Can smolting and maturation of hatchery-reared brown trout Salmo trutta L.be affected by food deprivation during the first and second years of rearing?

Smelting and maturation of 2+ brown trout Salmo trutta L. were evaluated af ter exposing the groups of trout to different feeding regimes during the su mmers at 0+ and 1+ ages. The hypothesis tested was based on the theory of s melting of a congeneric species, Atlantic salmon Salmo salar L., in which t he physiological smelting decision is expected to be taken at the end of Ju ly or beginning of August. During the first summer, the growth of the trout was restricted in two groups out of four by low feeding frequency. During the second summer, food was totally withheld for 3 weeks in June-July (i.e. before the expected sensitive period), in August or not at all (control), The proportion of sexually mature males in November was 5.2% in the groups fasted during August, but somewhat lower in the groups fasted in June-July (average 2.3%) or in control fish (3%). The tendency for smelting was evalu ated during the following spring in an artificial stream with the help of P IT-tag technology, which allowed monitoring of the movements of individuall y tagged trout. Seawater challenge tests were also carried out in April and Tune. Differences in osmoregulatory ability in seawater indicated that fee ding treatments had a slight effect on the timing of smolting, but no diffe rences were observed in movement behaviour between treatment groups, Mature and maturing males moved less at the peak migration time (mid-May) but mor e in October than immature fishes, These results suggest that the smelting decision in brown trout may be taken at a different time than in Atlantic s almon and that periodic poor growth conditions during the summer will not p revent smelting of trout, during the following spring.