security of water, food, and energy for humans in the 21 st century. Water is the primary resource for life and is the main input to produce agricultural goods in the field and throughout the entire agro-food supply chain. Energy is required to distribute water, pro- ABSTRACT: Aquaculture is globally the fastest growing sector of agriculture that needs to be sustainable and must also meet bioeconomic demands. In principle, aquaponics, the combination of aquaculture and horticulture within a single recirculating aquaponic system (SRAPS), provides a sustainable approach; however, it has lower productivity of both fish and plants in comparison to separate recirculating systems. The aim of our new concept for aquaponics is to improve sustainability and productivity concomitant with lowering environmental emissions. The aquaponic system for (nearly) emission free tomato and fish production in greenhouses (ASTAF-PRO) is a new combination of systemic parts, consisting of 2 independent recirculating units: an aquaculture system (RAS) for fish and a hydroponic unit for plants. Both systems are connected by a 1-way valve to deliver fish water containing nutrients into the hydroponic reservoir, where the fish water can be optimized as fertilizer in order to meet specific demands of the plant species. Thus, our double recirculation aquaponic system (DRAPS) can provide optimum conditions for both parts to increase productivity and to prevent any adverse interactions between plant and fish units. Water use is minimized by condensing the plant evapo-transpired water via air conditioning and returning it into the RAS. Testing of the ASTAF-PRO prototype successfully demonstrated the principle using a combination of tilapia and tomato production. Tilapia productivity was similar to single RAS, while tomato production at least indicated the potential for similar efficiency to conventional hydroponics. Thus, ASTAF-PRO improves sustainability and productivity while lowering environmental emissions, and might promote future application of aquaponics for food security.

Metabolism constitutes a fundamental property of all organisms. Metabolic rate is commonly described to scale as a power function of body size and exponentially with temperature, thereby treating the effects of body size and temperature independently. Mounting evidence shows that the scaling of metabolic rate with body mass itself depends on temperature. Across‐species analyses in fishes suggest that the mass‐scaling exponent decreases with increasing temperature. However, whether this relationship holds at the within‐species level has rarely been tested. Here, we re‐analyse data on the metabolic rates of four freshwater fish species, two coregonids and two cyprinids, that cover wide ranges of body masses and their naturally experienced temperatures. We show that the standard metabolic rate of the coregonids is best fit when accounting for a linear temperature dependence of the scaling of metabolic rate with body mass, whereas a constant mass‐scaling exponent is supported in case of the cyprinids. Our study shows that phenotypic responses to temperature can result in temperature‐dependent scaling relationships at the species level and that these responses differ between taxa. Together with previous findings, these results indicate that evolutionarily adaptive and phenotypically plastic responses to temperature affect the scaling of metabolic rate with body mass in fishes.

BackgroundSympatric species pairs are particularly common in freshwater fishes associated with postglacial lakes in northern temperate environments. The nature of divergences between co-occurring sympatric species, factors contributing to reproductive isolation and modes of genome evolution is a much debated topic in evolutionary biology addressed by various experimental tools. To the best of our knowledge, nobody approached this field using molecular cytogenetics. We examined chromosomes and genomes of one postglacial species pair, sympatric European winter-spawning Coregonus albula and the local endemic dwarf-sized spring-spawning C. fontanae, both originating in Lake Stechlin. We have employed molecular cytogenetic tools to identify the genomic differences between the two species of the sympatric pair on the sub-chromosomal level of resolution.ResultsFluorescence in situ hybridization (FISH) experiments consistently revealed a distinct variation in the copy number of loci of the major ribosomal DNA (the 45S unit) between C. albula and C. fontanae genomes. In C. fontanae, up to 40 chromosomes were identified to bear a part of the major ribosomal DNA, while in C. albula only 8–10 chromosomes possessed these genes. To determine mechanisms how such extensive genome alternation might have arisen, a PCR screening for retrotransposons from genomic DNA of both species was performed. The amplified retrotransposon Rex1 was used as a probe for FISH mapping onto chromosomes of both species. These experiments showed a clear co-localization of the ribosomal DNA and the retrotransposon Rex1 in a pericentromeric region of one or two acrocentric chromosomes in both species.ConclusionWe demonstrated genomic consequences of a rapid ecological speciation on the level undetectable by neither sequence nor karyotype analysis. We provide indirect evidence that ribosomal DNA probably utilized the spreading mechanism of retrotransposons subsequently affecting recombination rates in both genomes, thus, leading to a rapid genome divergence. We attribute these extensive genome re-arrangements associated with speciation event to stress-induced retrotransposons (re)activation. Such causal interplay between genome differentiation, retrotransposons (re)activation and environmental conditions may become a topic to be explored in a broader genomic context in future evolutionary studies.

Swimming performance is considered a main character determining survival in many aquatic animals. Body morphology highly influences the energetic costs and efficiency of swimming and sets general limits on a species capacity to use habitats and foods. For two cyprinid fishes with different morphological characteristics, carp (Cyprinus carpio L.) and roach (Rutilus rutilus (L.)), optimum swimming speeds (U(mc)) as well as total and net costs of transport (COT, NCOT) were determined to evaluate differences in their swimming efficiency. Costs of transport and optimum speeds proved to be allometric functions of fish mass. NCOT was higher but U(mc) was lower in carp, indicating a lower swimming efficiency compared to roach. The differences in swimming costs are attributed to the different ecological demands of the species and could partly be explained by their morphological characteristics. Body fineness ratios were used to quantify the influence of body shape on activity costs. This factor proved to be significantly different between the species, indicating a better streamlining in roach with values closer to the optimum body form for efficient swimming. Net swimming costs were directly related to fish morphology.

The aquaponic principle is the coupling of animal aquaculture (e.g. fish) with plant production (e.g. vegetables) for saving resources. At present, various definitions of aquaponics exist, some bearing the risk of misinterpretation by dismissing the original meaning or being contradictory. In addition, there is no standard terminology for the aspects of coupling between the aquaponic subsystems. In this study, we addressed both issues. (1) We developed new or revised definitions that are summarised by: Aquaponic farming comprises aquaponics (which couples tank‐based animal aquaculture with hydroponics) and trans‐aquaponics, which extends aquaponics to tankless aquaculture as well as non‐hydroponics plant cultivation methods. Within our conceptual system, the term aquaponics corresponds to the definitions of FAO and EU. (2) A system analysis approach was utilised to explore different aquaponic setups aiming to better describe the way aquaponic subsystems are connected. We introduced the new terms ‘coupling type’ and ‘coupling degree’, where the former qualitatively characterises the water‐mediated connections of aquaponic subsystems. A system with on‐demand nutrient water supply for the independent operating plant cultivation is an ‘on‐demand coupled system’ and we propose to deprecate the counterintuitive term ‘decoupled system’ for this coupling type. The coupling degree comprises a set of parameters to quantitatively determine the coupling's efficiency of internal streams, for example, water and nutrients. This new framework forms a basis for improved communication, provides a uniform metric for comparing aquaponic facilities, and offers criteria for facility optimisation. In future system descriptions, it will simplify evaluation of the coupling's contribution to sustainability of aquaponics.

Most fish species are regularly subjected to periods of starvation during which a reduction of energy turnover might be favourable for the animal. This reduction of energy flux may be achieved by changes in thermal behaviour and/or swimming activity. We investigated such behavioural changes during starvation and subsequent refeeding in roach, Rutilus rutilus, with respect to energetic benefits and growth maximisation. Roach, acclimated to a wide range of temperatures (4, 12, 20, 24, 27 and 30 °C), were fed to excess, subjected to 3 weeks of starvation and subsequently refed in order to determine the temperature dependence of feeding rates, growth rates and conversion efficiency (K) under control conditions and during compensatory growth. When exposed to a thermal gradient, control animals preferentially selected a temperature of 26.8±0.9 °C, which is in the range of the optimal temperatures for feeding, growth and conversion efficiency. Starving fish showed a distinct circadian pattern of the mean selected temperature (MST). They migrated to cooler water in the dark (MST=22.8±1.1 °C) but returned to warmer water during daytime. This behaviour may be regarded as a trade-off between the potentially higher food density in warmer water areas and the energetic benefit of selecting cooler water patches. The circadian pattern of MST was gradually abandoned upon refeeding and control values were reached again after 3 weeks. Energetically more effective than behavioural hypothermia was the reduction of swimming activity. During starvation, activity peaks were slightly lower than under control conditions and mean daily activity decreased by about 50%. Swimming velocity, however, was not affected by feeding regime. After a period of starvation fish showed compensatory growth at all temperatures, even below 12 °C, where these animals normally do not grow. This suggests that after a period of starvation the critical temperature for growth shifts to lower values.

Summary 1.Understanding the ecological forces that are responsible for the evolution and coexistence of closely related sympatric species is a major interest in evolutionary ecology. In a freshwater system context, flocks or pairs of sympatrically occurring fishes are commonly studied to identify causes and mechanisms of ecological divergence and speciation. 2. Whereas habitat and diet segregation along the pelagic-benthic axis is frequent in many species pairs in temperate freshwaters, two pelagic planktivores coexist in the post-glacial Lake Stechlin, Germany (common vendace, Coregonus albula and the endemic Fontane cisco, C. fontanae ). Accordingly, disruptive selection on traits not related to feeding may have contributed to divergence. Since both species differ slightly in their vertical distribution, species-specific physiological adaptations related to temperature are likely. 3. We investigated standard and active metabolic rates (AMR) over the range of environmental temperature, which both species experience naturally (4-15 ° C). Eighty-four specimens of 7-22 cm length were exposed to five relative flow velocities between 0·5 and 2·0 body lengths per second (BL s -1 ) in swim tunnel respirometers. 4. Fontane cisco showed a reduced standard metabolic rate (SMR) compared to vendace over the entire temperature range. Further, activity metabolism was associated with lower energetic costs in Fontane cisco at 4 ° C, but higher costs than in vendace at 8 ° C and 15 ° C. Total metabolic costs when swimming at 2 BL s -1 were higher for vendace at < 8 ° C, but higher for Fontane cisco if temperature exceeds 8 ° C. 5.The results indicate that species-specific physiological adaptations contribute to ecological divergence, thus preventing competitive exclusion between the pelagic coregonids of Lake Stechlin. The existence of a vertical gradient in water temperature was probably a crucial factor for the evolution of both competing temperature-related physiological strategies.

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