Turkish Journal of Fisheries and Aquatic Sciences
2005, Vol 5, Num, 2 (Pages: 69-74)
Predation Efficiency of Nile Catfish, Clarias gariepinus (Burchell, 1822) on Fry Nile Tilapia, Oreochromis niloticus (Linnaeus, 1758): Effect of Prey Density, Predator Size, Feed Supplementation and Submerged Vegetation
Mohsen Abdel-Tawwab 1
1 Fish Ecology Department, Central Laboratory for Aquaculture Research, Abbassa, Abo-Hammad, Sharqia, Egypt
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The overpopulation of tilapia in confined ponds is an obvious problem, and causes stunted growth due to the shortage
of natural food, particularly in semi-intensive culture. However, the control of tilapias population by predator culture has
been practiced worldwide. The factors affecting predation efficiency of Nile catfish, Clarias gariepinus (B.) for controlling
the overpopulation of Nile tilapia, Oreochromis niloticus (L.) were studied in four indoor experiments. Nile catfish with
different sizes was stocked with tilapia fry (2-3 g) at the ratios of 1:10 or 1:15 (catfish : tilapia) without feeding. In another
trial, Nile catfish : tilapia (1:15 ratio) with different sizes was frequently fed to satiation with fish diet (25% crude protein).
The number of eaten fry was counted after 6, 24, 48 and 72 hours. The predation rate of Nile catfish at different predator
sizes increased at the ratio of 1:15 more than 1:10 (catfish : tilapia) ratio. Predation rate of large Nile catfish was greater than
small ones. Artificial feeding reduced the predation rate of Nile catfish at different predator sizes, while it increased with
increasing predator size and tilapia stocking. In the fourth experiment, the leafless stems of phragmites plants (0.7 m long and
0.5 cm diameter) were used in this study at densities of 0, 5, 10, 20, 30 and 50 stems/m2. The aquarium was stocked with 15
fry (2.2 g) and 1 catfish (400 g). The number of eaten fry was counted closely for 6, 24, 48 and 72 hours. The fry used the
submerged macrophytes as a refuge to protect themselves from predator attack. It was concluded that predation rate of Nile
catfish is dependent on predator size, prey stocking density, supplemental feeding and period of stocking. Moreover, the
presence of submerged vegetation at moderate density (20-30 stem/m2) may reduce the number of eaten fry.
Keywords :
Nile catfish, Clarias gariepinus, predator, Nile tilapia, Oreochromis niloticus, prey, stocking ratio, artificial feeding, macrophytes