Background: Seed stunting is a process of suppressing the normal growth of fish by manipulating various factors affecting the growth process. The present study aimed at evaluating the influence of varied photoperiod and stocking density on the growth and survival of catla (Catla catla) during the stunting process. Methods: Five treatments including control were used in triplicate and stocked with catla fry (0.84 g, 38.8 mm). Control, T-1 and T-2 groups were stocked with fry at 20 m-3 densities and maintained at 12 hours light and 12 hours darkness (12L:12D), 6L:18D and 0L:24D, respectively to study the influence of varied photoperiod. T-3 and T-4 were stocked with fry at 30 and 40 m-3 densities respectively to study the effect of crowding on the growth. Control at 20 m-3 density and 12L:12D photoperiod served as control for both the studies. Result: There was a significant reduction in the survival, harvested body weight, total length and specific growth rate in the treatments T-1 and T-2 as compared to the control (P less than 0.05). Though these attributes were statistically similar (P greater than 0.05) between T-1 and T-2, the values were relatively higher in T-1 suggesting considerable photoperiod effect on fish growth. Similarly, the HBW, total length and SGR significantly reduced from T-3 to T-4 with increased density depicting effect of crowding on growth. Such results indicated that both increased stocking density and decreased photoperiod lead to growth suppression and can be used as tools for seed stunting in catla.

Stunted juveniles of Catla catla (Hamilton, 1822) were produced through 150 days of stunting with five combinations of density and photoperiod. These stunted juveniles were subsequently polycultured in grow-out ponds for eight months along with rohu (Labeo rohita) and mrigal (Cirrhinus mrigala). In grow-out trial, the five treatments with different combinations of stocking density and photoperiod comprised, control (20 m-3, 12L/12D), T-1 (30 m-3, 12L/12D), T-2 (40 m-3, 12L/12D), T-3 (20 m-3, 6L/18D) and T-4 (20 m-3, 0L/24D). After eight months of culture, growth curves of stunted catla in all treatments were non-convergent and inferior to control, indicating no compensatory growth response. Although survival (70-73%), average body weight, (ABW; 667-755 g) and weight gain (648-729 g) in grow-out phase were statistically similar in the groups with different stocking density (Control, T-1 and T-2) (p>0.05), the grow-out survival was relatively higher in T-2 (73.3%), indicating its positive correlation with higher stunting density. In contrast, juveniles stunted with reduced photoperiod (T-3 and T-4) showed significantly lower ABW and weight gain (p<0.05). The poor survival in T-3 and T-4 (40-43%) indicated significant effect of stunting with reduced photoperiod on subsequent grow-out survival and yield performance. Based on the results, the study recommend the use of rearing density up to 40 m-3 for juvenile stunting in catla.