黄颡鱼仔鱼食性研究

以人工孵化的黄颡鱼仔鱼为材料,对孵化20天的仔鱼的食性和生长进行了研究,实验结果表明:黄颡鱼仔鱼2日龄开始开口摄食,5日龄全部开口摄食,混合营养期1-4天,仔鱼的开口饵料以轮虫,枝角类为主,体长8-22毫米的仔鱼由轮虫,枝角类等浮游生物为主转变为寡毛类、摇蚊幼虫、水蚯蚓等底栖生物为主,仔鱼昼夜摄食率变化明显。仔鱼随着体长的增长肠胃饱满指数也逐渐增加。仔鱼的体长生长前期较快,后期减慢。     

池养线纹尖塘鳢仔、稚、幼鱼的食性与生长

对池养仔、稚、幼鱼的摄食与生长作了较深入研究.仔鱼的混合营养期短,仅2～3 d,并处在开食期内,开口摄食率低.5日龄仔鱼全长4.31 mm,开口饵料主要为100～150 μm轮虫:稚鱼饵料为350～800 μm裸腹溞、枝角类幼体和桡足类无节幼体,并逐渐转为枝角类为主:后期稚鱼可驯化摄食人工混合饲料.仔、稚、幼鱼具明显的昼夜摄食节率,属晚间摄食为主的昏晨摄食型鱼类.体长与日龄呈直线关系,体重与日龄呈指数函数关系,体长与体重呈幂函数关系,其曲线回归方程为W=0.0112L3.1827,b=3.1827,接近于3,属等速生长型.     

黄颡鱼仔鱼摄食习性研究

在６０ｍ＾３水泥试验池,对人工催产孵化的黄颡鱼仔鱼的摄食习性进行了研究。仔鱼孵出４ｄ后,即开口摄食外界食物,开口饵料为轮虫,小型枝角类及桡足类幼体。随着鱼体的生长,摄食种类逐渐增加,摄食强度及摄食习性有一定的规律。     

南方大口鲶仔鱼的生长和摄食

本文研究了南方大口鲶仔鱼的生长和摄食。研究结果表明,南方大口鲶仔鱼在0—15日龄内,全长与日龄之间里线性相关,L=4．5849＋1．7892T（r=0．9912）,体重与日龄呈幂函数相关W=3．2664de0.3221T（r2=0．9783）。个体之间的生长差异较为明显,变异系数由0日龄的5．59升至15日龄的9.95,日增重率随日龄的增长呈双峰抛物线下降曲线,8—13日龄仔鱼对鲤鱼水花和水丝蚓的摄食系数分别为4．76和4．02,对鲤鱼的摄食强度明显大于水丝蚓。通过对南方大口鲶仔鱼生物学习性观察,发现其仔鱼具有明显的负趋光性和昼夜摄食节律,对饵料生物的选择依消化器官和游泳器官的发育程度依次为轮虫、桡足类幼体──枝角类、桡足类──水丝蚓或家鱼水花。     

南方大口鲶仔鱼的生长和摄食的初步研究

本文研究了南方大口鲶仔鱼的生长和摄食。研究结果表明,南方大口鲶仔鱼在0～15日龄内,全长与日龄之间呈线性相关,L=4．5849＋1．7892T（r=0．9942）,体重与日龄呈幂函数相关W=3．2664e0．3221T（r2=0．9783）。个体之间的生长差异较为明显,变异系数由0日龄的5．59升至15日龄的9．95,目增量率随日龄的增长呈双峰抛物线下降曲线,8～13日龄仔全对鲤鱼水花和水丝蚓的援食系数分别为4．76和4．02,对鲤鱼的摄食强度较高。通过对南方大口鲶生物学习性观察,发现其仔鱼具有明显的负趋光性和昼夜摄食节律,对饵料生物的选择依消化器官和游泳器官的发育程度依次为轮虫、桡足类幼体──枝角类、桡足类──水丝蚓和家鱼水花。     

鲇仔鱼开口饵料的研究

取脱膜 4d的鲇仔鱼进行开口试验 ,分别喂以轮虫、枝角类、蛋黄、豆浆等饵料 ,结果发现 ,鲇仔鱼开口时口裂宽为 0 90～ 1 0 0mm ,开口摄食枝角类的机会最多。分组喂养 10d的结果显示 ,使用枝角类喂养的鲇仔鱼 ,其生长速度、养殖成活率均高于其他饵料组。     

云南光唇鱼开口饵料的研究

采用赤虫、轮虫+藻类、枝角类、蛋黄和人工配合饲料投喂云南光唇鱼仔鱼21d,研究其对云南光唇鱼仔鱼生长和成活率的影响,结果显示:轮虫+藻类、枝角类两组的成活率分别为91.33%、88.67%,显著高于其他三组;轮虫+藻类组生长速度最快,体长为12.32 mm,体质量为7.2 mg,其次为枝角类组,体长为12.15 mm,体质量为6.8 mg,优于其他组。结果表明轮虫+藻类是云南光唇鱼仔鱼的最适开口饵料。     

延迟投饵对瓦氏黄颡鱼仔鱼存活、摄食和生长的影响

以瓦氏黄颡鱼仔鱼为研究对象，将其分为15个处理组，每组200尾（各设3个平行组），分别在孵化后3、4、5、6、7．8、9、10、11、12、13、14、15和16d开始投喂大型涵，第15组为饥饿组，从不投饵。水温24．5～25．5℃，实验周期为30d。结果表明：（1）孵化后3d的瓦氏黄颡鱼仔鱼初次摄食，15日龄不能建立外源性营养的仔鱼进入PNR期，卵黄囊已耗尽。混合营养期持续4．12h。（2）瓦氏黄颡鱼仔鱼在不同饥饿阶段初次摄食率的变化为：开始较低，此后迅速上升，在4～10日龄达到高峰，最高初次摄食率为100％，此后逐步下降。（3）延迟5天投饵对瓦氏黄颡鱼仔鱼的存活率影响不显著，延迟6d投饵瓦氏黄颡鱼仔鱼的存活率随延迟投饵天数的增加而降低。延迟6d投饵，瓦氏黄颡鱼仔鱼的体长增长率随延迟投饵天数的增加而降低。     

涨渡湖黄颡鱼生长及资源利用

对涨渡湖黄颡鱼的形态特征、年龄与生长等进行了研究,得出年龄范围在1～4龄,其中以2～3龄为主,体长与体重的关系式为W=0.03L2.7996,为涨渡湖进一步利用和增养殖黄颡鱼提供了理论依据。     

黄颡鱼耳石初步研究

研究了黄颡鱼耳石的形态结构，并统计了黄颡鱼体长与耳石大半径的关系，两者回归方程为L=5．9249 6．8353R，复相关系数r=0．91。黄颡鱼体长和体重相关公式为W=0．0022L^3.4274。同时退算出黄颡鱼1龄、2龄和3龄时的平均体长分别为17、24．5、29．9cm，均比对应的实际体长小，符合李氏现象。     

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.     

Growth hormone (GH) and reproduction: a review

Interaction between growth and reproduction occurs in many vertebrates and is particularly obvious at certain stages of the life cycle in fish. Endocrine interactions between the gonadotropic axis and the somatotropic axis are described, the potential role of GH being emphasised. A comparative analysis of these phenomena in mammals, amphibians and fish, suggests a specific role of GH in the physiology of puberty, gametogenesis and fertility. It also shows the original contribution made by studies on the fish model in this field of investigations.     

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).     

Evaluation of a Fast Method Based on the Presence of Two Restriction Sites in the Mitochondrial ND5 (mt ND5) Gene for the Identification of Scomber Species

The purpose of this work was to evaluate the suitability of a method based on the presence of two restriction sites (for Hae III and Hindf I) in the mitochondrial NADH dehydrogenase subunit 5 (mt ND5) gene to identify Scomber species. The evaluation was performed on 144 reference and market samples by sequencing of the entire 505-bp fragment of the mt ND5 gene and of a 464-bp fragment of the Kocher fragment of the cytochrome b gene (mt Cytb). Sequence analysis of any of the two fragments allows the identification of each of the four Scomber species, but S. japonicus and S. colias had the same restriction sites at the ND5 amplicon and would not have been differentiated by this analysis. Similarly, loss of the Hae III site in some S. scombrus individuals would have misidentified them as not being Scomber. All the market products were correctly labeled except one acquired in Spain labeled as originating in the Atlantic and containing S. japonicus.     

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.     

Nitrogenous waste excretion and accumulation of urea and ammonia inChalcalburnus tarichi (Cyprinidae), endemic to the extremely alkaline Lake Van (Eastern Turkey)

The endemic, anadromous cyprinidChalcalburnus tarichi is the only fish species known to occur in alkaline Lake Van (Eastern Anatolia, Turkey). EightC. tarichi were maintained individually in Lake Van water (17 – 19°C; pH 9.8; 153 mEq·I^–1 total alkalinity; 22 total salinity) and tank water samples analyzed for 24 h in 2 to 4 h intervals. At zero time, < 1µM ammonia was present and urea was undetectable in the tank water; at 24 h, total ammonia and urea made up 114±32 and 35±25µM, respectively. Over the experimental period, ammonia-N and urea-N excretion averaged 1041±494 and 607±169moles·kg^–1 fish·h^–1, respectively. The extent of urea excretion was highly variable between specimens. Uric acid excretion was not detectable.Urea was present at high concentrations in all tissues and plasma (25 – 35moles·g^–1·ml^–1) of freshly caughtC. tarichi; total ammonia content of the tissues was by a factor of 1.9 (liver) to 3.0 (brain) lower. High arginase activity (2.4±0.2 U·min^–1·g^–1) was detected in the liver ofC. tarichi but ornithine carbamoylphosphate transferase, a key enzyme of the ornithine-urea-cycle, was absent. Ureagenesis is likely through degradation of arginine and/or uricolysis. High glutamine synthetase activity (11±0.6 U·min^–1·g^–1) and low ammonia content in brain suggest that, like other teleosts,C. tarichi has an efficient ammonia detoxification in the brain, but in no other tissue.Nitrogenous waste excretion at alkaline pH is discussed. The ability ofC. tarichi to excrete high levels of ammonia at extremely alkaline pH is unique among teleosts studied so far. The mechanism of ammonia excretion under Lake Van conditions remains to be elucidated.