Fisheries Research Station of Baden Wurttemberg

Langenargen, Germany

Fisheries Research Station of Baden Wurttemberg

Langenargen, Germany
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Schumann M.,Fisheries Research Station of Baden Wurttemberg | Schumann M.,University of Konstanz | Unger J.,University of Konstanz | Brinker A.,Fisheries Research Station of Baden Wurttemberg
Aquacultural Engineering | Year: 2016

The removal of solid wastes originating from faecal matter is one of the decisive challenges for future fish farming, in particular given the current emphasis on water reuse in aquaculture. This study compared solid waste removal performance in replicate recirculating systems in which the only difference was the removal concept being deployed. Rainbow trout (Oncorhynchus mykiss) of the test group were fed an innovative diet supplemented with 2.5% cork granules (0.5-1mm) resulting in buoyant faecal casts (density values below 1.00gcm-3). These were removed directly from the tank by a low cost slotted pipe at the water surface. The control group was fed a conventional diet, identical to the experimental feed except that it lacked the cork additive. The resulting solids in both systems were removed by sedimentation in a classic manure pit, which was drained to the drum filter twice a day. Wastewater from both treatments was mechanically cleaned by a drum filter and biologically treated by a moving bed bioreactor before being returned to the tanks.The cork treatment led to a substantially higher solid load being delivered to the drum filter via the wastewater outflow than in the control system. The average removal efficiency of cork-treated wastes was more than twice that achieved in the control system (59% vs. 25%). Total suspended solid (TSS) in the backwash stream of the drum filter was about five times greater in the cork diet treatment. There was no significant difference in the particle size distribution or TSS load of water passing the 100. μm gauze of the drum filter in the two systems. Cork supplementation did not affect growth or mortality of rainbow trout. The present study shows that the application of floating faeces is an exciting prospect in recirculating aquaculture systems, offering significant improvements in solid removal efficiency. © 2016 Elsevier B.V.

Becke C.,Fisheries Research Station of Baden Wurttemberg | Steinhagen D.,University of Veterinary Medicine Hannover | Schumann M.,Fisheries Research Station of Baden Wurttemberg | Brinker A.,Fisheries Research Station of Baden Wurttemberg | Brinker A.,University of Konstanz
Aquacultural Engineering | Year: 2016

Suspended solids are an unavoidable component of fish farming, and especially so in recirculating aquaculture systems (RAS) where fine particles accumulate over time. High levels of fine particles are widely regarded as harmful to fish health and welfare. However, little is known about the direct impact of these accumulating particles on stress, performance, health or other welfare parameters of fish. In this study, the effects of solids on rainbow trout were investigated specifically, uncoupled from other potentially confounding water parameters. To this end, the suspended solid load in a replicate RAS was artificially increased by a factor of 7 to over 30. mg total suspended solids (TSS)/L, alongside a sister system operating normally, with a maximum suspended solid concentration of 5. mg/L. At these levels, the concentrations of particles smaller than 32. μm amounted to 0.3. ±. 0.3. mg/L in the control system and to 8.0. ±. 2.7. mg/L in the treatment system. With the exception of turbidity, all further water parameters generally considered important to salmonid welfare were kept comparable and well below harmful levels. In consequence, fish performed well in both RAS, indicating good husbandry conditions. Feeding behavior was observed to differ slightly between control and treatment RAS, but without any apparent effect on performance.The impact of the accumulating particles on fish was examined using a wide range of physiological assays. No significant differences in stress markers (heat shock protein 70, plasma cortisol) were detected between fish in the control and treatment RAS. The same was found for hematological assays (differential leukocyte count, hematocrit, RBC indices, etc.). Fin condition was also unaffected by increased suspended solid load and most surprisingly, histological examination not only revealed no detrimental effects of particle accumulation, but showed the gill status of fish in the solid treatment to be better than that of control fish.Overall, this study shows that by itself, short-term exposure to suspended solids at concentrations of 30. mg/L has no detrimental effect on rainbow trout. © 2016 Elsevier B.V.

Brinker A.,Fisheries Research Station of Baden Wurttemberg | Friedrich C.,Albert Ludwigs University of Freiburg
Biorheology | Year: 2012

In the explosively growing aquaculture industry, the challenge of sustainability includes a requirement to produce more fish than are consumed by stock. A promising avenue of research is the substitution of the fish meal in feeds with plant protein. However, there are inherent risks in the development of such feeds, and serious consideration should be given not only to nutritional content, but also to the mechanical quality of resulting faecal wastes. The present study uses a plate on plate rheometer running in different flow modes (creep, oscillation) to assess the rheological properties of wastes resulting from different diets. All faeces were shown to be thixotropic in nature, independent of diet composition. Details of dietary composition influence the consistency and the characteristic stresses at which faecal structure changes from a viscoelastic solid into a viscoelastic liquid. Furthermore, in linking active food components with mechanical properties of chyme faeces, rheological studies may be used to understand and counteract some problematic properties. Substituting 100% of fish meal with plant proteins leads to faeces that rapidly disintegrate into very fine solids which threaten the viability of aquacultural operations. Adding just 0.3% of the rapidly hydrating non-starch polysaccharide, guar gum (GG), significantly increased the viscosity and elastic modulus of the faeces. These mechanical improvements increase the size of the resulting particles and the effectiveness with which they can be removed, thereby leading to optimized water quality. GG addition was sufficiently effective to counter the stability and particle size effects of a 50% substitution of fish meal, but could not mitigate those of a 100% substitution, wherein dissolution effects of an unknown emulsifier are suspected. © 2012 - IOS Press and the authors. All rights reserved.

Baer J.,Fisheries Research Station of Baden Wurttemberg | Brinker A.,Fisheries Research Station of Baden Wurttemberg
Fisheries Management and Ecology | Year: 2010

Since the mid-1980s, water quality has improved in German rivers, and fisheries have recovered. However, it is unsure whether the improvements are sufficient to maintain stocks and angling yield without supplementary stocking. This study examined the development in the local brown trout, Salmo trutta L., stocks and angling yield in the River Wutach following cessation of stocking in 2001, using electric fishing and an angler questionnaire. Natural reproduction was recorded in each year between 2001 and 2007, and a stable stock of trout >20 cm was found. Trout catches by anglers increased after stocking ceased and approximately 60% of the anglers were convinced that stocking was unnecessary to maintain the brown trout stocks or angler catch satisfaction. © 2010 Blackwell Publishing Ltd.

Brinker A.,Fisheries Research Station of Baden Wurttemberg | Reiter R.,Institute for Fishery
Aquaculture | Year: 2011

In a two-factorial experiment the effects of three rainbow trout diets were tested with respect to growth and health of fish stock, product quality and sustainability. The diets, comprising widely available and affordable raw ingredients, were iso-energetic and iso-carbohydrated, but contained protein of different provenances as follows: 100% of protein from fishmeal (FI diet), 50% of protein from fishmeal and 50% from plant sources (FP diet), and 100% plant protein supplemented with methionine/lysine (PL) diet. Three further diets were formulated, replicating FI, FP and PL, but enriched with 0.3% guar gum binder to counteract possible negative effects of excreted waste characteristics.Fish performed well on all diets. The observed significant differences were attributable almost entirely to protein provenance rather than to the presence or absence of binder. The post mortem data on gross body composition revealed that fillets from fish fed the PL diet were significantly leaner, with a greater percentage protein content than those from individuals raised on the FI or FP diets.Pathological alterations observed in the livers of fish fed the FI diet were in the expected range for fish reared on modern high energy diets. However, pathology was significantly reduced in fish receiving plant protein in their feed. Individuals raised on the PL diet exhibited almost completely healthy livers.The main shortcoming of the plant protein diets was a reduction in lipid digestibility, leading to slight depression in growth and feed conversion rates.The potential value of plant proteins as components in feeds to reduce eutrophication by fish farm wastes was confirmed. Their low intrinsic phosphorus content allows dietary levels to be easily adjusted to meet, but not exceed, the physiological needs of the fish, thus minimizing the excretion of excess phosphorus.A strong effect on hepatosomatic index (HSI), was observed, but was ascribed to the greater availability of carbohydrate in plant diets rather than to the origin of protein.Assessment of flesh quality parameters revealed slight differences between treatments, although these were not pronounced enough to be reflected in the results of organoleptic trials by a sensory test panel.In conclusion, even a 100% substitution of fishmeal proteins by affordable plant protein provides a competitive feed. Furthermore, some surprising health benefits for fish stock were also noted. The next challenge in developing a successful plant-based diet is to understand and counteract the effects on lipid digestibility and to identify the functional component that may be affecting fish health. © 2010 Elsevier B.V.

Stich H.B.,Institute for Lake Research State Institute for Environment | Brinker A.,Fisheries Research Station of Baden Wurttemberg
Global Change Biology | Year: 2010

Between 1951 and 1979, total phosphorous concentrations in Lake Constance increased from 7 to 87 μgL -1. Following wastewater treatment, phosphorus levels were brought under control, returning to 7.6 μgL -1 by spring 2007. The biological and chemical data from 1980 to 2004 were first modelled by seasonal time series analyses and then used to create a general model. Excluding collinear variables allowed the data set to be condensed to six variables that could be fitted into a general linear model that explained ~ 75% of the observed annual variation in chlorophyll a. A clear seasonal influence was apparent, with chlorophyll a tracking trends in temperature and the progress of spring. A nonseasonal influence was also observed in the interaction of two biological components, the proportion of phytoplankton biomass available to Daphnia (i.e. the percentage of ingestible size <30 μm) and the grazing intensity. In combination, these biotic variables had a negative impact on chlorophyll a levels. In contrast, the concentration of soluble reactive phosphorus (SRP) correlated positively with chlorophyll a. The effect of SRP showed a significant seasonal component, as it was more abundant in spring than at other times of year. In general, the model predicts a negative exponential response of chlorophyll a to further depletion of SRP in Lake Constance, while the temperature trends predicted by current global warming scenarios will result in a moderate increase in productivity. Data from 2005 to 2007 were used to verify the model. The modelled chlorophyll a values were nonbiased and showed a close match to the measured values (r 2: 75%). Thus the applicability, reliability, and informative value of the model for pelagic Lake Constance was confirmed. The approach might easily be applied to other waters. © 2009 Blackwell Publishing Ltd.

Gaye-Siessegger J.,Fisheries Research Station of Baden Wurttemberg
Knowledge and Management of Aquatic Ecosystems | Year: 2014

At lower lake Constance, the number of cormorants (Phalacrocorax carbo) has greatly increased during the last 15 years. An investigation of their diet can help to estimate the impact on fish and fisheries. Therefore, 282 cormorants were collected for stomach content analysis in autumn/winter 2011/12 and 2012/13. A total of 4019 fish or hard parts of 16 species were identified in the diet of cormorants. Fish length and weight were reconstructed from dimensions of hard parts using regression equations. Perch was the most frequent species (composition by number = 41.5%). Based on composition by weight, the most important species in the diet of cormorants was tench (Tinca tinca) with 47.0%, followed by Northern pike (Esox lucius), perch (Perca fluviatilis) and European whitefish (Coregonus lavaretus) with 23.9%, 7.2% and 6.9%, respectively. The dietary composition significantly differed between autumn and winter. Fish of high commercial value played a considerable part in the cormorants' diet. The impact of cormorants on grayling (Thymallus thymallus) could not be assessed due to the low number of birds from the spawning grounds of grayling at the outlet of lower lake Constance. © ONEMA, 2014.

Unger J.,Fisheries Research Station of Baden Wurttemberg | Unger J.,University of Konstanz | Brinker A.,Fisheries Research Station of Baden Wurttemberg
Aquaculture | Year: 2013

The rapid removal of suspended solids from aquacultural systems is of utmost importance in maintaining healthy stock and system stability and in addressing environmental concerns. This research tested a new approach, successfully manipulating fecal density to the point of floatation. Fecal casts floating at the water's surface can be transported quickly to a removal device. The speed of removal minimizes opportunity for leaching, and exposure to shear forces and turbulence caused by mechanical devices and fish motion. Waste thereby persists as larger particles, which are easier to remove by traditional microscreens or skimming apparatus. Four different low-density feed additives were tested in different dosages and gradings on duplicate groups of rainbow trout, in order to appraise the effects on fecal density, and on growth and health of fish stock. The control groups received the same basal diet without additives, which resulted in fecal densities in the upper ranges expected for commercial trout diets at 1.04gcm-3 and 1.05gcm-3 for water-soaked and intestinal feces, respectively. Five of the additive diets significantly reduced the density of both intestinal and water-soaked feces, with the most effective (cork; 0.5-1mm; 2%) leading to floating feces (4.39% to 1.00gcm-3 and 5.12% to 0.98gcm-3 for intestinal and water-soaked feces, respectively). The larger grade of cork granules performed significantly better than the smaller grade. The possibilities for reducing levels of effective cork incorporation and enhancing effects on density by other quality improvements are discussed.Feed efficiency and fish health were not impaired by the additives. It is suggested that the systematic manipulation of fecal density with low-density additives may achieve economic and ecological advances and offer a new and effective means of managing and optimizing waste output from aquaculture. The effects of floating feces on removal efficiency, leaching effects, water quality and operating costs in aquacultural systems have to be further explored. copy; 2013 Elsevier B.V.

Unger J.,Fisheries Research Station of Baden Wurttemberg | Unger J.,University of Konstanz | Brinker A.,Fisheries Research Station of Baden Wurttemberg
Aquacultural Engineering | Year: 2013

Basic data describing the physical characteristics of fish fecal waste are important in the design of effective solid waste management in aquaculture, especially in land-based facilities such as recirculating aquacultural systems (RAS).This study describes the physical properties of feces from rainbow trout fed eight different commercially available and widely used diets in Germany. Additional data from an earlier but unpublished study pertaining to feces derived from two rather extreme all-vegetarian diets are also presented for consideration of the settling properties. The diets were tested on duplicate groups of 50 rainbow trout in a flow-through aquaculture system. The effects of the diets on the physical properties of fecal particles such as particle size distribution (PSD), modeled settling velocity and rheological character were examined and the effects of each diet on fish health, growth and feed utilization were determined. Specific growth rate (SGR) and feed conversion ratio (FCR) for the different diets ranged from 0.98%d-1±0.012%d-1 to 1.39%d-1±0.012%d-1 and 0.97±0.017 to 1.61±0.017 (mean±S.E.), respectively. The density of presoaked feces was significantly lower than that of intestinal feces and ranged from 1.01013±0.00692gcm-3 to 1.04547±0.00692gcm-3 (mean±S.E.). Stability data were in the range from 390.12±29.4Pa to 1214.79±29.0Pa for elastic modulus and from 62.12±6.1Pas to 232.68±6.0Pas for dynamic viscosity. Based on the stability and PSD data theoretical efficiencies for removal of fecal waste using a drum filter showed remarkable variation, ranging from 82.5 to 95.9% (60μm gauze). Based on the same data, theoretical removal by a sedimentation basin with routinely using overflow rates of 0.057cms-1 to 0.394cms-1 ranged from 62.8 to 93.8%. Both fecal density and PSD have an exponential impact on settling performance. Increasing fecal density improves the removal efficiency of a sedimentation basin by about 20%, however sedimentation was seen to be a less robust and efficient removal technique than drum filtration. Sedimentation systems also experience additional problems with respect to leaching. Turbulence that was mimicked in this study reflects to an optimal fish farm, which means disintegrating effects are mainly caused by fish motion. If disintegrating units e.g. pumps are used, which are known to promote further particle breakdown the effects would be amplified.The results demonstrate the central importance of density of suspended solids in defining removal efficiencies and suggest that manipulation of fecal density might offer a new and effective means of managing and optimizing waste output from aquaculture operations. This study describes the basic properties of fecal wastes generated by commercial diets and can be used as a basis for further research. © 2012 Elsevier B.V.

Unger J.,Fisheries Research Station of Baden Wurttemberg | Unger J.,University of Konstanz | Schumann M.,Fisheries Research Station of Baden Wurttemberg | Schumann M.,University of Konstanz | Brinker A.,Fisheries Research Station of Baden Wurttemberg
Aquaculture Environment Interactions | Year: 2015

Recent developments in European recirculating aquaculture systems suggest expanding potential for this extremely water-efficient technique. However, the technology still faces challenges due to concerns over economic efficiency and system stability-both essential in minimizing the risk of financially and environmentally expensive failures. One key factor in maintaining stable production conditions in a recirculation loop is the effective removal of solid waste, i.e. fish faeces. This study tested a novel approach for solid control and demonstrates the value-adding potential of floating faeces under commercial conditions in a semi-recirculating fish farm in Germany. A commercial control diet was compared with an experimental diet in which the addition of 2.5% cork granules led to the production of floating faeces. Physiological assays indicated no pathologic tissue alterations associated with the experimental feed, and growth, survival and feed conversion were unaffected. Average single-pass removal by a specially developed surface separator accounted for 78.3% of floating solids, which accounted for 35.4% of total system solids. Total ammonia nitrogen concentrations in production water were roughly halved, from about 0.95 mg l-1 in the control to 0.47 mg l-1 using the cork diet, an improvement that in practice allowed a doubling of production on the same available water flow. This study shows that the application of floating faeces facilitates rapid and cost-effective removal of suspended solids, resulting in a considerable decrease of nutrient load in system and discharge water of the investigated farm. © The authors 2015.

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