Some Biological Observations on Rearing of Oreochromis niloticus in cage culture system at Gezera Irrigation Canals and the White Nile, Sudan.

Abstract

This study was carried out at two sites, namely Mabroka farm ponds in the Gezera irrigation canals (G.I.C), and Gebel Awlia reservoir of the White Nile (W.N). The study was conducted during the period January 2012 to March 2012, for rearing Nile tilapia fingerlings (Oreochromis niloticus) of average size 20.6 grams. Fixed and floated cages were designed and used for determining the fish growth rates and production functions under (mixed sexes) system. The fingerlings were stocked at a density of 50 fingerlings /m’ and were fed with commercial diet containing 33% crude protein at a rate of 3% of their body weight per day for 120 days. The results indicate that there are significant effects (p<0.05) on the survival, growth, and food conversion ratio of these fingerlings between the White Nile waters and Gezera irrigation canal waters. Fish growth increased, was high at W.N and it is significantly different fiom that obtained at G.I.C (p <0.05) of values 45.4 and 40.2 grams respectively. Also there was significant effects (p<0.05) on food conversion rate (F CR) of values 2.7 and 3.7 in the same order as well as the difference in average body weight gained (23.6 and 20.8 g). Also the calculated feed cost for one kg body weight gain is of values 4.1 and 5.6 SDG. The economic efficiency is 562% and 526% for the two sites respectively. While the survival rate of fish in White Nile was 90% and in the Irrigation canal was 99.7%. The statistical analysis of water parameters indicates that no significant differences (p>0.05) in water temperature, transparency, and pH values, but a significant difference (p<0.05) was observed in current speed between the two sites. In conclusion, the rearing of O. niloticus fingerlings as mixed sexes at White Nile has faster growth rate, higher production, and better feed efficiency than those grown in ponds with water coming from Gezera irrigation canal.