Feed intake and growth of fast and slow growing strains of rainbow trout (Oncorhynchus mykiss) fed by automatic feeders or by self-feeders

Rainbow trout (8.5-9.5 g) of two strains (C and M) differing in growth pote ntial were compared with respect to feeding motivation and feeding rhythms, over a 65-day experimental period, employing self-feeding or automatic fee ding. Growth rate, feed gain ratio, feed intake and pattern of feeding acti vity of fish fed with self-feeders, were recorded, as was body composition of both strains. The final weight of fish of the fast-growing strain, strai n C, fed using self-feeders, was significantly higher (82.6 g) than that ob served for fish of the slow-growing strain, strain M (69.3 g). When the aut omatic feeders were used, no significant differences were found between the strains in terms of body weight gain (65 g). Results observed for feed gai n ratio were also similar between the two strains. Although the voluntary f eed intake (VFI) did not vary significantly with the genetic origin of the fish, strain C displayed a consistently higher VFI compared to strain M. Th e retention efficiency of nutrients and energy were similar between strains but significantly different between feeding systems. With regard to body c omposition, when fish were fed by means of self-feeders, no significant dif ferences were found between the two rainbow trout strains. However, when fe d automatically, dry matter and lipid content were highest in the strain M fish. The energy and protein content of the whole fish were not significant ly influenced either by the feeding system or by the strain of the fish use d. (C) 2001 Elsevier Science B.V. All rights reserved.