Comparison on some biological aspects of Labeobarbus intermedius Rüppell 1835 and Labeo forskalii Rüppell 1836 in Beles and Gilgel Beles rivers, abay basin, Ethiopia

Although Ethiopia has high production potential and diversity of fi sh fauna, satisfactory fi shery investigations have been carried out only in a few of the numerous freshwater bodies. Substantial icthyofaunal information appeared in publication on Biology, Limnology and Ecology of the commercially important fi sh species in lakes and rivers: Lake Afdera [1], Lake Ziway , Lake Awassa [2], Lake Chamo Lake Hayq [3], Lake Tana [4,5], eco-regions, diversity and conservation of the freshwater fi sh fauna of Ethiopia [6] and introduction and transplantation of freshwater fi sh species in Ethiopia [7]. In addition, projects of the Joint Ethio-Russian Biological Expedition (JERBE) and the Wageningen Agricultural University, The Netherlands have explored the icthyofauna of Lake Tana and surrounding rivers [8]. JERBE [9,10] also assessed fi sh diversity in Beles and Gilgel Beles Rivers and found a total of 25 and 4 species of fi shes, repectively. Beles and its tributary Gilgel Beles rivers contain large population of edible fi sh species. L. intermedius and L. forskalii were the most abundant species on these rivers.


Background information
Although Ethiopia has high production potential and diversity of fi sh fauna, satisfactory fi shery investigations have been carried out only in a few of the numerous freshwater bodies.

Substantial icthyofaunal information appeared in publication on
Biology, Limnology and Ecology of the commercially important fi sh species in lakes and rivers: Lake Afdera [1], Lake Ziway , Lake Awassa [2], Lake Chamo Lake Hayq [3], Lake Tana [4,5], eco-regions, diversity and conservation of the freshwater fi sh fauna of Ethiopia [6] and introduction and transplantation of freshwater fi sh species in Ethiopia [7]. In addition, projects of the Joint Ethio-Russian Biological Expedition (JERBE) and the Wageningen Agricultural University, The Netherlands have explored the icthyofauna of Lake Tana and surrounding rivers [8]. JERBE [9,10]  of the major activities that degrade fi sh habitat. At present, we have no evidence of species extinction from Ethiopian freshwaters resulting from degradation of environment. One of the main reasons is a lack of defi nitive information on icthyofauna. The territory of Ethiopia seems to be among regions of the African continent which are least explored for their icthyofauna [11]. Beles and Gilgel Beles Rivers are fl owing to the lower course of Abay in which adequate attention has not been given in the study of biology and economical potential of the fi sh fauna due to the presence of some inaccessible mountains and rugged geographical features. The absence of fi shery data on these rivers triggers the researcher to conduct this study. Therefore, the study attempted to provide answers to the following leading research question: What does the biology (Reproduction, Condition Factor and Length-weight relationship) of L. intermedius and L. forskalii look like in of these rivers?
The general objective of this study was to generate base line scientifi c information/ data about fi sh biology of L. intermedius and L. forskalii for management and sustainable utilization of the resources, and recommend ways and means of conserving the diversity of the icthyofauna of the Beles and Gilgel Beles Rivers. Thus, the specifi c objectives of the study were to assess length -weight relationship of L. intermedius and L. forskalii, to compare the well -being of L. intermedius and L. forskalii with respect to sex and season and asses sex ratio and estimate fecundity of L. intermedius and L. forskalii.

Materials and methods
Site selection: A reconnaissance survey was conducted together with the research advisor to fi x sampling sites. The survey was conducted in four sub areas along the Beles and Gilgel Beles Rivers. Two sampling sites were selected from each river taking into consideration the velocity of water, habitat type, altitude, depth of water, vicinity to road and substrate type (Table 1). These sub areas are namely; sub area I (Gilgel Beles at Mender hullet), sub area II (Gilgel Beles at College), sub area III (Beles at bridge) and sub area IV (Beles at Babizenda) ( Figure 1). Babizenda sampling site is located below the confl uence of the rivers.in Guba woreda.
Fieldwork: Three surveys were conducted to collect specimens from the sampling sites. The samples were taken in November, March and May. November and May were wet months while March was dry month. Gill nets with 6 cm, 8 cm, 10 cm, 12 cm and 14 cm mesh sizes were used to collect fi shes. Monofi lament gill nets were also used to collect juvenile and smaller sized fi shes. Multiple hooks and lines were used in areas where gill nets were not suitable. The gill nets and multiple hooks and lines were set using swimmers across the river diagonally late in the afternoon (5:00 PM) and left in the rivers for about 15 hrs, and retrieved in the next morning (8:00 AM). However, monofi lament gill nets were set for an hour during daytime.
Immediately after retrieval, fi shes were removed and total length and total weight of each specimen were measured. Total length was measured to the nearest 0.1 cm and total weight was measured to the nearest 0.1 g. After length and weight measurement, each specimen was dissected and its sex determined by inspecting the gonads. Then, specimens and gonads of dominant species were preserved in 10 % and 5 % formalin, respectively.
During fi eldwork, beam balance, measuring board, buckets, plastic bowls, collection bottles, strings, camera, syringe, GPS and other materials were used when required.
Laboratory studies: The specimens were soaked in tap water for a week to wash the formalin from the specimens. Then, they were transferred to 75 % ethanol.
Data analysis: Generally, SPSS for Windows (version 10) and MINITAB (version 14) were used to perform the calculations and statistical analysis.

Length-weight relationship
The relationship between total length and total weight was calculated using least squares regression analysis [12] as follows: Where, TW = Total weight in grams TL = Total length in centimeters  Signifi cance of the relationship was statistically tested using ANOVA.

Condition factor
The well-being or plumpness was studied by calculating Fulton condition factor [12,13]. Fulton condition factor (%) was calculated as: Where, FCF= Fulton condition factor, TW= Total weight in grams, and TL= Total length in cms.

Estimation of sex ratio
Sex ratio (female: male) was calculated for total sample. Chi-square test was employed to test if sex ratio varied from 1:1 in the total sample.

Fecundity
Fecundity is the measure of reproductive potential in fi shes. Absolute fecundity was estimated by the Gravimetric method [14]. Three sub-samples of 1g eggs were taken from different part of the ovary and counted, and an average of these was calculated. Then, the total number of eggs per ovary was calculated by extrapolation from the mean calculated. The total number of eggs was estimated by the following formula: Relation between fecundity and total length, total weight and gonad weight were analysed using regression analysis.

Length frequency distribution of L. intermedius and L. forskalii
A total of 548 Labeobarbus Intermedius and Labeo forskalii fi shs were caught in Beles and Gilgel Beles Rivers.L intermedius, the most abundant species had a total length range of 10.6 cm to 69.5 cm with a mean ± SD of 26.419 ± 7.563 cm. L. forskalii, the second most abundant species had total length range of 10.2 cm to 44.7 cm with a mean ± SD of 26.951 ± 7.477 cm length ( Figure 2).

Some biological aspects of L. intermedius and L. forskalii
Length-weight relationship: The relationship between total weight and total length, for L. intermedius and L. forskalii, was curvilinear and statistically signifi cant (ANOVA, P < 0.05) ( Table 2). The line fi tted to the data was best described by the regression equations shown in Table 2, and Figs. 2 and 3. In fi shes, the regression coeffi cient b = 3 describes isometric growth. The value is exactly 3 if the fi shes retain the same shape and their specifi c gravity remains unchanged during lifetime [15]. However, some fi shes have value greater or less than 3, a condition described as allometric growth [12]. From Table 3, Figures 3,4, it can be seen that L. forskalii in Beles and Gilgel Beles Rivers show isometric growth, i.e. the weight of these fi shes increases as the cube of length because the b value is nearly 3. The b-value obtained in this study for L. forskalii in Beles and Gilgel Beles Rivers are close to the value reported for L. forskalii in Sanja River [16] and L. horie from Lake Chamo [17]. From Table 3, Figures 3,4, it can be seen that L. intermedius in Beles and Gilgel Beles Rivers show allometric growth. The result obtained in this study for L. intermedius in Beles and Gilgel Beles Rivers were not in agreement with Demeke Admassu and Elias Dadebo [2] for the species in Lake Awassa, Wassie Anteneh [18] and Nagelkerke, et al. [8] for Lake Tana and Genanew Tesfaye [16] for Angereb River and Sanja Rivers. Observed differences in parameters b calculated in the present study when compared with those obtained by other authors are likely due to differences in the number of specimens examined, differences in the utilized length ranges   or differing study seasons, food availability, feeding rate, gonad development and spawning period [12].

Fulton Condition Factor (FCF): L. forskalii and L. intermedius
were found in better condition in Gilgel Beles and Beles Rivers, respectively. Fulton condition factor values of L. intermedius ranged from 0.93 to 1.23 in Beles River and 0.43 to 1.73 in Gilgel Beles River. Fulton condition factor values of of L. forskalii ranged from 0.79 to 1.26 in Gilgel Beles River and 0.49 to 1.29 in Beles River. There were signifi cant differences in the mean Fulton condition factor for both L. forskalii and L. intermedius between Beles and Gilgel Beles Rivers (ANOVA, P < 0.05) ( Table  3). Females were found in better condition than males in both Beles and Gilgel Beles Rivers ( Table 5). The difference in mean Fulton condition factor for L. forskalii and L. intermedius was insignifi cant both in Beles and Gilgel Beles Rivers except L. intermedius in Beles River (ANOVA, P > 0.05) ( Table 4). Fulton condition factor calculated for L. intermedius in Beles and Gilgel Beles Rivers were comparable to those reported of L. intermedius in Lake Awassa [2] and in Sanja River [16]. Fulton fondition factor calculated for L. forskalii in Beles and Gilgel Beles Rivers were close to the value reported for L. forskalii in Angereb and Sanja Rivers [16].
Mean Fulton condition factor of L. forskalii was greater in dry season than wet season (ANOVA, P < 0.05) ( Table 5). However, mean Fulton condition factor of L. intermedius was greater in wet season than dry season (ANOVA, P > 0.05) ( Table 5). Demeke Admassu and Elias Dadebo [2] also found insignifi cant variation (ANOVA, P > 0.05) in Fulton condition factor for L. intermedius between dry and wet seasons in Lake Awassa. However, Genanew Tesfaye [16] reported signifi cant variation (ANOVA, P < 0.05) for L. intermedius and L. forskalii between dry and wet seasons in Sanja and Angereb Rivers.
The measure of fi sh condition can be linked to the general fi sh health, fat and lipid content, prey or food availability, reproductive potential, environmental conditions and water level fl uctuations. In general, high condition is associated with higher energy (fat) content; increased food base, reproductive potential, or more favorable environmental conditions [19]. For instance, better FCF of L. forskalii and L. intermedius in dry and wet seasons respectively was associated with large ovarian development. The low FCF of fi shes of the rivers is probably because of fl uctuations in factors such as food quantity and quality, water level, fl ow rate and temperature.

Reproductive biology
Sex ratio: In general, females were more numerous than males in the total sexed specimens ( Table 6). The sex proportions of each species were not signifi cantly different (Chi-square, P > 0.05) from the theoretical 1:1 ratio except L. intermedius ( Table 6). The imbalance was most probably related to vulnerability of fi sh to gears. Increased vulnerability of females by some gears due to increased ovarian development, as suggested by Tayler and Villoso (1994), can be the cause for the deviation from 1: 1 sex ratio.  Table  7). Fecundity of L. intermedius increased with an increase in fi sh size ( Table 7). Fecundity of L. intermedius was linearly related to total weight and gonad weight, and curvilinearly to   Where Gw, W, FL and AF are gonad weight, body weight, fork length and fecundity, respectively.
The information about fecundity of large Barbus fi sh species in Africa is scarce [20]. There are few data on the fecundity of Ethiopian large Barbus. The most recent studies and publications were done these of Alekseyev, et al. [21] and Wassie Anteneh [18] from Lake Tana and its tributaries. Compared to Lake Tana Labeobarbus spp., a similar size of female L. intermedius in Beles and Gilgel Beles Rivers laid more eggs. The fecundity of L. brevicephalus and L. truttiformis ranged from 1284 to 4563 and 1732 to 8134 eggs, respectively in Lake Tana [18]. The average fecundity of the small (precocious) and big (normal), 'intermedius' was 4.6 thousand and 11.7 thousand eggs, respectively in tributaries of Lake Tana (Gelda and Gumara Rivers) [21]. Fecundity of Labeobarbus in other African lakes is moderately high [22]. A 30 cm female L. aeneus in Orange River drainage system carries about 30,000 eggs on average but a similar size female L. intermedius in Beles and Gilgel Beles Rivers lays about 4690 eggs. According to Oliva-Paterna, et al. [23,24], fast growth, early maturity and high fecundity are characterstics of unstable environment. Therefore, the main cause for the above variations might be due to genetic or habitat differences. Generally, the fecundity of L. intermedius in Beles and Gilgel Beles Rivers was strongly correlated with their gonad weight, body weight and length. Similar result was obtained by Alekseyev, et al. [20], in tributaries of Lake Tana.

Conclusions
The length-weight relationships were curvilinear for L.
forskalii and L. intermedius in both Beles and Gilgel Beles Rivers.       found in better condition in Gilgel Beles River than Beles River (ANOVA, P < 0.05). However, Mean Fulton condition factor for L. intermedius was greater in Beles River than Gilgel Beles River (ANOVA, P < 0.05). Females L. intermedius and L. forskalii were found in better condition than males both in Beles and Gilgel Beles Rivers. Mean Fulton condition factor of L. forskalii was greater in dry season than wet season. However, Mean FCF of L. intermedius was greater in wet than dry season. There was signifi cant difference in the mean FCF for L. forskalii between dry and wet seasons in total catch (ANOVA, P < 0.05). However, there was no signifi cant variation in FCF of L. intermedius seasons (ANOVA, P > 0.05).
Fecundity of L. intermedius was linearly related to total weight and gonad weight, and curvilinearly to fork length in the two rivers.

Recommendation
In order to have a better knowledge of biology and behaviour of most of the species are still lacking. Therefore, further studies are required on the biology and behaviour of fi shes in the study area. In addition, detailed studies and investigations are required on diversity and abundance of fi sh species in Abay basin in general and in Beles and Gilgel Beles Rivers in particular, especially at the lower reaches of Beles River.