OFF-SEASON SPAWNING OF YELLOW PERCH

The thermal and light conditions for 2-year-old broodstock of yellow p erch Perca flavescens were shifted by 6 months in an effort to change spawning from spring to autumn and fall. The natural photothermal cond itions consisted of a chill period of 10 degrees C and 10 h of light d uring January-March followed by increases in temperature to 20-22 degr ees C and photoperiod to 15 h light during July-September. The natural spawning of yellow perch occurs in April-May at 12-14 degrees C and 1 2 h light. In the present study, the broodstock were maintained at a h igher temperature and a longer period of light during September-Februa ry (18 degrees C and 13 h light). The photothermal conditions were dec reased gradually until June. The chill period (10 degrees C and 11 h l ight) was 60 d in duration (June-July) and was followed by gradually i ncreased water temperature and longer daylight (12 degrees C and 19 h) . Following this period, 50% of the females were fully ovulated, and t hey were stripped or spawned naturally. The males spermiated during th e entire shifted spawning period, August-September. The average relati ve weight of ovulated eggs las a percentage of the female weight) was 26.6 +/- 10.7%. Embryo survival through the eyed stage was 56 +/- 24%. Larval skeleton abnormalities (45 +/- 15%) and a low frequency of swi m bladder inflation (44 +/- 34%) were observed.