Abstract
Eight earthen ponds (4-5 feddan pond-1) were used for polyculture of Mugil capito and Mugil cephalus. Each pond was assigned a rearing density and a nursery age for both M. capito and M. cephalus. For each species of mullet a 2 x 2 factorial design was assembled with two age groups (A1, A2) and two stocking densities in an experiment extended for 214-days. Juvenile M. capito (A1; 16 months and 3.32 ± 0.37: 4.23±0.37g) and M. cephalus (A1; 8 months and 6.86±0.55: 8.22±0.55 g) were distributed into two earthen ponds (pond no 1 and 2) and stocked at two densities; M. capito (Low stocking density “LSD”, 1200 fish feddan-1 and Low stocking density “HSD” 2000 fish feddan-1) whereas M. cephalus were stocked at rates of 500 fish feddan-1 (LSD) and 1000 fish feddan-1 (HSD). The second age group fish (A2) of each species; M. capito (A2; 28 months and 7.28±0.37: 7.61±0.37 g) and M. cephalus (A2; 20 months and 12.8±0.55: 13.29±0.55 g) were also distributed in another two ponds (pond no 3 and 4) with the same density trend applied for the first age group fish where each treatment was duplicated. The obtained results notify the significant effect (P < 0.05) of both nursery age (stunting) culture density in the growth of both species with regard to the FBW, TBG and SGR %. The highest FBW, TBG and SGR (%) was attained by M. capito and M. cephalus having longer nursery age (stunting) and cultured at LSD. Whereas the NFY and TFY increased as the culture density did. Additionally and irrespective of culture density the RTFY impressively improved (P < 0.05) as the nursery age (stunting) increased. This study clarified that increasing space and food availability as compared to what is happening in the nursery ponds together with the nursery age (stunting) had synergistic effects in the subsequent culture period. Also, increasing the nursery duration (stunting) had relieved the density effect for both species when compared to their younger mates maintained at LSD. Hence it can be concluded that stunted mullet species in this experiment showed compensatory growth in both stunted groups. Also, the availability of good-quality fry or juveniles together with the nursery age (stunting period), stocking density, as well as the market size preferability, would be of concern in polyculture of M. capito and M. cephalus.

Key words: Nursery age (stunting), Stocking density, polyculture, M. capito, M. cephalus.