~ 83 ~ International Journal of Fisheries and Aquatic Studies 2020; 8(5): 83-91 E-ISSN: 2347-5129 P-ISSN: 2394-0506 (ICV-Poland) Impact Value: 5.62 (GIF) Impact Factor: 0.549 IJFAS 2020; 8(5): 83-91 © 2020 IJFAS www.fisheriesjournal.com Received: 01-07-2020 Accepted: 03-08-2020 Yibeletal Aynalem Woldia University, Department of Animal Production, and Technology, P.O.Box 400, Woldia, Ethiopia Minwyelet Mingist Bahir Dar University, College of Agriculture and Environmental Sciences, Department of Fisheries, Wetlands and Wildlife Management, P.O.Box 79, Bahir Dar, Ethiopia Corresponding Author: Yibeletal Aynalem Woldia University, Department of Animal Production, and Technology, P.O.Box 400, Woldia, Ethiopia Length-weight relationship and reproduction of fishes in Gilgel Abay, Andassa, Jemma and Koga Rivers, Blue Nile, Amhara region, Ethiopia Yibeletal Aynalem and Minwyelet Mingist Abstract Length-weight relationship, frequency distribution and reproduction of fishes in Gilgel Abay, Andassa, Jemma and Koga Rivers were studied by using gillnets and monofilaments of different mesh sizes, cast nets, hook and lines. Fish species identification was done by using literature and specimen deposited in the laboratory. Totally, 1106 fish specimens were collected from four Rivers. Three families and thirteen species of fishes were identified four Rivers. Labeobarbus intermedius, Varicorhinus beso, L. nedgia and Clarias gariepinus were the most dominant fish species found in both rivers. Length-weight relationship of L. intermedius, V. beso, L. nedgia and C. gariepinus were curvilinear and statically significant (p<0.001). There was significant difference in Fulton condition factor for the dominant fish species between Andassa and Gilgel Abay Rivers. Absolute fecundity of L. intermedius, L. nedgia and V. beso was linearly related to total length, total weight and gonad weight. Four seasons detail data should be collected to have clear understanding on the reproductive biology of fishes. Labeobarbus intermedius and V. beso were the first and second most abundant fish species that had a total length ranged from 16 to 53.5 and 22 to 54.5 cm at Andassa River and 19 to 48- 18.6 to 35.1 cm at Gilgel Abay River, respectively. Labeobarbus nedgia was the third most abundant species that had a total length ranged from 23.4 to 52.9 and 18.5 to 48 cm at Andassa and Gilgel Abay Rivers, respectively. The fourth most abundant fish species was C. gariepinus with a total length ranged from 28 to 66.5 and 22 to 58.5 cm in Andassa and Gilgel Abay Rivers, respectively. Keywords: Length-weight relationship, length frequency distribution, fecundity, condition factor and sex ratio Introduction Ethiopia is a land locked country that depends on the inland waters for the supply of fish as a cheap sources of animal protein. It has a number of lakes and rivers with substantial quantity of fish stocks. The total area of the lakes and reservoirs stands at about7000-8000km 2 and the important rivers stretch over 7000km in the country [1] Sustainable utilization of the aquatic resources, particularly the fishery resources is necessary so as to support the increasing Ethiopian human population through inexpensive source of animal protein [1] . Specimen of fish species were identified to species level using taxonomic key as indicated in [2] and [3] Picture of fish specimens was taken for each species. Immediately after capture, a gentle pressure was applied on the abdomen to check whether spermiation or ovulation has occurred or not. Then, total length and fork length were measured to the nearest 1 cm using measuring board and total weight of all specimens of fish was measured to the nearest 0.1 cm using sensitive balance. After dissection, gonadal maturity of each fish specimen was identified, using a five point of maturity scale [1] . Gonad weight was measured to the nearest 0.1 g using sensitive beam balance. From specimen of matured females (fish at stage IV) egg sack was measured and preserved with 4% formalin for fecundity estimation. After taking the entire necessary information, individual specimens were preserved with 4% formalin and put in plastic jar and was transported to laboratory for further identification and measurement. Knowledge on length-weight relationship and some biological aspect of fish species of Ethiopia is poorly known. Relatively a large number of small, medium and even some large rivers have not been well studied and explored. Study on these rivers is a critical issue to be deal to fill such gaps. Gilgel Abay is the major river flowing into Lake Tana and Andasa River