Uncertainty in Paleoecological Studies of Mercury in Sediment Cores     

Gottgens  Johan F.  Rood  Brian E.  Delfino  Joseph J.  Simmers  Brenda S. 《Water, air, and soil pollution》1999,110(3-4):313-333

Increased recognition of the ecological damage of mercury (Hg) has focused attention on quantifying spatial and temporal patterns of Hg deposition. Studies are commonly based on core chronologies and use a combination of techniques to measure parameters such as bulk density, percent solids, Hg concentration, and radionuclide activity. Little attention is generally devoted to the propagated error associated with these measurements. We identified the impact of sources of uncertainty on stratigraphic Hg determinations for Florida Everglades and Lake Erie cores. Large errors may be introduced by converting wet sample Hg content to dry-weight concentrations. Drying of sediments at 55 °C caused Hg losses of 18%. Samples, air-dried at room temperature, retained considerable moisture and required corrections for remaining water content. Frozen sediments did not lose Hg during a 72-day storage. Random error in radionuclide analysis of cores resulted in dating uncertainty of ±1.2 yr in 10 yr old deposits. This error increased to ±20 yr in 100 yr old sediments. Propagation of small errors in each step of the analysis (while adhering to strict QA/QC criteria) produced compounded uncertainties of ±11 and ±29% in Hg concentrations under different analytical rigor, and errors of up to ±73% in Hg accumulation rates in older sediments. Enrichment factors, comparing uncertain recent and historic Hg accumulation rates, differed by as much as ±48%. Uncertainty in paleoecological studies of mercury needs to be documented in order to correctly evaluate trends and remediation efforts.  相似文献   

Local adaptation studies and conservation: Parasite–host interactions between the endangered freshwater mussel Unio crassus and its host fish          下载免费PDF全文

Lea D. Schneider  P. Anders Nilsson  Johan Höjesjö  E. Martin Österling 《水产资源保护:海洋与淡水生态系统》2017,27(6):1261-1269

Feeding ragworm (Nereis virens Sars) to common sole (Solea solea L.) alleviates nutritional anaemia and stimulates growth          下载免费PDF全文

Jeroen Kals  Robbert J W Blonk  Arjan P Palstra  Tim K Sobotta  Fulvio Mongile  Oliver Schneider  Josep V Planas  Johan W Schrama  Johan A J Verreth 《Aquaculture Research》2017,48(3):752-759

Common sole fed with commercial pellets develop anaemia and are restricted in their growth performance. The anaemia can be the result of a difference in feed intake, a nutritional deficiency, an inflammatory response to infection or combinations of these aspects. In this study, it was investigated whether feeding ragworm would alleviate the anaemia and stimulate growth. Sole were fed one of three diets: a commercial feed, a commercial feed treated with ragworm extract or chopped ragworm. By comparing groups, three hypotheses were tested: (1) feeding ragworm alleviates the anaemia and positively affectS the sole's metabolic performance reflected in feed intake, feed efficiency and growth; (2) anaemia is alleviated by a higher feed intake when feeding ragworm and (3) anaemia is caused by an inflammatory response to infection. The sole fed with a commercial diet suffered from anaemia. Feeding sole with ragworm alleviated the anaemia as the average haematocrit level nearly doubled in these fish as compared to fish fed pellets. Investigation of the expression of genes in the liver indicated that the anaemia in sole fed pellets is a nutritional anaemia and not an anaemia due to an inflammatory response. Sole fed ragworm showed improved growth which may be a consequence of the higher haematocrit levels in these fish increasing their oxygen carrying capacity. Addition of ragworm extract to the pellets levelled the feed intake between pellets and ragworm, but did not improve the anaemic state of sole and had only a limited effect on growth.  相似文献   

Geosmin depuration from European eel (Anguilla anguilla) is not affected by the water renewal rate of depuration tanks          下载免费PDF全文

Edward Schram  Tobias van Kooten  Jan W van de Heul  Johan W Schrama  Johan A J Verreth  Albertinka J Murk 《Aquaculture Research》2017,48(9):4646-4655

This study established that geosmin depuration from European eel is not affected by the water renewal rate of depuration tanks. A general fish bioaccumulation model extended with terms that account for effects of tank water renewal rate and system losses of chemicals, predicted strong effects of the water renewal rate of depuration tanks on geosmin depuration from European eel. Model predictions were validated in a depuration experiment with geosmin‐loaded European eel (n = 95) with a mean (SD) individual weight of 134.4 (5.0) g and a mean (SD) lipid content of 33.7 (2.8) % (w/w). Fish were depurated for 24, 48 or 72 h at three different tank water renewal rates (0.3, 3.3 and 33 day^?1). Treatments were installed by three different mean (SD) water flow rates (13.8 (1.3), 143.5 (9.2) and 1511 (80) L kg fish^?1 day^?1) over 30‐L tanks. Eels eliminated geosmin from their bodies, but unlike the model predicted, this was independent of the water renewal rate of the depuration tanks. Although being eliminated from the fish, geosmin hardly appeared and certainly did not accumulate in the water of the depuration tanks as the model predicted. This observation may be explained by geosmin being eliminated from eel as metabolite rather than the parent compound. Geosmin elimination from eel seems not to occur according to the generally accepted passive diffusion mechanism for excretion of lipophilic chemicals, and geosmin biotransformation by the eel seems indicated. Clearly geosmin depuration from European eel cannot be enhanced by increasing water renewal rates of depuration tanks.  相似文献   

The effect of food type (formulated diet vs. natural) and fish size on feed utilization in common sole,Solea solea (L.)          下载免费PDF全文

Stephan S W Ende  Saskia Kroeckel  Johan W Schrama  Oliver Schneider  Johan A J Verreth 《Aquaculture Research》2017,48(9):4696-4706

This study compares the effect of food type (formulated diet vs. natural food) and fish size on protein and energy utilization efficiencies for growth in common sole, Solea solea (L.). Replicate groups of common sole (mean initial body weight ± SD was 45.7 g ± 2.1 and 111.2 g ± 4.2) received the diets at five (natural feed) or four (formulated diet) feeding levels. The protein utilization efficiency for growth (k_gCP) was higher (P > 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.40 and 0.31). Likewise, the energy utilization efficiency for growth (k_gGE) was higher (P = 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.57 and 0.33). The protein maintenance requirement was not different between food types (P = 0.64) or fish size (P = 0.41) being on average 0.82 g kg^?0.8 day^?1. The energy maintenance requirement was not different between food type (P = 0.390) but differed between fish size (P = 0.036). The gross energy maintenance requirement of small common sole was 35 kJ g^?0.8 day^?1. The gross energy maintenance requirement of large common sole was 25 kJ g^?0.8 day^?1. In conclusion, the low growth of common sole fed formulated diets was related to reduced feed utilization.  相似文献   

Use of flubendazole as a therapeutic agent against rotifers (Brachionus plicatilis) in intensive cultures of the harpacticoid copepod Tisbe holothuriae     

Svend J Steenfeldt  Johan W Nielsen 《Aquaculture Research》2010,41(7):1089-1094

Copepods are well known to be the optimal live feed for most species of marine fish larvae. Still copepods are rarely used in marine hatcheries worldwide. Lack of efficient production techniques are among the reasons for this. Consequently, Artemia and rotifers are utilized in commercial settings. One problem in intensive production of copepods is contamination with rotifers. Rotifers have higher growth rates than copepods and consequently will compete out the copepods when accidentally introduced to the copepod production systems. Once contamination has occurred, the only cure has been to shut down production and subsequently use a therapeutic agent to eliminate all zooplankton in the system before restart with a stock culture free of rotifers. We tested flubendazole as a mean of controlling rotifers (Brachionus plicatilis) in intensive laboratory cultures of the harpacticoid copepod (Tisbe holothuria). Flubendazole was lethal to rotifers in concentrations as low as 0.05 mg L^?1. There was no significant effect on the concentration of copepods, even at the highest concentration tested, i.e. 5.0 mg L^?1 flubendazole. We conclude that flubendazole is an effective drug for control of B. plicatilis in T. holothuriae batch cultures.  相似文献   

Cell wall disruption: An effective strategy to improve the nutritive quality of microalgae in African catfish (Clarias gariepinus)     

Jeleel O. Agboola  Emma Teuling  Peter A. Wierenga  Harry Gruppen  Johan W. Schrama 《Aquaculture Nutrition》2019,25(4):783-797

The rigid cell walls of microalgae may hinder their utilization in fish feeds. The current experiment assessed the correlation between the accessibility of microalgae nutrients and their in vivo digestibility in African catfish. Nannochloropsis gaditana biomass was subjected to physical or mechanical treatments to weaken its cell wall; untreated—no disruption treatment (UNT), pasteurization (PAS), freezing (FRO), freeze‐drying (FRD), cold pasteurization (L40) and bead milling (BEM). Six experimental diets formulated from differently treated and untreated microalgae (at 30% diet inclusion level) were tested on growth performance and apparent nutrient digestibility (ADCs) in juvenile African catfish. A basal diet (REF) containing no microalgae was used as reference diet. Results showed that biomass gain and feed conversion ratio of fish fed L40 and BEM diets increased by 13% and 11%, respectively, relative to the UNT diet. Additionally, FRD, FRO, L40 and BEM cell wall disruption treatments improved protein digestibility by 0.5%, 5.9%, 8.4% and 16.3%, respectively, compared to the UNT treatment. There was a positive correlation between accessibility of microalgal nutrients and their digestibility in African catfish. Nutrient digestibility of microalgae was dependent on extent of cell disruption. Also, the impact of cell disruption on nutrient digestibility of microalgae differs between African catfish and Nile tilapia.  相似文献   

Effect of non‐starch polysaccharide composition and enzyme supplementation on growth performance and nutrient digestibility in Nile tilapia (Oreochromis niloticus)     

Roel M. Maas  Marc C. J. Verdegem  Johan W. Schrama 《Aquaculture Nutrition》2019,25(3):622-632

The experiment investigated whether the effect of enzyme supplementation on performance and nutrient digestibility is dependent on type of the ingredient(s) used, by incorporating wheat bran (WB), sunflower meal (SFM) and citrus pulp (CP) to a reference diet (REF). Those ingredients are known to be rich in different types of non‐starch polysaccharides (NSP). Diets were supplemented with and without (control) an enzyme mix (phytase 1,000 FTU/kg and xylanase U/kg) according to a 2 × 4 factorial arrangement. In total, 24 tanks (3 replicates/treatment) were used with 30 fish each (Nile tilapia, Oreochromis niloticus; mean initial body weight 41 g). Fish were restrictively fed the experimental diets for 43 days (80% of expected satiation). Enzyme supplementation affected the absolute growth (g/day) and FCR (p < 0.05), improving the growth of fish fed the WB and SFM diets, while fish fed the REF and CP diets did not benefit. NSP, energy, ash, phosphorous and calcium digestibility improved with enzyme supplementation (p < 0.05). There was an interaction effect on all growth parameters, as well as the digestibility of energy and phosphorus (p < 0.05). This indicates that the effectiveness of the enzymes was dependent on the NSP‐rich ingredient used and thus the composition of the NSP fraction.  相似文献   

Environmental influences on life history strategies in partially anadromous brown trout (Salmo trutta,Salmonidae)     

Marie Nevoux  Bengt Finstad  Jan Grimsrud Davidsen  Ross Finlay  Quentin Josset  Russell Poole  Johan Hjesj  Kim Aarestrup  Lo Persson  Oula Tolvanen  Bror Jonsson 《Fish and Fisheries》2019,20(6):1051-1082

This paper reviews the life history of brown trout and factors influencing decisions to migrate. Decisions that maximize fitness appear dependent on size at age. In partly anadromous populations, individuals that attain maturity at the parr stage typically become freshwater resident. For individual fish, the life history is not genetically fixed and can be modified by the previous growth history and energetic state in early life. This phenotypic plasticity may be influenced by epigenetic modifications of the genome. Thus, factors influencing survival and growth determine life‐history decisions. These are intra‐ and interspecific competition, feeding and shelter opportunities in freshwater and salt water, temperature in alternative habitats and flow conditions in running water. Male trout exhibit alternative mating strategies and can spawn as a subordinate sneaker or a dominant competitor. Females do not exhibit alternative mating behaviour. The relationship between growth, size and reproductive success differs between sexes in that females exhibit a higher tendency to migrate than males. Southern populations are sensitive to global warming. In addition, fisheries, aquaculture with increased spreading of salmon lice, introduction of new species, weirs and river regulation, poor water quality and coastal developments all threaten trout populations. The paper summarizes life‐history data from six populations across Europe and ends by presenting new research questions and directions for future research.  相似文献   

The nature of soil erosion and possible conservation strategies in Ntabelanga area,Eastern Cape Province,South Africa     

Cosmas Parwada  Johan Van Tol 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2016,66(6):544-552

Soil erosion is a major land degradation problem in South Africa (SA) that has economic, social and environmental implications due to both on-site and off-site effects. High rates of soil erosion by water are causing rapid sedimentation of water bodies, ultimately leading to water crisis in SA. Lots of financial and human resources are channelled towards controlling of soil erosion but unfortunately with little success. The level of soil erosion in a particular area is governed by the site properties. Therefore, it is inappropriate to generalize data on soil erosion at a large-scale spatial context. The literature on soil erosion in SA classifies Eastern Cape Province as a high-erosion-potential area using data collected at a large-scale spatial context. Collecting soil erosion data at a large spatial scale ignores site-specific properties that could influence soil erosion and has resulted in failure of many traditional soil erosion control measures applied in the province. Moreover, scientific principles underlying the processes and mechanisms of soil erosion in highly erodible soils are missing in SA. This review was to find effective soil erosion control measures by having an insight on what happens during soil erosion and how soil erosion occurs in Ntabelanga. The literature suggested that erosion in Ntabelanga could be influenced by both the erosivity and erodibility factors though the erodibility factors being more influential. Soil permeability contrast between the horizons could be influencing the rate and nature of soil erosion. To mitigate the impact of soil erosion in Ntabelanga, efforts should aim to improve the vertical flow capacity in the B horizon. Clay spreading, clay delving, addition of gypsum, deep ploughing and mulching could aid the water permeability problems of the subsurface horizons. However for effective soil management and control option, detailed studies of specific site properties are needed. The generated information can assist in formulating soil erosion policies and erosion control strategies in the Ntabelanga area and SA at large.  相似文献