Experimental evaluation of mass selection to improve red body colour in Fijian hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus)

Mass selection was trialed on Fijian hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus) to reduce the amount of black spots on otherwise red phenotypes. The responses of two selection intensities (low‐selection line, top 50% – L) and (high‐selection line, top 30% – H) were compared with that of a control line (no selection – C) across three generations. The relative growth performance of treatments (C, L and H) was examined in parallel in each generation to assess whether mass selection had a correlated negative effect on growth performance. The results show clearly that red phenotype can be improved significantly by applying mass selection, without affecting growth performance. We propose that black spots on an otherwise red phenotype could represent the allelic products of a second genetic locus influencing skin colour, which can be expressed in red individuals (genotype Rr) but which may be masked in black individuals (genotype rr).     

Nutrient composition and sensory evaluation of fillets from wild-type Nile tilapia (Oreochromis niloticus, Linnaeus) and a red hybrid (Florida red tilapia × red O. niloticus)

A comparison of composition and sensory evaluation were performed on fillets of Oreochromis niloticus (wild type) and red hybrid tilapia (RHT) (Florida red tilapia ♂× red O. niloticus♀). Fifty male tilapia, 25 O. niloticus (initial weight 159.3 g) and 25 red hybrid (initial weight 132.4 g), were placed in each of three 2.0 m³ volume tanks. The fish were fed a commercial feed containing 35.9% crude protein during the 120‐day experimental period and then killed in cold water (3°C). All the fish were filleted. Twelve fillets from each treatment were used for proximate analyses, five fillets from each treatment were used for fatty acids analyses and the remaining fillets were used for sensory evaluation. The compositional analyses showed similar moisture, true protein and ash content in both genetic groups, but a lower crude fat content was measured in the red hybrid fillets (0.70%) compared with that of O. niloticus fillets (0.97%). No differences between O. niloticus and the red hybrid were observed in their fillet profile of fatty acids. In the sensory evaluation test, a difference in fillet flavour between both genetic groups was perceived. Of the 112 consumers in the preference test, 81.2% perceived a difference in fillet flavour between the two tilapias, with a general preference for the red hybrid over the wild‐type O. niloticus. The benefits of cultivating a RHT with a low lipid content are discussed.     

盐酸土霉素在奥尼罗非鱼体内的药代动力学及残留研究

在水温(25±2)℃条件下,以15 mg/kg鱼体重的剂量给奥尼罗非鱼单次口灌盐酸土霉素,采用高效液相色谱法测定血浆和肌肉组织中的药物浓度,研究盐酸土霉素在奥尼罗非鱼体内的代谢及消除规律。结果显示:血药时间数据符合一级吸收二室开放模型,半衰期(T1/2Ka、T1/2α、T1/2β)分别为4.79、4.10、45.20 h,最大血药浓度为1.50μg/m L,达峰时间为7.30 h,药时曲线下面积(AUC)为42.35μg·h/m L。肌肉作为可食性组织,选取肌肉组织作为残留检测的靶组织,以0.1 mg/kg为最高残留限量,在本试验条件下,建议休药期不低于10 d。     

Mass selection for red colour in Oreochromis niloticus (Linnaeus 1758)

Mass selection in Oreochromis niloticus, Stirling strain, was used to obtain a red colour homozygous dominant population from a base population containing wild type and red fish with black blotches. Each selection generation included 28–80 breeders in a 1:1 male:female ratio and a density of 1 pair m^?2.First selection for red colour was done when fry reached 3 g, discarding those exhibiting wild type colouring or with a high black blotch incidence. Second selection was done before fish began the reproduction stage. To determine if red‐coloured fish were homozygous, a progeny test was done with the fifth selection generation using eight individual crosses of red males with wild type females and wild type males with red females. Red colour proportion increased from 5.6% in the first generation to 100% in the fifth generation. All fry in the progeny test were red colour, inferring that the population was homozygous dominant (RR). Accumulated inbreeding rate in the fifth selection generation was 1.79%. The selection process did not affect fecundity as fry production in red colour females was similar to that in wild type females. Mass selection to obtain a red homozygous population in O. niloticus, Stirling strain, was appropriate and was also effective in reducing black blotch incidence in the same species.     

Comparison of growth, fillet yield and proximate composition between Stirling Nile tilapia (wild type) (Oreochromis niloticus, Linnaeus) and red hybrid tilapia (Florida red tilapia×Stirling red O. niloticus) males

A comparison was made of some productive traits of Stirling Nile tilapia (wild type) (Oreochromis niloticus, Linnaeus) and red hybrid tilapia (Florida red tilapia× Stirling red O. niloticus) males during a 98‐day grow‐out period. Twenty‐two males from each genetic group with initial weights of 139.0 g for O. niloticus and 207.3 g for the red hybrid were placed in triplicate tanks. The fish were fed with a feed containing 36.8% crude protein. Survival was 97.0% for the red hybrid and 83.3% for O. niloticus. Daily individual weight gains were 2.95 and 2.50 g and final body weights were 473.0 and 348.8 g for the red hybrid and O. niloticus respectively. Fillet yield was similar for both the species, with 33.4% for the red hybrid and 32.0% for O. niloticus. Fresh fillet lipid content was perceptibly less in the red hybrid (0.33%) than in O. niloticus (2.07%). Some benefits of a red low‐fat tilapia genotype are discussed.     

Evaluation of replacing fish meal with corn protein concentrate in Nile tilapia Oreochromis niloticus fingerlings commercial diet

Four isocaloric‐isonitrogenous diets containing 0, 50, 100 and 190 g/kg corn protein concentrate (CPC) as replacement for dietary fish meal were fed to Nile tilapia Oreochromis niloticus fingerlings for 8 weeks. Tilapia growth parameters were not significantly (p > .05) different in fish fed diets with 0, 50 and 100 g/kg CPC and found to be superior compared to those fed on 190 g/kg CPC. Fish dressing ratios and body composition were similar among all treatments. The electron microscope indicated that the stomach size of control fish was slightly smaller and the wall was thinner while the stomach of the fish fed all other levels of CPC undergone a remarkable size increase and their walls were thicker after feeding diets with CPC. Total aerobic bacterial and coliform counts were significantly decreased in fish intestine when fed diets with 100 and 190 g/kg CPC compared with fish fed diets with 0 g/kg or 50 g/kg CPC. This study indicates that it is possible to replace up to 534 g/kg of dietary fish meal in tilapia fingerlings using 100 g/kg of CPC without any negative effect on fish growth and proximate body composition.     

吉富罗非鱼生长过程中氮收支变化的研究

为充实有关鱼类研究数据,提供实际生产理论依据,研究了吉富品系尼罗罗非鱼（Oreochromis niloticus）从鱼种（18 g）生长至成鱼（180 g）过程中氮收支变化。试验为期73 d,每日饱食投喂并收集鱼粪,溶解氧质量浓度为8.0-6.0 mg·L-1,pH为 7.5-6.5,水温为24-30 ℃。在鱼均质量达到50 g、100 g和180 g时测定并计算当前生长阶段氮收支。结果表明,生长氮比例在养殖初期最高（64%）,养殖中期最低（47%）;粪氮比例在养殖中期最高（9%）,养殖初期和末期分别为5%和4%;排泄氮比例随鱼的生长而逐渐增加。此外,试验期间水中总氮增加速度在养殖中期减慢,养殖末期再次加快。     

Water quality influences the presence of Streptococcus agalactiae in cage cultured red hybrid tilapia,Oreochromis niloticus × Oreochromis mossambicus

Attempts were made to identify the association between water quality parameters and the presence of Streptococcus agalactiae in cage cultured red hybrid tilapia, Oreochromis niloticus × O. mossambicus. Fish from commercial floating net cage‐culture systems in a river and lake were randomly sampled over a 24‐month period. Swabs from the brains, eyes and kidneys were streaked directly onto blood agar to isolate S. agalactiae. Water temperature, dissolved oxygen, pH, clarity, ammonia, nitrite, sulfide, rate of water flow and depth of water at sampling sites were measured at the same time of fish sampling. The prevalence of fish that were cultured positive to S. agalactiae was significantly higher in lake compared with river. The length and weight of the infected fish were between 9 and 33 cm, and between 20 and 760 g respectively. There was a significant and positive strong correlation between the presence of S. agalactiae and fish mortalities in lake. All water quality parameters showed significant differences between river and lake. However, only water temperature, clarity and pH of lake and the ammonia, temperature and dissolved oxygen in river showed significant correlation with the presence of S. agalactiae in the cultured fish. It was concluded that several unfavourable water quality in the fish farm influencing the presence of S. agalactiae in cultured red hybrid tilapia.     

Whole cell inactivated autogenous vaccine effectively protects red Nile tilapia (Oreochromis niloticus) against francisellosis via intraperitoneal injection

Francisella noatunensis subsp. orientalis is a pathogen of tilapia and other warm‐water fish for which no vaccines are commercially available. In this study, a whole cell formalin‐inactivated vaccine was developed for the first time using the highly virulent isolate STIR‐GUS‐F2f7 and the oil‐based adjuvant Montanide? ISA 763A VG. The efficacy of the vaccine was assessed in red Nile tilapia via intraperitoneal (i.p.) injection using homologous experimental infection and correlates of protection such as seral antibody production and bacterial loads in the spleen. For immunization, fish were i.p. injected with 0.1 ml of the vaccine, the adjuvant alone or PBS. At 840 degree days post‐vaccination, all fish were i.p. injected with 4.0 × 10³ CFU/fish of pathogenic bacteria. The RPS at the end of the trial was 100% in the vaccinated group with significantly higher survival than in the adjuvant and control groups. The RPS in the adjuvant group was 42%, and no significant difference was seen in survival between this and the PBS group. Moreover, significantly higher antibody titres in the serum and significantly lower bacterial loads in the spleen were detected in the vaccinated fish by ELISA and qPCR, respectively. These findings highlight the potential of autogenous vaccines for controlling francisellosis in tilapia.     

吉富罗非鱼成鱼胆碱的最适需要量

选用初始体质量为(220.00±8.34) g的吉富罗非鱼(Oreochromis niloticus)360尾, 随机分成6组,每组3重复(每重复20尾), 于1 m×1 m×1.5 m池塘网箱中饲养。分别饲喂胆碱含量为97.80(对照组)、375.04、565.74、974.27、      1 409.81、1 824.35 mg/kg的半纯化饲料10周, 研究胆碱对吉富罗非鱼成鱼生长、饲料利用、鱼体营养组成、胆碱蓄积量及部分血液生化指标的影响。结果显示, 经过10周的饲喂, 饲料中添加胆碱可显著提高鱼体增重率、特定生长率和饲料效率(P<0.05); 降低肝脂肪含量(P<0.05), 提高肌肉脂肪含量(P<0.05); 显著升高肝胆碱蓄积量(P<0.05); 胆碱添加组血清甘油三酯(TG)和总胆固醇(T-CHO)显著高于对照组(P<0.05), 并随饲料胆碱含量增加呈现升高的趋势; 肝甘油三酯(TG)和总胆固醇(T-CHO)随着胆碱含量的增加而显著降低(P<0.05); 血清谷草转氨酶(ALT)、谷丙转氨酶(AST)和碱性磷酸酶(ALP)均随着饲料胆碱含量的增大而显著降低(P<0.05)。结果表明, 饲料中添加适量的胆碱可以改善吉富罗非鱼成鱼的生长性能, 提高饲料利用效率, 降低肝脂肪含量, 促进肝脂肪转运; 对特定生长率进行回归分析, 得出吉富罗非鱼成鱼对饲料中胆碱的最低需要量为506.43 mg/kg, 而对肝胆碱蓄积量回归分析得出的需要量为981.38 mg/kg。

     

Sex reversal in Nile tilapia (Oreochromis niloticus Linnaeus) by androgen immersion

Two experiments were conducted to investigate the efficacy of three androgens applied through immersion treatments on the sex ratio of Nile tilapia (Oreochromis niloticus L.) fry. In experiment 1, 14 days post‐hatching (DPH) larvae were exposed to a single immersion treatment in 17α‐methyltestosterone (MT), 17α‐methyldihydrotestosterone (MDHT) or 17α‐ethynyltestosterone (ET) at 200, 600 and 1800 μg L^?1 over 4 h (130 larvae per treatment). In experiment 2, Nile tilapia larvae were exposed to the higher androgen concentration (1800 μg L^?1) applied as either a single immersion (14 DPH) or double immersion (10 and 14 DPH) over 4 h (125 larvae per treatment). Change in sex proportion within each experiment as well as between experiments was analysed by the chi‐square test. In experiment 1, MT, MDHT and ET were equally effective in significantly increasing the proportion of males when applied at 1800 μg L^?1 (86.0%, 90.0% and 86.7% respectively). At 200 μg L^?1 none of the androgens altered sex ratio. At 600 μg L^?1, only MDHT slightly, but significantly skewed the sex ratio towards males (73.0%). In experiment 2, a single immersion treatment at 14 DPH (1800 μg L^?1) significantly increased the proportion of males, but at this time the response was significantly hormone dependent (MDHT, 100.0%; MT, 91.6%; ET, 76.9%). When compared with a single immersion, two‐immersion treatments significantly increased the proportion of males in the MT‐treated group (from 91.6% to 98.3%), decreased the proportion of males in the MDHT group (from 100.0% to 93.4%) and had no significant effect the ET‐treated group (change from 76.9% to 82.5%). The overall comparison of the sex ratio among same treatments from different experiments (a single immersion in 1800 μg L^?1) was not significantly different.     

不同品系尼罗罗非鱼致死低温的研究

在室内自然降温条件下，研究了三个品系尼罗罗非鱼（吉富品系，“７８”品系，“８８”品系）对低温的耐受力，计算得出每个品系的半致死低温，并对降温过程中尼罗罗非鱼行为活动的变化进行了观察。试验结果表明，在上海地区，当温度降低到１１℃时，罗非鱼开始死亡，到７．４℃时，全部死亡。吉富罗非鱼死亡温度范围是１１℃￣８．４℃，“７８”品系是９．８￣７．４℃，“８８”品系是１１℃￣７．４℃。对三个品系半致死低温的研     

奥尼罗非鱼壬基酚慢性中毒的病理学研究

采用换水式毒性试验法进行了壬基酚(Nonylphenol,NP)对奥尼罗非鱼(Oreochromis niloticus×O.aureus)的慢性毒性试验和鱼体慢性中毒的病理组织学研究。结果表明,壬基酚对奥尼罗非鱼的鳃、肾脏、脾、肝脏均造成不同程度的病理损伤。主要表现为鳃小片上皮细胞增生;肾小球毛细血管萎缩,肾组织中出现嗜曙红物质,严重者出现坏死灶;脾组织淤血,变性,组织中出现大量血铁黄素沉淀,严重者脾组织大面积坏死;肝细胞变性,小叶中央静脉充血,严重者发生大面积肝组织的严重坏死。     

Evaluation of rubber seed oil as lipid source in red tilapia (Oreochromis sp.) diet

Rubber seed oil has a high potency to be used as a new lipid source within red tilapia diet. However, the rubber seed oil contains antinutritional factor such as hydrogen cyanide (HCN). HCN is classified into heat‐labile; therefore, heating effectively reduces the HCN content. Based on this fact, this research evaluated the use of rubber seed oil with and without heating as lipid source in red tilapia diet. Four isonitrogenous and isocaloric diets were prepared as experimental diet. Each test diet contains different lipid sources such as crude palm oil + corn oil (CTRL), crude palm oil + rubber seed oil with heating (CPO:PRSO), 100% rubber seed oil with heating (PRSO) and 100% RSO without heating (URSO). In average, there were no significant differences (Tukey: p < .05) among test diet except diet with 100% rubber seed oil without heating. It concluded that 100% rubber seed with heating within test diet has no effect on growth, feed performance, blood profile, cholesterol plasma, body and liver glycogen, malondialdehyde (MDA) and the activity of superoxide dismutase (SOD).     

Dietary taurine improves reproductive performance of Nile tilapia (Oreochromis niloticus) broodstock

This study was conducted to evaluate the effects of supplemental taurine on reproductive performance of Nile tilapia (Oreochromis niloticus) broodstock fed soybean meal‐based diets. Four isonitrogenous (350 g kg^?1 protein), isocaloric (18 MJ kg^?1) diets were formulated to contain 0, 5, 10 and 15 g kg^?1 taurine. The diets were fed to triplicate groups of juvenile Nile tilapia (10–15 g average body weight) at a female: male ratio of 3 : 1, to apparent satiation, three times per day for 130 days. The size at first maturation decreased with increasing dietary taurine to 10 g kg^?1 and levelled off with further taurine supplementation. The time to first spawning was also significantly shorter at 10 g kg^?1 taurine level. Spawning performances, including spawning frequencies, total number of spawnings per tank, number of spawnings per female and absolute fecundity, were all significantly improved with increasing dietary taurine up to 10 g kg^?1. However, the quadratic regression analyses indicated that the maximum spawning performance occurred at 8 g kg^?1 of supplemental taurine. Eggs produced from broodstock fed 10 g kg^?1 taurine exhibited significantly higher hatchability and required shorter time for hatching and yolk‐sac absorption and also resulted in higher larval weight than at other dietary taurine levels. The highest egg protein, total amino acids and taurine were also obtained at 10 g kg^?1 taurine. These results suggest that 8 g kg^?1 dietary taurine is required for optimum reproductive outputs of Nile tilapia broodstock.     

Detection of tilapia lake virus (TiLV) infection by PCR in farmed and wild Nile tilapia (Oreochromis niloticus) from Lake Victoria

Tilapia lake virus disease (TiLVD) has emerged to be an important viral disease of farmed Nile tilapia (Oreochromis niloticus) having the potential to impede expansion of aquaculture production. There is a need for rapid diagnostic tools to identify infected fish to limit the spread in individual farms. We report the first detection of TiLV infection by PCR in farmed and wild Nile tilapia from Lake Victoria. There was no difference in prevalence between farmed and wild fish samples (p = .65), and of the 442 samples examined from 191 fish, 28 were positive for TiLV by PCR. In terms of tissue distribution, the head kidney (7.69%, N = 65) and spleen (10.99%, N = 191), samples had the highest prevalence (p < .0028) followed by heart samples (3.45%, N = 29). Conversely, the prevalence was low in the liver (0.71%, N = 140) and absent in brain samples (0.0%, N = 17), which have previously been shown to be target organs during acute infections. Phylogenetic analysis showed homology between our sequences and those from recent outbreaks in Israel and Thailand. Given that these findings were based on nucleic acid detection by PCR, future studies should seek to isolate the virus from fish in Lake Victoria and show its ability to cause disease and virulence in susceptible fish.     

Osmoregulatory actions of growth hormone in juvenile tilapia (Oreochromis niloticus)

Growth hormone (GH) effectively promotes seawater (SW) adaptation in salmonids, but little is known of its effect in tilapias. Experiments were performed to investigate the effects of recombinant eel GH (reGH) on osmoregulatory actions and ultrastructural features of gill chloride cells in juvenile tilapia, Oreochromis niloticus. Tilapia showed a markedly improved SW survival, when directly transferred from freshwater (FW) to 62.5% SW 24h after a single reGH injection (0.25 or 2.5 µg g^-1) or 3 reGH injections (0.25 µg g^-1 every other day). Plasma Na+ and Mg²⁺ levels were significantly reduced by reGH (0.25 and 2.5 µg g^-1) compared with saline injections; Ca²⁺ concentrations were reduced significantly by high dose of reGH (2.5 µg g^-1) after SW transfer. However, fish failed to survive more than 24h when directly transferred to 70% SW, although the fish treated with reGH could survive longer than the controls. When examined by electron microscopy, the chloride cells were identified as mitochondrion-rich and an extensive tubular system was induced by GH treatment. The results of the present study suggest that, similar to its effect on salmonids, GH also exerts acute osmoregulatory actions and enhances SW adaptation in juvenile tilapia. GH also stimulates the differentiation of chloride cells toward SW adaptation.     

Economic profitability of Nile tilapia (Oreochromis niloticus L.) production in Kenya

Economic profitability of Nile tilapia production in Kenya was analysed using a model that simulated individual fish growth and took fish population dynamics in the pond into account. The results suggest that the currently practiced mixed‐sex tilapia culture is economically unsustainable. It is suggested that research and extension efforts be geared towards developing monosex Nile tilapia production systems. Nile tilapia culture with African catfish predation should be viewed as an intermediate step towards all‐male Nile tilapia culture. This will allow accumulation of both physical and human capital to support all‐male tilapia culture. Under all‐male culture, economic returns are high enough to justify investment in Nile tilapia culture using borrowed capital. However, the success of monosex culture will depend on the availability and affordability of quality fingerlings and low‐cost fish feeds. The results have a wide application in Sub‐Saharan Africa where mixed‐sex Nile tilapia culture is common.