LHRH-A对尼罗罗非鱼生长及生长轴相关基因表达的影响

促性腺激素释放激素(GnRH)的主要作用是刺激脑垂体促性激素(GtH)的释放, 亦可促进鱼类生长激素(GH)的释放。促黄体素释放激素类似物(LHRH-A)是哺乳类GnRH的类似物, 为了分析LHRH-A对尼罗罗非鱼生长调节的作用, 设计了长期和短期2个实验, 采用腹腔注射(剂量0.1 μg/g体重)方法, 分析LHRH-A对尼罗罗非鱼绝对生长率、特定生长率、肝体系数和肥满度的影响, 并应用荧光实时定量PCR方法检测在注射LHRH-A后不同时段(6h、12h、24h、2周)尼罗罗非鱼垂体GH、肝脏GHR和肝脏IGF-I基因的表达变化。结果表明, LHRH-A组尼罗罗非鱼的绝对生长率、特定生长率、肝体系数、肥满度均显著高于对照组(P<0.05); 注射LHRH-A后12h、24h垂体GH mRNA表达水平均显著升高(P<0.05), 2周后恢复到对照组水平; 注射LHRH-A后24h和2周肝脏GHR mRNA表达水平显著上升(P<0.05); 注射LHRH-A后6h肝脏IGF-I mRNA表达水平显著升高(P<0.05), 12h、24h和2周恢复到对照组水平。以上结果提示, LHRH-A可显著上调尼罗罗非鱼生长轴相关基因的表达, 从而促进鱼类的生长。     

A place preference test in the fish Nile tilapia

The Nile tilapia fish (Oreochromis niloticus) has a high potential to be used as a model in neuroscience studies. In the present study, the preference of the Nile tilapia between a gravel-enriched (GEE), a shelter-enriched (SEE) or a non-enriched (NEE) environment was determined, for developing a place preference model. Nile tilapia had an initial preference for GEE, but after 1 day of observation, the fish stabilized their frequency of visits among compartments. Hence, any stimulus motivating tilapia increase in compartment visiting indicates a positively reinforcing effect. This feature is very useful for the development of new behavioural paradigms for fish in tests using environmental discrimination, such as the conditioning place preference test.     

The introduced Oreochromis niloticus is spreading on the Kaufe floodplain,Zambia

The Nile tilapia, Oreochromis niloticus, escaped from a fish farm in Mazabuka, probably in 1987, and was found in September 1992 on a 75 km stretch of the river, mainly downstream from the site of release. In most areas, except near Mazabuka, O. niloticus was relatively uncommon and so far does not seem to have hybridized with the local tilapias.     

Time-place learning in food-restricted Nile tilapia

Time-place learning based on food association was investigated in eight food-restricted Nile tilapias. Each fish was individually housed for 10 days in an experimental tank for adjustments to laboratory conditions, and fed daily in excess. Feeding was then interrupted for 17 days. Training was then started, based on a food-restricted regime in a tank divided into three interconnected compartments. Daily food was offered in one compartment (left or right side) of the tank in the morning and on the opposite side in the afternoon, for a continuous 30-day period. Frequency of choices on the right side was measured on days 10, 20 and 30 (during these test days, fish were not fed). Following this 30-day conditioning period, the Nile tilapias were able to switch sides at the correct period of the day to get food, suggesting that food restriction facilitates time-place learning discrimination.     

Cryptic microsporidian parasites differentially affect invasive and native Artemia spp.

We investigated the host specificity of two cryptic microsporidian species (Anostracospora rigaudi and Enterocytospora artemiae) infecting invasive (Artemia franciscana) and native (Artemia parthenogenetica) hosts in sympatry. Anostracospora rigaudi was on average four times more prevalent in the native host, whereas E. artemiae was three times more prevalent in the invasive host. Infection with An. rigaudi strongly reduced female reproduction in both host species, whereas infection with E. artemiae had weaker effects on female reproduction. We contrasted microsporidian prevalence in native A. franciscana populations (New World) and in both invaded and non-invaded Artemia populations (Old World). At a community level, microsporidian prevalence was twice as high in native compared with invasive hosts, due to the contrasting host-specificity of An. rigaudi and E. artemiae. At a higher biogeographical level, microsporidian prevalence in A. franciscana did not differ between the invaded populations and the native populations used for the introduction. Although E. artemiae was the only species found both in New and Old World populations, no evidence of its co-introduction with the invasive host was found in our experimental and phylogeographic tests. These results suggest that the success of A. franciscana invasion is probably due to a lower susceptibility to virulent microsporidian parasites rather than to decreased microsporidian prevalence compared with A. parthenogenetica or to lower microsporidian virulence in introduced areas.     

饲料中糖水平对不同食性海水鱼类PEPCK基因表达和酶活性的影响

磷酸烯醇式丙酮酸羧激酶(Phosphoenolpyruvate carboxykinase, PEPCK, E.C.4.1.1.32)是水生生物糖异生代谢的关键限速酶. 实验以杂食性罗非鱼(Oreochromis niloticus)、温和肉食性卵形鲳鲹(Trachinotus ovatus)、凶猛肉食性军曹鱼(Rachycentron canadum)三种不同食性海水养殖鱼类为研究对象, 以糊精为饲料糖源, 分别设置不同饲料糖添加水平(低糖组LD、中糖组MD、高糖组HD)等氮等能饲料, 每种鱼分别随机选取60尾体格均匀的幼鱼进行为期8周的饲养实验, 同时克隆卵形鲳鲹胞质型PEPCK基因cDNA全长序列, 以期探讨不同饲料糖水平对不同食性鱼类PEPCK活性及其mRNA表达的影响. 结果显示: 卵形鲳鲹PEPCK基因cDNA共2652 bp, 含1个编码624个氨基酸的开放阅读框, 三种不同食性海水鱼类PEPCK的生物信息学比较分析显示相似度达90%以上, 在结构和功能上具有较高的保守和同源性. 养殖实验结果显示: 随着饲料糖水平的增加, 三种鱼肝脏中PEPCK酶活性均降低, 其中卵形鲳鲹、军曹鱼HD组PEPCK活性比LD组分别显著降低28.05%和26.03% (P0.05). 而其肝脏中PEPCK mRNA表达水平同样均随饲料碳水化合物水平增加而受到抑制, 其中罗非鱼、卵形鲳鲹、军曹鱼中LD组PEPCK的mRNA分别是HD组的100倍、4.3倍和4.77倍. 结果表明鱼类的糖异生能力可能与其食性有关, 三种鱼PEPCK酶活性与基因表达量随着饲料糖水平的增加而受到显著抑制, 且mRNA表达抑制程度随食性不同而具有较大差异, 以杂食性罗非鱼受抑制程度最高, 凶猛肉食性军曹鱼受抑制程度最低.       

Spatial and temporal pattern of introduced Bombus terrestris abundance in Hokkaido, Japan, and its potential impact on native bumblebees

A commercial colony of Bombus terrestris (L.) was introduced to Japan in 1992 for crop pollination in greenhouses. Since then wild colonies have developed and spread in some regions. In the present study, we measured the spatial distribution and temporal change in abundance of B. terrestris in the Chitose River Basin, Hokkaido, Japan to elucidate the relation of greenhouses to the bees distribution and to evaluate its potential effects on native bumblebees. Bumblebees were collected with window traps in windbreak forests roughly 1, 2, 4, and 6 km NNW and SSE of a large greenhouse. The peak catch of B. terrestris queens occurred in early June, suggesting that they had successfully hibernated in the field. The distributions of B. terrestris and the native B. ardens were mutually exclusive, while the native B. hypocrita appeared at all sites. Catches of B. terrestris were restricted to within 4 km of the nearest greenhouse, suggesting that the invasion was still in the initial phase in this area. The reduction in abundance of the native bumblebees in the sites of high B. terrestris abundance suggests the presence of interspecies competition between B. terrestris and the native bumblebees during the early part of the colony activity, although such reduction in B. ardens can be explained by habitat suitability.     

Growth and IGF-I response of juvenile Nile tilapia (Oreochromis niloticus) to changes in water temperature and dietary protein level

Water temperature and dietary protein level play an important role in influencing the growth and insulin-like growth factor I (IGF-I) in Nile tilapia juveniles. The combined effect of temperature (20–34 °C) and dietary protein level (25–50%) on the specific growth rate (SGR), feed efficiency (FE), serum IGF-I level and hepatic IGF-I mRNA level was examined under laboratory conditions by employing central composite design and response surface method. Results showed that the linear effects of temperature and dietary protein level on the SGR, FE, serum IGF-I and hepatic IGF-I mRNA level were significant (P<0.05); the quadratic effects of temperature and dietary protein level on the FE and serum IGF-I were significant (P<0.05). The interaction of temperature and dietary protein level on the FE, serum IGF-I and hepatic IGF-I mRNA level all proved significant (P<0.05). The optimal temperature/dietary protein level combination was determined, i.e., 29.9 °C/40.3%, at which the greatest SGR (2.748%/d) and FE (0.775) were simultaneously arrived. Both SGR and FE were linearly correlated with serum IGF-I or hepatic IGF-I mRNA level. These results suggested that optimum combination of temperature and dietary protein level would enhance tilapia growth efficiency and IGF-I would regulate growth and FE.     

Spatio-temporal variation in seed predation by a native weevil in the invasive Prunus serotina

Invasive species may escape the enemies from their native range (‘enemy release’), but they can also acquire new enemies in their introduced range, which will affect the invasion process. For the invasive tree species Prunus serotina, seed predation by the native weevil Furcipus rectirostris has been reported in forests in its introduced range. In this study, we quantified how common the infestation of P. serotina seeds by F. rectirostris is in a 4000 km² area in northern Belgium. Seeds were sampled on P. serotina trees in different habitats and in two years, i.e., with low and high P. serotina fruit production. Infestation was found throughout the study region, in 43 and 62% of the sampled trees in the two years of the study; the maximum infestation levels of infested seed samples were 50 and 69%. Overall, predation occurred in 4.4 and 10.8% of the sampled seeds. The level of infestation differed between habitats and years, and the number of fruits per raceme was inversely related to the infestation level. Notwithstanding the rather high incidence of F. rectirostris infestation in our study, the impact on P. serotina's invasiveness might remain low seeing the overall high seed production and dispersal capacity of the species.     

Effects of water temperature on growth and sex ratio of juvenile Nile tilapia Oreochromis niloticus (Linnaeus) reared in geothermal waters in southern Tunisia

Growth of juvenile Nile tilapia, Oreochromis niloticus (Maryut strain) was studied under laboratory conditions. Four thermal regimes (22, 26, 30, and 34 °C) were tested on 480 20-day-old fry.     

Selective crab predation on native and introduced bivalves in British Columbia

Experiments were conducted to determine whether locally abundant crab species prefer co-occurring littleneck clams, Protothaca staminea (Conrad, 1837) and Tapes philippinarum (A. Adams and Reeve, 1850), relative to a recently introduced species, the varnish clam, Nuttallia obscurata, (Reeve, 1857). Prey preference, handling time, pick-up success, profitability and consumption rates were investigated for two crab species, Dungeness crab, Cancer magister (Dana, 1852) and red rock crab, Cancer productus (Randall, 1839) crabs. Both crab species preferred varnish clams over the native species. This may be attributable to the lower handling time, higher pick-up success and increased profitability of consuming varnish clams. Handling time appeared to be a factor not only in species preference, but also in the degree of preference, with shorter handling times corresponding to stronger preference values. Both native and introduced bivalves burrow into the substratum, with the varnish clam burrowing deepest. When feeding on clams in limited substratum both crab species preferred the varnish clam. In the unlimited substratum trials Dungeness crabs preferred varnish clams (although to a lesser degree) while red rock crabs preferred littleneck clams. This was likely due to the significantly deeper burial of the varnish clam, making it less accessible. Although the morphology (i.e. thin shell, compressed shape) of the invader increases its vulnerability to predation, burial depth provides a predation refuge. These results demonstrate how interactions between native predators and the physical characteristics and behaviour of the invader can be instrumental in influencing the success of an invasive species.     

外来养殖鱼类的入侵风险评估及防控对策——以尼罗罗非鱼为例

[目的]筛选合适的指标建立一套外来养殖鱼类的生物入侵风险评估体系,并对外来养殖鱼类的生物入侵防控提出对策建议。[方法]通过文献资料的收集和整理,对外来养殖鱼类中典型入侵物种的入侵过程、影响危害和入侵生物学特性进行分析和归纳,从适应能力、繁殖能力、扩散能力3方面指示其入侵性;从对生物的影响和对环境的影响2方面指示其生态影响;从自然因素和人为因素2方面指示环境可入侵性,以上述3方面为框架进行评估体系构建。[结果]筛选20个指标构建了外来养殖鱼类的生物入侵风险评估体系,并举例说明该评估体系的应用。从法规政策、科学研究、治理技术和公众参与等4个方面针对性地提出外来养殖鱼类生物入侵风险防控对策。[结论]防范和治理入侵生物是一个系统工程。对于外来养殖鱼类的管理,既不能只考虑经济效益而置生态风险于不顾,也不能片面放大外来养殖良种的入侵风险。科学管控的关键在于完善制度建设、加强风险评估、发展防治手段、促进公众参与,使外来鱼类养殖业在严格受控的前提下发挥其经济效益,将其潜在的生态危害效应降到最低。     

Muscle growth in Nile tilapia (Oreochromis niloticus): histochemical,ultrastructural and morphometric study

Muscle growth in Nile tilapia (Oreochromis niloticus) was studied focusing on histochemical, ultrastructural, and morphometric characteristics of muscle fibers. Based on body length (cm), we studied four groups: G1=1.36+/-0.09, G2=3.38+/-0.44, G3=8.90+/-1.47, and G4=28.30+/-3.29 (mean+/-S.D.). All groups showed intense reaction to NADH-TR in subdermal fibers and weak or no reaction in deep layer fibers. In G3 and G4, an intermediate layer was also observed with fibers presenting weak reaction; in G4, groups of fibers with intense reaction were observed in the subdermal region. The myosin ATPase (m-ATPase) activities were acid-stable and alkali-labile in subdermal fibers; most deep layer fibers were alkali-stable and acid-labile. Intermediate fibers were acid-labile and alkali-stable. Two fiber populations were observed near deep muscle layer: one large presenting weak acid- and alkali-stable and the other small alkali-stable.During growth, muscle fiber hypertrophy was more evident in intermediate and white fibers for G3 and G4. However, in these groups, the presence of fiber diameters < or =21 microm suggested that there is still substantial fiber recruitment, confirmed by ultrastructural study, but hypertrophy is the main mechanism contributing to increase in muscular mass.     

Testosterone levels and gular pouch coloration in courting magnificent frigatebird (Fregata magnificens): variation with age-class, visited status and blood parasite infection

Male magnificent frigatebirds (Fregata magnificens) possess a seasonally expressed skin ornament, namely the red and inflatable gular pouch, and are, therefore, a convenient model for the study of some theories related to the evolution of possible testosterone-dependent sexual skin coloration. Here we report the findings of a study performed over four consecutive mating seasons in the Mexican national park Isla Isabel. We investigated differences in testosterone level and gular pouch coloration in courting males in relation to the categories: age-class, visited status and blood parasite infection. Gular pouch color saturation increased with age-class. Investigated frigatebirds were infected only with Haemoproteus iwa (Haemosporida, Haemoproteidae), with an overall prevalence infection of 15.5%. Prevalence of the infection increased with birds' age-class. Testosterone levels were significantly higher in infected males, who also had lighter colored gular pouches. In non-infected males, those visited by a female had higher testosterone levels than non-visited males. Gular pouch lightness and redness were negatively correlated but only redness in non-visited non-infected males was positively correlated with testosterone levels. Gular pouch saturation in visited and infected males was positively correlated with body mass, which also increased with age-class. Mated males had lower testosterone levels and lighter, less red and saturated gular pouch coloration than courting males. In summary, we found that coloration of the male skin ornament could reflect age-class (saturation), parasite infection (lightness) and mated status (all), together with indications of condition and testosterone dependency of ornament expression.     

Sperm quality analysis in XX, XY and YY males of the Nile tilapia (Oreochromis niloticus)

In Nile tilapia (Oreochromis niloticus), individuals with atypical sexual genotype are commonly used in farming (use of YY males to produce all-male offspring), but they also constitute major tools to study sex determinism mechanisms. In other species, sexual genotype and sex reversal procedures affect different aspects of biology, such as growth, behavior and reproductive success. The aim of this study was to assess the influence of sexual genotype on sperm quality in Nile tilapia. Milt characteristics were compared in XX (sex-reversed), XY and YY males in terms of gonadosomatic index, sperm count, sperm motility and duration of sperm motility. Sperm motility was measured by computer-assisted sperm analysis (CASA) quantifying several parameters: total motility, progressive motility, curvilinear velocity, straight line velocity, average path velocity and linearity. None of the sperm traits measured significantly differed between the three genotypes. Mean values of gonadosomatic index, sperm concentration and sperm motility duration of XX, XY and YY males, respectively ranged from 0.92 to 1.33%, from 1.69 to 2.22 ×10⁹ cells mL⁻¹ and from 18′04″ to 27′32″. Mean values of total motility and curvilinear velocity 1 min after sperm activation, respectively ranged from 53 to 58% and from 71 to 76 μm s⁻¹ for the three genotypes. After 3 min of activity, all the sperm motility and velocity parameters dropped by half and continued to slowly decrease thereafter. Seven min after activation, only 9 to 13% of spermatozoa were still progressive. Our results prove that neither sexual genotype nor hormonal sex reversal treatments affect sperm quality in male Nile tilapias with atypical sexual genotype.     

Isolation and Physical Mapping of Sex-Linked AFLP Markers in Nile Tilapia (Oreochromis niloticus L.)

Gynogenetically produced XX and YY Nile tilapia (Oreochromis niloticus) and diploid control groups were screened for amplified fragment length polymorphisms (AFLPs) to search for sex-linked or sex-specific markers. Family-level bulked segregant analysis (XX and YY gynogenetic family pools) and individual screening (XX and YY gynogenetics and XX and XY control individuals) identified 3 Y-linked (OniY425, OniY382, OniY227) and one X-linked (OniX420) AFLP markers. OniX420 and OniY425 were shown to be allelic. Single locus polymerase chain reaction assays were developed for these markers. Tight linkage was demonstrated between the AFLP markers and the sex locus within the source families. However, these markers failed to consistently identify sex in unrelated individuals, indicating recombination between the markers and the sex-determining loci. O. niloticus bacterial artificial chromosome clones, containing the AFLP markers, hybridized to the long arm of chromosome 1. This confirmed previous evidence, based on meiotic chromosome pairing and fluorescence in situ hybridization probes obtained through chromosome microdissection, that chromosome pair 1 is the sex chromosomes.     

Distribution,diversity and drivers of blood-borne parasite co-infections in Alaskan bird populations

Avian species are commonly infected by multiple parasites, however few studies have investigated the environmental determinants of the prevalence of co-infection over a large scale. Here we believe that we report the first, detailed ecological study of the prevalence, diversity and co-infections of four avian blood-borne parasite genera: Plasmodium spp., Haemoproteus spp., Leucocytozoon spp. and Trypanosoma spp. We collected blood samples from 47 resident and migratory bird species across a latitudinal gradient in Alaska. From the patterns observed at collection sites, random forest models were used to provide evidence of associations between bioclimatic conditions and the prevalence of parasite co-infection distribution. Molecular screening revealed a higher prevalence of haematozoa (53%) in Alaska than previously reported. Leucocytozoons had the highest diversity, prevalence and prevalence of co-infection. Leucocytozoon prevalence (35%) positively correlated with Trypanosoma prevalence (11%), negatively correlated with Haemoproteus prevalence (14%) and had no correlation with Plasmodium prevalence (7%). We found temperature, precipitation and tree cover to be the primary environmental drivers that show a relationship with the prevalence of co-infection. The results provide insight into the impacts of bioclimatic drivers on parasite ecology and intra-host interactions, and have implications for the study of infectious diseases in rapidly changing environments.     

盐度对新吉富罗非鱼受精卵孵化和仔稚鱼活力的影响

研究了盐度梯度对新吉富罗非鱼(Oreochromis niloticus)受精卵孵化和仔鱼活力的影响。水温(28±0.5)℃下,观察比较了8个梯度的盐度(3‰、6‰、9‰、12‰、15‰、18‰、21‰、24‰)及纯净淡水(盐度为0)条件下,新吉富罗非鱼受精卵的孵化时间、孵化周期、孵化率和畸形率。同时在不同盐度条件下对4批初孵仔鱼进行耐饥饿实验,测定其不投饵存活系数(SAI)值。结果表明,新吉富罗非鱼受精卵在盐度6‰～15‰时,孵化率较高(89.0%～92.7%);盐度低于3‰和高于18‰时,孵化率较低。仔鱼生存适宜盐度3‰～15‰,最适盐度6‰～9‰。新吉富罗非鱼仔鱼在盐度0～3‰及18‰～24‰时,仔鱼的SAI值较低,不适宜仔鱼培育;盐度为6‰～15‰时,仔鱼的活力较高。仔鱼的SAI值与受精卵的孵化率呈正相关关系。