The Benefish consortium reports on the influence of system water refreshment rates on realized feed load, weight development, fish physiology and behaviour in turbot

Farmers with recirculation aquaculture systems (RAS) have a greater necessity and capacity to control the culture conditions of their farms than farmers with other aquaculture systems. Water quality is one of the factors that is closely monitored and managed in order to maintain the optimal levels of oxygen, ammonia, temperature, pH, and CO2. Effects of these parameters on growth and health are well studied and almost immediately noticeable. In RAS it often occurs that, although water quality conditions seem to be optimal, the feed intake of the fish might suddenly diminishes, thus reflecting a situation of sub optimal welfare of the animals. This phenomenon is particular relevant in marine RAS where these situations of reduced feed intake occur even though the normally monitored water quality parameters and husbandry conditions appear to be optimal. Similar phenomena also occur in other aquaculture culture systems, such as flow through systems, where feed intake fluctuates whilst the reasons are not always known, although there is typically less control and monitoring compared with RAS. It is therefore necessary to actively monitor deviation of expected feed intake, in combination with the monitoring of culture conditions and farm management on pilot-scale level. Only through this intermediate level experimental work and farm observations for the assumed relationship between deviation of expected feed intake and fish welfare can be validated. It is furthermore necessary to provide refinements to causative relationships expected to be found on commercial farms, where it is often claimed that e.g. lower system water refreshment rates or more closed RAS are leading to growth retardation and lower feed intake in fish and thus lower production. The present study is, therefore, intending to prove the hypothesis that changes in feed intake can be associated with changed fish welfare status, using turbot as model species. It is furthermore hypothesized that this changed fish welfare status is caused by different system water refreshment rates and fish and system management. As a final result, feed intake should relate by same efficiency to lower fish growth in closed RAS compared to flow through systems. The objectives are therefore to validate the relationships between deviation from expected feed intake and fish welfare, and their causative factors on the commercial farms interpreting data on feed intake, behavior, endocrinology and immune patterns as welfare indicators

Endocrine disruptor activity in waters from turbot aquaculture

International audienc

Intensification of landbased aquaculture production in single pass and reuse systems

Over the last 20 years, the productivity in hatcheries and farms producing fry and smolt of trout and salmon has increased substantially. These land-based farms are mainly situated along the coast and discharge effluent water directly to the sea. Such production is the basis of the recruitment of marine salmon and trout cage farms in Chile, Scotland, Norway and some other temperate countries with a coastline. Similarly, productivity and use of recirculation systems for the production of both seawater and freshwater fish has increased throughout the world. In many cases, the use of recirculation systems has ecological advantages over other technologies, especially those relying on flow through operations. The Norwegian authorities required a minimum flow supply of 1.5 m3 per 100,000 salmon smolt produced annually since the mid-80's. Without oxygenation of the water, the specific flow rate fluctuated between 0.5 and 2.5 L kg-1 min-1 throughout the year. Addition of pure oxygen then significantly reduced the flow requirements, now typically in the range 0.3 – 0.5 L kg-1 min-1. According to another regulation for licensing of hatcheries, the lowest allowable flow in single flow-through systems was 0.3 L kg-1 min-1. Water quality parameters have however been introduced recently as criterion instead of water flow requirements (concentrations of oxygen, carbon dioxide and ammonia). Mainly due to the usage of oxygenation technology, the water consumption at most smolt farms is at present 100 – 200 m3 kg-1 produced fish compared to 1,000 – 1,700 m3 kg-1 some 20 years ago. When the water flow is reduced, there is a build-up of both carbon dioxide and total ammonia, whilst pH is reduced. Both carbon dioxide and pH may become limiting factors when the water flow is decreased due to oxygen injection. There is however a lack of information regarding safe levels of carbon dioxide concentrations for Atlantic salmon smolts. Increased ventilation frequency and reduced growth have been observed in smolts exposed to reduced water flow. Effects observed during long-term experiments with rainbow trout and Atlantic salmon exposed to elevated carbon dioxide in fresh water include reduced growth and feed utilisation and nephrocalcinosis. Recirculation systems allow in the same time to reduce the make up water needs, to control the recirculated water quality and facilitates the treatment of the effluents (lower flow rate and higher concentration). They were developed at commercial scale in several countries and for various marine or freshwater fish species. In this article, some recirculation systems adapted to different fish life stages (from breeders to commercial size fish) and environments (Europe and USA) will be described. Improved feed quality, better feeding control and other factors have strongly reduced the waste production from farms. Since the mid-80's, the mean feed conversion ratio (FCR) in the Norwegian smolt industry as in other developed countries has decreased from 1.5 – 1.8 to less than 1.0 (kg feed kg-1 produced fish) which indicates a halved effluent load of organics and nutrients per kg produced fish. Additionally, many farms have introduced end-of-pipe treatment for solid removal before release to recipient

Endocrine disruptor activity in waters from turbot aquaculture

International audienc

Comparison of two methods for evaluating waste of a flow though trout farm

European water legislation enforces increasingly restrictive measures with regards to reduction of water consumption and waste emission in order to minimise the potential environmental impact of the agro industry sector. Fish farms are particularly concerned, but legislation covering effluent discharge varies significantly from country to country. However, recommendations and directives from institutional, national or regional bodies suggest the enforcement of increasingly strict waste reduction measures and the development of waste treatment. Before treatment, it is necessary to evaluate waste production in terms of composition and quantity. The waste quantification methods used today for fish culture systems are either based on direct measurements of nutrient and suspended solid fluxes or on indirect evaluation based on the digestibility coefficients of the feed constituents. The objective of the present study is to evaluate the waste of a freshwater flow through farm using both approaches and to discuss their applicability, drawbacks and advantages from the viewpoints of fish farmers and control authorities. Waste production on the farm was monitored during several 24 hour cycles in order to characterise the effluents of the system. The predictions and measurements for the total nitrogen (TN) parameter were well correlated, but measured and predicted suspended solids (SS) and total phosphorus (TP) values presented a weaker correlation coefficient. The hydrobiological method gives details on the N and P forms of waste but this method is heavy and it is difficult to obtain representative samples and flow rate measurements. The nutritional method is the simplest to use, provided that feed data are available. (C) 2007 Elsevier B.V. All rights reserved

New developments in recirculating aquaculture systems in Europe: a perspective on environmental sustainability

The dual objective of sustainable aquaculture, i.e., to produce food while sustaining natural resources is achieved only when production systems with a minimum ecological impact are used. Recirculating aquaculture systems (RASs) provide opportunities to reduce water usage and to improve waste management and nutrient recycling. RAS makes intensive fish production compatible with environmental sustainability. This review aims to summarize the most recent developments within RAS that have contributed to the environmental sustainability of the European aquaculture sector. The review first shows the ongoing expansion of RAS production by species and country in Europe. Life cycle analysis showed that feed, fish production and waste and energy are the principal components explaining the ecological impact of RAS. Ongoing developments in RAS show two trends focusing on: (1) technical improvements within the recirculation loop and (2) recycling of nutrients through integrated farming. Both trends contributed to improvements in the environmental sustainability of RAS. Developments within the recirculation loop that are reviewed are the introduction of denitrification reactors, sludge thickening technologies and the use of ozone. New approached towards integrated systems include the incorporation of wetlands and algal controlled systems in RAS. Finally, the review identifies the key research priorities that will contribute to the future reduction of the ecological impact of RAS. Possible future breakthroughs in the fields of waste production and removal might further enhance the sustainabilty of fish production in RAS

Impact assessment of various rearing systems on fish health using multibiomarkers response and metal accumulation

International audienceEuropean sea bass were reared in three different systems: one flow-through (FTS), one recirculating (RAS), and one recirculating with a high-rate algae pond (RAS + HRAP). After 1 year of rearing, the final fish weight was 15% lower in the RAS compared to the FTS. The accumulation of a growth-inhibiting substance in the RAS is the main hypothesis explaining this difference. As in environmental risk assessment, fish bioaccumulation markers and biomarkers were used to demonstrate exposure to and effects of the rearing water in the three rearing systems. Thirty fish per system were sacrificed before their condition factor (CF) and liver somatic index (LSI) were calculated. Nine biomarkers, including ethoxyresorufin-O-deethylase (EROD) and superoxide dismutase (SOD), were measured in liver and twelve metals including As, Cd, Cu, Pb, Cr, and Zn, for which there are regulations regarding human consumption, were measured in liver and muscle. In all systems, CF and LSI were not significantly different and no correlation was found with biomarker activity or metal concentration. EROD and SOD activities were significantly increased in RAS. Accumulation of seven and four metals in muscle and liver, respectively, was significantly higher in the RAS relative to FTS. The HRAP prevented metal accumulation except for chromium and arsenic. Eight metal concentrations were significantly higher in liver than in muscle. Concentrations of toxic metals were similar to reported values and below FAO/WHO recommended values for human consumption