Spatial and temporal segregation of Labeobarbus species migrating to Arno-Garno River
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Abstract
The spawning migration of Labeobarbus species of Lake Tana to Arno- Garno River was studied from July to December 2010. Five sampling sites, based on the nature, velocity of the flowing river, human interference and suitability for fish spawning were selected by preliminary survey. Fish were sampled monthly in the non-peak spawning season (July, November and December) and bimonthly in the peak spawning season (August to October) using 6, 8, 10, 12 and 14 cm stretched mesh size gillnets. A total of 1077 Labeobarbus specimens were collected. Labeobarbus intermedius, L. brevicephalus, L. nedgia and L. tsanensis were the dominant species,contributing 93.03% of the total catch. The monthly gonad-somatic index indicated that the spawning season for Labeobarbus species was from August to October. Labeobarbus intermedius and L. tsanensis were the first species to aggregate at the river mouth starting from July and L. brevicephalus and L. nedgia aggregate starting from September. However, L. intermedius was the first to migrate to the upstream sites starting from the end of July followed by L. tsanensis. The last migrant species was L. brevicephalus starting from the fourth week of August. Pair-wise comparison of the Labeobarbus spp. showed temporal segregation in all sampling months, except L. intermedius and L. brevicephalus that did not show temporal segregation with L. nedgia. The best management option to protect these species is closed season that should be strictly implemented during the spawning season (from June to October).
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