39. At a weight of about 5g, fry are transferred to small ponds, plastic tanks or concrete raceways which are typically 0.3-0.6m in depth. Having attained a weight of about 40g, the fish are transferred, often by fish pump, to ponds, concrete raceways or circular tanks (up to 10m in diameter and 1-1.3m in depth).
40. Facilities for growing trout vary greatly although the most popular systems are Danish style earth ponds, concrete and brickwork raceways and circular, self-cleaning tanks. Holding facilities should be of a design such that injury is not caused to the fish. Outdoor holding facilities are generally protected by a frame of netting to prevent predation (see paragraphs 222-229). The requirements of trout for environmental stimulation are not fully understood and the relationships between these requirements and the welfare of fish could usefully be investigated.
41. Fish pumps are used to move fish around the farm through a large bore pipe. In some ponds, and especially in warm weather, oxygen levels are enhanced by the operation of aeration equipment. In some raceways the use of parallel systems can reduce the likelihood that fish will be kept in water of too low a quality. Dead or moribund fish are usually removed using hand-held nets. On some farms we noted that older fish were being reared in the outflow channel of raceway systems. There is potential for the welfare of these fish to be poor if the water is not of adequate quality.
42. Trout are fed proprietary pellets of appropriate size by hand, by automatic food dispenser or by demand feeder operated by the fish. The practice of feeding by hand at some time each day is welcomed as it affords a good opportunity to assess the welfare of the fish. Automatic equipment must be checked frequently and properly maintained.