Compensatory growth, feed utilization and activity in gibel carp, following feed deprivation

Following a period of food deprivation, gibel carp compensated for growth through increased feed intake and conversion efficiency, but increased conversion efficiency was not achieved by increasing digestibility or reducing activity.     

基于微卫星标记的5个尼罗罗非鱼品系的遗传多样性分析

为了对生产上应用的5个尼罗罗非鱼(Oreochromis niloticus)品系的遗传背景进行本底调查,以期为育种工作提供基础数据, 本文用19对微卫星引物对5个尼罗罗非鱼品系(苏丹品系、台湾品系、吉富品系、超雄品系Ⅰ和超雄品系Ⅱ)进行了遗传多样性分析,计算并统计了等位基因数、多态信息含量( PIC)、杂合度、遗传相似性系数、遗传距离等参数。结果表明19个微卫星位点在5个罗非鱼品系中共检测到113个等位基因,平均期望杂合度在0.578–0.692之间,平均多态信息含量在0.473–0.628之间。5个尼罗罗非鱼品系有较丰富的遗传多样性,而超雄品系Ⅰ的遗传多样性相对较为贫乏。     

Subordination stress in Nile tilapia and its effect on plasma lysozyme activity

Dominant Nile tilapia had significantly higher lysozyme activity than did subordinate fishes (α=0·05). Plasma lysozyme level was not correlated with sex, parental origin, rearing length, weight, condition factor or rearing density.     

Physiological responses in Nile tilapia exposed to different photoperiod regimes

After conditioning Nile tilapia Oreochromis niloticus for 2 weeks, the photoperiod regime of 12 tanks of fish was changed to a 6L : 6D photoperiod while 12 further tanks were retained on the conditioning photoperiod regime (12L : 12D). Blood samples were collected 3 days (first sampling) and 3 months (second sampling) after changing the photoperiod regime. Blood was collected at 6 h intervals from both photoperiod regimes (1000, 1600, 2200 and 0400 hours). At the first sampling time, fish in the 6L : 6D had significantly higher cortisol both in the light and dark phases than levels in fish in the 12L : 12D photoperiod. At the second sampling time, the levels were significantly higher only in the light phase. The levels of cortisol, glucose and Cl⁻ in fish exposed to the 6L : 6D photoperiod, however, were far lower than those of acute stress‐induced levels observed in fish exposed to a stress experiment. Furthermore, there were no significant differences in overall values of all the variables between the photoperiod regimes at the second sampling time. This indicated that the fish exposed to the 6L : 6D photoperiod were not chronically stressed. Significantly higher blood lymphocyte counts were observed in fish exposed to the 6L : 6D compared to those of the 12L : 12D photoperiod during the light phase at the second sampling time. Other variables (glucose, Cl⁻, haematocrit and neutrophil) did not show a significant difference between the treatments at either sampling time. These results demonstrated that the artificial photoperiod regime did not cause a significant acute or chronic stress response in Nile tilapia.     

Acute aerocystitis in Nile tilapia bred in net cages and supplemented with chromium carbochelate and Saccharomyces cerevisiae

Oreochromis niloticus bred in net cages were supplemented with cell wall of Saccharomyces cerevisiae (Sc) (0.3%) or chromium carbochelate (Cr) (18 mg/kg of feed) or in association (Sc + Cr), for 90 days. After this period, acute inflammation was induced in the swim bladder by inoculation of 3 × 10⁸ CFU of inactivated Streptococcus agalactiae, and another group received 0.65% saline solution (control). Twelve, 24, and 48 h after stimulation, the inflammation was evaluated through total and differential counting of accumulated cells, and through leukocyte respiratory burst in the blood, cortisolemia, glycemia and serum lysozyme concentration. The results showed that there were greater total numbers of cells in the exudate of fish inoculated with inactivated bacterium than in those injected with saline solution, with predominance of lymphocytes, thrombocytes, macrophages and granulocytes. Tilapia supplemented with Cr presented increased total numbers of cells with significant accumulation of lymphocytes and reductions in cortisolemia and glycemia, but the different treatments did not have any influence on leukocyte respiratory burst or serum lysozyme concentration. Tilapia supplemented with Sc and the Cr + Sc association did not present significant changes to the variables evaluated, despite higher accumulation of lymphocytes in the inflammatory exudate from fish treated with Sc. The results indicate that tilapia bred in net cages and supplemented with Cr presented higher total accumulation of cells at the inflammatory focus, thus indicating an increase in the inflammatory response induced by the bacterium, probably due to the reduction in cortisolemia and higher glucose consumption. Thus, supplementation with Cr had beneficial action, which facilitated development of acute inflammation induced by the bacterium, but did not affect neither leukocyte respiratory burst in the blood nor serum lysozyme concentration.     

Mitochondrial DNA differentiation among East and West African Nile tilapia populations

Variation of the ND5/6 mtDNA fragment was studied in six Nile tilapia populations using PCR and RFLP analysis. The observed variation allows a strict discrimination between eastern and western African populations.     

The effects of tryptophan supplementation on stress and aggression in Nile tilapia

Nile tilapia farmers must deal with production challenges, such as increased aggressiveness and high stress levels, which potentially diminishes fish welfare. Tryptophan supplementation is a strategy to cope with such problems. However, data is scarce on how tryptophan affects the aggressiveness of this species and other aspects need to be understood on how it influences stress in fish. In this study, we investigate how a 1× (0.32%), 4× (1.28%) and 8× (2.56%) supplemented tryptophan diet affects aggressiveness and stress in Nile tilapia. Aggressiveness in fish was assessed after short-term exposure (7 days) to a tryptophan supplemented diet while stress in fish was assessed after long-term exposure (60 days). The 4x and 8x diets reduced aggressiveness in fish, while the 8x diet reduced aggressiveness more effectively than the 4x diet. Also, long-term exposure to the 8x diet reduced stress in fish, before and after they were exposed to an acute stress. In conclusion, this study showed that a tryptophan supplemented diet can diminish aggressiveness and stress in Nile tilapia, thus demonstrating a potential to improve fish welfare.     

一种新的异育银鲫病原———腐败希瓦氏菌

【目的】江苏盐城一家养殖场的异育银鲫暴发疾病,通过对病原进行研究,旨在为该病的防治提供理论依据和参考。【方法】从病鱼体表病灶和内脏中分离出优势菌株,经人工感染试验证实为病原菌。采用传统的形态、生理生化表型鉴定与16S rDNA序列分析相结合的方法确定菌株的分类地位。运用K-B琼脂法对病原菌株进行药物敏感性测定。【结果】综合菌株形态、生理生化表型以及16S rDNA序列分析的结果,确定该分离株为腐败希瓦氏菌(Shewanella putrefaciens)。回接感染试验证实腐败希瓦氏菌即是导致此次异育银鲫发病死亡的致病原,其半数致死量(LD50)为2.1×103cfu/g。该株腐败希瓦氏菌对吡哌酸、萘啶酸、氟哌酸、氟啶酸、氟苯尼考、利福平、美满霉素、氟罗沙星、恩诺沙星、复达欣、菌必治、先锋Ⅳ、罗红霉素和左氟沙星等抗生素敏感。【结论】首次报道了异育银鲫一种新的病原,说明腐败希瓦氏菌作为一种潜在的新病原也可能会对异育银鲫的养殖造成威胁。     

Metabolic and molecular responses in Nile tilapia,Oreochromis niloticus during short and prolonged hypoxia

The strictly aquatic breathing Nile tilapia, Oreochromis niloticus is an extremely hypoxia-tolerant fish. To augment our understanding of the effects of hypoxia on anaerobic glycolysis in the Nile tilapia, we studied the effect of short-term for 1 day (trial 1) and long-term for 30 days (trial 2) hypoxia on a selected glycolytic enzymes activity and mRNA expression in liver and white muscle. The hypoxic oxygen concentrations used in the two trials were 2, 1, and 0.5 mg O₂ L^?1 for comparison with a control normoxic group 8 mg O₂ L^?1. The activity of phosphofructokinase (PFK), pyruvate kinase (PK), and lactate dehydrogenase (LDH) in liver and white muscle except liver LDH decreased in trial 1 and increased in trial 2. Assessments of mRNA levels in trial 1 revealed that PFK was downregulated and LDH was upregulated in liver and white muscle, while PK fluctuated between upregulation in liver and downregulation in white muscle. Meanwhile, PK and LDH were upregulated while PFK was similar to control values in both tissues in trial 2. Comet assay results demonstrated an increase in DNA damage that was directly proportional to increasing hypoxic concentrations. This damage was more pronounced in trial 1. This suggests that the Nile tilapia cope better with long-term hypoxic conditions, possibly as an adaptive response.     

Social facilitation of learning in mixed-species schools of common carp Cyprinus carpio L. and Nile tilapia Oreochromis niloticus (L.)

The process of learning to associate a visual cue with food was studied in groups of common carp Cyprinus carpio and Nile tilapia Oreochromis niloticus by means of a classical conditioning paradigm. In the first phase of the study, fishes were conditioned in either single-species or mixed-species groups to associate a blinking blue light with food. In the second phase, group composition was altered so that only single species were reconditioned, composed of individuals previously paired with the same or the other species. In the first phase, in the single-species groups, Nile tilapia rapidly formed an association between the visual cue and food, whereas common carp failed to do so. In mixed-species groups, both Nile tilapia and common carp associated a visual cue with food. In the second phase of the study, Nile tilapia retained that ability irrespective of whether they had previously been trained in single-species or mixed-species groups, common carp previously trained with Nile tilapia, were not repelled by the blinking blue light and gradually approached it from a distance, whereas common carp previously trained in homogenous groups continued to be repelled by the blinking light. Fish arrivals and departures from the feeding zones as well as fish position in the testing apparatus were analysed and contrasted in single-species and mixed-species groups outside the training sessions, revealing mutual impacts of one species on the other in mixed-species groups. The findings of this study demonstrated interspecific social facilitation of learning to associate a visual cue with food.     

Molecular characterization and immunohistochemical localization of tilapia piscidin 3 in response to Aeromonas hydrophila infection in Nile tilapia

The antimicrobial activity of tilapia piscidin 3 (TP3) was determined in vitro against a locally isolated Aeromonas hydrophila. A 388 bp fragment was amplified from the TP3 cDNA and sequenced. The coding sequence (CDS) of TP3 was estimated to be 231 bp codes for 76 amino acids long and stop codon. In silico analysis was performed to detect both the signal peptide and the prodomain cleavage sites to follow the amino acids number 22 and 70, respectively. Based on this, a peptide 23 amino acids long with a remarkably high computed antimicrobial probability was synthesized and used in the subsequent experiments. The antimicrobial activity of TP3 was determined with minimum inhibitory concentration (MIC) and minim um bactericidal concentration (MBC) methods. TP3 exhibited relatively weak antimicrobial activities against the tested bacteria. A challenge experiment was then performed in Nile tilapia with low and high doses of A. hydrophila, followed by timely recognition; after 3, 6, 24 h, and 7 days of the specific TP3 gene expression, immunohistochemical localization was also performed. Histopathological examination revealed provoked inflammatory responses and congestion in the same organs of TP3 expression. Immunohistochemical localization showed that A. hydrophila induced tilapia fish to express TP3 after 24 h within the gills, intestine, hepatopancreas, spleen, and posterior kidney. In quantitative real time (RT)‐polymerase chain reaction analysis, the high dose showed higher mRNA expression levels than the low dose, and its expression levels increased in the A. hydrophila‐infected fish. It was therefore concluded that TP3 plays an essential role in fish immunity.     

Structure and enzymatic removal of the chorion of embryos of the Nile tilapia

Dechorionation or partial digestion of the egg chorion is necessary for introducing embryonic stem cells into blastulas for chimera production and for harvesting blastulas. Several methods to digest the Nile tilapia Oreochromis niloticus chorion were tried and it was found that the chorions of most clutches of eggs were digested in <3 h using hatching medium [produced by allowing embryos to hatch in Hanks balanced salt solution (HBSS) in an incubator], or 2 mg ml⁻¹ pronase P6911 in 10% Ca/Mg free HBSS. The chorion of Nile tilapia possesses multiple lamellae as found in most teleost species that have been studied. It was found to be thinner than that of medaka Oryzias latipes and thicker than that of zebrafish Danio rerio . During natural hatching the chorion was digested from the inner surface, and tail movements helped to break the remaining chorion; however, chorion digestion has to be complete for experimental dechorionation, because digestion starts at the external surface. The zona radiata externa remained intact after experimental digestion with hatching media but was disrupted by pronase. Embryos dechorionated at the cleavage or blastula stage only survived for 2 or 3 days, but some dechorionated at the gastrula stage or early segmentation stage developed until the natural hatching time. If the chorion was partially digested at the cleavage or blastula stage, some embryos survived to hatch.     

Effects of different food restrictions on somatic and otolith growth in Nile tilapia reared under controlled conditions

.Nile tilapia Oreochromis niloticus , initial age 12 days, were given an unrestricted (NR) or restricted (R) ration over 93 days which resulted in fish of very different sizes although the body condition factor ( K ) and the viscero-somatic index ( I _V) remained almost unchanged. In a second stage (64 days) each group (NR & R) was divided into three subgroups that were subjected to 0 (NR0, R0), 15 (NR15, R15) and 30 (NR30, R30) days of food restriction, respectively. The impact of the different treatments on the somatic growth during the second stage of the experiment had an effect, with a highly significant difference between the mean ± S.D. masses ( M _T) in the different subgroups (NR0= 115.0 ± 26.6 g; NR15 = 94.8 ± 24.9 g; NR30 = 56.3 ± 28 g; R0 = 76.4 ± 20.1 g; R15 = 72.l ± 17.6 g; R30 = 43.6 ± 17.2 g). Similarly, K and I _V decreased. Irrespective of the initial feeding condition, the width of the otolith microincrements started to decrease at the end of the first or second day of restricted feeding. In the subgroups given a restricted food ration for 30 days (NR30 and R30), this decrease reached a plateau at about day 30, which was maintained even when the restriction had ended. This slowed growth did not lead to any marked halt in microincrement formation, since there were no significant differences (ANOVA; P >0.05) in the numbers of increments counted in the various subgroups. The results show that in 153 day old fish, a period of severe food restriction, even if prolonged (15 to 30 days), had no influence on the timing of the laying down of microincrements but only affected their growth.     

Effects of the pyriproxyfen and fenthion on the gonadal morphology of Nile tilapia (Oreochromis niloticus: Perciformes,Cichlidae)

Commercially available insecticides present acute toxicity to the health of fish and other aquatic organisms, which may impair the local aquaculture. This study evaluated the gonadal morphology of freshwater fish exposed to pyriproxyfen and fenthion. Forty-five juvenile male Nile tilapias (Oreochromis niloticus) were divided into control, pyriproxyfen-exposed (0.01 g/L), and fenthion-exposed (0.001 g/L) groups. They were evaluated in three moments (30, 60, and 90 days). The variables analyzed were the gonadosomatic index (GSI), weight to length ratio, seminiferous tubules morphometry (diameter and height), tissue damage, and immunohistochemical analysis for caspase-3, tumor necrosis factor alpha (TNF-α), and vascular endothelial growth factor (VEGF). Pyriproxyfen and fenthion injured the seminiferous tubule tissue, and the damage progressed according to the exposure time. In addition, the GSI gradually reduced over time in all groups compared with the first moment (30 days), while caspase-3, TNF-α, and VEGF values increased only in the fenthion-exposed group. Therefore, pyriproxyfen and fenthion changed the gonadal morphology of male Oreochromis niloticus, which may affect their reproduction in the wild or captivity.     

Cyto-histopathological and protein polymorphism alterations in five populations of Nile tilapia (Oreochromis niloticus) as biomonitor for water heavy metal pollution

Cytological, histopathological and sodium dodecyl sulphate polyacrylamide gel analyses were carried out on five populations of common Nile tilapia fish (Oreochromis niloticus) occurring in five sites – River Nile (reference site), Bahr Yusef canal, Ibrahimia canal, Irrigation drain and El Moheet drain of El Minia Province, Egypt – to evaluate the usability of Nile tilapia as a biomonitor for water heavy metal contaminants. Water surface samples were collected from the five sites, and lead (Pb) concentration was shown to surpass the limits defined by WHO. Ni and Cd levels were shown to be elevated in Ibrahimia canal samples. Moreover, the concentration of heavy metals in fish muscles collected from Bahr Yusef canal and El Moheet drain was the highest in comparison with those of the other water sites. Cytological examinations of blood smears showed not only a significant percentage of micronuclei in Irrigation drain population but also a significant percentage of binucleated cells in Ibrahimia canal and El Moheet drain populations. In addition, pathological alteration was observed in blood cells, especially in samples collected from Irrigation drain and El Moheet drain. Histopathological changes were strongly observed in the liver and the kidneys of El Moheet and Irrigation drain population. Moreover, total protein band pattern profiles showed extra bands in both Ibrahimia canal and Irrigation drain more than that recorded for the River Nile population. In conclusion, cyto-histopathological and total protein band pattern results confirmed that O. niloticus responds sensitively to the excess of heavy metals present in the water.     

Treatment with an aromatase inhibitor suppresses high-temperature feminization of genetic male (YY) Nile tilapia

High temperature (36° C) treatment during sexual differentiation caused significant changes in sex ratio in YY male Nile tilapia Oreochromis niloticus fry (64.5% males compared to 100.0% males at 28° C), while dietary treatment with a chemical aromatase inhibitor (AI: Fadrozole™ CGS16949A) during this period suppressed the high temperature feminization (98.9% males). This implies that cytochrome P450 aromatase is mechanistically associated with temperature-dependent sex determination (TSD) in this species. XY male fry did not show significant sex reversal at 36° C. In XX female fry, high temperature treatment resulted in significant masculinization (62.5% males compared with 21.9% males at 28° C), while treatment with AI at either temperature resulted in very high proportions of males (100.0% males at 36° C; 99.0% males at 28° C). These results confirm the importance of aromatase in sexual differentiation in the Nile tilapia below the TSD threshold and suggest that it also plays a role in TSD, at least in the YY genotype.     

Bone development in the jaw of Nile tilapia Oreochromis niloticus (Pisces: Cichlidae)

East African cichlids have evolved feeding apparatus morphologies adapted to their diverse feeding behaviors. The evolution of the oral jaw morphologies is accomplished by the diversity of bone formation during development. To further understand this evolutionary process, we examined the skeletal elements of the jaw and their temporal and sequential emergence, categorized by developmental stages, using the Nile tilapia Oreochromis niloticus as a model cichlid. We found that chondrogenesis started in Stage 17. The deposition of osteoid for the dermal bones commenced in Stage 18. The uptake of calcium dramatically shifted from the surface of larvae to the gills in Stage 20. The bone mineralization of the skeleton began in Stage 25. These data provide important information regarding the sequential events of craniofacial development in East African cichlids and lay the groundwork for studying the molecular mechanisms underlying adaptation of jaw structure to feeding behavior.     

粪便收集时间和饲料中肉骨粉含量对异育银鲫(Carassius auratus gibelio) 消化率的影响

本研究探讨了通过收集器不同粪便收集时间和饲料中肉骨粉(MBM)含量对异育银鲫干物质、蛋白、能量、磷的表观消化率 (ADC) 影响.不同梯度(0, 20, 40, 60, 80 ,100%)的肉骨粉替代鱼粉(FM) 蛋白配制成六种等氮 (粗蛋白: 410 g/kg) 等能 (总能: 18 kJ/g) 的饲料,通过11周的饲养实验,实验开始后2周开始收集粪便,收集时间分别是:排粪后 1 min, 投喂后4h和16h. 结果表明,干物质、蛋白、能量、磷的消化率明显随粪便收集时间增加而升高(p<0.05),但在高肉骨粉替代饲料中差异不显著(p>0.05). 干物质、蛋白、能量、磷的消化率随饲料中肉骨粉含量的增加呈线性或近线性下降.因此,在消化率测定中应该尽快收集排出的粪便以保证消化率的真实性.消化率是影响肉骨粉利用一个因素.     

银鲫肌酸激酶M3-CK cDNA的克隆及其表达特征

用抑制性差减杂交结合SMART cDNA合成和RACE—PCR技术克隆到雌核发育银鲫(Carassius auratus gibelio)肌酸激酶M3-CK基因的全长cDNA。银鲫M3-CK cDNA全长1551bp，编码380个氨基酸，与普通鲤鱼(cyprinus carpio)M3-CK的氨基酸序列同源性高达95％。种系分析表明，银鲫M3-CK与其它脊椎动物的肌肉型肌酸激酶聚为较近的一支，与鲤鱼的M3-CK聚在一起，与脑特异型肌酸激酶及线粒体型肌酸激酶分歧较大。虚拟Northern杂交显示银鲫M3-CK基因在胚胎发育中差异表达。RT—PCR表明，银鲫M3-CK基因在成熟卵母细胞和胚胎发育早期可检测到少量的转录产物，在胚胎发育期间从肌肉效应期开始转录，并一直持续表达。组织RT—PCR表明，银鲫M3-CK基因只在心脏和肌肉表达。     

Homogeneously sized groups increase aggressive interaction and affect social stress in Thai strain Nile tilapia (Oreochromis niloticus)

Social fish raised in farms are usually kept in groups of similar-sized individuals. However, social animals of similar size typically have similar fighting ability, which increases aggressive interaction for social rank establishment, as well as social stress. We compared Thai strain Nile tilapia fish, Oreochromis niloticus (L.), held under two treatments: (1) The Homogeneous one, with five adult male fish of similar size and (2) the Heterogeneous treatment with five adult males of different sizes. We recorded the frequency of aggressive interactions and checked social stability and stress levels (cortisol) after five days in the groups. Grouping similar sized Thai Nile tilapia increased the aggressive interactions and delayed rank stability with increased body injuries as a consequence. Homogeneous-sized individuals showed a similar level of stress while heterogeneous-sized individuals showed different stress levels with dominants being more stressed than subordinates. The data indicate that the practice of selecting fish of similar size in aquaculture management could reduce the welfare of social fish and that the effect is observed in different lineages.