Nutrient retention efficiencies in integrated multi-trophic aquaculture

One of the bottlenecks for commercial implementation of integrated multi-trophic aquaculture (IMTA) is the difficulty in quantifying its environmental performance. We reviewed a large body of literature to determine the variability in nutrient dynamics within different IMTA systems (open sea-cages, land-based flow-through and recirculating aquaculture systems), with the aim to provide a generic framework to quantify nutrient retention efficiencies in integrated aquaculture systems. Based on the eco-physiological requirements of the cultured species, as well as the response of “extractive” species to waste from “fed” species, the maximum retention efficiency was defined for a conceptual four-species marine IMTA system (fish–seaweed–bivalve–deposit feeder). This demonstrated that 79%–94% of nitrogen, phosphorus and carbon supplied with fish feed could theoretically be retained. In practice, however, various biological and environmental factors may limit retention efficiencies and thereby influence the bioremediation of IMTA systems. These biological (waste production, stoichiometry in nutrient requirements) and environmental (temporal and spatial connectivity) factors were therefore evaluated against the theoretical reference frame and showed that efficiencies of 45%–75% for closed systems and 40%–50% for open systems are more realistic. This study is thereby the first to provide quantitative estimates for nutrient retention across IMTA systems, demonstrating that a substantial fraction of nutrients released from fish culture units can be retained by extractive species and subsequently harvested. Furthermore, by adapting this framework to the design and the condition prevailing for a specific IMTA system, it becomes a generic tool to analyse the system's bioremediation potential and explore options for further improvement.publishedVersio

Effect of dietary macronutrient composition and buffering capacity on chyme characteristics and digestion kinetics in the gastrointestinal tract of freshwater rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the impact of dietary macronutrient composition and buffering capacity (BC) on chyme characteristics and digestion kinetics in freshwater rainbow trout (Oncorhynchus mykiss). Dietary macronutrient composition was altered by changing the protein-to-energy ratio (P:E) while keeping the fat-to-starch ratio constant. Dietary BC was increased by supplementation of CaCO3. The experiment lasted for 6 weeks. Fish were fed four diets having high and low P:E ratio and high and low CaCO3 level. This experiment was planned according to a 2x2x2 factorial design. The three factors were dietary P:E ratio, BC and time sampling after feeding (3 and 7 h). Chyme was collected from four gastrointestinal tract (GIT) segments (stomach, proximal, middle and distal intestine) and analysed for dry matter (DM), pH, osmolality, crude protein (CP) and mineral content. Relative water fluxes (RWF), electrolyte fluxes, kinetic of digestion and faecal digestibility (ADCs) were measured using yttrium oxide (Y2O3) as an inert marker. All chyme characteristics (including water fluxes) were not influenced by the interaction effect between dietary factors and sampling time (p > 0.05). Both dietary treatments did not affect chyme DM in the stomach. Low P:E diet increased (p < 0.001) chyme DM in all the intestinal segments. Dietary CaCO3 only affected (p < 0.05) chyme DM in the distal intestine. Low P:E diet decreased (p < 0.001) chyme pH in all GIT segments compared to the high P:E diet. Low CaCO3 diet decreased chyme pH in the proximal and middle intestine (p < 0.05) compared to the high CaCO3 diet. RWF were affected only by the dietary P:E ratio in the stomach and in the proximal intestine. Fish fed the high P:E diet had a lower water influx in the stomach and a higher water influx in the proximal intestine than fish fed the low P:E diet. Dietary P:E ratio affected electrolyte fluxes in the GIT, while no effect of CaCO3 was detected. Both dietary factors had a minimal or no effect on the kinetic of digestion in the different GIT segments, while a significant effect was present in all ADCs. Our findings suggest that dietary macronutrient composition, rather than buffering capacity, is the primary factor responsible for changes in chyme characteristics, water and ion fluxes in the GIT of freshwater rainbow trout. Furthermore, changes in dietary macronutrient composition and buffering capacity significantly affect faecal digestibility but are not reflected in digestion kinetics.publishedVersio

Application of polychaetes in (de)coupled integrated aquaculture: an approach for fish waste bioremediation

ABSTRACT: Development of benthic components within integrated multi-trophic aquaculture (IMTA) systems warrants more attention, and the development of polychaetes as an extractive component in IMTA systems is ongoing. This study estimates the bioremediation potential of Capitella sp. and Ophryotrocha craigsmithi for coupled and decoupled salmon-driven IMTA. In coupled IMTA, polychaetes receive fresh faeces, while in decoupled IMTA, preservation of faeces is applied. Respiration and ammonia excretion rates were measured for polychaetes fed fresh, oven-dried or acidified salmon faeces, and combined with nutrients incorporated into tissue growth, to estimate nutrient requirements. Nutrient requirements were subsequently used to evaluate bioremediation potential. Metabolic rates were highest for O. craigsmithi and contributed notably to their overall nutrient requirement (20-30%). For the 2 polychaete species, nutrient requirements ranged from 5 to 26 mg C and from 2 to 6 mg N g-1 AFDW d-1. These requirements were comparable with or higher than other polychaete species, highlighting the potential for fish waste bioremediation by Capitella sp. and O. craigsmithi. Preserved diets reduced bioremediation potential 1.5 and 3-5 times for, respectively, Capitella sp. and O. craigsmithi. Assuming that polychaetes are efficient fish-faeces convertors, the bioremediation potential indicates that benthic cultivation units containing 65000-95000 ind. m-2 of Capitella sp. or 36000-194000 ind. m-2 of O. craigsmithi can convert the daily organic waste flux deposited below an average salmon farm. These densities were within ranges reported for wild populations, indicating that, based on the bioremediation potential, development of benthic IMTA with these 2 polychaete species seems realistic and efficient for waste conversion.publishedVersio

Metabolic and transcriptional responses of gilthead sea bream (Sparus aurata L.) to environmental stress: New insights in fish mitochondrial phenotyping

The aim of the current study was to phenotype fish metabolism and the transcriptionally-mediated response of hepatic mitochondria of gilthead sea bream to intermittent and repetitive environmental stressors: (i) changes in water temperature (T-ST), (ii) changes in water level and chasing (C-ST) and (iii) multiple sensory perception stressors (M-ST). Gene expression profiling was done using a quantitative PCR array of 60 mitochondria-related genes, selected as markers of transcriptional regulation, oxidative metabolism, respiration uncoupling, antioxidant defense, protein import/folding/assembly, and mitochondrial dynamics and apoptosis. The mitochondrial phenotype mirrored changes in fish performance, haematology and lactate production. T-ST especially up-regulated transcriptional factors (PGC1α, NRF1, NRF2), rate limiting enzymes of fatty acid β-oxidation (CPT1A) and tricarboxylic acid cycle (CS), membrane translocases (Tim/TOM complex) and molecular chaperones (mtHsp10, mtHsp60, mtHsp70) to improve the oxidative capacity in a milieu of a reduced feed intake and impaired haematology. The lack of mitochondrial response, increased production of lactate and negligible effects on growth performance in C-ST fish were mostly considered as a switch from aerobic to anaerobic metabolism. A strong down-regulation of PGC1α, NRF1, NRF2, CPT1A, CS and markers of mitochondrial dynamics and apoptosis (BAX, BCLX, MFN2, MIRO2) occurred in M-ST fish in association with the greatest circulating cortisol concentration and a reduced lactate production and feed efficiency, which represents a metabolic condition with the highest allostatic load score. These findings evidence a high mitochondrial plasticity against stress stimuli, providing new insights to define the threshold level of stress condition in fish. © 2014 Elsevier Inc.This work was funded by the EU AQUAEXCEL (Aquaculture Infrastructures for Excellence in European Fish Research, FP7/2007/2013; grant agreement No. 262336), and the Spanish AQUAGENOMICS (CSD2007-00002, Improvement of aquaculture production by the use of biotechnological tools) projects. Additional funding was obtained by Generalitat Valenciana (research grant PROMETEO 2010/006).Peer Reviewe

Integrated multi-trophic aquaculture : Nutrient retention efficiency and valorisation of waste nutrients

With the increasing demand for fish and seafood, further growth of the aquaculture sector is foreseen. This growth associates with ecological concerns, including pressure on natural resources, a growing demand for high-quality aquafeeds and an increased waste production (i.e. uneaten feed, metabolic waste and faeces) with potential detrimental effects if discharged into the environment. Therefore, sustainable aquaculture approaches are needed, to keep up with the increasing demand for food and resources while minimizing adverse impacts on the environment. Integrated Multi-Trophic Aquaculture (IMTA) is an approach with the ambition to fulfil this need. In IMTA systems, fed species aquaculture (i.e. dependent on external feed supply) is combined with extractive species aquaculture (i.e. extract nutrients from their environment), so that waste resulting from fed species is recycled in extractive species biomass. This approach strives to reduce aquaculture waste losses by improving resource use efficiencies and transforming linear monocultures into circular systems.The general concepts and principles of IMTA have been extensively addressed in the literature. Still, the environmental benefits of IMTA are mainly conceptually described and insufficiently quantified. The aim of this thesis is to investigate nutrient retention efficiencies in different marine IMTA systems (i.e. open-water sea cages, land-based flow-through and recirculating aquaculture systems [RAS]) by quantifying the fluxes involved in nitrogen (N), phosphorus (P) and carbon (C) retention and exploring the impact of biological and environmental factors on retention efficiency and waste valorisation.Based on an extensive literature review, this thesis shows that it is feasible to recycle 22-32% N, 41% P and 7-37% C of the feed input via extractive species in a four-species marine land-based closed IMTA systems, while in an open-water IMTA system this is 7% for N, 16% for P and 2-12% for C. In addition to the literature review, experimental work with seaweed and benthic deposit feeders was done to address specific knowledge gaps. Under moderate to high nitrogen (0.5-5 mM) and phosphorus (0.01-0.1 mM) concentrations, performance of the seaweed species Ulva spp. is not influenced by (unfavourable) stoichiometry and high nitrate concentrations do not limit phosphorus uptake. This is promising for closed IMTA systems with Ulva spp. as extractive species. Orthophosphate concentrations of 0.9 mM are toxic for Ulva spp., and these conditions should be avoided in the design and management of closed IMTA systems. Two benthic polychaete species were studied, Capitella sp. and Ophryotrocha craigsmithi and both species are interesting for IMTA systems, as they show good bioremediation and growth potential when fed fresh salmon faeces. Moreover, albeit the salmon faeces fed to the polychaetes contained relatively low polyunsaturated fatty acid levels, the worms studied were rich in polyunsaturated fatty acids. This indicates that the polychaetes are able to convert low-quality fish faeces into a high-quality resource, containing for fish essential fatty acids. Potentially, this makes them a valuable resource for fish feed formulation. Overall this thesis creates more insight in the (re)cycling of fed nutrients by extractive species in IMTA, and the waste valorisation potential of seaweed and polychaetes.&nbsp;&nbsp;&nbsp; &nbsp;&nbsp

Effect of temperature on the metabolism, behaviour and oxygen requirements of Sparus aurata

We investigated the effect of temperature on the limiting oxygen saturation (LOS) of gilthead sea bream Sparus aurata. This threshold was defined as the % O2 saturation where fish no longer upheld their routine metabolic rate (RMR, the metabolic rate of fed and active fish) during a progressive decline in oxygen saturation. S. aurata (398 ± 10 g, mean ± SE) were kept in 3 replicate tanks and subjected to 3 changes in temperature: 16 to 20°C, 20 to 16°C and 16 to 12°C. At each temperature, fish were left to acclimatize for 8 to 10 d, before daily feed intake (DFI), the routine oxygen consumption rate (routine MO2, mg kg-1 min-1) and the LOS were measured. In addition, at 20°C the swimming speed was measured in fish subjected to a decline in O2 from full air saturation to levels below the LOS (minimum of 8-10% O2). For the temperature range tested (12-20°C), DFI, MO2 and LOS increased exponentially with temperature (7.5-, 3.6- and 2.2-fold, respectively) with mean (± SE) LOS being 17 ± 1, 21 ± 0 and 35 ± 5% O2 at 12, 16 and 20°C, respectively. A gradual decline in swimming activity was observed as O2 declined below the LOS, indicating increasing metabolic stress and/or a 'sit-out' coping strategy which may prolong survival time in severe hypoxia. The results show the importance of temperature as an influential variable over the environmental O2 requirements of S. aurata. © The authors 2015.The study was funded by the EU Seventh Framework Programme by the AQUAEXCEL (FP7-2007-2012; grant agreement no. 262336) and the Norwegian Research Council through the Centre for Research-based Innovation in Aquaculture Technology, CREATE.Peer Reviewe

Nutrient retention efficiencies in integrated multi-trophic aquaculture

One of the bottlenecks for commercial implementation of integrated multi-trophic aquaculture (IMTA) is the difficulty in quantifying its environmental performance. We reviewed a large body of literature to determine the variability in nutrient dynamics within different IMTA systems (open sea-cages, land-based flow-through and recirculating aquaculture systems), with the aim to provide a generic framework to quantify nutrient retention efficiencies in integrated aquaculture systems. Based on the eco-physiological requirements of the cultured species, as well as the response of “extractive” species to waste from “fed” species, the maximum retention efficiency was defined for a conceptual four-species marine IMTA system (fish–seaweed–bivalve–deposit feeder). This demonstrated that 79%–94% of nitrogen, phosphorus and carbon supplied with fish feed could theoretically be retained. In practice, however, various biological and environmental factors may limit retention efficiencies and thereby influence the bioremediation of IMTA systems. These biological (waste production, stoichiometry in nutrient requirements) and environmental (temporal and spatial connectivity) factors were therefore evaluated against the theoretical reference frame and showed that efficiencies of 45%–75% for closed systems and 40%–50% for open systems are more realistic. This study is thereby the first to provide quantitative estimates for nutrient retention across IMTA systems, demonstrating that a substantial fraction of nutrients released from fish culture units can be retained by extractive species and subsequently harvested. Furthermore, by adapting this framework to the design and the condition prevailing for a specific IMTA system, it becomes a generic tool to analyse the system's bioremediation potential and explore options for further improvement

Effect of temperature on the metabolism, behaviourand oxygen requirements of Sparus aurata

We investigated the effect of temperature on the limiting oxygen saturation (LOS) of gilthead sea bream Sparus aurata. This threshold was defined as the % O2 saturation where fish no longer upheld their routine metabolic rate (RMR, the metabolic rate of fed and active fish) during a progressive decline in oxygen saturation. S. aurata (398 ± 10 g, mean ± SE) were kept in 3 replicate tanks and subjected to 3 changes in temperature: 16 to 20°C, 20 to 16°C and 16 to 12°C. At each temperature, fish were left to acclimatize for 8 to 10 d, before daily feed intake (DFI), the routine oxygen consumption rate (routine MO2, mg kg-1 min-1) and the LOS were measured. In addition, at 20°C the swimming speed was measured in fish subjected to a decline in O2 from full air saturation to levels below the LOS (minimum of 8-10% O2). For the temperature range tested (12-20°C), DFI, MO2 and LOS increased exponentially with temperature (7.5-, 3.6- and 2.2-fold, respectively) with mean (± SE) LOS being 17 ± 1, 21 ± 0 and 35 ± 5% O2 at 12, 16 and 20°C, respectively. A gradual decline in swimming activity was observed as O2 declined below the LOS, indicating increasing metabolic stress and/or a ‘sit-out’ coping strategy which may prolong survival time in severe hypoxia. The results show the importance of temperature as an influential variable over the environmental O2 requirements of S. aurata

Application of polychaetes in (de)coupled integrated aquaculture: an approach for fish waste bioremediation

ABSTRACT: Development of benthic components within integrated multi-trophic aquaculture (IMTA) systems warrants more attention, and the development of polychaetes as an extractive component in IMTA systems is ongoing. This study estimates the bioremediation potential of Capitella sp. and Ophryotrocha craigsmithi for coupled and decoupled salmon-driven IMTA. In coupled IMTA, polychaetes receive fresh faeces, while in decoupled IMTA, preservation of faeces is applied. Respiration and ammonia excretion rates were measured for polychaetes fed fresh, oven-dried or acidified salmon faeces, and combined with nutrients incorporated into tissue growth, to estimate nutrient requirements. Nutrient requirements were subsequently used to evaluate bioremediation potential. Metabolic rates were highest for O. craigsmithi and contributed notably to their overall nutrient requirement (20-30%). For the 2 polychaete species, nutrient requirements ranged from 5 to 26 mg C and from 2 to 6 mg N g-1 AFDW d-1. These requirements were comparable with or higher than other polychaete species, highlighting the potential for fish waste bioremediation by Capitella sp. and O. craigsmithi. Preserved diets reduced bioremediation potential 1.5 and 3-5 times for, respectively, Capitella sp. and O. craigsmithi. Assuming that polychaetes are efficient fish-faeces convertors, the bioremediation potential indicates that benthic cultivation units containing 65000-95000 ind. m-2 of Capitella sp. or 36000-194000 ind. m-2 of O. craigsmithi can convert the daily organic waste flux deposited below an average salmon farm. These densities were within ranges reported for wild populations, indicating that, based on the bioremediation potential, development of benthic IMTA with these 2 polychaete species seems realistic and efficient for waste conversion.publishedVersio

Ulva spp. performance and biomitigation potential under high nutrient concentrations : implications for recirculating IMTA systems

The growth, tissue content and nutrient removal rates of Ulva spp., when exposed to moderate to high nitrogen (0.5–5 mmol L−1) and phosphorus (0.01–0.9 mmol L−1) concentrations, were examined to get a better understanding of recirculating IMTA (Integrated Multi-Trophic Aquaculture) systems with fish and seaweed. It was hypothesized that fish waste effluents might lead to unfavorable nutrient stoichiometry and/or toxic conditions, which might harm seaweeds and, specifically for the present study, reduce Ulva spp. performance. Results demonstrate that: (I) the unfavorable N:P stoichiometry (N:P ≠ Atkinson atomic ratio of 30:1) did not restrict Ulva spp. growth nor tissue content; this indicates that supply of both nutrients exceeded the minimum requirements; (II) a high orthophosphate concentration (0.9 mmol L−1) was toxic to Ulva spp., whereas (III) a high nitrate concentration (5 mmol L−1) did not inhibit phosphorus uptake; (IV) Ulva’s growth was not enhanced when nitrate was exchanged for similarly high ammonium concentrations. However, tissue nitrogen content was 1.4 times higher when exposed to ammonium than nitrate, suggesting that the former N-form was stored faster in the seaweed’s tissue. Therefore, other factors must have limited growth with the high ammonium concentrations. This study also highlights the importance of relatively long acclimatization periods (one week) when maintenance uptake (Vm) is evaluated, as surge uptake (Vs) may result in considerably different and more variable rates. Results of this study contribute to a better understanding of the application of Ulva spp. as extractive component in closed IMTA systems, thus advancing sustainable and circular production techniques