Using truss networks to estimate the biomass of Oreochromis niloticus, and to investigate shape Characteristics

Truss and length measurements were made on 463 tilapia Oreochromis niloticus of known mass. These measurements were then used to build mathematical models to estimate tilapia biomass. Two different approaches were used to build the models. The first was to take some simple mathematical models, and to optimize them using least squares regression. The second approach was to build models using artificial neural network software. Models were built for two different but overlapping size ranges and both approaches were successful in creating models that estimated the total biomass to within ±1%. The truss measurements were also used to assess the principal shape components of different sized tilapia.     

Kinetic and immunological differences between the retinal specific C4- and B4-lactate dehydrogenase of the cichlid fish Oreochromis mossambicus

The eye-specific C₄-lactate dehydrogenase (LDH) and the widely distributed B₄-LDH isozymes from the fish Oreochromis mossambicus were purified to homogeneity using DEAE Sepharose ion-exchange chromatography and oxamate-linked sepharose affinity-chromatography. Kinetic analysis was performed on pure B₄- and C₄-LDH. The Michaelis-Menten constant (K_m) for B₄-LDH and pyruvate was 32.3μM, for B₄-LDH and lactate 717 μM for C₄-LDH and pyruvate 14.1 μM and for C₄-LDH and lactate 1898 μM. The pure C₄-isozyme was subjected to SDS-polyacrylamide gel electrophoresis and the Coomassie Brilliant Blue-stained band injected into a rat to produce antiserum. The antiserum proved to be C₄-LDH monospecific, which will allow using it to localize the isozyme in the retina at a light and electron microscopical level.     

碱度胁迫对尼罗罗非鱼鳃离子细胞形态以及鳃、肾和肠中HCO3-转运因子的影响

采用扫描电镜观察了不同碱度(0、2、4 g/L Na HCO_3)胁迫对尼罗罗非鱼(Oreochromis niloticus)鳃离子细胞形态变化的影响,并采用免疫组化技术观察了鳃、肾、肠中4个HCO_3~-转运因子碳酸酐酶(CAⅡ、CAⅣ)、碳酸氢钠协同转运载体(SLC4A4)、Cl~-/HCO_3~-离子交换体(SLC26A6)的阳性反应变化。扫描电镜结果表明,鳃离子细胞分布在鳃小片基部。根据其表面开孔形状和尺寸,可分为Ⅰ型、Ⅱ型、Ⅲ型和Ⅳ型4种亚型,各亚型离子细胞的开孔尺寸随碱度胁迫强度增高呈正比增大,Ⅲ型离子细胞开孔尺寸变化最明显(P0.01);离子细胞总数目也随碱度升高而增加,Ⅲ型离子细胞数目上升最为显著(P0.01)。免疫组化结果表明,在淡水、碱水组中,CAⅡ、CAⅣ、SLC4A4、SLC26A6在鳃小片基部和肾中均有阳性反应,且随着碱度升高,阳性反应增强,但在肠道中未观察到阳性反应。本研究结果初步表明,尼罗罗非鱼可通过鳃离子细胞形态和数量调节适应碱度变化,鳃和肾为主要应答调节器官。     

Non‐specific immunity and disease resistance are enhanced by the polysaccharide fraction of a marine chlorophycean macroalga in Oreochromis niloticus (Linnaeus, 1758)

Polysaccharides (PF) from marine macroalgae, Caulerpa scalpelliformis were extracted and tested for its potential immunostimulatory and disease resistance properties in fish. Five groups of Nile tilapia (n = 6), Oreochromis niloticus (Linnaeus, 1758) were intraperitoneally administered with the different doses of PF (2, 20 or 200 mg/kg body weight) or with yeast‐derived commercial immunostimulant, Macrogard^? (20 mg/kg body weight), to compare the effectiveness. An untreated control group was also maintained. A total of fifteen fibre reinforced plastic tanks (150 L, ambient temperature and light conditions) were used, with triplicate tanks for each group. Only four fish per tank (totally 12 fish from a group) were taken at random and assayed. PF enhanced all the tested non‐specific serum immune responses namely lysozyme, myeloperoxidase, antiprotease, and bactericidal activities. There was an upregulation of the genes encoding IL‐1β, lysozyme and TNF‐α in the spleen of PF injected fish as compared to the control group. In order to study the overall functional immunity, disease resistance test was conducted. Another five groups of fish (n = 10) were treated by intraperitoneal injection with different doses of PF or Macrogard^? or untreated as mentioned earlier in triplicates (30 fish per group in three tanks, totally 150 fish in 15 tanks). Seven days post treatment, fish were challenged by intraperitoneal administration of live virulent Aeromonas hydrophila. PF treated fish were protected with significant reduction in the mortality and the consequent increased relative percent survival (RPS) of 92 in the least (2 mg/kg) and middle dose (20 mg/kg) groups. The disease resistance experiment was repeated again but this time, fish were challenged 21 days post treatment that resulted in RPS of 50 for the middle dose. The results clearly show that the intraperitoneal administration of the polysaccharide fraction had a stimulating effect on the non‐specific immune responses, immune gene expression and disease resistance.     

Fluorescent labelling of Na+,K+-ATPase in intact cells by use of a fluorescent derivative of ouabain: Salinity and teleost chloride cells

Summary Anthroylouabain, a fluorescent derivative of ouabain, was used to localize Na⁺,K⁺-ATPase in transport epithelia of two species of teleosts. Exposure of the opercular membrane of seawater-adapted tilapia (Oreochromis mossambicus) and the jaw skin of the long-jawed mudsucker (Gillichthys mirabilis) to a 2 M anthroylouabain solution resulted in the appearance of cells stained bright blue. These were deemed to be chloride cells by their large size, distinct morphology and co-localization of DASPEI fluorescence, a mitochondrial stain. Addition of ouabain (1 mM final concentration) greatly decreased anthroylouabain fluorescent staining of chloride cells of seawater-adapted fish. Exposure of opercular membranes from freshwater tilapia to 2 M anthroylouabain did not result in significant staining. Anthroylouabain is therefore a useful vital stain for localizing Na⁺,K⁺-ATPase in chloride cells of seawater-adapted teleosts, and may be useful for fluorescent labelling of ouabain-sensitive Na⁺,K⁺-ATPase in other tissues and species.     

The ultrastructure of chloride cells in the gills of the teleostOreochromis mossambicus during exposure to acidified water

Summary Branchial chloride cells, which actively take up ions in the gills of freshwater fish, were studied in tilapia (Oreochromis mossambicus) exposed to sublethally acidified freshwater. Structural damage of cells, resulting in cell death by necrosis, only occurred transiently, when the reduction of water pH was acute rather than gradual. The most prominent effects of water acidification were the rapid increase in the number of chloride cells and the changes in frequency of the different stages of the chloride cell cycle. In the opercular inner epithelium, a twofold increase in cells occurred 48 h after gradual acidification. Cell density stabilized after 4 weeks at a level 5 times that of control fish. Four transitory stages were distinguished in the chloride cell cycle: accessory or replacement cells, immature, mature, and degenerating (apoptotic) cells. In control fish, mature chloride cells dominated (over 50%) with immature and apoptotic cells totalling about 40%. After 4 weeks in acid water, only 13% of the cells were mature. Immature and apoptotic cells dominated, each representing about 40% of the total number of chloride cells. Mature cells apparently age rapidly under these conditions. Thus, chloride cells turn over quickly in acid water, with a minor increase in ion transport capacity of the gills. This conclusion is supported by the observation that opercular and branchial Na⁺/K⁺ ATPase activities in treated fish are only 40%–50% higher than in controls.     

Innate-immune responses of tilapia (Oreochromis mossambicus) exposure to acute cold stress

In this present study, Oreochromis mossambicus tilapia were transferred to cold water at 12°C for various time intervals (1, 4, 8, 24, and 48 hr) and its innate immune response was analyzed by studying cellular and humoral parameters. In vivo, alternative complement pathway activity in blood plasma was rapidly increased at 1 hr of cold water (12°C) exposure. Lysozyme activity and cortisol levels of plasma were increased at 4 and 1 hr, respectively. Surprisingly, only plasma cortisol levels remained unchanged through 24 hr of cold water transfer. Phagocytic ability, phagocytic capacity, and respiratory burst (RB) activity of head kidney (HK) leukocytes and splenocytes showed no any significant changes. In peripheral blood leukocytes, phagocytic capacity, and RB activity were increased at 24 hr of cold water exposure. The expressions of genes involved innate immunity in splenocytes and HK leukocytes of tilapia cold water exposure were analyzed, messenger RNA (mRNA) expressions of HSP70, HSP90, and immunoglobulin M failed to change upon exposure to cold stress. Major histocompatibility complex-I and II mRNAs were significantly increased in tilapia splenocytes at 1 hr of cold water transferred. Whereas myxovirus (Mx) expression was increased in splenocytes and HK leukocytes of tilapia after 1 hr of cold water exposed. Our result reveals that the exposure of tilapia to acute cold stress condition significantly enhances plasma acid phosphatase activity and both phagocytic capacity and RB activity. Furthermore, cold stress significantly stimulates Mx gene expression in splenocytes and HK leukocytes.     

Evolutionary relationships of the Lake Malawi Oreochromis species: evidence from allozymes

Three tilapiine species belonging to the endemic Lake Malawi species flock known as' chambo' Oreochromis ( Nyasalapia ) karongae , O. (N.) lidole and O. (N.) squamipinnis and the species Oreochromis (Oreochromis) shiranus were collected from the wild. These four species were analysed at 43 enzyme loci using starch gel electrophoresis. No significant deviations from Hardy-Weinberg equilibrium were observed after correcting for multiple simultaneous testing. The expected heterozygosity ( H _e) was lowest in O. (O.) shiranus ( H _e=0.082). The three chambo species had higher levels: H _e=0.103 to H _e=0.116. The three chambo species as a whole were polymorphic (99%) at 16 different loci sharing 10 of these in common. No fixed differences between the three chambo species were observed but highly significant allele frequency differences existed between all the chambo species. The F _ST calculated for the three chambo species was 0051, closer to intra-specific than to inter-specific levels. O. (O.) shiranus could be clearly separated from all chambo species at five fixed loci. Comparison of the allozyme data from these species with five species from the same sub genera support the hypothesis that the chambo form a monophyletic group and that O. (N.) macrochir or a related species represents the sister taxon.     

我国新引进吉富品系尼罗罗非鱼群体的遗传多样性分析

选取罗非鱼(Oreochromis spp.)第二代遗传连锁图谱中的26个微卫星位点,对淡水渔业研究中心引进的、由60个家系组成的吉富品系尼罗罗非鱼(O.niloticus)群体进行遗传结构分析。结果显示,26个微卫星位点在吉富罗非鱼群体中共检测到124个等位基因,各位点的等位基因数为3～7个,平均4.8个。片段长度104～322 bp,平均杂合度观测值为0.622 1,平均杂合度期望值为0.642 3,平均多态信息含量(PIC)为0.633 4。所检测的26个位点中,有25个位点属于高度多态位点(PIC0.5),占所检测位点的96.15%;1个位点属于中度多态位点。结果表明,该吉富罗非鱼群体多态信息含量丰富,遗传多样性水平较高。因而该群体仍然具有较大的选育潜力,可以作为选育的基础群体开展进一步的选育工作。     

Higher parasite richness, abundance and impact in native versus introduced cichlid fishes

Empirical studies suggest that most exotic species have fewer parasite species in their introduced range relative to their native range. However, it is less clear how, ecologically, the loss of parasite species translates into a measurable advantage for invaders relative to native species in the new community. We compared parasitism at three levels (species richness, abundance and impact) for a pair of native and introduced cichlid fishes which compete for resources in the Panama Canal watershed. The introduced Nile tilapia, Oreochromis niloticus, was infected by a single parasite species from its native range, but shared eight native parasite species with the native Vieja maculicauda. Despite acquiring new parasites in its introduced range, O. niloticus had both lower parasite species richness and lower parasite abundance compared with its native competitor. There was also a significant negative association between parasite load (abundance per individual fish) and host condition for the native fish, but no such association for the invader. The effects of parasites on the native fish varied across sites and types of parasites, suggesting that release from parasites may benefit the invader, but that the magnitude of release may depend upon interactions between the host, parasites and the environment.