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Title: OBSERVATIONS ON THE AGGRESSIVE BEHAVIOUR OF Heterobranchus bidorsalis and Oreochromis niloticus IN CO-CULTURE.
Authors: OKONJI, V. A.
Keywords: Heterobranchus bidorsalis
O. niloticus
Aggressive behaviour
Issue Date: 2004
Publisher: Nigerian Journal of Applied Science
Series/Report no.: 22;
Abstract: Observation was made on the aggressive behaviour of the fingerlings of two fish species, Heterobranchus bidorsalis and Oreochromis niloticus commonly used in polyculture. Fairly even sized fish of 50 ± 0.4g H. bidorsalis and 30 ± 0.3g O. niloticus were used. The study was carried out using indoor aquarium tanks measuring 30cm x 45cm x 60cm. The observation was made in three treatments namely Heterobranchus bidorsalis alone, O. niloticus alone and combination of H. bidorsalis and O. niloticus. Each treatment was replicated thrice; and a total of nine(9) tanks were used in all. Observation was made and recorded by using a five point scale designated as 1- unbruised (non aggressive), 2-slighly bruised (slightly aggressive), 3 – moderately bruised (moderately aggressive), 4- highly bruised (highly aggressive), and 5 mortality (death). Observation on aggressive behaviour was made and noted during feeding. Survival rate was taken. The fishes were fed 3% of their body weight divided into two daily rations; with a feed containing 30% crude protein. The experiment was designed as a complete randomized. Data were analysed using table of analysis of variance. The results on observation showed that there was significant difference in the aggression ratings of the treatments (P<0.05). The rating showed that the treatment containing Heterobranchus bidorsalis only had the highest aggression rating of 4 (i.e highly bruised or aggressive) and lower survival rate (50%). This indicated that the intra-specific aggression was highest among H bidorsalis. This was followed by the combination of H bidorsalis and O. niloticus with a mean rating of 3 – (moderately aggressive). Bruised were observed mainly at the dorsal, ventral and caudal sides of H bidorsalis. It was noted that though highly cannibalistic, the length of H bidorsalis, makes it easily prone to attack by other fishes of the same species, particularly when it is feeding and loses it guard. The uniform size of O. niloticus combined with H bidorsalis, and the sharp guard and speed of O. niloticus makes for easy escape from the highly cannibalistic H bidorsalis. It was recommended that stocking of H bidorsalis and O. niloticus in polyculture will increase the survival rate and harvestable number of H bidorsalis..
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