Wet Fish Research Articles

Nutrient Excretion Rates of Anadromous Alewives during Their Spawning Migration

AbstractExcretion is one of the processes through which anadromous fishes move marine‐derived nutrients into freshwater ecosystems, but no direct estimates of nutrient excretion rates by anadromous fish exist. We estimated the mass‐specific nutrient excretion rates of anadromous alewives Alosa pseudoharengus during their spring spawning migration into Bride Lake, Connecticut. Anadromous alewives excreted an average of 2.17 μg of phosphorus per gram of wet fish mass per hour and 24.71μg of nitrogen. The mean N:P ratio (by mass) of nutrient excretion was 11.7. Most of the nitrogen excreted was in the form of NH4+. Our results suggest that excretion by anadromous fish can affect local food webs and ecosystem function when ecosystems are relatively small and fish aggregate at high densities, such as at the peak of the spawning run.

Global overview on the use of fish meal and fish oil in industrially compounded aquafeeds: Trends and future prospects

The finfish and crustacean aquaculture sector is still highly dependent upon marine capture fisheries for sourcing key dietary nutrient inputs, including fish meal and fish oil. This dependency is particularly strong within compound aquafeeds for farmed carnivorous finfish species and marine shrimp. Results are presented concerning the responses received from a global survey conducted between December 2006 and October 2007 concerning the use of fish meal and fish oil within compound aquafeeds using a questionnaire sent to over 800 feed manufacturers, farmers, researchers, fishery specialists, and other stakeholders in over 50 countries. On the basis of the responses received, it is estimated that in 2006 the aquaculture sector consumed 3724 thousand tonnes of fish meal (68.2% total global fish meal production in 2006) and 835 thousand tonnes of fish oil (88.5% total reported fish oil production in 2006), or the equivalent of 16.6 million tonnes of small pelagic forage fish (using a wet fish to fish meal processing yield of 22.5% and wet fish to fish oil processing yield of 5%) with an overall fish-in fish-out ratio of 0.70. At a species-group level, calculation of small pelagic forage fish input per unit of farmed fish or crustacean output showed steadily decreasing fish-in fish-out ratios for all cultivated species from 1995 to 2006, with decreases being most dramatic for carnivorous fish species such as salmon (decreasing from 7.5 to 4.9 from 1995 to 2006), trout (decreasing from 6.0 to 3.4), eel (decreasing from 5.2 to 3.5), marine fish (decreasing from 3.0 to 2.2) and to a lesser extent shrimp (decreasing by 1.9 to 1.4 from 1995 to 2006. Net fish producing species in 2006 (with fish-in fish-out ratios below 1), included herbivorous and omnivorous finfish and crustacean species, including non-filter feeding Chinese carp (0.2), milkfish (0.2), tilapia (0.4), catfish (0.5), and freshwater crustaceans (0.6). On the basis of increasing global fish meal and fish oil costs, it is predicted that dietary fish meal and fish oil inclusion levels within compound aquafeeds will decrease in the long term, with fish meal and fish oil usage increasingly being targeted for use as a high value specialty feed ingredient for use within higher value starter, finisher and broodstock feeds, and by so doing extending supply of these much sought after and limited feed ingredient commodities.

Determination of Mercury in Fish Tissue Using a Minianalyzer Based on Cold Vapor Atomic Absorption Spectrometry at the 184.9 nm Line

A sensitive method was proposed and optimized for the determination of total mercury in fish tissue by using wet digestion, followed by cold vapor atomic absorption spectrometry (CVAAS) at the main resonance line of mercury (184.9 nm). The measurements were made using a new type of a non-dispersive mercury minianalyzer. This instrument was initially designed and built for atmospheric mercury-vapor detection. For determining mercury in aqueous samples, the minianalyzer was linked with a mercury/hydride system, Perkin Elmer Model MHS-10. To check the method, the analyzed samples were spiked with a standard solution of mercury. The recoveries of mercury spiked to wet fish tissue were >90% for 0.5 - 0.8 g samples. The results showed a better sensitivity (about 2.5 times higher) when using the mercury absorption line at 184.9 nm compared with the sensitivity obtained by conventional CVAAS at 253.7 nm.

Mercury Concentration in Frozen Whole-Fish Homogenates Is Insensitive to Holding Time

Current recommended holding times for the analysis of total mercury (Hg) in fish tissue ranges from 28 to 180 days. In 2006, we evaluated the effect of an extended holding time on Hg concentrations by reanalyzing whole-fish wet homogenates that were analyzed originally in 2002 and had been stored frozen at -20 degrees C since that time. Seven species, 13-15 samples each, were reanalyzed. Comparisons of concentration differences between 2006 and 2002 indicated that no statistically significant changes in Hg concentrations occurred in any of the seven fish species. These results indicate that wet fish tissue homogenates can be held frozen for at least four years without affecting analytical results, thus extending holding times far beyond those currently recommended.

Comparison of Diet, Reproductive Biology, and Growth of the Pig Frog (Rana Grylio) from Harvested and Protected Areas of The Florida Everglades

Distinct differences in body size exist among three Rana grylio populations in areas of the Florida Everglades that differ in frog harvest pressure and hydroperiod. Frogs from two populations are harvested regularly throughout the year, while those in the third are protected from harvest. We compared seasonal and sex differences in diet, reproduction, and growth across these populations to examine life-history patterns. By volume, crayfish and anurans were the most abundant prey items for all adults across sites. Frogs from drier sites consumed more crayfish than frogs from the wettest site. Anurans were abundant in the diet during the wet season, while crayfish and fish were abundant during the dry season. More frogs with empty stomachs were captured during the wet season than the dry season. Feeding, growth, and fat deposition were greatest during the dry season across all sites. Although females were found in all reproductive stages throughout the year, the highest percentage of females had mature ova during the late dry season and spent ovaries during the early wet season. Individual patterns of growth were similar across all sites and matched historical growth data from the 1950s. Differences in body size among sites were most likely attributable to differential mortality (i.e., harvest pressure, predation) rather than to differences in food access or growth.

New certified and candidate certified reference materials for the analysis of PCBs, PCDD/Fs, OCPs and BFRs in the environment and food

Three new matrix-type certified reference materials (CRMs) have been produced for polychlorinated biphenyls (PCBs) in sterilized and wet (shell) fish matrices – BCR-682 (PCBs in mussels), BCR-718 (PCBs in herring) and BCR-719 (non-ortho PCBs in chub). Additional feasibility studies have been carried out to evaluate the conditions under which production and certification of CRMs are feasible for brominated flame retardants (BFRs), chlorinated dibenzo- p-dioxins and furans (PCDD/Fs), PCBs and organochlorine pesticides (OCPs) in various food, animal feed and environmental matrices. The results of these feasibility studies indicate that homogeneous and stable CRMs can be produced for all materials with the protocols developed during these studies. The user of these materials may need to apply simple rehomogenization of the material prior to use (e.g., for the milk material, slight phase separation resulting from sterilization was observed). The decreased precision or accuracy of applied analytical methods close to the method detection limit was found to affect the homogeneity and the stability for some low-concentration compounds studied. For example, as a result, the homogeneity and the stability of 1,2,3,4,7,8,9-HpCDF in the fish material could not be confirmed. However, based on analogy with compounds with the same degree of chlorination, we do not expect that 1,2,3,4,7,8,9-HpCDF would not be stable or homogeneously distributed over the sample matrix. The BCR-682, −718 and −719 CRMs are strong quality-assurance tools to support laboratories analyzing (non-ortho) PCBs in fish and shellfish samples at the (low) levels determined in everyday routine samples. The materials from the feasibility studies can also support laboratories that analyze BFRs, OCPs, PCDD/Fs and dioxin-like PCBs (dl-PCBs) in the matrices investigated. However, these materials are currently not available for laboratories.

Uptake and loss of absorbed dissolved cadmium to Clarias angullaris fingerlings

The uptake and loss of dissolved cadmium in media by the African mud fish (Clarias angullaris) fingerlings was studied in water of 25 mg/ L hardness, pH 6.8, at 27 ±2°C in a static test system. The uptake experiments involved exposure of fish to 0.5 and 1.0 mg Cd2+/L test solutions from which the fish absorbed and retained 1.1011 mg and 1.3060 mg Cd2+/g wet fish weight, approximately 550 and 653 times the recorded normal tissue level, respectively, after 8 days. In the loss experiments, after fourteen (14) days, the fish that had 0.8320 mg Cd2+/g wet weight in the 0.5 mg Cd2+/L test medium reduced the internal concentration to 0.1121 mg Cd2+/g; and in the 1.0 mg Cd2+/L test solution, the reduction is from 0.9820 mg Cd2+/L to 0.1142 mg Cd2+/L wet weight

An in Situ Estimate of Food Consumption by Icefish in Lake Chaohu, China

ABSTRACT The icefish (Neosalanx taihuensis) of Lake Chaohu, China, foraged almost exclusively on crustacean zooplankton in both spring and summer. The icefish showed diurnal feeding periodicity, with peak feeding in the morning. No food was observed in icefish guts collected at night. Our results indicate that that the icefish was a particulate feeder and light intensity greatly affected its foraging on zooplankton. Daily consumption of zooplankton by icefish varied significantly both diurnally and among seasons, which ranged from 0.22 to 2.23 g (wet weight) per 100 g wet fish weight at temperatures between 16.3 OC (spring) and 28.8 °C (summer).

Occurrence of phthalate esters in the environment of the Netherlands

Overviews of levels of n-dibutylphthalate (DBP) and di(2-ethylhexyl)phthalate (DEHP) found in freshwater, marine water, sediment, and fish in the Netherlands are given. Sampling spanned a 9-month period (all seasons except winter) and allowed assessing whether phthalate levels are season dependent. Results obtained are compared to data reported for other Western European countries and a fugacity-based modeling approach is used to assess whether there is equilibrium among the various compartments. Highest levels of dissolved DBP and DEHP were found in freshwater samples, whereas these compounds were usually below the limit of detection (LOD) in marine water and sediment. Median levels were log-normally distributed; statistical analysis showed that sampling season is not a relevant determinant parameter. Similar results were obtained for the freshwater sediment compartment, with DEHP levels exceeding concentrations of DBP. DBP levels in fish were often below the LOD. Nevertheless, mean values around 1.8 μg kg −1 wet fish were found for both DEHP and DBP. Fugacity calculations revealed that especially for DEHP there is no equilibrium among the compartments. DEHP emissions are directed to water, whereas the calculations reveal that sediments provide a sink for DEHP and there is net transport to air. Although it has been suggested that water is the primary compartment for DBP, fugacity plots suggest that air is the compartment to which emissions are directed dominantly. The data reported are in line with values found in Western Europe.

Effect of feeding level and feeding frequency on specific dynamic action in Silurus meridionalis

The effect of feeding level (FL; 0·5 to 4% dry diet mass per wet fish body mass) and feeding frequency (once every 4 days to twice per day) on postprandial metabolic response was investigated in southern catfish Silurus meridionalis at 27·5° C. The results showed that there was no significant difference in the specific dynamic action (SDA) coefficient among the groups of different feeding levels (P > 0·05). The duration increased from 26·0 to 40·0 h and the peak metabolic rate increased from 207·8 to 378·8 mg O2 kg−1 h−1 when the feeding level was increased from 0·5 to 4%. The relationship between the peak metabolic rate (RP, mg O2 kg−1 h−1) and FL could be described as: RP = 175·4 + 47·3 FL(r2 = 0·943, n = 40, P < 0·001). The relationship between the SDA duration (D, h) and FL could be described as D=30·97FL0·248 (r2=0·729, n=40, P < 0·001).

Hydroperiod and seasonal effects on fish decomposition in an oligotrophic Everglades marsh

Abstract In the Everglades, the majority of fish detrital inputs occur during the dry season, when water-level drawdown reduces aquatic habitat. While these mortality events are highly seasonal, the remineralization and recycling of fish detrital nutrients may represent an important stimulus to the ecosystem in the following wet season. The goal of this study was to quantify the rate of detrital fish decomposition during three periods of the year to determine seasonal variations in decomposition patterns in this ecosystem. A multiple regression analysis showed that hydroperiod and water depth both played a role in determining fish decomposition rates within this ecosystem. Decomposition rates ranged from a low of 13% day−1 in December 2000 to a high of 50% day−1 in April 2001, the height of the dry season. Phosphorus analysis showed that Gambusia holbrooki, the dominant small fish species in the Everglades, contains 7.169 ± 1.46 mg P g−1 wet fish weight. Based on the observed decomposition rates and the a...

Fishing vessel profitability and local economic link obligations—the case of Norwegian trawlers

This paper investigates to what extent limited entry licence local-link obligations hamper economic performance of Norwegian wet fish trawlers. For 1999 average landing prices, gross revenue, net profit and some other economic indicators are compared for three groups of trawlers: (A) vessels that had local-link licence obligations and complied with them; (B) vessels that had such obligations but did not comply; and (C) vessels without local-link obligations. Average operating profit was highest for Group C. Group B vessels’ operating profit was just above that of Group A, despite significantly higher revenues. For all fish species, except redfish, Group C trawlers received higher prices than the other vessels.

A comparative evaluation of accelerated solvent extraction and Polytron extraction for quantification of lipids and extractable organochlorine in fish

Optimal conditions for extraction methods using an accelerated solvent extractor (ASE) and a Polytron homogenizer were established for quantification of (crude) lipids and extractable organochlorine (EOCl) in fish. The two methods, an ASE consecutive extraction at 55 and 100 °C for ground, freeze-dried filets, and a Polytron extraction at room temperature with four repetitions for ground, wet filets and with two repetitions for wet fish livers were evaluated in terms of reproducibility and comparability. With respect to lipid measurement, the two methods have comparable reproducibility and the experimental errors are relatively small compared to natural variations of fish to fish within a sampling site. For EOCl measurement, the relative standard deviation tends to increase with decreasing levels of EOCl in specimens. An important factor for the relative standard deviation of measurements of analytes present at trace levels in fish matrices is sampling error in taking aliquots. Statistical analysis using a paired comparison design showed that measurement values (crude lipids or EOCl) obtained from these two extraction methods are, in general, not equivalent. There is a good correlation between the two methods for lipid measurement; whereas for EOCl measurements, high degrees of correlation exist within the exposed fish group, but not in the reference group.

Effect of temperature and phytoplankton concentration on Nile tilapia Oreochromis niloticus (L.) filtration rate

Nile tilapia Oreochromis niloticus (L.) held in timed-pulse feeding chambers, were provided with algal-rich water dominated by either green algae (Scenedesmus, Ankistrodesmus, Chlorella and Tetraedron) or cyanobacteria (Microcystis) to determine the effect of temperature and phytoplankton concentration on filtration rates. Green algae and cyanobacteria filtration rates were measured as suspended particulate organic carbon (POC) kg−1 wet fish weight h−1. Ivlev's filter-feeding model described the relationships between filtration rates and suspended POC concentration of green algae and cyanobacteria. Filtration rates of both green algae and cyanobacteria increased linearly as water temperature increased from 17 °C to 32 °C and were significantly higher in the warm-water regime (26–32 °C) than in the cool-water regime (17–23 °C). Filtration rates at 95% saturation POC (FR95) in green algal and cyanobacterial waters were 700 mg C kg−1 h−1 and 851 mg C kg−1 h−1 in the warm-water regime and 369 mg C kg−1 h−1 and 439 mg C kg−1 h−1 in the cool-water regime respectively. The FR95 in warm water were achieved at lower POC concentrations than in cool water.

Using trimethylamine dehydrogenase in an enzyme linked amperometric electrode. Part 1. Wild-type enzyme redox mediation.

An amperometric enzyme electrode was studied based on the wild-type protein trimethylamine dehydrogenase (TMADH), which catalyses the oxidative N-demethylation of trimethylamine to produce dimethylamine and formaldehyde. Ferrocene derivatives were investigated electrochemically, as free diffusing electron acceptors for recycling of the prosthetic groups of the immobilised enzyme. Ferricinium had the highest rates but, inhibited the enzyme, possibly as a result of a conformational change initiated at the Val-344 residue where it binds close to the 4Fe-4S cluster, interrupting the electron transfer between flavin mononucleotide (FMN) and 4Fe-4S by changing the redox potential of one or both of the prosthetic groups. (Dimethylamino)methylene ferrocene (DMAMFe) (k(s) = 0.93 x 10(5) M(-1) s(-1)) did not show inhibition and was used as a comparison for steady-state characterisation. The sensor response was studied over the pH range 6.0-1.0. Plots of kcat/KM revealed two ionisations with pKa values of 7.5 and 10. The pKa of 10 was attributed to the ionisation of the secondary amine in DMAMFe, whereas the pKa of 7.5 was thought to reflect the ionisations of the intramolecular electron pathway. A TMADH/DMAMFe amperometric enzyme electrode was successfully used for the determination of TMA in different fish samples (detection limit: 2 mg TMA-N per lOOg wet fish muscle). The obtained results compared well with a reference method based on picric acid.

Comparative Nile tilapia and silver carp filtration rates of Partitioned Aquaculture System phytoplankton

Abstract Nile tilapia ( Oreochromis niloticus ) and silver carp ( Hypophthalmichthys molitrix ) held in timed-pulse feeding chambers were provided water dominated either by green algae ( Scenedesmus , Ankistrodesmus and Tetraedron ) or by cyanobacteria ( Microcystis ) to compare filtration rates (FRs). FRs were expressed as suspended particulate organic carbon (POC)/kg wet fish weight/h and as phytoplankton units filtered based on counts. Nile tilapia and silver carp filtration significantly reduced phytoplankton number of both taxonomic groups with the larger phytoplankton being filtered proportionally more than the smaller phytoplankton. Nile tilapia FR of green algae was significantly higher than silver carp; however, silver carp FR of cyanobacteria was higher than Nile tilapia. Ivlev's 90% saturation FRs (FR 90 ) in green-algal and cyanobacterial water sources were 702 and 812 mgC/kg/h for Nile tilapia and 414 and 1028 mgC/kg/h for silver carp, respectively. Silver carp were observed to reach these FR 90 values at lower POC concentrations than Nile tilapia with both green algae and cyanobacteria.

Filtration of green algae and cyanobacteria by Nile tilapia, Oreochromis niloticus, in the Partitioned Aquaculture System

Nile tilapia, Oreochromis niloticus, held in a timed pulse fed Continuous Stirred Tank Reactor (CSTR) were provided Partitioned Aquaculture System (PAS) algal-rich water dominated by green algae (i.e., Scenedesmus and Ankistrodesmus) and cyanobacteria (i.e., Microcystis and Merismopedia) to determine filtration rates (FR). A similar number and size of tilapias were stocked at 1.5 kg/tank into each of the six CSTRs (127 l) for 58-h experiment period. The cell counts of phytoplankton in water filtered by tilapias indicated significant reduction in green algae and cyanobacteria. Nile tilapia was more effective filtering the larger particle size taxa in both water sources. FR measured as mg of particulate organic carbon (POC) per kg wet fish weight per hour increased as POC increased. A curvilinear filter-feeding rate model provided a maximum filtration rate (FR max) of 641 mgC/kg/h at 26 mgC/l in green algal-dominated water. The projected FR max of cyanobacterial-dominated water was 865 mgC/kg/h at 59 mgC/l. The derived filter-feeding rate models will help to describe Nile tilapia filtration kinetics in the PAS and the potential for control of nuisance cyanobacteria.

An in situ estimate of food consumption of five cyprinid species in Lake Balaton

Daily rations of five cyprinid species, bream Abramis brama, silver bream Blicca bjoerkna, roach Rutilus rutilus, gibel Carassius auratus gibelio and carp Cyprinus carpio, in Lake Balaton, a large shallow lake, estimated by the Eggers model differed from that of the Elliott – Persson model by only − 4.3 to +7.3% (the differences were insignificant). Daily rations varied within the range of 0.23–0.69 in bream, 0.55–3.61 in silver bream, 0.69–4.65 in roach, 0.38–3.16 in gibel and 0.50–9.74 g dry 100 g wet fish mass−1 day −1 in carp at temperatures ranging from 8.7–25.8% C. Daily ration was related exponentially with temperature in silver bream, roach, gibel and carp. For bream, a significant relationship was obtained only when a daily ration value was excluded from the analysis. Annual rations were assessed using the relationships between the daily ration estimates from the Elliott—Persson model and water temperature, and the long-term averages of the monthly water temperature data. From these estimates the bream population consumed 104%, silver bream 424%, roach 487%, gibel 363% and carp 913% dry mass of food of its wet biomass annually.

An in situ estimate of food consumption of five cyprinid species in Lake Balaton

Daily rations of five cyprinid species, bream Abramis brama, silver bream Blicca bjoerkna, roach Rutilus rutilus, gibel Carassius auratus gibelio and carp Cyprinus carpio, in Lake Balaton, a large shallow lake, estimated by the Eggers model differed from that of the Elliott – Persson model by only − 4.3 to +7.3% (the differences were insignificant). Daily rations varied within the range of 0.23–0.69 in bream, 0.55–3.61 in silver bream, 0.69–4.65 in roach, 0.38–3.16 in gibel and 0.50–9.74 g dry 100 g wet fish mass−1 day −1 in carp at temperatures ranging from 8.7–25.8% C. Daily ration was related exponentially with temperature in silver bream, roach, gibel and carp. For bream, a significant relationship was obtained only when a daily ration value was excluded from the analysis. Annual rations were assessed using the relationships between the daily ration estimates from the Elliott—Persson model and water temperature, and the long‐term averages of the monthly water temperature data. From these estimates the bream population consumed 104%, silver bream 424%, roach 487%, gibel 363% and carp 913% dry mass of food of its wet biomass annually.

Foodborne pathogenic bacteria in prepackaged fresh retail portions of farmed rainbow trout and salmon stored at 3 °C

Twelve lots of fresh unskinned fillets of rainbow trout ( Oncorhynchus mykiss) and 10 lots of fresh sliced salmon ( Salmo salar) prepacked in trays wrapped with an oxygen-permeable film were obtained immediately after packing from two supermarkets having in-plant facilities for packaging wet fish. During storage at 3 °C, Listeria innocua was detected in eight lots of trout fillets after 4 days storage. L. monocytogenes was recovered from a single lot also contaminated with L. innocua. Initial numbers of aeromonads were significantly ( p<0.05) lower in trout fillets (3.35±0.62 log cfu g −1) than in salmon slices (4.20±0.89 log cfu g −1). In both fish products, these bacteria significantly ( p<0.05) increased up until spoilage. Most Aeromonas spp. isolates from trout fillets were assigned to A. veronii biovar sobria HG8 (hybridisation group 8), A. caviae HG4, A. eucrenophila HG6, A. hydrophila HG1 and A. veronii biovar veronii HG10. Strains of HG12 ( A. schubertii), HG4 and HG8 formed the majority of aeromonads recovered from salmon slices.