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¹ University of Lucknow, Department of Zoology, Fish Biogenetics Research Lab, Lucknow-226007 (U.P.), INDIA DOI : 10.4194/1303-2712-v18_1_10 Viewed : 4042 - Downloaded : 2942 The influence of different photoperiods was studied on the growth and behaviour of the giant gourami, Trichogaster fasciata. Fish (weight=1.1g; length=4.36cm) were subjected to photoperiod regimes of 0 L: 24 D, 8 L: 16 D, 12 L: 12 D and 16 L: 8 D for 90 days in triplicates. The growth rate was highest (weight=4g) and lowest (weight=2.36g) in the groups subjected to 16L: 8D and 0 L: 24 D photoperiods respectively. The mean body weight and mean total length were significantly higher (p < 0.05) while standard length and caudal fin length (p > 0.05) were not significant in the 16 hours light. Mean values of food conversion ratio and condition factor were lowest while various growth parameters were found to be maximum in the 16 hours light. 16 L: 8 D photoperiod regime produced pronounced effects on the welfare of giant gourami as shown by the nonintrusive welfare indicators. The photoperiodic signals were found to be capable of modifying the behavioural activities where male aggression related to territory or defence and female selection were reduced in control group. The optimum photoperiod (16 L: 8 D) was an environmental cue for the better growth, welfare and behaviour. Keywords : Aggression, Female selection, Growth, Photoperiod, Welfare indicators