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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. Source


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. Source


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. Source


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. Source


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. Source

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