Diversity, Relative Abundance and Biology of Fishes in Beles and Gilgel Beles Rivers, Abay Basin, Ethiopia
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Date
2007-02
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Addis Ababa University
Abstract
Diversity, relative abundance and biology of fish species of Beles and Gilgel Beles
Rivers were studied during November 2005 to May 2006. Physical and chemical
parameters were also measured during this study. Fishes were sampled using gill
nets of various stretched mesh sizes, and hooks and lines. Identification of fish was
made to species level by comparing the sample characters with taxonomic keys
found in literatures and specimens deposited. An index of relative importance (IRI)
and Shannon diversity index (H`) were used to evaluate relative abundance and
species diversity of fishes, respectively. Mean temperature, river width and secchi
depth showed apparent longitudinal trends. A total of 1124 individual fishes
belonging to 5 orders, 7 families, 13 genera and 23 species were caught in Beles
and Gilgel Beles Rivers. Cyprinidae was best-represented family with the highest
number of fish species in the rivers while Labeo and Labeobarbus were the bestrepresented
genera. A higher number of species were recorded in the Beles River
(22 species) than in the Gilgel Beles River (5 species). L. nedgia, L. forskalii, L.
intermedius and O. niloticus were found in both rivers. The diversity index was
higher in the Beles River (H´=2.43) than in the Gilgel Beles River (H´ = 0.88).
Among sampling sites, diversity index was highest at Babizenda (H’ = 2.32) and
lowest at College (H’ = 0.76). Cyprinidae was the most dominant family in Beles
and Gilgel Beles Rivers. L. intermedius was the most abundant species according to
IRI (38.86%), while L. forskalii was second (24.68%) and L. bynni third (18.36%)
in total catch. L. intermedius was the most abundant species in the total catch
during the wet season, while L. forskalii in the dry season. L. intermedius had better
mean % IRI in Gilgel Beles River than in Beles River (P < 0.05). However, there
was no significant difference in % IRI between the two rivers for L. nedgia, L.
forskalii and O. niloticus (P > 0.05). L. forskalii showed isometric growth while L.
intermedius exhibited positive allometric growth in Beles and Gilgel Beles Rivers. L.
forskalii and L. intermedius were found to be in better condition in both rivers
(ANOVA < 0.05). Females were in better condition than males in both rivers. L.
forskalii had a better condition factor (FCF) in the dry than in the wet season (ANOVA < 0.05). However, L. intermedius had better mean FCF in wet than in dry
season (ANOVA > 0.05). Females were more numerous than males in the total
sexed specimens. Absolute fecundity of L. intermedius increased with an increase in
fish size, and ranged from 1535 to 13864 with a mean of 3173 eggs. In general,
Beles River is richer than Gilgel Beles River, in terms of total numbers of fish
caught and number of species recorded. In order to have a better knowledge of the
fish populations in the study area, further studies are required on diversity,
abundance and biology of the fishes.
Key words/phrases: Rivers, Beles, Gilgel Beles, relative Abundance, diversity,
Length-weight relationship, Fulton condition factor, Fecundity, Sex ratio.
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Keywords
Rivers, Beles, Gilgel Beles, relative Abundance, diversity, Length-weight relationship, Fulton condition factor, Fecundity, Sex ratio