J. Duston et Rl. Saunders, ADVANCING SMOLTING TO AUTUMN IN AGE 0-TERM PERFORMANCE IN SEA-WATER( ATLANTIC SALMON BY PHOTOPERIOD, AND LONG), Aquaculture, 135(4), 1995, pp. 295-309
Smelting in autumn in age 0 + Salmo salar was improved by 2 months of
short photoperiod in an otherwise constant long photoperiod regime. Fo
ur groups of fry were reared under either constant-long photoperiod (L
D 17:7), or LD17:7 interrupted by LD7:17 for one (Imo-short; July 27-S
eptember 1) or 2 months (2mo-short; June 30-September 1), or simulated
natural day length (LDN). Bimodality in size-frequency developed in a
ll groups by August. Probability of an individual entering the upper-m
odal group (UMG) was related positively to fork length in late June. T
he LDN regime had the highest proportion of both lower-modal group fis
h (46% vs. 25-27%), and 0 + sexually mature males of the four groups (
26% vs. 10-12%). Smelt development in autumn was highest in the 2mo-sh
ort group, but was inferior to normal spring smelts, as judged by hypo
osmoregulatory ability and gill Na+ K+ ATPase activity. Following tran
sfer of UMG fish to a sea-cage in November, the 2mo-short group exhibi
ted best survival and growth over winter. From spring onwards all grou
ps grew well, reaching harvest size (3-4 kg) in August after 20 months
in sea water. Mortality in sea water was 24% and 28% in the 2mo- and
1mo-short groups, and 54% and 67% in the constant-long and LDN groups,
The study indicated the feasibility of stabilising the undesirable se
asonal fluctuation in commercial salmon production by producing 'off-s
eason' smolts 6 months out-of-phase from regular spring smelts.