WINTER GROWTH OF SIX FISH SPECIES OF CARPS, TILAPIAS, AND MULLETS IN POLYCULTURE SYSTEM IN EGYPT

This study was conducted in the Central Laboratory for Aquaculture Research (CLAR) during winter months in 1990/1991 sea­son. Mean water temperature throughout the study was 13.6°C and 17.1°C when temperature was measured at 930 and 1430 hours, re­spectively. Weight changes for common carp Cyprinus carpio, silver carp Hypophthalmichthys molitrix, grass carp Ctenopharyngodon idella, blue ti­lapia Oreochromis aureus, Nile tilapia Oreochromis niloticus, and mullet Mugil cephalus were evaluated during winter months when commonly grown in earthen ponds under feeding and non-feeding systems. Weight gain for common carp was 63.0 and 64.8% under feeding and non-feeding conditions, respectively, while it was 8.0 and 11.1% for silver carp, 18.7 and 14.1% for grass carp, 15.3 and 25.5% for blue tilapia, 4.8 and 10.4% for Nile tilapia and finally 47.5 and 33.0% for mullet. Per­centages of population that gained weight were 100% in common carp, grass carp and mullet, while they were 98% for silver carp, 95.4% for blue tilapia and 87% for Nile tilapia. The data suggest the possibility of the extension of production season to include a part or all winter months in Egypt and in regions with similar climates whenever common carp and mullets are major fish species in the culture system, especially during moderate warm winters.