Growth, maturation and survival of out-of-season 0+ and 1+ Atlantic salmon (Salmo salar) smolts

Out-of-season 0 + and 1 + smelts were reared at a Scottish hatchery using two photoperiod regimes. Potential S2 parr (group 1 +) were reared under a 7-month compressed photoperiod regime beginning on the 22nd of February. Potential S1 parr (group 0 +) reared in heated water under LL were exposed to a photoperiod of LD 8:16 from the 9th of August to the 4th of October when the photoperiod was increased to LD 18.6. Changes in condition factor and hypo-osmoregulatory ability were used to assess the completion of smoltification in the two groups. 27 000 1 + smelts (group 1 +) were transferred to sea water on the 15th of November (mean weight 109 +/- 3.1 g) and 54000 0 + smelts (group 0 +) were transferred on the 21st of December (mean weight 59.8 +/- 1.4 g). The group 1 + fish were harvested after 12 months in sea water at harvest weights ranging from 2.5-2.7 kg. The group 0 + fish were harvested over a 5-month period, which began 15 months after seawater transfer, harvest weights ranged from 2.3 to 4.2 kg. The growth rates over the entire cycle were similar (range 0.9-0.99% day(-1)) in the two out-of-season groups and a group of natural smelts transferred during April. However, the pattern of growth during the production cycle differed between out-of-season and natural smelts. Cumulative mortality did not exceed 8% and maturation did not exceed 6.5% for the out-of-season smelts during the seawater period. It is concluded that the overall performance of out-of-season smelts parallels that of natural smelts and that their production provides a commercially important strategy for spreading the availability of market-sized (3-4 kg) salmon. (C) 1998 Elsevier Science B.V. All rights reserved.