆根结线虫的鉴定

运用线虫比较形态学、结合同工酶、mtDNA-PCR、rDNA-IGS-PCR技术,对采自中国广东和海南2个省的根结线虫进行鉴定.在海南省定安的木豆(Cajanus cajan)、海南省海口的木豆和番石榴(Psidium guaja-va)、广东省番禺的辣椒(Capsicum annuum)和南瓜(Cucrbita mosechata)及广东省遂溪的豇豆(Vigna sinensis)上发现象有耳豆根结线虫(Meloidogyne enterolobii).这是首次在海南省外发现象耳豆根结线虫,同时还发现该线虫的2个新寄主,即木豆和南瓜.     

不同栽培技术对马铃薯水份利用率的影响

在三种不同的栽培技术中,地膜覆盖平均WUE为1.69kg/mm较平作平均WUE1.26kg/mm提高34.13%水分利用率,垄作平均WUE为1.47kg/mm较平作提高16.67%水分利用率,脱毒马铃薯的平均WUE为1.60kg/mm,未脱毒马铃薯的平均WUE为1.34kg/mm,水分利用率提高19.35%。平作种植方式马铃薯现蕾至成熟期需水量占整个生育期到90%左右;垄作种植方式76.86~83.3%;地膜覆盖种植方式73.08~77.08%,垄作与地膜覆盖后马铃薯水分的利用趋于合理。进行地膜覆盖和垄作后能使植株健壮,单窝薯重,大中薯商品薯率高,从而提高马铃薯的产量。     

Cost minimization and input substitution in the production of gilthead seabream

Abstract

This paper studies cost minimization decisions by utilizing a simple bioeconomic model for gilthead seabream (Sparus aurata). This model is based on a biological growth model which accounts for the effects of temperature and ration size. Although the implicit production function derived from the growth model is shown to be quasiconcave, it is not homothetic nor quasilinear. Further, technology shows increasing returns with respect to ration size and harvesting time. Optimization decisions are analyzed in two different contexts, a restricted biological setting and an expanded economic problem. It is shown that the optimal ration size increases for the latter context, reaching values commonly accepted in current industrial practice. Even though the elasticity of substitution to the shadow input prices is positive at the optimal ration size, the latter is rather robust to changes in input prices. However, optimal costs show larger sensitivity to the labor price than to the feeding and managerial costs.     

Habitat associations of dolphinfish larvae in the Gulf of Mexico

The aim of this study was to investigate the role of the northern Gulf of Mexico (Gulf) as essential habitat of common dolphinfish (Coryphaena hippurus) and pompano dolphinfish (C. equiselis) during early life and to characterize conditions in which they were found. Eight ichthyoplankton surveys were conducted during the summer months from 2007 to 2010 in northern Gulf waters off Texas and Louisiana (26–28°N, 87–93°W), during which 1145 dolphinfish larvae were collected. C. hippurus, the dominant dolphinfish species, were collected in 57% of sampling sites with an overall mean density of 0.73 larvae 1000 m^?3, whereas C. equiselis were only collected at 18% of sites with a mean density of 0.12 larvae 1000 m^?3. Generalized additive models (GAMs) were used to examine the relationship between several environmental parameters and C. hippurus presence/absence and density. Both presence/absence and density GAMs indicated that catches of C. hippurus larvae increased near fronts and eddies and that increased abundances were most strongly associated with higher salinities and cooler temperatures. In addition, our models showed that C. hippurus larvae were positively associated with C. equiselis larvae, suggesting that C. hippurus and C. equiselis use similar habitats. Results of this study indicate that the Gulf may represent important spawning and/or nursery habitat of dolphinfishes and that mesoscale features and physicochemical conditions influence the distribution and abundance of C. hippurus larvae in this region.