Final Report Summary - RACEWAYS (A hyperintensive fish farming concept for lasting competitiveness and superior production) The European aquaculture industry has expanded extensively in the last decade, but is almost exclusively dominated by the production of some few pelagic fish species. The aquaculture of bottom-dwelling fish species has thus not expanded at the same rate. At present, farming of bottom-dwelling species is very space-demanding. By introduction of the hyper-intensive production method the small- and medium-sized enterprises (SMEs) can expand their activities further, causing a fast growth in European land-based fish production. Thoroughly tested prototype units or modules of the sediment retention system (SRS) with a variety of fish species, will form the basis for the subsequent construction of commercial-sized farms among the SMEs in the consortium. These first farms may continue the innovation with focus on introduction of new fish species in European culture. All the auxiliary logistic elements needed to operate the farm efficiently, might be implemented in full-scale farming operation. Among these is the recirculation aquaculture system (RAS) in conjunction with the SRS, a technology package that though will need some further elaboration when implemented in commercial-scale farms. Finally, operational protocols will be available so that the running of any farm will be efficient and adequate. It has been demonstrated that growth and feed conversion efficiency of juvenile Atlantic halibut can be improved by rearing fish at intermediate salinities. The general trend with lower plasma: sodium, glucose, CO2, pH and HCO3 at 15 correspond to the observed higher growth and feed conversion efficiency in Atlantic halibut at this salinity. The results clearly show that the optimum conditions for farming Atlantic halibut, both with respect to growth rate and feed conversion, is at salinities lower than 32 % with optima between 15-25 %. This is an important finding for the halibut industry. Our findings clearly show that that growth and feed conversion efficiency can be improved in turbot and spotted wolf fish culture by rearing the fish in shallow raceways. These findings may have important consequences for optimisation of commercial production of these species and could be applicable to other bottom dwelling species. Experiments demonstrated a generally high tolerance to iron in young turbot, and low acute toxicity was seen. Some mortality occurred at 1 000 micrograms per litre. There were some effects from the treatments reflected in blood gas physiology. Depending on the success and quality of the results scientific publication will be considered with recommendation of iron values to be used in land-based culture of turbot. Results from FISKEY's trials with forced settlement of Atlantic halibut in shallow raceways were positive with high survival rates (up to 81 %), but there are still some challenges as to the correct design of the raceways in terms of water inlet/outlet, water velocity (due to the unevenness of the salmon egg trays used as raceways), and the fact that the live feed (Artemia) used was transported through and out of the raceways very quickly. In several short-duration experiments implications of passing threshold limits for water quality parameters will be quantified for turbot organised in sub-populations and being exposed to gradually increasing use of water and thus experiencing gradually increasing levels of metabolites (i.e. ammonia and CO2). Through these experiments it will be possible to form an image of the metabolic activity of the fish, and the strain they put on the rearing water under natural production routines and identify the threshold values causing reduced growth performance. Such data may provide a tool for foreseeing carrying capacity in facilities based on a species tolerance limit to critical water quality parameters. Globally, the results obtained point in the direction of no visible effects of water reuse when turbot is cultivated in 15+15 m long shallow raceways in series, with within-tank sedimentation in their outlet, solids settling boxes using recycled seawater and high oxygen levels. This agrees with the first year experiments using one raceway partitioned in four replicated chambers. As no apparent effect of water quality was seen in juvenile turbot (even under the high level of CO2 registered at the outlet) this may be a result of a fish adaptation to the typical water quality values of the system.It has been demonstrated that easily analysed blood physiological parameters may be useful welfare indicators in turbot reared in land-based systems. The following observations of physiological alterations related to production system and water supply may be used for practical purposes in monitoring of turbot welfare: - Blood ions: Na+ and K+ are influenced by salinity and decreases when salinity decreases. Baseline values of both in full salinity water are well known.- Blood gases: Partial pressure of CO2 in blood increases when CO2 in water increases. A similar increase may be observed under hyperoxic conditions due to a reduction in gill ventilation frequency. - Acid-base balance: An increase in blood pH may indicate an increase in water CO2 content. The pH increase is a compensatory effect arising ionoregulatory adjustments that lead to a rise in plasma HCO3- concentration. - Urea content: An increase in blood urea content may indicate an increase in water ammonia content, and is a detoxification process where ammonia is converted to the less toxic urea compound. Related documents Final Report RACEWAYS (A hyperintensive fish farming concept for lasting competitiveness and superior production)
