Population dynamics of the Nile tilapia (Oreochromis niloticus L. 1758) stock in Lake Langeno, Ethiopia

Nile tilapia, Oreochromis niloticus, is a widely distributed and economically most import fish species in Ethiopia. Effective management is essential to sustain their fisheries and the benefits for the local communities. However, little is known about the population dynamics of the Nile tilapia stock in Lake Langeno. Vital parameters of its population were determined using length frequency data collected from 5,949 specimens ranging from 8.5 to 35.7 cm total length (tl). These specimens were collected from August 2017to July 2018. The population parameters were determined using the elefan I routine in FiSAT software. Estimated von Bertalanffy growth parameters were asymptotic length (L∞) = 35.70 cm, growth curvature (K) = 0.32 yr-1, age at length zero (to) = -0.49, and growth performance index (Փ') = 2.61. Instantaneous total mortality (Z), natural mortality (M), and fishing mortality (F) rates were determined from length-converted catch curve and empirical models, respectively, and their values obtained were Z = 2.31 yr-1, M = 0.82 and F =1.56 yr-1, respectively. The exploitation rate (E) of Nile tilapia computed from its mortality rates was 0.67 yr-1, suggesting state of overfishing. The size at first capture (Lc) was estimated at 14.0 cm which is much lower than the size at first maturity (Lm=16.62 cm), which further substantiated the state of overfishing. The results of the study are very useful for fishery managers and scientists who wish to manage and further explore the Nile tilapia stock in Lake Langeno

Reproductive biology and condition factor of the African catfish, Clarias gariepinus (Burchell 1822) in Lake Koka, Ethiopia

The study was conducted to investigate the breeding season, sex ratio, size at maturation, fecundity and condition factor of African catfish Clarias gariepinus in Lake Koka. A total of 754 fish specimens were collected from October 2020 to August 2021. Total length and weight were measured and sexes were identified and gonad maturity levels were recorded. The sex ratio of African catfish in different size classes was similar to that of a hypothetical 1:1 ratio. The length at first maturity (L50) was 51.8 cm in total length. The mean Fulton’s condition factor of female African catfish ranged from 0.65 ± 0.05 – 0.71 ± 0.14, while the males ranged from 0.62 ± 0.04 – 0.7 ± 0.11. The Fulton’s condition factor was significantly higher in August for females than in the rest of the sampling months. The highest ripe gonads were recorded in the rainy season and the lowest was in the dry season, with the percentage of ripe gonads being 27.5%, while the males showed similarly extended maturity patterns among seasons. Fisheries management for African catfish should therefore take into account the estimated L50 value and the main breeding season to sustain the fishery and benefits the fishermen

Longitudinal river zonation in the tropics: examples of fish and caddisflies from endorheic Awash river, Ethiopia

Primary Research PaperSpecific concepts of fluvial ecology are well studied in riverine ecosystems of the temperate zone but poorly investigated in the Afrotropical region. Hence, we examined the longitudinal zonation of fish and adult caddisfly (Trichoptera) assemblages in the endorheic Awash River (1,250 km in length), Ethiopia. We expected that species assemblages are structured along environmental gradients, reflecting the pattern of large-scale freshwater ecoregions. We applied multivariate statistical methods to test for differences in spatial species assemblage structure and identified characteristic taxa of the observed biocoenoses by indicator species analyses. Fish and caddisfly assemblages were clustered into highland and lowland communities, following the freshwater ecoregions, but separated by an ecotone with highest biodiversity. Moreover, the caddisfly results suggest separating the heterogeneous highlands into a forested and a deforested zone. Surprisingly, the Awash drainage is rather species-poor: only 11 fish (1 endemic, 2 introduced) and 28 caddisfly species (8 new records for Ethiopia) were recorded from the mainstem and its major tributaries. Nevertheless, specialized species characterize the highland forests, whereas the lowlands primarily host geographically widely distributed species. This study showed that a combined approach of fish and caddisflies is a suitable method for assessing regional characteristics of fluvial ecosystems in the tropicsinfo:eu-repo/semantics/publishedVersio

Food and feeding habits of Nile Tilapia, Oreochromis niloticus (L.) (Pisces: Cichlidae), in Lake Langeno, Ethiopia

The study aimed to determine the diet composition, dietary change and diel feeding pattern of Oreochromis niloticus, in Lake Langeno. Fish specimens were collected monthly from July 2017 to June 2018 using a beach seine with 40 mm mesh size and scoop-net with small mesh size (1.0 mm). A total of 264 non-empty fish stomachs were examined for dietary analysis. The relative importance of different food items was analyzed using frequency of occurrence (%FO) and numerical abundance (%N). The most frequently encountered food items in the stomach of O. niloticus were phytoplankton, zooplankton, macrophytes and detritus. Among the phytoplankton groups, the genera Microcysts (%FO = 85.25), Cyclotella (65.51), Anabaena (%FO = 50.0), Cymbella (%FO = 65.15), and Chlorella (%FO = 54.17) contributed the most. Numerically, Cyanophyta, Chlorophyta, Bacillariophyta, and Zooplankton contributed 5.2%, 3.4%, 53.03% and 42.28%, respectively, to the total food items. Insect and fish remains occurred in rare occasions in the stomach content of all length groups of fishes. The dominance of animal-based food items progressively decreased as the fish grew to larger size while the importance of macrophytes and detritus increased. O. niloticus feeds mainly during the day time and stomach fullness peaked at 16:00 hr. The daily food consumption rate and gastric evacuation rate were 9.0% body weight and 48% per hr, respectively. Crude protein dominated nutrient composition of the fish and this could be attributed to the high  percentage in frequency of nutritious diets like Rotifers (64.0%), Cladoceras (63.6%) and Microcystis (85.6%). It can be concluded that juvenile Oreochromis niloticus feeds mainly on animal food sources whereas adults feed primarily on macrophyte food items

A new species of Enteromius (Actinopterygii, Cyprinidae, Smiliogastrinae) from the Awash River, Ethiopia, and the re-establishment of E. akakianus

Volume: 902Start Page: 107-15

An evidence of past introgressive hybridization between Labeobarbus ethiopicus and L. intermedius in the Ethiopian Rift Valley, East Africa

Analyses of nucleotide sequences of mitochondrial DNA (cytochrome b fragment) in 30 common barbs (Labeobarbus intermedius) from Lake Langano in the Ethiopian Rift Valley revealed the genetic heterogeneity of the samples. Whereas 29 individuals shared the same haplotype similar to those found in the poorly structured assemblage of L. intermedius sensu lato inhabiting the Rift Valley and basins of western Ethiopia, a single individual possessed a haplotype found exclusively in small-scaled Ethiopian barb L. ethiopicus. The latter species is phylogenetically distant from L. intermedius from any Ethiopian basins and differs from it by the substantially increased lateral line scale counts. Labeobarbus ethiopicus is the narrow range endemic of the Lake Zway basin. Presently barb migration from Zway to Langano is impossible because of the high water mineralization of Lake Abijata located on route. Past introgressive hybridization between two barb species could be enhanced by higher water level in the Zway-Langano-Abijata-Shala lake basin during humid periods in the course of paleoclimatic oscillations. Additionally, the increased lateral line scale counts were found in the Langano barbs compared to other barb population from the central part of the Ethiopian Rift valley, while the barbs from this region exhibited the increased values of this character compared to any other L. intermedius populations from Ethiopia and Kenya. These increased values could be a result of gene flow from L. ethiopicus to L. intermedius. The endangered status of L. ethiopicus as well as L. intermedius population from lakes Zway and Langano is highlighted.Keywords/phrases: Labeobarbus, Introgressive hybridization, Paleoclimatic oscillation

New data on Garra makiensis (Cyprinidae, Labeoinae) from the Awash River (Ethiopia) with remarks on its relationships to congeners on the Arabian Peninsula

On the African continent, the genus Garra consists of several species often insufficiently separated from each other by diagnostic characters. Herein, a detailed morphological redescription of Garra makiensis from the Awash River drainage is presented, together with additional data on the type specimens of G. makiensis and G. rothschildi. Mitochondrial CO1 sequence data are also provided, including the historic paralectotype of G. makiensis, with a comparison to Garra species from Africa and the Middle East. Based on these sequences, G. makiensis clusters outside the group of African congeners and is a sister lineage to species from the south-east of the Arabian Peninsula. Although morphologically variable, G. makiensis is characterised by having a single unbranched pectoral-fin ray, a short distance between vent and anal-fin origin (7.3–19.7 % of pelvic – anal distance), chest and belly covered with scales, and a prominent axillary scale at base of pelvic fin (18.8–35.5 % of pelvic-fin length)