大亚湾海域鱼类分类多样性研究

根据20世纪80年代起大亚湾海域鱼类调查研究的历史资料,采用Nelson分类系统对鱼类物种组成进行了系统整理,从不同分类阶元分析了大亚湾海域鱼类的多样性。分类阶元包含指数(TINCL_i),分类多样性指数(Δ⁺和∧⁺),目级和科级水平丰富度(R)以及目级和科级水平相似性系数(C)为本研究的主要研究指数,其中分类阶元包含指数TINCL_i为本文首次提出。结果显示,大亚湾海域共记录鱼类22目94科206属,以鲈形目种类居绝对优势。采用分类阶元包含指数分析,大亚湾海域鱼类组成目、科、属所分别拥有的(科、属、种),(属、种)和(种)的平均数目分别为(4.27、9.36、14.55),(2.19、3.40)和(1.55),高于东海陆架,而低于东沙群岛海域,并且与纬度梯度成反比,证明低纬度海域的鱼类分类多样性低,种类组成主要集中分布于较少数的分类类群。使用PRIMER 5.2软件计算了平均分类差异指数Δ⁺和分类差异变异指数∧⁺,数值分别为62.2和110.0,其中Δ⁺低于东海陆架区(65.7),高于东沙群岛海域(55.2),说明大亚湾海域鱼类的亲缘关系比东海陆架区海域鱼类近,比东沙群岛海域鱼类的远,并且分布较不均匀。3个海区的相似性系数比较结果显示,在目级水平上,大亚湾海域鱼类组成同东沙群岛接近,而科级水平上同东海陆架区更为接近。本研究在种以上的分类阶元审视大亚湾海域鱼类组成,以期增加对大亚湾鱼类多样性的认识,为该区域鱼类资源的开发、利用和保护提供参考依据。     

西沙群岛重要珊瑚礁海域鱼类区系

根据1998年5月、1999年5月和2003年5月在西沙群岛北礁、永兴岛、琛航岛、华光礁、浪花礁、金银岛、东岛和玉琢礁等8个岛礁的调查资料,研究了西沙群岛岛礁水域的鱼类区系。在8个岛礁共捕获鱼类48科261种,其中礁栖性鱼类占78.93%,在8个岛礁广泛分布的鱼类只有33种,各礁区之间种类的相似度不超过41%,因此,种类多样性高和相似度低是该区域鱼类区系的2个主要特征。与南沙岛礁(1998～1999)延绳钓、刺网和手钓以及南沙群岛西南陆架区(1991)、南海北部海域等底拖网鱼类相比较,物种相似度分别为34.0%、5.1%和6.8%。     

西沙群岛七连屿礁栖鱼类物种和分类多样性

为探讨以西沙群岛七连屿（16°55''N~17°00''N,112°12''E~112°21''E）为代表的典型小尺度范围内珊瑚礁生态系统的物种组成及分类多样性,本文以20世纪70年代、2018—2019年南海七连屿鱼类调查资料为基础,总结七连屿礁栖鱼类物种组成,并利用分类学多样性指数和（科级）多样性测度指数对七连屿珊瑚礁鱼类物种组成及分类多样性进行研究。结果显示,七连屿海域礁栖鱼类隶属于8目33科70属175种,其中鲈形目（Perciformes）鱼类占绝对优势,占比81%;平均分类差异指数（Δ⁺）约为54.19,分类差异变异指数（低于东海陆架、大亚湾和渚碧礁;其G-指数）平均值为3.09,标准化的F-指数、指数综合来看,七连屿礁栖性鱼类物种多样性较高,且其科、属的分布在历史上较为合理,但2018—2019年科属多样性显著降低,建议对其及时予以保护。     

南海珊瑚礁海域鱼类分类多样性大尺度分布格局

珊瑚礁区生物多样性是当今生态学研究热点之一,为更全面地了解南海诸岛珊瑚礁海域鱼类物种多样性分布格局,系统整理了20世纪70年代以来南海东沙、西沙和中沙及南沙群岛珊瑚礁海域鱼类资源调查的历史资料,研究了南海珊瑚礁鱼类分类学多样性.种类统计结果表明,目前东沙记录鱼类种类514种,西沙和中沙632种,南沙548种;各礁区记录鱼类物种数目少于预测数目,也少于全球其他生境相似的海域记录的鱼类种数.估算了南海珊瑚礁鱼类平均分类差异指数△+和分类差异变异指数∧+,结果显示,东沙△+和∧+分别为55.1、121;西沙、中沙△+为60.2,∧+为164;南沙△+为56.6、∧+为150;各礁区海域鱼类△+值均小于东海陆架海域,而∧+值均高于东海陆架海域.在种和科的分类水平上,计算了南海珊瑚礁海域与卡拉棉群岛、米尔恩湾、南沙群岛西南陆架和南海北部陆架海域鱼类的相似性系数,结果表明,西、中沙群岛与其他礁区海域鱼类在种级分类阶元上的相似性系数相差较大,所有珊瑚礁海域鱼类在科级分类阶元上的相似性系数较为接近;另外,所有珊瑚礁海域鱼类种(科)间相似性均高于其与陆架海域鱼类种(科)间相似性.对南海珊瑚礁、卡拉棉群岛和米尔恩湾等海域典型礁栖性鱼类的科的物种相对丰富度进行了Kruskal-Wallis检验,结果表明,其差异均不显著(P＞0.05).结论认为,物种多样性较高而分类多样性较低是南海珊瑚礁鱼类多样性大尺度分布格局的主要特征.     

北极茴鱼形态性状对体重影响效果分析

为探明北极茴鱼(Thymallus arcticus)形态性状与体重的关系, 以 1⁺ ~3⁺ 龄北极茴鱼为研究对象, 测定了体重(Y) 和体厚(X₁)、眼间距(X₂)、体长(X₃)、体高(X₄)、头长(X₅)、眼径(X₆)、吻长(X₇)、尾柄长(X₈)、尾柄高(X₉)等 9 个形态性状, 利用相关分析、通径分析和多元回归分析等方法, 筛选出影响北极茴鱼体重的主要形态性状, 并建立回归方程。结果显示: (1) 不同年龄阶段, 与北极茴鱼体重显著相关(P＜0.05)的形态性状种类不同, 且数量也随着年龄的增加而降低。(2) 通径分析在 1⁺ ~3⁺ 龄北极茴鱼中分别保留了 4、4 和 2 个形态性状, 1⁺ 龄北极茴鱼中体长(X3)的直接作用最大(0.345), 尾柄高(X9)的间接作用最大(0.745); 2⁺ 龄北极茴鱼中体高(X4)的直接作用最大(0.473), 体厚(X1)的间接作用最大(0.378); 3⁺ 龄北极茴鱼中体厚(X₁)的直接作用最大(0.635), 尾柄高(X₉)的间接作用最大(0.344)。(3) 通径分析保留的形态性状对 1⁺ ~3⁺ 龄北极茴鱼体重的总决定系数较高, 分别为 0.943、0.778 和 0.997。(4) 多元回归分析拟合出 1+ 龄北极茴鱼形态性状(Xi)与体重(Y)回归方程为 Y=?90.510+15.345X₁+3.638X₃+10.473X₄+16.884X₉, 2+ 龄北极茴鱼形态性状(Xi)与体重(Y)回归方程为 Y=?142.449+29.023X₁+81.082X₂+27.126X₄?47.376X₇, 3⁺ 龄北极茴鱼形态性状(Xi)与体重(Y)回归方程为 Y=?228.922+75.063X₁+107.864X₉。本研究丰富了北极茴鱼基础生物学数据, 同时为将来人工养殖利用过程中北极茴鱼的选择育种提供待选形态性状。     

赤水河流域鱼类物种、功能和分类多样性研究

赤水河是长江上游的一条一级支流,同时也是长江上游珍稀特有鱼类国家级自然保护区的重要组成部分,在鱼类生物多样性保护方面具有重要价值。本文基于2019年和2020年对赤水河流域30个样区的鱼类调查数据,对鱼类物种丰富度(Richness)、Shannon-Weiner指数(H)、功能丰富度(FRic)、功能均匀度(FEve)、功能离散度(FDiv)、平均分类差异指数(Δ⁺)和分类差异变异指数(Λ⁺)等多样性指数的空间分布格局及其相关性进行了分析。调查期间共采集到鱼类125种(亚种),隶属于7目20科80属。其中,土著鱼类112种(亚种),隶属于6目17科71属;外来鱼类13种(亚种),隶属于5目6科11属。7个多样性指数均呈显著的纵向梯度格局,上游到下游也呈增加趋势,但FEve、FDiv和Δ⁺这三个指数在河段间的增量相对较小。不同生物多样性指数之间的相关性差异较大,从不显著到显著正相关,综合使用不同层面的多样性指数能够有助于更好地理解淡水鱼类分布格局,为鱼类资源保护提供科学依据。     

强壮箭虫摄食生态的实验研究

实验研究了强壮箭虫对几种食物的摄食选择性和几种生态因子对其摄食率的影响，以及摄食的昼夜节律。结果表明，强壮箭虫首先选食蒙古裸腹，其次哲水蚤，再其次猛水蚤，不摄食褶皱臂尾轮虫。食物密度、温度和盐度对其摄食率均有极显著的影响，其关系式分别 为（1）Y =-0.0394X^{2+1.5861X-4.0500(R2=0.9235)，（2）Y=-0.0514X2+1.3238X+7.3833(R2=0.9510) ，（3）Y=-0.0275X2+1.3992X-6.3571(R2=0.9041)。摄食的最适食物密度为每升100个裸腹（生物量15～20 mg·L-1），摄食率为11.9 ind·d-1；摄食的最适水温为12.9 ℃，摄食率15.9 ind·d-1；摄食的最适盐度为25.4，摄食率为11.4 ind·d-1。强壮箭虫在夜间或弱光条件下，摄食较为强烈，早晨8点到12点摄食率最低，午后4点到8点达到摄食高峰。}     

大口黑鲈形态性状对体重的影响效果分析

对大口黑鲈全长、体长、体高、体宽、眼间距、头长、吻长、尾柄长、尾柄高和体重共 10个性状进行测定,运用相关分析、通径分析和多元回归分析,剔除与体长存在显著共线性的全长、体高、头长,尾柄高及回归方程中不显著的吻长和尾柄长,计算以体宽、体长、眼间距 3个形态性状为自变量,体重为依变量的相关系数、通径系数、决定系数及相关指数,定量分析大口黑鲈形态性状对体重的影响效果。结果显示,3个形态性状与体重的相关系数（0.942,0.979,0.928）均达到极显著水平（P＜0.01）;通径分析中,3个形态性状对体重的通径系数亦达到极显著水平（P＜0.01）,它们是直接影响体重的重要指标,其中体宽（P⁴=0.599）对体重的直接影响最大。所选形态性状与体重的相关指数R²＝0.980 ,说明所选性状是影响体重的主要形态性状。应用逐步多元回归分析建立了以体重为依变量(Y),体宽(X⁴)、体长(X²)和眼间距(X⁵)为自变量的回归方程：LgY=1.065 + 0.765 LgX²＋1.441 LgX⁴+0.543 LgX⁵。以上形态性状对体重影响效果相关数据的获得为大口黑鲈选育测量指标的确定提供了理论依据。     

星康吉鳗形态性状与体重的通径分析及生长曲线拟合

为探明星康吉鳗（Conger myriaster）形态性状和体重的关系,测定了体重（Y）及全长（X₁）、肛长（X₂）、尾长（X₃）、头长（X₄）、吻长（X₅）、眼径（X₆）、眼后头长（X₇）、背鳍前长（X₈）、躯干长（X₉）、头宽（X₁₀）、眼间距（X₁₁）等11个形态性状,通过相关分析、通径分析、回归分析等方法研究了形态性状对体重的影响;通过曲线拟合获得4个形态性状与体重的最佳拟合模型。结果表明,星康吉鳗各形态性状之间以及形态性状与体重之间均呈极显著正相关关系（P< 0.01）。相关分析发现肛长（X₂）与体重的相关系数最大（0.970）;通径分析发现肛长（X₂）对体重的直接作用最大（0.450）,头宽（X₁₀）通过肛长（X₂）对体重的间接作用最大（0.431）;决定系数分析发现,肛长（X₂）对体重的直接决定系数最大（0.203）,肛长（X₂）和头宽（X₁₀）的共同决定系数最大（0.172）。形态性状（X）与体重（Y）的多元回归方程为Y=-113.859+6.481X₂+49.213X₆+11.514X₇+20.145X₁₀（R²=0.954）。星康吉鳗肛长（X₂）、眼后头长（X₇）、头宽（X₁₀）与体重的最佳拟合模型为指数函数,模型方程分别为Y=1.466e^0.287X、Y=1.435e^1.328X、Y=1.970e^1.974X,眼径（X₆）与体重的最佳拟合模型为线性,方程为Y=-77.460+222.093X。结论认为,在星康吉鳗选育时,应以肛长（X₂）和头宽（X₁₀）为主要选择性状,以眼径（X₆）和眼后头长（X₇）为辅助选择性状。     

海南岛东岸、南岸浅水礁区近10年珊瑚礁鱼类种类分布及多样性探讨

根据2004—2013年海南岛东岸、南岸浅水礁区珊瑚礁鱼类监控数据,利用截线样条法、分类学多样性指数、相对丰富度及相似性指数等方法技术对海南岛东岸、南岸浅水礁区珊瑚礁鱼类种类组成及生物多样性进行研究。结果显示,海南东岸、南岸浅水礁区近10年调查珊瑚礁鱼类共计6目32 科64属130种,其中鲈形目居绝对优势;珊瑚礁鱼类密度大致呈现由南向北逐渐递减的趋势;科级多样性平均值为4.41,属级多样性指数平均值为3.09,标准化的G-F指数平均值为0.30;鲈形目珊瑚礁鱼类相对丰富度占有绝对优势,相对丰富度较高的6个科分别为雀鲷科、隆头鱼科、蝴蝶鱼科、天竺鲷科、四齿鲀科及玻甲鱼科;珊瑚礁鱼类在目级极为相似,相似性指数在0.86～1之间;科、属、种级相似性指数较低,均在0.5以下,通过Jaccard's种类相似性指数分析,海南岛东岸、南岸珊瑚礁鱼类种类较多,物种丰富。珊瑚礁鱼体长范围6～10 cm区间的数量最多,其次为0 ～5 cm区间,21～40 cm区间的珊瑚礁鱼类在浅水礁区分布极少。本研究通过对海南岛东岸、南岸浅水礁区珊瑚礁鱼类近10 a的种类分布及多样性进行探讨,旨在为海南岛珊瑚礁生态系统及珊瑚礁鱼类保护与研究提供基础数据及理论依据。     

Rare serotype occurrence and PFGE genotypic diversity of Streptococcus agalactiae isolated from tilapia in China

Previously, we reported 10 PEGE types of 85 tilapia Streptococcus agalactiae(GBS), which shifted from Streptococcus iniae in China, by using PEGE method. Presently, larger and more representative tilapia GBS were isolated, for the ?rst time in China, to characterize their serotypes and genetic diversities more precisely than had done before. 168 GBS strains were distributed in ?ve provinces of China, in which Guangdong, Guangxi and Hainan were the major ones, holding36.9%(62/168), 37.5%(63/168) and 19.6%(33/168), respectively. Serotypes, Ia, Ib and III, were observed in these strains and the most predominant one was Ia(95.2%), which mainly distributed in Guangdong, Guangxi and Hainan. Ia initially occurred in 2009, it shoot up to 32.1% in 2010,but decreased to 16.1% in 2011 before went up to 45.2% in 2012. Ib sporadically occurred during2007–2011, III onlyoccurred in 2012. 14 different PFGE types, including 4 new types(N, O,P and Q), were observed, in which B, D, F and G were the predominant types, holding 83.9%(141/168) of the total GBS strains. Ia corresponded to 11 PFGE types(A–H, N–P), in which type D predominated(51%). Ib represented 3 genotypes(I, J and Q) and III harbored only 2genotypes(N and F). Type N and Fsynchronously presented in Ia and III. In summary, the genetic diversity of tilapia GBS varied by serotypes and changed with geographical locations and years.Although Iastillpredominated, new rareserotypeIII alreadyoccurred in China.     

Purification and partial characterization of GtHs (cfLH and cfFSH) from Indian walking catfish (Clarias batrachus) (L.) and development of a homologous ELISA for cfLH

Two gonadotropins (GtH; Qa and Qb) were purified by gel filtration and ion exchange chromatography from the pituitaries of Indian walking catfish (Clarias batrachus). The presence of GtH during purification was assessed by in vitro oocyte maturation and in vivo steroidogenic activity, and their identities were determined by elution profiles, molecular weight, biological activities and yield. The molecular weights of Qa and Qb were 37 and 42 kDa, respectively, and composed of distinct subunits (Qa: 20 and 14 kDa and Qb: 26 and 18 kDa). Polyclonal antibodies raised against Qa immunostained Qa, Qb and pituitary GtH cells. A competitive Qa‐ELISA was developed whose sensitivity was 6.25 ng mL^?1 (1.25 ng well^?1) with intra‐ (3.5%) and inter‐ (12.4%) assay coefficients of variation. Displacement curves parallel to the standard were obtained with plasma and pituitary extracts of catfish, Qb and carp GtHII. The assay was validated by measuring the plasma Qa levels after LHRH treatment and in relation to ovarian growth in the female catfish during different reproductive phases. Based on the results, Qa and Qb corresponded to fish LH and FSH respectively. The findings will increase the knowledge of the mechanisms controlling fish reproduction and identification of sensitive phases in fish in captivity for hormonal manipulation.     

Controlled infection of Poecilia reticulata Peters (guppy) with Tetrahymena by immersion and intraperitoneal injection

Tetrahymena is a protozoan parasite, which infects guppy, Poecilia reticulata Peters, and causes substantial economical losses in commercial farms worldwide. Studies of guppy infected by Tetrahymena require standardized infection protocols. The LD50 for Tetrahymena infection of guppies by intraperitoneal (IP) injection was calibrated, and the level obtained was 946 parasites per fish. Guppy infection with Tetrahymena by immersion, imitating the natural route of infection via the integument, was studied under normal or stress conditions. Exposure to cold and netting (CNI) and to cold only (CI) followed by immersion exposure to 10 000 Tetrahymena per mL resulted in 22.5% and 19.2% mortality, respectively, as compared to 14.2% and 10% in groups that were netted only (NI) or non‐stressed (I). Histopathology revealed that immersion infection resulted in a systemic infection. Lysozyme levels, measured 3 weeks after infection, were significantly higher in the CNI group (288 μg per mg protein) compared with CI‐, NI‐ and I‐treated groups (94.5, 64 and 62.3 μg mg^?1, respectively). There was no evident parasite immobilization activity in body homogenates, suggesting no development of acquired immunity. Re‐infection by IP injection revealed no increase in protection in any of the treatment groups, mortality range of 56.3–75%, higher than in the non‐exposed control (40.6% mortality).     

Imported ornamental fish are colonized with antibiotic‐resistant bacteria

There has been growing concern about the overuse of antibiotics in the ornamental fish industry and its possible effect on the increasing drug resistance in both commensal and pathogenic organisms in these fish. The aim of this study was to carry out an assessment of the diversity of bacteria, including pathogens, in ornamental fish species imported into North America and to assess their antibiotic resistance. Kidney samples were collected from 32 freshwater ornamental fish of various species, which arrived to an importing facility in Portland, Oregon from Colombia, Singapore and Florida. Sixty‐four unique bacterial colonies were isolated and identified by PCR using bacterial 16S primers and DNA sequencing. Multiple isolates were identified as bacteria with potential to cause disease in both fish and humans. The antibiotic resistance profile of each isolate was performed for nine different antibiotics. Among them, cefotaxime (16% resistance among isolates) was the antibiotic associated with more activity, while the least active was tetracycline (77% resistant). Knowing information about the diversity of bacteria in imported ornamental fish, as well as the resistance profiles for the bacteria will be useful in more effectively treating clinical infected fish, and also potential zoonoses in the future.     

Effect of iodophor disinfection of non‐hardened Salmo trutta eggs on their bacterial and fungus load

This study investigated the efficiency of iodophor disinfection (135 ppm active iodine for 15–30 min) of non‐hardened Salmo trutta eggs against different groups of bacteria and against fungus. Egg samples were taken from non‐disinfected and from disinfected eggs, microorganisms were cultured on specific nutrient media and their mass was measured by turbidimetric methods. Bacteria and fungus mass of non‐hardened eggs could be reduced but not eliminated by iodophor disinfection with 135 ppm active iodine for 15 min. The extent of reduction was 47–65% (Experiment 1). The efficiency of disinfection increased with disinfection time as the reduction in bacteria and fungus mass was 40–55% after 15 min and 58–74% after 30 min (Experiment 2). Disinfection efficiency of iodophor solution diluted in water (reduction 49–57%) and of iodophor solution diluted in sodium chloride solution iso‐osmolar to the oocytes (reduction 52–61%) was similar (Experiment 3). The reduction in bacteria and fungus mass was persistent as it was 39–72% lower in embryos deriving from disinfected eggs than in embryos deriving from non‐disinfected ones (Experiment 4). In conclusion, the tested disinfection method is inadequate to eliminate pathogens completely but it could positively influence immune defence of eggs and embryos.     

Influence of the antibacterial herbs, Solanum trilobatum, Andrographis paniculata and Psoralea corylifolia on the survival, growth and bacterial load of Penaeus monodon post larvae

The indiscriminate use of antibiotics and chemicals in shrimp hatcheries has led to biomagnification and that in turn could lead to rejection of a whole consignment. The application of the bioencapsulation technique as a tool for curative treatment in shrimp larvae was investigated. Herbs having antibacterial properties such as Solanum trilobatum, Andrographis paniculata and Psoralea corylifolia (methanolic extracts) were bioencapsulated in Artemia and fed to Penaeus monodon post larvae PL 1–25. The post larvae were reared in a medium inoculated with pathogenic bacteria such as Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella typhi and Vibrio sp. Post larvae reared in the non-inoculated water and fed with non-enriched Artemia exhibited 90% survival, highest specific growth rate (12.43%) and reduced bacterial load. P. monodon reared in the bacterial inoculated water and fed with the non-enriched Artemia exhibited the lowest survival (10–30%), specific growth rate (8.42–9.1%) and increased bacterial load (2.86 × 10³ to 3.76 × 10⁵ cfu/g). The methanolic extracts of the herbs helped to increase survival and specific growth rate and reduced bacterial load in the P. monodon culture system. Among the three herbal extracts, P. corylifolia enriched Artemia fed post larvae showed the tendency to higher survival (>50%), growth rate (11.5 averaged) and low bacterial load (1.12 × 10⁵ cfu/g). This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of cortisol on hepatic carbohydrate metabolism and responsiveness to hormones in the sea raven,Hemitripterus americanus

The sea raven, Hemitripterus americanus, is a sit-and-wait, low metabolic rate, marine teleost. The objective of this study was to determine i) whether cortisol implantation (50 mg. kg^-1) for 7 days altered hepatocyte metabolism, and hepatocyte responsiveness to epinephrine, glucagon and insulin, and ii) whether 8 weeks of food-deprivation modified the above response. Cortisol implantation significantly increased hepatocyte total glucose production and oxidation from alanine compared to the sham group. There was no cortisol effect on glycogen breakdown, suggesting that the activation of other pathways, including gluconeogenesis, are required to account for the increased glucose production. Epinephrine-mediated (10^-5M) glycogen breakdown and insulin-mediated (10^-8M) total glucose production were enhanced in hepatocytes of cortisol implanted sea ravens, but there were no change in any glucagon (10^-7M) effects. The enhanced glycogen breakdown in the absence of similar increases in total glucose production with epinephrine indicates mobilization of carbohydrate reserves for endogenous use by the liver. Food-deprivation for 8 weeks significantly decreased condition factor, plasma cortisol concentration and liver glycogen content in the sea raven, but had no effect on plasma glucose concentration. Hepatocyte total glucose production and flux rates from alanine increased significantly with food-deprivation. Moreover, food-deprivation increased responsiveness of total hepatocyte glucose production to the actions of glucagon and insulin, but not to epinephrine; none of these effects were modified by cortisol implantation. Our results indicate that cortisol in the sea raven exerts both a direct and an indirect or permissive effect on hepatocyte metabolism by modifying hepatocyte responsiveness to epinephrine and insulin stimulation. Cortisol implantation did not modify the effects of glucagon or food-deprivation in this species.     

Simulation and quantification of enrichment and retention processes in the southern Benguela upwelling ecosystem

Important environmental processes for the survival and recruitment of early life stages of pelagic fishes have been synthesized through Bakun's fundamental triad as enrichment, concentration and retention processes (A. Bakun, 1996, Patterns in the Ocean. Ocean Processes and Marine Population Dynamics. San Diego, CA, USA: University of California Sea Grant). This conceptual framework states that from favourable spawning habitats, eggs and larvae would be transported to and/or retained in places where food originating from enrichment areas would be concentrated. We propose a method for quantifying two of the triad processes, enrichment and retention, based on the Lagrangian tracking of particles transported within water velocity fields generated by a three‐dimensional hydrodynamic model. We apply this method to the southern Benguela upwelling ecosystem, constructing putative maps of enrichment and retention. We comment on these maps regarding main features of the circulation in the region, and investigate seasonal variability of the processes. We finally discuss the results in relation to available knowledge on the reproductive strategies of two pelagic clupeoid species abundant in the southern Benguela, anchovy (Engraulis encrasicolus) and sardine (Sardinops sagax). Our approach is intended to be sufficiently generic so as to allow its application to other upwelling systems.     

Effects of capture,loading density and transport stress on the mortality,physiological responses,bacterial density and growth of rohu <Emphasis Type="Italic">Labeo</Emphasis><Emphasis Type="Italic"> rohita</Emphasis> fingerlings

This study evaluated the effects of three levels of loading density (200, 300 and 400 g L⁻¹) and four levels of duration (1, 3, 6 and 9 h) on the mortality, plasma cortisol and chloride levels and growth of rohu Labeo rohita fingerlings in a transport simulation. While total immediate mortality was low (4–12%), delayed mortality was high (27–49%). Initial capture and handling were found to constitute the most stressful phase as indicated by elevated plasma cortisol. The levels of cortisol continued to rise at 6 and 9 h after transport, with the highest level observed at 9 h after transport. The level of plasma chloride fell after transport across all density levels and treatment durations. Specific growth rate (SGR, %/day) and total bacterial density (cfu/g) were not different between and within treatments, and between treatments and the controls. This study demonstrates that transport has a profound effect on the stress responses of rohu fingerlings. Although the level of immediate mortality was low, the higher level of delayed mortality has serious implications in terms of production inefficiency for grow-out farmers.     

The effects of introduced tilapias on native biodiversity

• 1. The common name ‘tilapia’ refers to a group of tropical freshwater fish in the family Cichlidae (Oreochromis, Tilapia, and Sarotherodon spp.) that are indigenous to Africa and the southwestern Middle East. Since the 1930s, tilapias have been intentionally dispersed worldwide for the biological control of aquatic weeds and insects, as baitfish for certain capture fisheries, for aquaria, and as a food fish. They have most recently been promoted as an important source of protein that could provide food security for developing countries without the environmental problems associated with terrestrial agriculture. In addition, market demand for tilapia in developed countries such as the United States is growing rapidly.
• 2. Tilapias are well‐suited to aquaculture because they are highly prolific and tolerant to a range of environmental conditions. They have come to be known as the ‘aquatic chicken’ because of their potential as an affordable, high‐yield source of protein that can be easily raised in a range of environments — from subsistence or ‘backyard’ units to intensive fish hatcheries. In some countries, particularly in Asia, nearly all of the introduced tilapias produced are consumed domestically; tilapias have contributed to basic food security for such societies.
• 3. This review indicates that tilapia species are highly invasive and exist under feral conditions in every nation in which they have been cultured or introduced. Thus, the authors have concluded that, despite potential or observed benefits to human society, tilapia aquaculture and open‐water introductions cannot continue unchecked without further exacerbating damage to native fish species and biodiversity. Recommendations include restricting tilapia culture to carefully managed, contained ponds, although exclusion is preferred when it is feasible. Research into culture of indigenous species is also recommended.

Copyright © 2005 John Wiley & Sons, Ltd.