Shallow raceways as a compact, resource-maximizing farming procedure for marine fish species

To develop a compact farming system, a shallow raceway has been tested on f ive flatfish, three bottom-dwelling species and three open-water species, T he main effort has been on turbot Scophthalmus maximus L., Atlantic halibut Hippoglossus hippoglossus L. and spotted wolffish Anarhichas minor (Olafse n). The system is almost a standard raceway, but with a very low water leve l (7 mm for fish at about 100 mg; 25 cm for fish above 2 kg). The system is a package with some crucial preconditions. These include high fish density (often 100-500 kg m(-3)), no countercurrent in the levelled raceways (no j et currents), adjustment of water intake with the most remote fish in mind and feeding with floating pellets, Self-cleaning is easily obtained in the system, The system has been tested for a wide size range of raceways (0.07- 80 m(2)) and fish sizes (2 mg to 10 kg), normally with growth and survival rates as good as with traditional rearing systems, There seems to be a 'lea rning window'; the earlier the fish are introduced to shallow raceways, the better they perform. The results indicate that a variety of fish species c an be produced in shallow raceways; these can be stacked in racks, which fa cilitate re-use of water from level to level. A very compact and cost-effec tive farming system will be the outcome.