International Journal of Aquaculture, 2017, Vol.7, No.20, 126-133
127
head of Blue Nile River (de Graaf, 2003; Oumer et al., 2011). The fish fauna of Debbis River is a mixture of Nilo
Sudanic (
Labeo forskalii
), East African highland (
Labeobarbus intermedius
,
Garra chebera
and
G.quadrimaculata
) and an endemic (
Varichorhinus beso
) species. A total of 2389 fishes weighing 23.8 kg were
caught. The total number of fishes collected was 941,764 and 684 respectively from the stations Deb
1
, Deb
2
and
Deb
3
(Table 1). The total length of the fishes ranged from 5 to 33 cm for
Varichorhinus beso
, 4.4 to 13.6 cm for
Garra chebera
, 3.9 to 12.1 cm for
G.quadrimaculata
, 23 to 37 cm for
Labeo forskalii
and 21.4 to 32.8 cm for
Labeobarbus intermedius
. The total weight ranged from 1.7 to 306 gm for
V. beso
, 1.3 to 28.8 for
G. chebera
, 1 to
20.3 for
G. quadrimaculata
, 167.4 to 415 for
Labeo forskalii
and 109 to 415 grams for
Labeobarbus intermedius
.
Table 1 Number and species composition of fishes
Species
Deb
1
Deb
2
Deb
3
Total
Varichorhinus beso
199
182
148
529
Garra chebera
315
304
204
824
G.quadrimaculata
427
278
186
891
Labeobarbus intermedius
-
-
83
83
Labeo forskalii
-
-
62
62
Total
941
764
684
2389
Garra quadrimaculata
was the most dominant fish species (37.14%), followed by
G.chebera
(34.37%) and
V.
beso
(22.05%) while
Labeobarbus intermedius
and
Labeo forskalii
were least the abundant, 3.46% and 2.58%
respectively.
All the five species were collected from Deb
3
, however
V. beso
,
G. quadrrimaculata
and
G. chebera
are common
to all sites. The two species,
L. forskalii
and
L. intermedius
were collected only from Deb
3
(Table 1). The number
of specimens caught was higher for Deb
1
with (941) and lower at Deb
3
(684). The Shannon diversity index was
higher (H’=1.52) at Deb
3
and lower (H’=1.053) at Deb
1
(Table 2).
Table 2 Shannon diversity index (H’) at the sampling sites
Index
Sampling sites
Deb
1
Deb
2
Deb
3
H’
1.053
1.076
1.52
N
3
3
5
From the head of Blue Nile River Oumer et al. (2011) reported the occurrence of 17 species while Tedlo Awoke
(2015) observed 8 species from Lake Tana. It was generally accepted that the low species diversity of fishes may
be related to the flow variability which has an effect on fish assemblage and productivity of rivers as high flows
could destroy fish habitat and wash away the already laid fish eggs. The presence of few fish species and
dominance of few families in this study seemed that cyprinid fishes being riverine in origin are specifically
segregated or adapted in the Blue Nile and its tributaries. Biodiversity patterns are directly and indirectly
influenced by the geomorphology of riverine landscapes, which may be perceived as a nested hierarchy (Ward,
1998). The numbers of fish species in Debbis River appears to be negatively correlated with altitude. The increase
in number of fish species from Deb
1
to Deb
3
sampling sites coincide with decline in elevation. The elevation with
each site Deb
1
, Deb
2
and Deb
3
were (1919, 1902 and 1886) m.a.s.l respectively. The main pattern documented in
this study was the occurrence of a distinct headwater fauna, and a sequential downstream shift in species
composition. The decrease in number of fish species from lower to upper reaches were consistent with the studies
carried out in other areas by Nikolsky (1963) and Golubtsov and Mina (2003). The increase in species number
from upstream sites to downstream sites was associated with change in catchment area, canopy closure, substrate
type, and distance from source, depth and width of rivers (Toham and Teugels, 1998). The deep habitats at the
downstream site probably favor fish species richness because they potentially allow the coexistence of numerous
fish species, as suggested by Sheldon (1968). These variables reflect longitudinal gradient in the study area. Width
of river was the most important variable that coincided with increase in species number from Deb
1
to Deb
3
sites.
A total of five (5) fish species found in Deb
3
with its mean river width of 57.5 ±3.74 m while the lowest number
