Nitrite-induced methemoglobinemia in Nile tilapia, Oreochromis niloticus

Exposure of Nile tilapia, Oreochromis niloticus (mean weight, 55.72 ± 4.30 g), to two sublethal NO₂–N concentrations was studied for 24 and 48 h in a static test. In nitrite exposure tests, the percentages of methemoglobin, external nitrite, plasma nitrite, hemoglobin and hematocrit were assessed. Nitrite exposure in the range of 0.50 and 1.38 mg l⁻¹ NO₂–N caused an increase in methemoglobin levels; however, methemoglobin percentages ranging from 16% to 42% represented a mild methemoglobinemia. Levels of methemoglobin were unrelated to environmental and plasmatic nitrite concentrations. The nitrite concentration in the blood did not seem to be linked to time of exposure. Nitrite exposure in Nile tilapia was associated with a marked reduction in hemoglobin and hematocrit.     

A novel sex-determining QTL in Nile tilapia (Oreochromis niloticus)

Background

Fish species often exhibit significant sexual dimorphism for commercially important traits. Accordingly, the control of phenotypic sex, and in particular the production of monosex cultures, is of particular interest to the aquaculture industry. Sex determination in the widely farmed Nile tilapia (Oreochromis niloticus) is complex, involving genomic regions on at least three chromosomes (chromosomes 1, 3 and 23) and interacting in certain cases with elevated early rearing temperature as well. Thus, sex ratios may vary substantially from 50%.

Results

This study focused on mapping sex-determining quantitative trait loci (QTL) in families with skewed sex ratios. These included four families that showed an excess of males (male ratio varied between 64% and 93%) when reared at standard temperature (28°C) and a fifth family in which an excess of males (96%) was observed when fry were reared at 36°C for ten days from first feeding. All the samples used in the current study were genotyped for two single-nucleotide polymorphisms (rs397507167 and rs397507165) located in the expected major sex-determining region in linkage group 1 (LG 1). The only misassigned individuals were phenotypic males with the expected female genotype, suggesting that those offspring had undergone sex-reversal with respect to the major sex-determining locus. We mapped SNPs identified from double digest Restriction-site Associated DNA (ddRAD) sequencing in these five families. Three genetic maps were constructed consisting of 641, 175 and 1,155 SNPs from the three largest families. QTL analyses provided evidence for a novel genome-wide significant QTL in LG 20. Evidence was also found for another sex-determining QTL in the fifth family, in the proximal region of LG 1.

Conclusions

Overall, the results from this study suggest that these previously undetected QTLs are involved in sex determination in the Nile tilapia, causing sex reversal (masculinisation) with respect to the XX genotype at the major sex-determining locus in LG 1.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1383-x) contains supplementary material, which is available to authorized users.     

Taste preferences and feeding behaviour in the facultative herbivorous fish,Nile tilapia Oreochromis niloticus

Taste preferences in fishes are known mainly for carnivorous species, whereas herbivorous consumers were rarely used in such studies. The main goal of the present study was to evaluate the taste preferences in the herbivorous African cichlid fish, Nile tilapia Oreochromis niloticus. In laboratory settings, the palatability of widely used taste substances (four taste substances that are considered to be sweet, sour, bitter and salty for humans – sucrose, citric acid, calcium chloride and sodium chloride; 21 free L -amino acids; 12 sugars and artificial sweetener Na-saccharin; 0.1–0.0001 M) was evaluated. In each trial, a standard agar pellet flavoured with a substance was offered for fish individually. The consumption of pellet, the number of grasps and the retention time before the pellet was finally ingested or rejected were registered. Overall, 21 of 38 substances were palatable, whereas other substances did not shift consumption of pellets in relation to blank pellets. Pellets containing citric acid, L -cysteine, L -norvaline, L -isoleucine, L -valine, Na-saccharin and D -sorbitol were consumed in >85% of trials. Taste attractiveness of amino acids was highly species-specific and was not associated with the trophic category of the 19 species compared. Moreover, it did not correlate with dietary quantitative requirements of Nile tilapia (r_s = 0.27; P > 0.05). Palatability of sugars for O. niloticus and their sweetness for humans did not correlate as well (r_s = 0.21; P > 0.05); nonetheless, Na-saccharin has the most attractive taste for both O. niloticus and humans. The most palatable amino acids lost their effect if the concentration was lowered to 0.01 M for L -cysteine and 0.001 M for L -norvaline (lower than 242.3 μg and 23.4 μg per a pellet, respectively). Single pellet grasp was characteristic of O. niloticus feeding behaviour (>95% of trials), and this pattern may be related to the social lifestyle of this species. Fish spent 4–8 s on average for orosensory evaluation of pellet edibility. The retention time correlated with the palatability of substances and was significantly longer in trials that ended up with pellet swallowing. It is suggested that prolonged orosensory evaluation of food before swallowing provides a reliable and accurate sensory evaluation, which, in turn, can reduce the probability that inadequate food will be consumed.     

Sex reversal in Nile tilapia (Oreochromis niloticus) using a nonsteroidal aromatase inhibitor

Several studies have demonstrated that steroid hormones can influence sex differentiation in nonmammalian vertebrates and it has been hypothesized that male and female sex differentiation are driven by androgen and estrogen hormones, respectively. Estrogen biosynthesis is mediated by the steroidogenic enzyme cytochrome P450 aromatase, which converts androgens to estrogens. In the present study we examined the efficacy of a potent nonsteroidal aromatase inhibitor incorporated into the food, on sex reversal of Nile tilapia (Oreochromis niloticus) larvae. Nile tilapia larvae were divided in seven groups, which were fed with diets containing different amounts of the aromatase inhibitor Fadrozole (0, 50, 75 and 100 mg/kg) during 15 and 30 days, starting 9 days after hatching. Independent of the period, the proportion of males was significantly higher in the treated groups. Treatment with the highest doses (75 and 100 mg/kg) for 30 days produced 100% males. Histological examination revealed no differences in gonadal tissues between control males and treated fish. Furthermore, one intersex fish was identified in the group treated with 50 mg Fadrozole/kg for 30 days. This study reports that a 100% Nile tilapia male population can be obtained by suppressing aromatase activity and suggests that besides steroid hormones, nonsteroidal compounds, such as aromatase inhibitors, have potential for production of monosex population in tilapia. J. Exp. Zool. 290:177-181, 2001.     

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.

     

Interactions between Nile tilapia (Oreochromis niloticus) and cladocerans in ponds (Khartoum,Sudan)

Juvenile Nile tilapia (Oreochromis niloticus) are omnivorous, and the question asked in this study is how they affect on their environment? Do they mainly act as predators on the cladoceran zooplankton or do they compete with the cladocerans for phytoplankton? This problem was studied in three ponds with and three ponds without small tilapia (3–5 cm). The fish growth rate, the succession of plankton species and the changes in abiotic conditions, were monitored over a period of 67 days. The fish biomass was kept low and the mean was approximately constant (12.6 g m^?2) during the experiment. Phosphate was added to avoid phytoplankton nutrient limitation. Although the diet of Nile tilapia contained both phytoplankton and zooplankton, the fish affected the ecosystem in a similar way as zooplanktivorous fish. The fish ponds got more phytoplankton due to increase of Chlorophyta. Effects on the other phytoplankton groups Euglenophyta, Bacillariophyta, Cryptophyta and Cyanophyta could not be registered. The ponds without fish had higher densities of Daphnia lumholtzi and D. barbata. The other Cladocerans seemed less influenced by fish presence. The relative fish growth rate was most positively correlated with the density of Daphnia lumholtzi, Diaphanosmoa excisum and Bosmina longirostris. Tilapia seemes to have two feeding modes: (1) preying on large zooplankton and (2) unselective filtration of small planktonic organisms such as phytoplankton. In our experiment the first feeding mode affected the ecosystem more than the second.     

Aluminum as an endocrine disruptor in female Nile tilapia (Oreochromis niloticus)

The effects of aluminum on plasma ion, lipid, protein and steroid hormone concentration were evaluated in Oreochromis niloticus broodstock females. Lipid and protein concentrations from the gonads and liver were also measured. Experiments were performed at neutral and acidic water pH. Four groups of fish were tested for 96 h: 1) control conditions at neutral water pH; 2) control conditions at acidic water pH (CTR-Ac); 3) aluminum at neutral water pH (Al-N); and 4) aluminum at acidic water pH (Al-Ac). Aluminum and acidic water pH exposure caused no ionoregulatory disturbances. Total lipid concentration increased in the mature gonads and decreased in the liver, suggesting an acceleration of lipid mobilization to the ovaries in animals exposed to aluminum. However, a decreased protein concentration in ovaries was also observed. Exposure of control fish to acidic water pH caused an increased concentration of plasma 17α-hydroxyprogesterone. However, females exposed to aluminum at acidic water pH showed a decreased of plasma 17α-hydroxyprogesterone and cortisol. No differences in plasma 17β-estradiol were observed. The physiological mechanisms underlying the disturbances observed are discussed focusing on reproduction. We suggest that aluminum can be considered an endocrine disrupting compound in mature O. niloticus females.     

Clock-controlled endogenous melatonin rhythms in Nile tilapia (Oreochromis niloticus niloticus) and African catfish (Clarias gariepinus)

The purpose of this work was to investigate the circadian melatonin system in two tropical teleost species characterized by different behavioral habits, Nile tilapia (diurnal) and African catfish (nocturnal). To do so, fish were subjected to either a control photoperiod (12L:12D), continuous light (LL) or darkness (DD), or a 6L:6D photoperiod. Under 12L:12D, plasma melatonin levels were typically low during the photophase and high during the scotophase in both species. Interestingly, in both species, melatonin levels significantly decreased prior to the onset of light, which in catfish reached similar basal levels to those during the day, demonstrating that melatonin production can anticipate photic changes probably through circadian clocks. Further evidence for the existence of such pacemaker activity was obtained when fish were exposed to DD, as a strong circadian melatonin rhythm was maintained. Such an endogenous rhythm was sustained for at least 18 days in Nile tilapia. A similar rhythm was shown in catfish, although DD was only tested for four days. Under LL, the results confirmed the inhibitory effect of light on melatonin synthesis already reported in other species. Finally, when acclimatized to a short photo-cycle (6L:6D), no endogenous melatonin rhythm was observed in tilapia under DD, with melatonin levels remaining high. This could suggest that the circadian clocks cannot entrain to such a short photocycle. Additional research is clearly needed to further characterize the circadian axis in teleost species, identify and localize the circadian clocks, and better understand the environmental entrainment of fish physiology.     

Dietary lipid sources affect cold tolerance of Nile tilapia (Oreochromis niloticus)

This study was carried out to evaluate the effects of dietary lipid sources on growth performance, fatty acids composition and cold tolerance of Nile tilapia (Oreochromis niloticus) fingerlings (7.00 ± 0.50 g/fish). The fish were fed four isonitrogenous (28% crude protein), isocaloric (500 kcal/100 g) diets containing four lipid sources; fish oil (FO), corn oil (CO), coconut oil (COCO) or fish oil/ corn oil mixture (1:1 ratio) (oil mix). The diets were offered to the fish at a daily rate of 3% of their body weights (BW), twice a day for two months. After the feeding trial, the fish were exposed to decreasing water temperature from 25 °C until the appearance of death symptoms. The results revealed that FO-based diets (FO and oil mix) produced the best growth rates and feed efficiency, followed by corn oil diet, while COCO resulted in the lowest performance. Fish fed on CO and oil mix showed higher body unsaturated fatty acids (UFA) and lower lethal temperature than those fed on FO- or COCO-based diets. These results indicate that cold shock can modify the lipid metabolism in Nile tilapia by lowering total body saturated fatty acids and raising n-6 and n-3 UFA. This finding suggests that the inclusion of high levels of plant oils in Nile tilapia feeds can enhance their cold tolerance.     

Identification and partial characterisation of a chitinase from Nile tilapia, Oreochromis niloticus

Measurement of chitinase activity in extracts from stomach, intestine, and serum of Nile tilapia with the artificial substrates 4-methylumbelliferil beta-D-N,N'-diacetylchitobioside and 4-methylumbelliferil beta-D-N,N'N"-triacetylchitotrioside (4MU[GlcNAc](2,3)) showed that an endochitinase was involved in the liberation of the fluorophore 4-methylumbelliferone (MU). Enzymes were isolated from tilapia serum by a combination of gel filtration, ion exchange, and reverse-phase chromatography. The molecular mass of the enzyme was estimated to be 75 kDa by SDS-PAGE, suggesting that the enzyme occurs as a monomer. The partially purified enzyme showed maximal activity at pH 7.0 when assayed with 4MU[GlcNAc](2) and lost its activity below pH 5.0 and above pH 8.0. The optimal pH of the purified enzyme toward the substrate 4MU[GlcNAc](3) was pH 9.0 and activity was lost below pH 8.0 and above pH 9.0. Our study has revealed the presence of a chitinolytic enzyme in the gastrointestinal tract and serum that may play a role in digestion and/or defense.     

Muscle growth in Nile tilapia (Oreochromis niloticus): histochemical,ultrastructural and morphometric study

Muscle growth in Nile tilapia (Oreochromis niloticus) was studied focusing on histochemical, ultrastructural, and morphometric characteristics of muscle fibers. Based on body length (cm), we studied four groups: G1=1.36+/-0.09, G2=3.38+/-0.44, G3=8.90+/-1.47, and G4=28.30+/-3.29 (mean+/-S.D.). All groups showed intense reaction to NADH-TR in subdermal fibers and weak or no reaction in deep layer fibers. In G3 and G4, an intermediate layer was also observed with fibers presenting weak reaction; in G4, groups of fibers with intense reaction were observed in the subdermal region. The myosin ATPase (m-ATPase) activities were acid-stable and alkali-labile in subdermal fibers; most deep layer fibers were alkali-stable and acid-labile. Intermediate fibers were acid-labile and alkali-stable. Two fiber populations were observed near deep muscle layer: one large presenting weak acid- and alkali-stable and the other small alkali-stable.During growth, muscle fiber hypertrophy was more evident in intermediate and white fibers for G3 and G4. However, in these groups, the presence of fiber diameters < or =21 microm suggested that there is still substantial fiber recruitment, confirmed by ultrastructural study, but hypertrophy is the main mechanism contributing to increase in muscular mass.     

Identification of a sex-determining region in Nile tilapia (Oreochromis niloticus) using bulked segregant analysis

Sex determination in the Nile tilapia (Oreochromis niloticus) is thought to be an XX-XY (male heterogametic) system controlled by a major gene. We searched for DNA markers linked to this major locus using bulked segregant analysis. Ten microsatellite markers belonging to linkage group 8 were found to be linked to phenotypic sex. The putative Y-chromosome alleles correctly predict the sex of 95% of male and female individuals in two families. Our results suggest a major sex-determining locus within a few centimorgans of markers UNH995 and UNH104. A third family from the same population showed no evidence for linkage of this region with phenotypic sex, indicating that additional genetic and/or environmental factors regulate sex determination in some families. These markers have immediate utility for studying the strength of different Y chromosome alleles, and for identifying broodstock carrying one or more copies of the Y haplotype.     

Immunotoxicity and hepatic function evaluation in Nile tilapia (Oreochromis niloticus) exposed to diazinon

The LC(50) of the organophosphorus pesticides (OPs) diazinon to Nile tilapia (Oreochromis niloticus) was determined, thereafter, hepatic activity, phagocytic index, percentages of active cells, relative spleen weight, total IgM concentration and lymphoproliferation rates were compared between diazinon exposed groups (LC(50) and (1/2)LC(50)) and non-exposed control group. Experimental data show that diazinon is highly toxic for juvenile Nile tilapia (LC(50)=7.830 ppm) and presents immunotoxic properties which affect both the innate and cellular adaptive immune responses of this fish, as revealed by the fact that splenocyte proliferation and phagocytic indices were significantly decreased after acute exposure to the pesticide. However, the hepatic biochemical parameters and the total circulating IgM concentrations were not affected in this experimental model.     

Protein and energy needs for maintenance and growth of Nile tilapia (Oreochromis niloticus)

A trial was undertaken with juvenile Nile tilapia fed graded levels of dietary protein (0–35% DP) over 7 weeks (28°C). Measurements of nitrogen and energy utilization were made using data on ADC, comparative carcass analyses, nitrogen excretion and oxygen uptake. Data indicate that the daily protein intake for maximum N gain was c. 12 g/kg/d and the maintenance protein requirements were about of 2g/kg/d. The optimal DP/DE ratio was found to be 18mg/kJ. Differences were observed in the data on endogenous nitrogen and energy utilization depending on the dietary treatments as well as on the criteria used.     

Genetic characterization of four strains of Nile tilapia (Oreochromis niloticus L.) using microsatellite markers

Four domesticated strains of Nile tilapia (Oreochromis niloticus L.) were genetically characterized using 14 microsatellite markers and 64 animals per strain. Two strains, Chitralada (AIT) and International Development Research Centers (IDRC) were obtained from the AIT institute, Bangkok, Thailand. The GIFT strain (5th generation) came from NAGRI, Thailand, and the GÖTT strain was supplied by the University of Göttingen, Germany. The average numbers of alleles per marker were 5.0 (GÖTT), 5.4 (AIT), 5.6 (IDRC) and 7.5 (GIFT). Private alleles were found at all markers with the exception of two. No fixation of alleles was found at any marker. Population differentiation, F_ST, was 0.178 (great genetic differentiation) and confirmed grouping of the animals in strains. The expected level of heterozygosity ranged from 0.624 to 0.711, but the observed level of heterozygosity significantly deviated from the expected level in three strains. This was probably because of small population size. Moderate to great genetic differentiation was found between strains. A phylogenetic tree reflected the strains known histories. Application of the Weitzman approach showed that all strains have added value for the total genetic diversity and thus should be retained.     

Effects of vitamin E on expressions of eight microRNAs in the liver of Nile tilapia (Oreochromis niloticus)

Currently, microRNAs (miRNAs) are known to regulate cellular processes such as apoptosis, differentiation, cell cycle, and immune functions, and their expression can be altered by distinct stress conditions, such as oxidative stress. In immune systems of fish, vitamin E (VE) has a defined role as an antioxidant. In order to understand the molecular mechanism of vitamin E defending from oxidative stress, three groups of juvenile Nile tilapia (Oreochromis niloticus) (initial weight 3.25 ± 0.02 g) were fed to satiation with 3 semi-purified diets containing VE (dl-α-tocopherol acetate) of 0, 50, and 2500 mg/kg supplementation, respectively, with the expressions of eight miRNAs (miR-21, miR-223, miR-146a, miR-125b, miR-181a, miR-16, miR-155 and miR-122) in the liver of tilapia subsequently detected after 8-week growth experiment. Results showed that VE-deficient (0 mg/kg supplementation) decreased the activity of superoxide dismutase (SOD), and decreased the expressions of miR-223, miR-146a, miR-16 and miR-122, while excessive supplementation of VE (2500 mg/kg) decreased SOD activity and increased the expressions of all the eight miRNAs. The targets of the eight miRNAs were further predicated with bioinformatic approach and the possible regulating mechanisms of VE via miRNAs were analyzed. The present study confirmed that the differences in dietary VE affected expression of hepatic miRNAs which may partly demonstrate the molecular mechanism of VE, and the new idea of introducing miRNAs into research will provide the basic data for researches of molecular nutrition.     

Dietary folic acid (FA) requirement of a genetically improved Nile tilapia Oreochromis niloticus (Linnaeus, 1758)

The present study was conducted to determine the dietary folic acid (FA) requirement of genetically improved Nile tilapia, Oreochromis niloticus. Experimental diets were supplemented with 0.04, 0.22, 0.48, 0.96, 2.25, or 4.07 mg/kg FA, respectively, and fed to three replicate groups of 15 tilapia (mean initial weight = 60.23 ± 2.60 g; mean ± SD) for 12 weeks. Results showed that the weight gain rate increased linearly with increasing dietary FA from 0.04 to 0.40 mg/kg, then remained stable with higher supplementation. Similarly, hepatic FA concentration, red blood cell count (RBC), hemoglobin concentration (HB) and hematocrit (HCT) all markedly increased in fish fed with 4.07 mg/kg FA compared to those fed a control diet (p < .05). Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities decreased with increasing dietary FA (p < .05). The FA requirement was estimated to be 0.4 mg/kg based on weight gain rate, and 0.7 mg/kg based on liver FA accumulation.     

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.