An efficient immersed boundary-lattice Boltzmann method for the hydrodynamic interaction of elastic filaments

We have introduced a modified penalty approach into the flow-structure interaction solver that combines an immersed boundary method (IBM) and a multi-block lattice Boltzmann method (LBM) to model an incompressible flow and elastic boundaries with finite mass. The effect of the solid structure is handled by the IBM in which the stress exerted by the structure on the fluid is spread onto the collocated grid points near the boundary. The fluid motion is obtained by solving the discrete lattice Boltzmann equation. The inertial force of the thin solid structure is incorporated by connecting this structure through virtual springs to a ghost structure with the equivalent mass. This treatment ameliorates the numerical instability issue encountered in this type of problems. Thanks to the superior efficiency of the IBM and LBM, the overall method is extremely fast for a class of flow-structure interaction problems where details of flow patterns need to be resolved. Numerical examples, including those involving multiple solid bodies, are presented to verify the method and illustrate its efficiency. As an application of the present method, an elastic filament flapping in the Kármán gait and the entrainment regions near a cylinder is studied to model fish swimming in these regions. Significant drag reduction is found for the filament, and the result is consistent with the metabolic cost measured experimentally for the live fish.     

Amperometric Sniffer for Volatile Amines Based on Paper‐Supported Room Temperature Ionic Liquids Enabling Rapid Assessment of Fish Spoilage

A gas sensors based on a room temperature ionic liquid (RTIL) supported on paper is proposed as amperometric sniffer for monitoring volatile amines (VAs) released from fish samples, in order to gain indication of their state of turning spoiled. It was used as a paper electrochemical detector (PED) for a flow injection system in which controlled headspace volumes in equilibrium with ice‐stored fish samples were directly injected. The performance of this RTIL‐PED sensor was preliminarily tested on synthetic samples of trimethylamine (TMA), dimethylamine (DMA), methylamine (MA) and ammonia (i.e. the main species responsible for the typical flavor of spoiled fish), thus verifying that only TMA, DMA and MA can be detected because NH₃ oxidation occurred beyond the solvent discharge. This notwithstanding, detection of the sole TMA, DMA and MA as a whole turned out to be well suited for the rapid assessment of fish spoilage, since during storage the release enhancement for these amines is largely predominant over that of NH₃. Repeatable (8 % RSD) sharp peaks were detected for all amines above over a wide range (5–1000 nmol) and a detection limit of a little more than 3 nmol was inferred for a signal‐to‐noise ratio of 3. This approach was applied to the detection of VAs released from real fish samples (sardines), in parallel to the determination of their total volatile basic nitrogen (TVBN), which is a conventional indicator frequently adopted for the chemical quality assessment of fish. A substantially satisfactory agreement was found by comparing the data achieved by these two approaches.     

Methylmercury determination in sediments and fish tissues from the Nerbioi-Ibaizabal estuary (Basque Country, Spain)

The analysis of methylmercury in extracts from environmental solid samples by gas chromatography coupled to microwave induced plasma atomic emission spectrometry (GC-MIP/AES) after the ethylation of the extract and the preconcentration of the volatile products in hexane has been critically investigated. In order to correct potential sources of random error along the analytical procedure affecting the overall repeatability of the analysis, the use of the inorganic mercury naturally occurring in the sample as internal standard in the analysis of methylmercury is proposed. A study to establish the best conditions to achieve a quantitative recovery of methylmercury without damaging its chemical structure has also been carried out. Magnetic stirring (without heating) of the sediment or fish tissue with 2 mol dm⁻³ HNO₃ or 10% methanolic KOH, respectively, during 90 min has been considered as the most effective procedure to release methylmercury preserving its structure. The proposed method has been validated using certified reference materials (CRM-580, CRM-463 and DOLT-2), assessing its quality in terms of accuracy, repeatability and detection limit. Finally, several sediment and fish samples collected in the estuary of the Nerbioi-Ibaizabal (Bilbao, Basque Country) have been analyzed following the procedures proposed. The results obtained show the validity of the proposed method to analyze real samples.     

Determination and comparison of heavy metals in selected seafood, water, vegetation and sediments by inductively coupled plasma-optical emission spectrometry from an industrialized and pristine waterway in Southwest Louisiana

Samples of crab, fish, sediments, vegetation and waters were collected from a pristine (Rockefeller Wildlife Refuge) and historically polluted (Bayou d'Inde) waterway in Southwest Louisiana. After sample preparation via microwave digestion to obtain a solution, cadmium, mercury, nickel and lead were determined by inductively coupled plasma-optical emission spectrometry. A comparison of results showed that there was very little difference in concentrations for the four metals between the two areas, typically in the 10 μg/g range for crabs and fish, around 0.05 μg/mL or lower for waters, and somewhat higher for sediments and vegetation of around two to three times.     

Trace metal concentrations in single specimens of the intestinal broad flatworm (Diphyllobothrium latum), compared to their fish host (Oncorhynchus mykiss) measured by total reflection X-ray fluorescence spectrometry

The aim of this study was to investigate (1) whether intestine endoparasites (Diphyllobothrium latum) accumulate trace elements related to its body size and (2) whether parasites bioconcentrate more trace elements than their host. Freshwater fish (rainbow trout Oncorhynchus mykiss) were sampled in the deep, oligotrophic and uncontaminated Lake Riñihue in Southern Chile. The element concentration of different organs (intestine, muscle, liver) and of the intestine endoparasites were analyzed using total reflection X-ray fluorescence spectrometry. The results showed that the mass fraction for Mn, Fe, Ni, Cu, and Pb decreased significantly with the body size (dry weight) of the endoparasite. Only Zn did not reveal such a relationship. Small parasites accumulated up to 80 times more Fe, Ni, Mn, Pb, and Cu than large parasites. Compared to the fish organs, small parasites accumulated in maximum 35 to 307 times more Mn, 5 to 255 times more Fe, 98 to 220 times more Ni, 3 to 175 times more Cu, and 0.4 to 12 times more Zn than the fish. Lead was only found in the endoparasite, but not in the fish organs. We conclude that (1) D. latum is a good indicator for trace element accumulation in fishes and that (2) small endoparasites are more sensitive as bioindicators because they showed higher bioconcentrations of trace metals than larger parasites.     

Optical enzyme sensor for determining <Emphasis Type="SmallCaps">l</Emphasis>-lysine content using <Emphasis Type="SmallCaps">l</Emphasis>-lysine oxidase from the rockfish <Emphasis Type="BoldItalic">Sebastes schlegeli</Emphasis>

l-Lysine (l-Lys) in living bodies is critical for metabolism; therefore, determination of its levels in food is important. Most enzymatic methods for l-Lys analysis are performed using l-lysine oxidase (LyOx), but commercially manufactured LyOx is generally not highly selective for l-Lys among amino acids. We previously isolated LyOx as an antibacterial protein secreted from the skin of the rockfish Sebastes schlegeli. In the present study, we developed an optical enzyme sensor system for rapid and continuous determination of l-Lys using this LyOx. The system comprised an immobilized LyOx membrane, an optical oxygen probe, a flow system, and a personal computer. The amount of l-Lys was detected as a decrease in the oxygen concentration due to the LyOx reaction. The specificity of the sensor was examined against various amino acids. The sensor response was specific for l-Lys. Good reproducibility was obtained in 58 assays. The response of the sensor using commercially prepared LyOx was unstable compared with the response using LyOx isolated in our laboratory. Our sensor system could be used for 5 weeks without our having to change the enzyme membrane. The calibration curve for a standard l-Lys solution was linear from 0.1 to 3.0 mmol L⁻¹. One assay could be completed within 2 min. The sensor was applied to determine the l-Lys content in food samples such as bonito cooking water and scallop hepatopancreas. The values obtained using the sensor and conventional high-performance liquid chromatography methods were well correlated.     

Development of a group selective molecularly imprinted polymers based solid phase extraction of malachite green from fish water and fish feed samples

A group selective molecularly imprinted solid phase extraction (MISPE) for malachite green (MG) from fish water and fish feed samples was developed. Using MG as template molecule, methacrylic acid as functional monomer, ethylene glycoldimethacrylate as linking agent and bulk polymerization as synthetic method, the molecularly imprinted polymers (MIPs) were synthesized and characterized with rebinding experiment. The Scatchard polt's analysis revealed that the template-polymer system showed the two-site binding behavior with dissociation constants of 0.3194 μmol L⁻¹ and 15.70 μmol L⁻¹, respectively. MG and two structurally related compounds, leucomalachite green (LMG) and crystal violet (CV) were employed for selectivity test. The MIPs exhibited the highest selective rebinding to MG, but also displayed 83.0% and 87.5% of cross-reactivity with LMG and CV, demonstrating that MIPs could be used as group recognition sorbents in solid phase extraction. The extraction conditions of MISPE column for MG were optimized. Tap water samples spiked with MG at concentration of 0.5-10 ng mL⁻¹ were extracted by MISPE column and analyzed by high performance liquid chromatography. The recoveries of MISPE column for MG extraction were found to be 76.8-93.7% with the relative standard deviations of 2.12-10.09%, indicating the feasibility of the prepared MIPs for MG extraction. No detectable MG was observed in one fish farming water sample and two fish feed samples; while the MG concentrations in two pet fishpond water samples were found at 1.50 ng mL⁻¹ and 0.67 ng mL⁻¹, respectively.     

Environmentally friendly solid‐phase microextraction coupled with gas chromatography and mass spectrometry for the determination of biogenic amines in fish samples

In this work, a facile and environmentally friendly solid‐phase microextraction assay based on on‐fiber derivatization coupled with gas chromatography and mass spectrometry was developed for determining four nonvolatile index biogenic amines (putrescine, cadaverine, histamine, and tyramine) in fish samples. In the assay, the fiber was firstly dipped into a solution with isobutyl chloroformate as derivatization reagent and isooctane as extraction solvent. Thus, a thin organic liquid membrane coating was developed. Then the modified fiber was immersed into sample solution to extract four important bioamines. Afterwards, the fiber was directly inserted into gas chromatography injection port for thermal desorption. 1,7‐Diaminoheptane was employed as internal standard reagent for quantification of the targets. The limits of detection of the method were 2.98–45.3 μg/kg. The proposed method was successfully applied to the detection of bioamines in several fish samples with recoveries ranging 78.9–110%. The organic reagent used for extraction was as few as microliter that can greatly reduce the harm to manipulator and environment. Moreover, the extraction procedures were very simple without concentration and elution procedures, which can greatly simplify the pretreatment process. The assay can be extended to the in situ screening of other pollutant in food safety by changing the derivatization reagent.     

Effect of different lipid extraction methods on δ13C of lipid and lipid-free fractions of fish and different fish feeds

For many ecological applications of stable carbon isotope techniques, it is necessary to separate the lipid and lipid-free fractions. The effect of different lipid extraction methods on the isotope signature of the remaining lipid-free matter as well as the lipid fraction was tested. A hot extraction form of the Soxhlet method using petrol-ether was compared with two liquid-liquid extraction methods for lipid determination described by Bligh and Dyer and Smedes. Solid samples of fish and different natural food items were subjected to extraction and the carbon isotope ratios in lipid and lipid-free matter determined by IRMS. All methods were suitable for lipid extraction from all samples analysed here and did not cause biologically relevant differences (>1) in carbon isotopic ratios, except the Bligh and Dyer extraction method using chloroform which caused systematic errors for δ ¹³C when applied to diatoms.