SPAWNING MIGRATION OF LABEOBARBUS SPP. (PISCES: CYPRINIDAE) OF LAKE TANA TO ARNO-GARNO RIVER, LAKE TANA SUB-BASIN, ETHIOPIA

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, flow-rate of the 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 gonado-somatic index indicated that the peak 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. Labeobarbus 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. Pairwise 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 July to October)

Spawning migration of Labeobarbus species to some tributary rivers of Lake Tana, Ethiopia

Spawning migration of Labeobarbus species was studied from August to December 2013 in some tributary rivers (Qimon, Guanta, Shini, and Chibirna) of Lake Tana. Fish specimens and physico-chemical parameters were measured bimonthly in August and September but monthly from October to December. Adult fish specimens were caught using 6 and 8 cm stretched mesh size monofilament gillnets and 6, 8, 10 and 12 cm mesh size multifilament gillnets. A total of 933 adult Labeobarbus specimens were collected during the study period. Labeobarbus intermedius was the most abundant species followed by L. brevicephalus. The peak spawning season of L. intermedius was from fourth week of August to end of September and for L. brevicephalus it was from fourth week of August to beginning of October. Both species were found to spawn in all sampling rivers. However L. truttiformis spawned only at Guanta and Qimon Rivers during August while L. nedgia in Shini and Chibirna Rivers at the end of September. This implies the presence of micro-spatial segregation among species. Pair-wise comparison of Labeobarbus species showed temporal segregation in all sampling months, except L. brevicephalus and L. nedgia. The present findings showed that small tributary rivers and streams are the main spawning grounds for Labeobarbus species of Lake Tana. Therefore, main spawning grounds or routes should be protected from the deleterious effects of anthropogenic activities like illegal fishing, irrigation and sand mining for wise use of the fish resources.Keywords: Fecundity, Fish, Migration, River, Spawnin

Food and feeding habits of the large cyprinid fishes in the upper Blue Nile River, Ethiopia

Food and feeding habits of large cyprinid fishes (Labeobarbus intermedius, Labeobarbus nedgia, and Labeo forskalii) had been investigated in the upper Blue Nile River, Ethiopia. Four sampling sites were selected and specimens were sampled during the post-rainy (November 2016) and dry (March 2017) seasons by gillnets of 6 cm, 8 cm, 10 cm, 12 cm, and 14 cm mesh sizes. Totally 401 fishes were collected and about 30.4% (122) of the samples were documented with empty guts and 279 (69.6%) of them were with non-empty guts. The whole contents of all non-empty gut specimens were taken, labeled, and preserved using a 5% formaldehyde solution for further analysis. In the laboratory, gut contents were examined and identified using compound and stereo microscopes. The relative importance of different food items in the diet compositions was analyzed using a frequency of occurrence and volumetric analysis. During the post-rainy season, insects and phytoplankton were mostly ingested as food items. However, during the dry season, phytoplankton was the most important food item in the diet of all cyprinid fishes of the river. Based on current study results, L. intermedius and L. nedgia might be omnivores in their diet but Labeobarbus forskalii seemed to be detritivorous

In vivo and in vitro effects of Rhizopus extract (RU) on body growth and steroid production in masu salmon, Oncorhynchus masou Brevoort

This study investigated in vivo and in vitro effects of Rhizopus (filamentous fungus) extract (RU) in masu salmon Oncorhynchus masou Brevoort. Underyearling fish were fed with RU for 16 months. Monthly changes in body growth, gonadal maturation and serum levels of sex steroids were monitored. Gonads were also incubated at 0, 1, 10, 100 and 1000 μg RU mL^[-1] Leibovitz's L-15 medium for 18 h. Levels of steroids in serum and cultured medium were measured. It was determined that RU-fed immature and mature males, when compared to control groups, showed significantly higher body growth during spring, summer, and the spawning period. Similarly, immature RU-fed females showed significantly higher fork length and body weight in autumn, spring and summer. Furthermore, RU-fed males showed significantly higher levels of serum testosterone (T) and 11-ketotestosterone (11-KT) levels in pre-spawning season, and 17α,20β-dihydroxy-4-pregnen-3-one (DHP) in spawning season. In vitro RU incubation of gonads showed a dose-dependent and significant increase in T, 11-KT, estradiol-17β and DHP release in the medium. It appears that the causes of enhanced body growth and increased steroid production herein observed in salmonids are the physiologically active substances that may be contained in the mycelium of the fungus

Short CommunicationDiversity and relative abundance of fishes in the head of Blue Nile River, Ethiopia

Diversity and relative abundance of fishes in the head of the Blue Nile River (from the outlet of Blue Nile River in Lake Tana to Tisisat Fall) were studied from fish samples collected in wet (October 2009) and dry (March 2010) seasons. Fish sampling was done using multifilament gillnets (6, 8, 10, 12 and 14 cm stretched mesh) and monofilament gillnets (5-55 mm stretched mesh), and hook and lines. A total of 929 fish specimens, belonging to three families and seventeen species, were identified from the river. From Index of Relative Importance (IRI) analysis, the four most dominant fish species in the river were Labeobarbus intermedius (62.4%), L. crassibarbis (11.8%), Clarias gariepinus (10.1%) and Varicorhinus beso (4.04%). The cyprinid fish, L. intermedius, was the most dominant fish during the two sampling seasons. Length-weight relationships for the dominant species were found to be curvilinear. Generally, there was no species composition difference between Lake Tana and the head of Blue Nile River. Keywords/phrases: Abundance, Conservation, Diversity, Labeobarbus, Species compositionEthiop. J. Biol. Sci., 10(2): 207-212, 201

Some reproductive aspects of species of Labeobarbus (cyprinidae: teleostei) in Gilgel Abay river and its tributaries, Ethiopia

Six sampling sites of Gilgel Abay River and its tributaries, were sampled by using monofilaments (5-55 mm) and gillnets having mesh sizes of 6, 8, 10, 12 and 14 cm stretched bar mesh with a length of 25 m and depth of 1.5 m, twice each month from August to October, and once in November, 2011. Fishes were identified to the species level. Fork length (FL), total weight (TW) and gonad weight (GW) of each specimen were measured. The relationship between FL and TW for the dominant species of Labeobarbus showed curvilinear relationship. Condition factor of L. intermedius, L. brevicephalus and L. nedgia showed that there was significant difference (p<0.001) between sexes in all three species. In all catch, females were more numerous than males. The highest GSI (15.54%) was recorded for L. brevicephalus but the maximum mean monthly GSI (7.01%) was recorded for L. longissimus in September and minimum GSI (0.45%) for L. macrophtalmus in August. Absolute fecundity, mean fecundity and mean FL for L. intermedius was the highest than the rest. The relationship between absolute fecundity (AF) and FL, TW, and GW of L. intermedius, L. brevicephalus, and L. nedgia were linear (AF=596.4FL 8990, R2=0.79; AF=19.78TW+978.1, R2=0.79 and AF=371.5 GW+573.5, R2=0.93). There was also strong relationship between AF and FL, TW, and GW (p<0.001) in the three species.Key words/phrases: Abay basin, Condition factor, Conservation, Fecundity, Lake Tan

Food and feeding habits of Labeobarbus intermedius in the recently built Ribb Reservoir, Northwest Ethiopia

Food and feeding habits of Labeobarbus intermedius were studied from the newly constructed Ribb Reservoir, Ethiopia during the dry (December–March) season and wet season (June–August) of 2021. The objective of the study was to determine the diet composition, seasonal variation, and ontogenetic dietary shift in the diets of the dominant cyprinid fish in Ribb Reservoir. In this study, frequency of occurrence and volumetric analysis methods were used to present the results. From a total of 203 fish samples, 132 (65%) guts contained food items. Macrophytes (29.4%), phytoplankton (27.2%), detritus (14.8%), and insects (13.6%) were the major food items in the diets volumetrically. During the dry season, L. intermedius was mainly dependent on phytoplankton (58.2%), insects (15.2%), and zooplankton (13.7%) volumetrically. Whereas, macrophytes (50.3%) and detritus (23.3%) were the dominant food items in the wet season. The frequency occurrence and volumetric contribution of the diets of L. intermedius varied significantly (χ2 test, p < 0.05) between seasons. Schoener’s diet overlap index revealed a slight ontogenetic dietary shift in the diets of L. intermedius. While insects, nematodes, and zooplankton were the main diets of small-sized L. intermedius, macrophytes and detritus were ingested by large-sized L. intermedius. Generally, L. intermedius fed both plant and animal-origin food items and is considered an omnivorous feeder in Ribb Reservoir