Significant Effect Of Salinity Research Articles

Differential metabolic rearrangements improve biomass and enhance the tolerance of two dwarf cashew (<i>Anacardium occidentale</i> L.) genotypes to salt stress

<abstract> <p>Salinity is one of the abiotic stresses that affect crop productivity and plant development the most. We aimed to analyze the physiological and biochemical responses of dwarf cashew (<italic>A. occidentale</italic> L.) genotypes subjected to salt stress. The experiment was carried out in a greenhouse with a completely randomized design in a 5 × 2 factorial scheme, with five salinity levels (0, 25, 50, 75, and 100 mM NaCl) and 2 dwarf cashew genotypes (Embrapa51 and CCP76). There was no significant effect of salinity on plant height, leaf number, and stem diameter; however, the dry biomass was significantly reduced. Chlorophylls, starch, and total free amino acids decreased with salt stress, mainly with 75 and 100 mM NaCl. The CCP76 genotype salt-stressed increased carotenoids, anthocyanins, total soluble carbohydrates, reducing sugars, sodium, and potassium ions compared to Embrapa51. Free proline was increased in response to salt stress in dwarf cashew genotypes. Interestingly, sucrose declined in Embrapa51 and increased in CCP76 in response to salinity. When submitted to 75 and 100 mM NaCl, i.e., under severe stress, CCP76 presented more sucrose than Embrapa51. Our results indicated that sucrose accumulation plays an important role in the acclimation of CCP76 to salinity. This disaccharide induces metabolic rearrangements, mostly in the levels of soluble carbohydrates and amino acids, which contribute to rebalancing the osmotic potential and help to maintain favorable plant metabolism under salt stress. Overall, the dwarf cashew CCP76 was more tolerant to salinity than Embrapa51.</p> </abstract>

The role of salinity on genome-wide DNA methylation dynamics in European sea bass gills.

Epigenetic modifications, like DNA methylation, generate phenotypic diversity in fish and ultimately lead to adaptive evolutionary processes. Euryhaline marine species that migrate between salinity-contrasted habitats have received little attention regarding the role of salinity on whole-genome DNA methylation. Investigation of salinity-induced DNA methylation in fish will help to better understand the potential role of this process in salinity acclimation. Using whole-genome bisulfite sequencing, we compared DNA methylation patterns in European sea bass (Dicentrarchus labrax) juveniles in seawater and after freshwater transfer. We targeted the gill as a crucial organ involved in plastic responses to environmental changes. To investigate the function of DNA methylation in gills, we performed RNAseq and assessed DNA methylome-transcriptome correlations. We showed a negative correlation between gene expression levels and DNA methylation levels in promoters, first introns and first exons. A significant effect of salinity on DNA methylation dynamics with an overall DNA hypomethylation in freshwater-transferred fish compared to seawater controls was demonstrated. This suggests a role of DNA methylation changes in salinity acclimation. Genes involved in key functions as metabolism, ion transport and transepithelial permeability (junctional complexes) were differentially methylated and expressed between salinity conditions. Expression of genes involved in mitochondrial metabolism (tricarboxylic acid cycle) was increased, whereas the expression of DNA methyltransferases 3a was repressed. This study reveals novel links between DNA methylation, mainly in promoters and first exons/introns, and gene expression patterns following salinity change.

The Effect of Salinity Stress on Enzyme Activities, Histology, and Transcriptome of Silver Carp (Hypophthalmichthys molitrix).

A 56-day study was performed to examine the effect of freshwater (FW) and brackish water (BW 6‱ salinity) on the antioxidant ability, Na+/K+-ATPase (NKA) activities, histology, and transcriptome of the gill and kidney tissue in juvenile silver carp (Hypophthalmichthys molitrix). The results show that when juvenile silver carp were exposed to 6‱ salinity, the activities of superoxide dismutase (SOD) and catalase (CAT) were shown to be substantially increased (p < 0.05), while glutathione peroxidase (GSH-PX) activities in gill were not significantly affected (p < 0.05). In kidney tissue, SOD, CAT, and GSH-PX, enzyme activities peaked at 24, 8, and 4 h, respectively, but were not significantly different compared with the control group (p < 0.05). In addition, significant effects of salinity were observed for the NKA level in both the gills and kidney tissues (p < 0.05). The gill filaments of juvenile silver carp under the BW group all underwent adverse changes within 72 h, such as cracks and ruptures in the main part of the gill filaments, bending of the gill lamellae and enlargement of the gaps, and an increase in the number of mucus and chloride-secreting cells. Transcriptome sequencing showed 171 and 261 genes in the gill and kidney tissues of juvenile silver carp compared to the BW group, respectively. Based on their gene ontology annotations, transcripts were sorted into four functional gene groups, each of which may play a role in salt tolerance. Systems involved in these processes include metabolism, signal transduction, immunoinflammatory response, and ion transport. The above findings indicate that the regulation processes in juvenile silver carp under brackish water conditions are complex and multifaceted. These processes and mechanisms shed light on the regulatory mechanism of silver carp osmolarity and provide a theoretical foundation for future research into silver carp growth in brackish water aquaculture area.

The longevity of subtidal mussel beds in the Dutch Wadden Sea

Soft-bottom beds of the blue mussel (Mytilus edulis) are of high ecological importance in intertidal and subtidal habitats. They create habitat, shelter and food for other organisms, and play a dominant role in energy flow and nutrient cycling. Intertidal beds are much better studied than subtidal beds. Though it is often assumed that subtidal mussel beds resemble their intertidal counterparts, major differences in factors driving recruitment, growth and survival can be expected. The aim of our study was to estimate survival chances of the mussel beds in the subtidal parts of the Dutch Wadden Sea in relation to environmental variables, and to compare the results with those obtained previously from the intertidal areas. We used data from a long-term annual survey, resulting in a survival analysis of 365 individual subtidal mussel beds. The average life span of subtidal mussel beds, once they have survived their first winter, was estimated at 2.3 years. This is lower than what was found in the intertidal (3.4 years) in a previous study. However, the survival of subtidal mussel beds in less-saline areas is comparable to survival of intertidal mussel beds, whereas survival of subtidal mussel beds in more-saline areas is significantly lower. The strong, significant effect of salinity is most likely an indication of an effect from starfish predation, since starfish (Asterias rubens) are virtually absent from the intertidal and their abundance is strongly reduced in the subtidal at lower salinities. Furthermore, the survival of individual beds is positively correlated with their size. This may be a direct effect of the bed size itself, or also an indirect effect of environmental factors that can affect the size of newly settled beds. A secondary aim was to compare two methods, based on different types of field data: 1) empirical point data and 2) estimated bed contours based on the point data and additional sources of information. Both methods give similar results. Advantages and disadvantages of both methods are discussed.

Enrichment of heavy metals as function of salinity and pH of estuarine sediments, South East Coast of India

ABSTRACT A predictive model was developed to determine the combined effect of salinity and pH on sediments enrichment of heavy metals; (EF) of Zn, Pb, Cu, and Ni in Uppanar estuary, India. Data covered four seasons of 2008–2009 and 2009–2010, and corresponded to fivestations scattered along Uppanar estuary. Salinity, pH, EFZn, EFPb, EFCu and EFNi were 17.85 ± 9.46, 7.62 ± 0.35, 9.51 ± 2.01, 3.54 ± 1.96, 10.85 ± 1.97, and 0.70 ± 0.20, respectively. For each metal, we fitted a regression model with EF as response, and the interaction between salinity and pH as predictor. We found that the interaction of salinity and pH predicts EFPb (F3,36 = 9.03, P < 0.001) and EFNi (F3,36 = 3.22, P = 0.034). Specifically, salinity and pH were positively associated with EFPb and negatively associated with EFNi. We found no significant effect of salinity and pH interaction on EFZn (F3,36 = 2.56, P = 0.069) and EFCu (F3,36 = 1.68, P = 0.188). We conclude that a joint effect of salinity and pH on EF varies with heavy metals species, and when significant, takes a different pattern depending on the predominant geochemical phase and source of heavy metals

Effect of biofloc system at different salinities and crude protein levels on water quality, growth performance, and survival rate of flathead grey mullet (Mugil cephalus).

The present trial was conducted to study the effects of C/N ratio to biofloc technology (BFT) at different salinities on water quality, growth performance, and economic feasibility of flathead grey mullet fingerling. BFT was in natural light (12:12h light: dark schedule) with concrete tanks (size 6m3 water), filled with underground marine and tab water, representing three salinities (fresh, brackish 15.5ppt, and saline 33ppt). Diets contain crude protein (20%, 24%) were applied under the biofloc system, two levels of C/N ratio through adding 60% starch of the produced daily diet. Two biofloc treatments under different salinity were managed. BFT ponds were aerated and agitated using an air blower. Forty-two fingerlings with an initial body weight of 10.89 ±0.12 g/fish of grey mullet were stocked in each pond. Feed was applied daily at 3% of the total fish biomass in each pond. Survival rates of the mullet were above 91%, with a significant (P≤0.05) difference for the brackish water with both (20%, 24% CP). Regarding growth performances of the grey mullet at the three salinities with 60% starch, the highest final body weight (FBW), weight gain (WG), and specific growth rate (SGR) values were recorded for fish reared in fresh and brackish water, respectively with no significant differences due to salinities or diets. Water quality parameters alternated between safe values except for nitrate, and no significant (P>0.05) difference was recorded for zooplankton counts. No significant effects of salinity on the mullet growth were recorded under BFT.

Water salinity and postprandial effects on transcription of peptide and amino acid transporters in the kidney of Mozambique tilapia (Oreochromis mossambicus)

Preservation of amino acids is highly important, as these are vital nutrients that support many physiological and biochemical processes. During fish osmoregulation, the kidney reabsorbs amino acids and short peptides that are filtered from the blood into the nephron. However, little is known about reabsorption systems in teleost kidney. To identify transporters involved in this process, we examined by PCR the expression of eight genes, coding to peptide and amino acid transporters, as well as of two ion transport systems, in the kidney of the euryhaline Mozambique tilapia (Oreochromis mossambicus). We found that three amino acid transporters (slc1a5, ASCT2; slc7a9, b0,+AT; slc6a19, B0AT) and one peptide transporter (slc15a2, PepT2) were expressed in the kidney, as were the two ion transporters VHA and NHE3 (coded by atp6v1a and slc9a3, respectively). Next, to investigate transcriptional interactions of these transporters with osmoregulation and nutritional status, we compared by qPCR expression levels in fish acclimated to either fresh or saltwater and at three time points after feeding (6, 24, 72 h). Significant effect of salinity was detected on the expression of ASCT2 and VHA, whereas time after feeding affected PepT2 and VHA transcripts. Interactions between salinity and feeding significantly affected NHE3 transcription. PepT2 expression was an order of magnitude higher than free amino acid transporters, indicating the importance of peptide reabsorption in the kidney of Mozambique tilapia. Immunofluorescence staining of PepT2 showed an apical staining while, b0,+AT antibody stained the basolateral membrane of the nephrons epithelial cells. The two transporters expression were found in separates segment of the nephrons. These results reveal specific transporters involved in kidney reabsorption of amino acids and short peptides and their response to the fish osmotic and nutritional status.

Salinity mediates the effects of nitrogen enrichment on the growth, photosynthesis, and biochemical composition of Ulva prolifera.

To study the combined effects of multiple nitrogen (N) sources and salinity on the growth and physiology on macroalgae, we cultured Ulva prolifera under three N levels (N0, 0.1235 mg L-1; N1, 0.6 mg L-1; and N2, 4.4 mg L-1; the ratios were 18:74:8 for NH4-N, NO3-N, and NO2-N, respectively) and three salinity conditions (15, 25, and 35). Then, the growth, pigment content, photosynthetic performance, superoxide dismutase (SOD) activity, and contents of soluble protein and carbohydrates were measured. The results showed the following: (1) Compared to that grown at salinity 25, the growth of U. prolifera decreased under salinity 35, especially under the N0 and N2 levels, but there were no significant effects of salinity 15 under any of the N levels. (2) There were no significant effects of salinity on the chlorophyll a (Chla) content, but compared to the content at salinity 25, the chlorophyll b (Chlb) content was enhanced by salinity 15 and 35; lower ratio values between Chla and carotenoids (Car) occurred under the salinity 25 treatment. Under each salinity condition, the pigments were enhanced by a high N level. (3) A relatively higher salinity level decreased the photosynthetic oxygen evolution rate, while a higher N level increased this value. Compared to the rate at salinity 25, the dark respiration rate (Rd) significantly increased at salinity 15 under the N0 condition. (4) SOD activity was enhanced by a high N level, but no significant effects of salinity were observed. (5) The carbohydrate content was enhanced at salinity 35 under the N0 and N1 levels, and under salinity 15, this value increased with increasing N levels. In conclusion, although the growth of U. prolifera decreased at high N levels under high salinity conditions, a high N level induced an increase in photosynthesis, while no significant decrease in growth occurred. These findings indicate that low salinity and high N levels may be nonnegligible reasons why this species thrives, and low salinity was the better choice when this species was used for wastewater treatment.

The effects of salinity and photoperiod on aerobic scope, hypoxia tolerance and swimming performance of coho salmon (Oncorhynchus kisutch) reared in recirculating aquaculture systems

Land-based recirculating aquaculture systems (RAS) have been used to rear salmon from smolt to market-sized adults, but high operating costs have limited their wide spread adoption. One clear advantage of using RAS for salmon aquaculture over open net pens is that fish can be reared under optimal conditions in an attempt to maximize growth and physiological performance and reduce overall production costs. However, few studies have attempted to define the optimal conditions for the long-term rearing of salmon. Thus, the goal of this study is to determine the effects of salinity and photoperiod, two factors that can be easily manipulated in RAS, on the physiological performance of coho salmon (Oncorhynchus kisutch) during long-term rearing. To address this goal, post-smolt coho salmon were reared for 150 days in replicate RAS at 2.5, 5, 10 and 30 ppt under either 12:12 and 24:0 (light:dark) photoperiods. Routine metabolic rate, maximum metabolic rate, aerobic scope and hypoxia tolerance were measured at 60 and 120 days of rearing, while swimming performance was assessed at 60 and 150 days of rearing. There were no effects of salinity or photoperiod on metabolic rate measurements, hypoxia tolerance or swimming performance at any sampling time. There were, however, significant effects of salinity and photoperiod on post-swimming hematology. The results suggest that physiological disturbances continue to manifest due to different environmental conditions, despite acclimation, but do not hinder the animal's ability to cope with physiological stressors. Overall, rearing salinity and photoperiod had very few measurable effects on the physiology and performance of coho salmon except the ionoregulatory disturbances following swimming at salinities of 2.5 and 30 ppt.

Influence of salinity and linoleic or α-linolenic acid based diets on ontogenetic development and metabolism of unsaturated fatty acids in pike perch larvae (Sander lucioperca)

Combinations of nutritional requirements and husbandry rearing conditions during early ontogeny are poorly studied in pikeperch (Sander lucioperca). The substitution of marine oils with vegetable oils has reduced stress tolerance and caused neurophysiological changes in pike perch larvae, but effects of environmental cues are limited. Saline water influences on a range of physiological functions during early fish larval ontogeny and may affect FA metabolism, − elongation and desaturation - activity when given diets limited in LC PUFAs, but rich in shorter chain n-3 or n-6 PUFAs. Consequently, live Artemia differing in 18:2n-6 (LA) and 18:3n-3 (ALA) content by enrichment with sunflower oil (SFO) or linseed oil (LO) were fed to 10 days post hatch (DPH) larvae and reared up to isosmotic salinities (0, 5, 10 ppt) until 30 DPH. Larval tissue FA composition was examined at 15, 25 and 30 DPH. Besides, an in vivo assay was performed on 20 DPH larvae with 14C labelled FA including LA; ALA; 20:4n-6 (ARA); 20:5n-3 (EPA) or 22:6n-3 (DHA) to establish FA incorporation and metabolism. At 30 DPH, performance, digestive enzymatic activity, eicosanoid activity, skeletal anomalies and stress sensitivity were further evaluated. Results on larval FA profiles suggest a low desaturation and elongation capability over LA and ALA, with no significant effects of salinity or larval age on modulation of unsaturated fatty acid metabolism. In vivo assays revealed that regardless of salinity or diet, pikeperch possess a marked specificity to incorporate ARA and EPA compared to a poorer incorporation of DHA. Larvae exposed to a confinement stress test caused high acute mortality in all experimental groups except for a control group fed with Artemia enriched by a commercial DHA Selco emulsion. Growth performance was not significantly affected by salinity or dietary enrichment with SFO or LO, but influenced on larval enzymatic activity of pepsin, aminopeptidase, trypsin and alkaline phosphatase, while lipase activity was not significantly affected. Increased saline conditions significantly decreased hormonal prostaglandin eicosanoid PGE2, PGE3 activity with the highest activity at 0 ppt. The prevalence of severe skeletal anomalies was generally high, affecting over 75% of the larval population with negative effects by increase in salinity. The incidence of anomalies was higher on endochondral bones, namely maxillary, ranging from 58 to 83% of the population. These results agree well with those from expression of sox 9 and twist2 genes; involved in chondrocyte ossification and differentiation.

Effect of salinity on medium- and low-pressure UV disinfection of Vibrio cholerae.

The problem of biological invasions attributed to ballast water release is an ongoing problem that threatens ecosystems and human health. Ultraviolet (UV) radiation has been increasingly used for ballast water treatment mainly due to the advantages of short contact time and minimized harmful disinfection by products. In this study, the impact of salinity on the inactivation of Vibrio cholerae (NCTC 7253) was examined, and comparison of inactivation level and disinfection kinetics after medium-pressure (MP) (1 kW) and low-pressure (LP) (10 W) UV irradiation was made. MP UV exposure resulted in higher inactivation efficacy against V. cholerae than LP UV exposure especially at lower UV doses (≤3 mJ cm-2) and salinity had a negative impact on both MP and LP UV disinfection, especially at higher UV doses (≥3 mJ cm-2 for MP and ≥4 mJ cm-2 for LP). To understand the mechanisms of salinity effect on V. cholerae, the enzyme-linked immunosorbent assay (ELISA) was employed to determine the number of cyclobutane pyrimidine dimers (CPDs), one major type of DNA damage. No significant effects of salinity were found at the CPDs level except for 3% artificial seawater after LP UV exposure case. It is imperative that site-specific conditions of salinity be taken into account in the design of UV reactors to treat V. cholerae and other species.

Growth and physiological responses of Sporobolus robustus kunth seedlings to salt stress

ABSTRACTSeedlings of S. robustus were exposed to increasing NaCl concentrations (0, 50, 100, 150, 200, 250, and 300 mM) for 50, 100, and 150 days, in greenhouse conditions. Total dry weight and salt tolerance index decreased gradually with increasing NaCl concentrations. The optimum growth of S. robustus (4.12 to 5.25 g · plant−1) was obtained between 0 and 150 mM at 150 days after salt stress. Foliar chlorophyll a and total chlorophyll contents increased with NaCl concentration at 50 days after treatment. There was no significant effect of salinity on chlorophyll a, b and total chlorophyll contents at 100 and 150 days after treatment. Higher Na contents were found in the shoots as compared to the roots. The Na content increased, while K decreased with increasing NaCl concentrations, suggesting competitive inhibition between absorptions of Na and K as a consequence, the K/Na ratios in shoots and roots decreased with increasing salinity. The proline contents in S. robustus were more pronounced at 300 mM (2.02 µmol/g), 250 mM (2.64 µmol/g), and 200 mM NaCl concentrations (2.98 µmol/g) for 50, 100, and 150 days, respectively, as compared to the treatment without added NaCl. Overall, S. robustus could be considered as salt tolerant on the basis of their performance in biomass production, accumulation of Na, similar foliar chlorophyll a, chlorophyll b and total chlorophyll contents, and accumulation of proline with increasing salinity. The potential ability of S. robustus to accumulate significant amounts of Na makes this halophyte promising as a desalinization tool of salted soils.

Salinity stress response in estuarine fishes from the Murray Estuary and Coorong, South Australia.

Estuaries are unstable ecosystems and can be changed by the environmental and anthropogenic impact. The Murray Estuary and Coorong were degraded by drought and low freshwater input in the last decade and therefore transformed into the largest hyper-saline lagoon in Australia. This study evaluates the physiological stress of two estuarine fish species (small-mouthed hardyhead Atherinosoma microstoma and Tamar goby Afurcagobius tamarensis) to the induced salinity change in captivity. The test fishes were collected from the Coorong and transported to the laboratory in the water from the Coorong. Each fish species was exposed to different levels of salinity, and a number of enzymes were assessed to measure the stress response of fish to salinity change. The activity of reactive oxygen species was significantly increased with the salinity change in both fish species compared with the fish in the control. Significant salinity effect on superoxide dismutase activity was observed on Tamar goby but not on small-mouthed hardyhead. Conversely, the impact of salinity on catalase activity was detected on small-mouthed hardyhead but not on Tamar goby. The study reveals that the induction of physical stress by salinity changes occurred in both Tamar goby and small-mouthed hardyhead despite the varying response of antioxidant enzymes between fish species. The study provides an insight into the understanding of physiological adaptation in estuarine fish to salinity change. The results could improve our knowledge on stress response and resilience of estuarine fish to hypo- and hyper-salinity stress.

Differential expression of amino-acid transporters along the intestine of Mozambique tilapia (Oreochromis mossambicus) and the effect of water salinity and time after feeding

Nutrients are absorbed through transporters located in the brush border of intestinal absorptive epithelial cells. These transporters are complexes of proteins that control the uptake or removal of different compounds through cell and organelle membranes. Ingested proteins are catabolized to short-peptide and amino acids, which are absorbed through specified intestinal transporters. Two key complexes in this process are the B0AT (encoded by the SLC6A19 gene) and B0,+AT (encoded by the SLC3A1 and SLC7A9 genes), that transfer neutral and cationic amino acids. This research was conducted in Mozambique tilapia (Oreochromis mossambicus), with the aim of characterizing the dynamic of their expression along different intestinal sections at different time-points after feeding, in different water salinities. Our results demonstrated the dynamic of gene expression patterns along the intestine, with significant salinity effect on the genes encoding to the B0,+AT. Differences in expression levels with time after feeding were found in all three genes, with the highest expression observed at 6h after feeding, in the middle intestine. Some of our results differ from what was expected based on data from mammalian organisms, and with only few previous studies on these transporters in any fish species, this is one of the first steps toward characterization of their regulation in fish. Statement of RelevanceThe results can lead to better food utilization.

Photoperiod buffers responses to salt and temperature during germination of two coastal salt marsh colonizers Juncus acutus and Juncus maritimus

Juncus acutus and J. maritimus are two colonizers of coastal marsh rangeland with worldwide distribution. We tested the effect of salt, temperature, and photoperiod on the germination capacity of seeds of the two Juncus from the Rhône delta (south of France). We measured the first day of germination, the mean time, speed, and rate of germination on seeds subjected to five salinity levels, three Dark–Light temperatures and two D-L photoperiods (12–12 and 10–14). The 10–14 D-L photoperiod, although it corresponds to one of the two main germination periods of J. acutus and J. maritimus in the northern Mediterranean, has never been previously used to study their germination capacity. Analyses showed significant effects of salinity and temperature on the germination parameters tested, and for these two factors we found results comparable to those of previous studies. Salinity slowed down and reduced the germination process while spring temperatures had a positive effect. A surprising result was obtained by changing the D-L photoperiod from 12–12 to 10–14 which then largely buffered the negative effect of salt and high temperatures on germination. This capacity of J. acutus and J. maritimus to withstand salty conditions during the germination phase due to the spring photoperiod could be decisive in the ability of both species to colonize saline environments.

Salinity Tolerance Ranking Of Various Wheat Landraces From The West Of The Urmia Saline Lake In Iran By Using Physiological Parameters

In recent years, considerable interest has been focused on the use of physiological parameters as selection criteria in salt tolerance ranking. Eighteen bread wheat (Triticum aestivum L.) landraces from the west area of the Urmia Saline Lake were grown in a greenhouse in the Department of Plant Biology and Halophytes Biotechnology Center, Azarbaijan University of Tarbiyat Moallem, Tabriz, Iran to study the effects of increasing levels of sodium chloride (NaCl) (control, 75, and 150 mM) on the plant leaves. The experimental design was factorial with a randomized complete block with three replications. The results showed salinity caused an obvious decrease in growth of all landraces. Physiological parameters such as lipid peroxidation, hydrogen peroxide (H2O2) content, and cell membrane injury increased with increasing salinity levels with different degrees among the landraces. Salt stress increased the sodium (Na+) accumulation coupled with a decrease in leaf potassium (K+) depending on salinity levels. The analysis of variance showed significant effects of salinity, landraces and their interactions in all studied parameters. The landraces were ranked for salt tolerance indexes, and cluster group ranking ordered landraces from tolerant to sensitive and their properties for salt stress tolerance are open for further research.

염분농도에 따른 해양미세조류(Nannochloropsis oculata)의 지질 및 지방산의 변화

The quality and quantity of food organisms in fish seed production are important. The marine microalgae Nannochloropsis oculata are used as initial food organisms in the field. We investigated the effects of salinity (0, 10, 20, 30, 40 and 50 psu) on the lipid and fatty acid composition of N. oculata. Cultivation of N. oculata at varying salinities showed the highest growth rate at 20 psu. Total lipid content ranged from 17.26 to 18.63% at salinities from 0 to 50 psu). The nonpolar lipid content increased markedly at 30 psu and was highest at 15.55%. The polar lipid content was lowest at 30 psu, by 84.45%. It was also found that the omega-3 and EPA contents were inversely proportional to salt concentration. For the polar and nonpolar lipid compositions, there was no significant effect of salinity. Omega-3 polyunsaturated fatty acid content especially the content of EPA in the seawater larvae is the essential fatty acid in this food organism. It is thus advantageous to culture N. oculata at 20 psu.

Calanipeda aquaedulcis and Arctodiaptomus salinus are exceptionally euryhaline osmoconformers: evidence from mortality, oxygen consumption, and mass density patterns

Mortality, respiration rate, and body mass density of the estuarine copepods Cala- nipeda aquaedulcis and Arctodiaptomus salinus and their eggs were studied over a wide range of salinities. Empirical hydrodynamic modeling was applied to calculate body mass density using the sinking speed of the copepods. According to the index of median lethal salinity (LS50), the salinity tolerance ranges of C. aquaedulcis and A. salinus reared at 18 psu were 0.1 to 50 and 0.1 to 35 psu, respectively. No significant effect of salinity on the specific oxygen consumption rate was found in the range from 0.1 to 40 psu in both species, while mean body mass density increased iso-osmoti- cally with water salinity from (mean ± SD) 1.053 ± 0.007 to 1.077 ± 0.005 g cm �3 in C. aquaedulcis and from 1.039 ± 0.004 to 1.062 ± 0.007 g cm �3 in A. salinus. However, body density contrast and sinking speed were stable in both species, allowing them to avoid buoyancy problems with changing salinity. The mean mass density of resting eggs in A. salinus gradually increased iso- osmotically following gradual changes in salinity. In contrast to resting eggs, the mass density of subitaneous eggs was not altered by changes in the surrounding salinity, suggesting a hysteresis response in these eggs.

Partitioning of respiratory energy and environmental tolerance in the copepods Calanipeda aquaedulcis and Arctodiaptomus salinus

Total and basal metabolism was studied in the widely distributed copepod species Calanipeda aquaedulcis and Arctodiaptomus salinus of both genders in order to estimate respiratory energy partitioning. Specific oxygen consumption was found to double in C. aquaedulcis than in A. salinus, and double in males than in females both in terms of total and basal metabolism. Respiration rates in females carrying ovisacs were 1.49 and 1.43 times higher than those in females without ovisacs for C. aquaedulcis and A. salinus, respectively. Extra energy expenditures are due to carrying ovisacs and egg respiration. There was no significant effect of salinity (0.1–40), oxygen concentration (1–8 mg O2 l−1) or crowding on oxygen consumption confirming the hypothesis that C. aquaedulcis and A. salinus are the animals with a type of respiratory metabolism independent of salinity and oxygen concentration. At critical oxygen concentrations less than 1 mg O2 l−1 respiration rate fell notably by approximately an order of magnitude in both species and in both genders.

An experimental study on food and salinity preferences of two Brachionus plicatilis rotifer strains from Iran

Effects of feeding on four algal species (Chlorella vulgaris, Nannochloropsis oculata, Isochrysis galbana and Scenedesmus obliques) at salinities of 5, 15 and 25 on the population growth parameters of two Iranian strains of the widespread rotifer species Brachionus plicatilis were examined. Maximum specific growth rate of 0.55±0.02 day−1 and final population density of 7 961±3 267 ind. ml−1 were observed in the Ba strain fed with Chlorella at a salinity of 15. The minimum population density of 10±0 ind. ml−1 occurred in the Ba strain fed with Scenedesmus at a salinity of 5. There were significant differences in the egg ratio (number of eggs/number of females) between the two rotifer strains when fed with Scenedesmus at a salinity of 15. Multivariate post hoc comparisons demonstrated the significant effects of algal species on all estimated parameters in both rotifer strains and the significant effects of salinity and salinity × algae on specific growth rate and population density of the Ba strain.