Periodicity of reproductive behaviour by the blue tilapia,Oreochromis aureus

Synopsis Oreochromis aureus exhibits a diel periodicity of spawning when maintained on a controlled 14:10 light:dark photoperiod, with a peak in spawning activity during the 11th hour of light. That this periodicity of spawning is a response to light is supported by phase-shifting the light cycle by seven hours. This results in a corresponding shift in the times of spawning.     

The effects of short-term acute cadmium exposure on blue tilapia,Oreochromis aureus

Synopsis Disease-free blue tilapia,Oreochromis aureus, exposed to cadmium (0.5 ppm and 10 ppm) showed very significant and dramatic decrease in food consumptions. Food consumptions returned to near normal 21 days after fish were returned to cadmium-free water. Along with anorexia there were decreases in body weights during the period when fish were exposed to cadmium. Fish in cadmium-free water that were pair-fed to cadmium-exposed fish (0.5 ppm) did not gain weight but there were no decreases in body weights. Cadmium was still in tissues 34 days after the fish were placed in cadmium-free water and the accumulation was highest in the kidney; this was followed by liver, brain, gill filaments and muscles. The accumulations of the heavy metal (in kidneys and gills) were significantly higher in fish exposed to high than low cadmium levels. There were no differences in complement levels (haemolytic acitivity) in cadmium-exposed and cadmium-free fish. However, cadmium-exposed fish did not produce detectable haemagglutinating antibodies against sheep red blood cells while cadmium-free fish responded well to the antigen. The anorexia in cadmium-exposed fish contributed to the depression in antibody production.     

Experimental trophic ecology of juvenile largemouth bass,Micropterus salmoides,and blue tilapia,Oreochromis aureus

Synopsis The potential for feeding competition between largemouth bass, Micropterus salmoides, and blue tilapia, Oreochromis areus, in Lake Fairfield, Texas was evaluated experimentally. Largemouth bass and blue tilapia were grown in cages alone and in combination with each other. The fish were allowed to feed on the natural food within the lake. Largemouth bass grown in combination with blue tilapia were significantly shorter and weighed less than largemouth bass grown alone. Blue tilapia grown in combination with largemouth bass were statistically significantly longer and heavier than blue tilapia grown alone. Largemouth bass grown alone had diets (volume and number of food items) significantly different than the largemouth bass grown with the blue tilapia. Largemouth bass fed primarily on chironomid larvae and pupae, and odonates, whereas blue tilapia consumed vegetable matter, detritus, and chironomid larvae. Length and weight differences between large-mouth bass grown alone and in combination with blue tilapia, in conjunction with the largemouth bass diet shift, support the theory that these two species compete for food resources.     

Growth,survival, and foraging abilities of early life history stages of blue tilapia,Oreochromis aureus,and largemouth bass,Micropterus salmoides

Synopsis I compared growth, survival, and foraging abilities of early life history stages of blue tilapia,Oreochromis (=Sarotherodon = Tilapia) aureus, and largemouth bass,Micropterus salmoides, at equivalent prey (zooplankton) densities in the laboratory. Survival and growth of blue tilapia exceeded those of largemouth bass and, at comparable ages, blue tilapia were superior to largemouth bass in ability to prey on zooplankton; the enhanced survival and growth of blue tilapia appeared to result from their larger initial (egg) size. Predatory abilities of the species at equivalent sizes were similar. The success of blue tilapia in colonizing new systems and rapidly achieving high abundances in Florida may be a consequence of large initial size.     

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.     

O-antigen structure in a virulent strain of Aeromonas hydrophila

Abstract Lipopolysaccharide (LPS) was isolated from a strain of Aeromonas hydrophila which had displayed serological, bacteriophage attachment and virulence properties similar to those found in strains of Aeromonas salmonicida . The structure of the O-antigen was determined and had many points of similarity with that previously elucidated for the O-antigen of A. salmonicida . Methylation analysis, chromium trioxide oxidation and ¹H-n.m.r. were used to confirm that the repeating unit of the O-chain had the following structure:
     

Toxicity of crude extracellular products of Aeromonas hydrophila in tilapia, Tilapianilotica

Extracellular products (ECP) secreted from Aeromonas hydrophila with haemolytic andproteolytic activity were studied with respect to temperature and time of incubation as well as thelethal toxicity on tilapia, Tilapia nilotica . The highest production of the haemolysin productwas achieved when Aer. hydrophila was grown at 35°C for 30 h. Tilapia erythrocytewas found to be more susceptible than sheep erythrocyte for determining the haemolytic activity.The haemolytic activity against tilapia erythrocyte was completely inactivated after heating theECP at 60°C for 10 min or 55°C for 15 min. The proteolytic activity was maximized whenthe bacterium was grown at 30°C for 36 h. Complete inactivation of the protease enzyme wasperformed after heating the ECP at 80°C for 10 min or 70°C for 15 min. Aeromonashydrophila was found to produce haemolytic and proteolytic exotoxin lethal to tilapia (LD₅₀ 2·1 × 10⁴ cell/fish), as well as heat stable unknown virulent factors thatwere responsible for 20% mortality. The lethality of ECP was decreased by heating andcompletely inactivated by boiling at 100°C for 10 min.     

Identification of putative sex chromosomes in the blue tilapia, Oreochromis aureus, through synaptonemal complex and FISH analysis

Sex determination in the blue tilapia, Oreochromis aureus, is primarily a ZW female-ZZ male system. Here, by analysis of the pachytene meiotic chromosomes of O. aureus, we demonstrate the presence of two distinct regions of restricted pairing present only in heterogametic fish. The first, a subterminal region of the largest bivalent is located near to the region of unpairing found in the closely related species O. niloticus, while the second is in a small bivalent, most of which was unpaired. These results suggest that O. aureus has two separate pairs of sex chromosomes.     

Nonadditive expression of lipid metabolism pathway-related genes in intestine of hybrids of Nile tilapia females (Oreochromis niloticus) and blue tilapia males (Oreochromis aureus)

Nonadditive expression contributes to heterosis in hybrids. In this study, the expression profiles of twelve lipid metabolism pathway-related genes were investigated in the intestine of Nile tilapia (Oreochromis niloticus) ♀?×?blue tilapia (Oreochromis aureus) ♂ hybrid. The expression of genes from the hybrid were assigned to nonadditive and additive expression pattern groups and compared with expression patterns from Nile tilapia and blue tilapia. In the intestine of the hybrid, apoA4B was expressed at intermediate levels, but apoB and MTP were assigned to ELD-B and ELD-N categories, respectively. The LPL and LRP1 showed transgressive up-regulation in the hybrid, but LDLR was assigned to the ELD-B category. For fatty acid uptake related genes, only FABP11a was categorized as nonadditive expression with transgressive up-regulation, while CD36 and FABP3 were categorized as additive expression in the intestine of the hybrid. Two genes in triacylglycerol metabolism, namely, FAS and DGAT2, showed transgressive up-regulation in the hybrid. Most of the genes analyzed in the present study showed nonadditive expression (8 in 12), and five genes showed transgressive up-regulation. These results indicated that the stimulation of lipid metabolism in the hybrid compared to that of its parents. The hyperactive expression of these genes in the hybrid may be associated with the growth and lipid usage vigor.

     

Babylonia spirata (Linnaeus, 1758) on biochemical and nutritional composition levels are altered by Aeromonas hydrophila infection

The present study comprises the biochemical and nutritional composition level of control and infected host of B. spirata with A. hydrophila. The healthy species were collected from the Therespuram coast, Southeast coast of India. After the acclimatization period, 15 snails were selected and infected with seven different bacterial pathogens by intramuscular injection. The snails which shows the maximum mortality rate after the bacterial infection was selected for the biochemical composition nutritional level. It was then analyzed and compared to the control group. Based on this result, the FTIR spectrum, DNA fragmentation, SDS PAGE Profile, amino acids (phenylalanine), fatty acids (linolenic acids), minerals (aluminum and copper) was recorded maximum in control and minimum in infected tissue of B. spirata. The result of the present study showed, presences of rich nutrition composition good protein profile in this species add more value of economic importance.     

Growth, mortality and reproduction of the blue tilapia Oreochromis aureus (Perciformes: Cichlidae) in the Aguamilpa Reservoir, Mexico

Tilapia production has increased in Aguamilpa Reservoir, in Nayarit, Mexico, in the last few years and represents a good economic activity for rural communities and the country. We determined growth parameters, mortality and reproductive aspects for 2413 specimens of blue tilapia Oreochromis aureus in this reservoir. Samples were taken monthly from July 2000 through June 2001, of which 1 371 were males and 1 042 were females. Standard length (SL) and total weight (TW) were measured in each organism. The SL/TW relationships through power models for sexes were determined. The growth parameters L infinity k, and t0 of the von Bertalanffy equation were estimated using frequency distribution of length through ELEFAN-I computer program. Finally the reproductive cycle and size of first maturity were established using morph chromatic maturity scale. The results suggested that the males and females had negative allometric growth (b < 3). Significant differences were found between SL/TW model for the sexes, suggesting separate models for males and females. Results indicate that there are no differences in growth rates between sexes; the proposed parameters were L infinity = 43.33 cm standard length, k = 0.36/year and t0 = -0.43 years. Natural and fishing mortality coefficients were 0.83/year and 1.10/year, respectively. The estimated exploitation rate (0.57/year) suggested that during the study period the fishery showed signs of overfishing. Blue tilapia reproduces year-round; the highest activity occurs from January through May and size of first maturity was 23 cm SL. We conclude that it is necessary to establish a minimum catch size in this reservoir based on the reproductive behavior of this species.     

Effect of oral immunization with Aeromonas hydrophila ghosts on protection against experimental fish infection

Aims:  To investigate whether oral immunization with Aeromonas hydrophila ghosts (AHG) vaccine can elicit mucosal and systemic immune responses of Carp ( Carassius auratus gibelio ) compared to conventional formalin-killed bacteria (FKC).
Methods and Results:  Fish were fed diets coated with AHG, FKC or phosphate buffered saline (PBS) alone, after immunization, more antigen-specific antibody was significantly detected in serum and intestinal mucus in AHG group than FKC group and PBS group. In addition, after challenged with the parent strain J-1, the survival of bacterial ghost-vaccinated fish was higher than PBS group and FKC group, the relative per cent survival (RPS) being 76·8%, 58·9%, respectively.
Conclusions:  Oral immunization with A. hydrophila ghosts can elicit systemic and mucosal adaptive immune responses and has higher potential to induce protective adaptive immunity than normal vaccine.
Significance and Impact of the Study:  Oral immunization with bacterial ghosts is a promising new solution with potential application to prevent diseases in fish.     

Soft-tissue accumulation of lead in the blue tilapia,Oreochromis aureus (steindachner), and the modifying effects of cadmium and mercury

The interaction of mercury and cadmium with lead was investigated by exposingOreochromis aureus to two heavy metals simulataneously. The chronic accumulation prolife of lead was determined by analyzing the liver, brain, gill filaments, intestine, caudal muscle, spleen, trunk kidney, and gonads following exposure to lead alone and in mixtures with mercury and cadmium. Nominal exposure concentrations of lead were 0.05, 0.10, 0.50, and 1.00 mg/L. Mixtures of lead (0.50 or 0.05 mg/L) with cadmium (0.05 mg/L) and lead (0.50 or 0.05 mg/L) with mercury (0.05 mg/L) were also used. Following 140 d of exposure to lead, the highest concentrations of lead consistently accumulated in the trunk kidney. The concentration of lead in the kidney was decreased by coexposure to mercury or cadmium, but increased in the muscle and liver. Under all exposure regimes, the median concentration of lead in the muscle exceeded safety levels recommended for human consumption. In a food fish, such asO. aureus, a knowledge of toxic metal accumulation patterns is of great importance.     

Structure,composition, mechanics and growth of spines of the dorsal fin of blue tilapia Oreochromis aureus and common carp Cyprinus carpio

The structural, compositional and mechanical properties of the spines of the dorsal fin in mature anosteocytic blue tilapia Oreochromis aureus and osteocytic common carp Cyprinus carpio are described, as well as their temporal growth pattern and regenerative capacities. The three‐dimensional architecture of both spines, from macro to sub‐micron levels, is shown to be axially oriented and therefore highly anisotropic and the spines of both species are able to regenerate after partial amputation.     

Immunomodulatory effect of dietary Saccharomyces cerevisiae, β-glucan and laminaran in mercuric chloride treated Nile tilapia (Oreochromis niloticus) and experimentally infected with Aeromonas hydrophila

Six hundred and forty Nile tilapia (Oreochromis niloticus) weighing 80–100 g were randomly allocated into eight equal groups (80 each). The first group acts as control. Groups S, B and L were fed on a ration supplemented with Saccharomyces cerevisiae, β-glucans and laminaran, respectively for 21 days. Groups M, MS, MB and ML were subjected throughout the experiment to sublethal concentration of mercuric chloride (0.05 ppm). Gps. MS, MB and ML were fed on a ration containing S. cerevisiae, β-glucan and laminaran respectively for 21 days. Fish were challenged with Aeromonas hydrophila (0.4 × 10⁷ cells mL^?1) via intra-peritoneal injection and the mortality rate was recorded up to 10 day post-challenge. The non-specific defense mechanisms, cellular and humoral immunity, beside the total and differential leukocytic count were determined.Lymphocyte transformation index, phagocytic activity percent, phagocytic index, total lymphocyte count, serum bactericidal activity and nitric oxide as well as the survival rate were insignificantly changed after 21 day in gps. MS&ML, when compared with mercuric chloride immune depressed group M. These parameters as well as the neutrophil adhesion, serum nitric oxide and survival rate were significantly increased in gp. MB when compared with gp. M. Meanwhile the cellular and humoral immunity beside the survival rate were significantly increased in groups S, B, L when compared with control group.It could be concluded that the whole yeast S. cerevisiae, β-glucan and laminaran can be used as immunostimulants for the farmed Nile tilapia. The β-glucans could be used in farmed Nile tilapia, under immune depressive stressful condition to increase their resistance to diseases.     

The effect of temperature on Aeromonas hydrophila infection in goldfish, Carassius auratus

The effect of temperature on Aeromonas hydrophila infection in goldfish, Carassius auratus , was studied using A. hydrophila strain A-3500. After comparison of four different infection methods, subcutaneous injection was selected. Different test temperatures were also tested and higher mortality was observed at 17 and 25°C during a 15-day period. SDS-PAGE analysis of outer membrane proteins prepared from A. hydrophila cultured at 10, 17, 25 and 32°C in formulated salt water showed different protein profiles. For example, a 40-kDa band was found only at 17 and 25°C. Phagocytic rates of A. hydrophila by goldfish macrophages at 10, 17, 25 and 32°C were 20.46 ± 2.07, 16.15 ± 1.39, 15.94 ± 1.85 and 22.22 ± 2.49%, respectively. The results indicated that temperature affects both the cell membrane structure of A. hydrophila and phagocytic activity of goldfish macrophages, resulting in varying fish mortality when infected at different temperatures.     

Live recombinant Lactococcus lactis vaccine expressing aerolysin genes D1 and D4 for protection against Aeromonas hydrophila in tilapia (Oreochromis niloticus)

Aims: To evaluate a live recombinant Lactococcus lactis vaccine expressing aerolysin genes D1 (Lac‐D1ae) and/or D4 (Lac‐D4ae) in protection against Aeromonas hydrophila in tilapia (Oreochromis niloticus). Methods and Results: The polymerase chain reaction (PCR)‐amplified 250‐ and 750‐bp sequences coding for domains D1 and D4 of aerolysin were individually cloned into pNZ8048 and electrotransformed into L. lactis. The recombinant vaccine candidates were then either orally fed or injected intraperitoneally into tilapia. The development of antibodies in sampled fish compared to control groups implied that the recombinant epitopes expressed in L. lactis were able to elicit an immunogenic response in tilapia. Interestingly, the lower doses of both Lac‐D1ae and Lac‐D4ae gave higher antibody levels over the study period. Fish immunized with Lac‐D1ae and Lac‐D4ae together showed the highest level of protection, and the mortality was reduced significantly compared to control strains in both modes of vaccination. Conclusions: The recombinant L. lactis strain expressing D1 and D4 produced aerolysin‐specific serum IgM in tilapia. Both D1 and D4 promoted 55–82% relative per cent survival (RPS) against Aeromonas infection through intraperitoneal injection, whereas the RPS following oral feeding of the vaccine was 70–100%. Significance and Impact of the Study: The D1 and D4 regions of the aerolysin protein have been successfully identified as immunogenic regions that can elicit antibody production in tilapia and protect against challenge with Aer. hydrophila. A promising oral vaccine using L. lactis harbouring the D1 and D4 regions has been developed to control Aer. hydrophila.     

A deleterious effect associated with UNH159 is attenuated in twin embryos of an inbred line of blue tilapia Oreochromis aureus

Offspring of a highly inbred gynogenetic line of Oreochromis aureus displayed 12‐fold increase in twinning rate compared to the outbred population. Asymmetric conjoined twins, which consist of a normal embryo attached to a malformed‐atrophic twin, were frequently encountered in both gynogenetic (90·7%) and outbred (38·2%) embryos. The monozygotic origin of these twins was determined using five microsatellite markers. Progeny of heterozygous parents for the microsatellite UNH159 were separated into sub‐sets of twins and normal full‐sibs. Consistent with previous reports, the normal embryo sub‐set exhibited elimination of both types of homozygotes for the UNH159 genetic marker at 2–8 days after fertilization. Unexpectedly, this elimination was less frequent in twins. The UNH159 marker as well as RNA‐binding motif protein, X‐linked (rbmx), SRY‐box containing gene 3 (sox3) and alpha‐thalassemia/mental retardation syndrome X‐linked (atrx) genes were mapped to linkage group 2. These gene orthologues are all located on the mammalian X chromosome and atrx is necessary for the X‐chromosome inactivation.