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Influence of Photoperiod on Growth of Juvenile Atlantic Salmon and Development of Salinity Tolerance during Winter–Spring
Author(s) -
Saunders Richard L.,
Harmon Paul R.
Publication year - 1990
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1990)119<0689:iopogo>2.3.co;2
Subject(s) - photoperiodism , salinity , zoology , salmo , biology , juvenile , photostimulation , darkness , fish <actinopterygii> , fishery , ecology , horticulture , botany , neuroscience
Underyearling Atlantic salmon Salmo salar were subjected to extended day length beginning in early August or early September; the photoperiod was 18 h light and 6 h darkness (LD 18:6) during August‐October (A–O), September‐October (S–O), and September–November (S–N). A control group experienced simulated natural photoperiod. The LD 18:6 regimes stimulated growth and, by fate October, treatment fish were significantly larger than the controls. The 3‐month S–N and A–O regimes promoted growth more effectively than the 2‐month S–O regime, Stimulation of growth from August through October was not as effective as that from September through November. Thus, duration (2 versus 3 months) and time of onset of extended day length and return to simulated natural photoperiod appeared to influence photostimulation of growth. Bimodality in length‐frequency distribution in the S–O and control groups was clearly developed by mid‐December. Photostimulation of growth and continued entry offish into the upper modal groups in the A–O and S–N treatments may have prevented development of bimodality by that time, The fish from the upper modal groups under all photoperiod regimes developed high levels of salinity tolerance (to 35‰) during December. This tolerance disappeared during January–March and appeared again, first in the controls and then in the A–O, S–O and S‐N groups, in that order, during April–May. Gill Na + K + ATPase activity was not elevated in any group during December when high salinity tolerance was observed. This finding is at variance with several previous studies that have shown positive correlations, and suggested causal relationships, between gill Na + K + ATPase activity and salinity tolerance, The rise in gill ATPase activity, corresponding with completion of smolt development in the spring, appeared first in the controls and later in the treatment groups; the S–N fish did not show increased ATPase activity by early May.