Juvenile green abalone, Haliotis fulgens (31.3 ± 0.1 mm, 3.7 ± 0.04 g live weight) were reared in laboratory for six months in order to determine their survival, growth, tissue composition, feed consumption ( C), feed conversion ratio (FCR) and protein efficiency ratio (PER) under two temperatures (20 °C and 25 °C) and three photoperiods (00:24, 12:12 and 24:00 light:dark hours). Survival was ca. 100% at 20 °C, and between 68% and 75% at 25 °C. The highest gross growth rate (109 ± 4.3 μm d − 1 , 69 ± 3.9 mg d − 1 ) was observed in abalone from the combination 20 °C–00:24 L:D. Slowest GGR (38 ± 4.1 μm d − 1 , 26 ± 1.5 mg d − 1 ) was observed in the combination 25 °C–24:00 L:D. Organisms from 25 °C exhibited signs of the withering syndrome at the end of the experiment. Gross energy content (4.4 to 4.6 kcal g − 1 tissue dry wt, TDW) and crude protein (60 to 68% TDW) were not significantly affected by either temperature or photoperiod, but organisms from 20 °C exhibited lower moisture content (86.8 to 88.6%) and higher tissue:shell ratio (0.34–0.40) than those from 25 °C (88.9 to 92.1%; 0.22–0.31 respectively). Feed consumption markedly increased at night, decreased with age, and was higher at 25 °C than 20 °C, irrespective of photoperiod. Highest C was observed under continuous darkness (0.66 to 0.95% BW d − 1 at 20 °C and 0.84 to 1.25% BW d − 1 at 25 °C), and was lowest under continuous light (0.50 to 0.82% BW d − 1 at 20 °C and 0.71 to 1.02% BW d − 1 at 25 °C). FCR and PER were both affected by temperature but not by photoperiod. Higher PER (2.2 to 3.4) and lower FCR values (0.69 to 1.05) were observed at 20 °C, when compared to 25 °C (PER 1.35 to 2.09, FCR 1.10 to 1.86). Sex ratios were ca. 1:1 in the 00:24 and 12:12 L:D photoperiods, yet ca. 50% of abalone from the 24:00 L:D photoperiod were immature at the end of the experiment. It is concluded that H. fulgens can be best cultured at 20 °C and 00:24 or 12:12 L:D regimes, while sustained temperatures at or above 25 °C may result in cumulative stress, altered physiological rhythms, and delayed maturation.