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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.

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.

For the past 13 years, the National Fisheries and Aquatic Life Research Center (NFALRC) have intervened with small-scale fish farming trials in South West and West Shewa zones of Oromia Region, Ethiopia. Opportunities and challenges of the trial, farmers’ awareness, and attitude towards small-scale fish farming and its economics have already been studied and documented. However, the studies were not comprehensively reviewed, synthesized, and presented to inform further intervention. This paper is meant to fill this gap. Desk review of those studies and others supported by prior experience of the author to intervention areas is the core approach followed. As a result, seven key lessons were learned: the need for redefining core challenges of small-scale fish farming, gender inclusion in small-scale fish farming, need for a revision of public sector-led formal extension service delivery linked to the change in the conventional extension approach followed by NFALRC, emphasis on awareness creation on fish farming, the importance of participatory approaches and the need for repeating research trials in the economics of small-scale fish farming. Among these, awareness creation, the use of participatory approaches, and changes in conventional extension service delivery by NFALRC should be given priority., Journal of Agriculture and Environmental Sciences, Vol 6 No 2 (2021)

The objectives of the study were to determine the breeding season, fecundity rate, size at first maturity and sex ratio of O. niloticus in Lake Chamo. Data (total length (TL), total weight (TW), sex, maturity stages and number of eggs) were collected. A total of 1,245 samples (968 females and 277 males) were collected during the sampling period (December 2019 to November 2020). The collected data were summarized using descriptive statistics (percentage, graphs, tables) and analyzed with the application of Microsoft Excel 2010 and Sigma plot 13.0 Software. There was significant deviation in sex ratio (Females: Males) from hypothetical 1:1 ratio (χ2 = 393.0; p, Journal of Agriculture and Environmental Sciences, Vol 6 No 2 (2021)

አህፅሮት የቆቃ የዓሣ ሀብት በዙሪያው በሚገኙ የማህበረሰብ አባላት የምግብ እና ስነ-ምግብ ዋስትናን በማረጋገጥ እንዲሁም በመተዳደሪያ የገቢ ምንጭነት የሚሰጠው ጠቀሜታ ከፍተኛ ነው፡፡ ይህን ጠቀሜታ ከትውልድ ትውልድ ለማስቀጠል ዘለቂነት ያለው የዓሣ ሀብት አጠቃቀም መተግበር በጣም አስፈላጊ ነው፡፡ በአሁኑ ወቅት የቆቃ ሀይቅ የዓሣ ሀብት ያለበት ደረጃ በደንብ አይታወቅም፡፡ ስለዚህ የዚህ ጥናት ዋና ዓላማ የዓሣ ሀብት ምርት መጠን ግምገማ ዘዴን ከኢኮኖሚዊ ትንተና ጋር በማጣመር በቆቃ ሀይቅ የሚገኙ በአጥማጆች ተፈላጊ የሆኑ የዓሣ ዝርያዎች የአጠቃቀም ሁኔታ ከሥነ-ህይወታዊ እና ኢኮኖሚያዊ ጠቀሜታ አንፃር ዘላቂነት አላቸው ወይስ ማስተካከያ የሚያስፈልጋቸው መሆኑን ማወቅ ነው። ዘለቂነት ያለው ከፍተኛ የዓሣ ምርት የሚሰጥ መጠን (MSY)፣ ከፍተኛ ኢኮኖሚያዊ ጠቀሜታ የሚሰጥ የምርት መጠን (MEY) እና እነዚህን የምርት መጠኖች ለማምረት የሚያስፈልጉት የማጥመድ ጥረቶች (fMSY & fMEY) ጋር የተዛመዱ የዓሣ ሀብቱን በአግባቡ ለመጠቀምና ለመጠበቅ የሚያስችሉ የማመሳከሪያ ጠቋሚ ነጥቦችን (management reference points) ለመገመት የባዮማስ ተለዋዋጭ ሞዴሎች (ሚዛናዊ እና ሚዛናዊ ያልሆነ)፣ የባዮኢኮኖሚክስ ሞዴል እና የቶምሰን እና ቤል የዓሣ ምርት መተንበያ ሞዴል ተጠቅሚያለሁ። የቶምሰን እና ቤል ሞዴልን በመጠቀም የተገኙት የማመሳከሪያ ጠቋሚ ነጥቦች (reference points) ሚዛናዊ ካልሆኑት ሞዴሎች በእጅጉ የተለዩ ባይሆኑም የቀድሞው ሞዴል ከሌሎቹ ሞዴሎች የተሻለ ተለዋዋጭ (flexible) ግምት ሰጥቷል። ከተሞከሩት ሞዴሎች ውስጥ አንዳቸውም በአጥማጆች ተፈላጊ የሆኑ የዓሣ ዝርያዎች ከመጠን በላይ መመረታቸውን አላመላከቱም፡፡ በመሆኑም የቆቃ ሀይቅ ዓሣ ሀብት አጠቃላይ ሁኔታ ጤናማና የዓሣ ሀብቱ በተገቢው ሁኔታ እየተመረተ መሆኑን ጥናቱ ያመለክታል፡፡ ነገር ግን በአሁን ወቅት በአጥማጆች በመያዝ ላይ ያለው ዝቅተኛ የዓሣ መጠን (Lc) ወደ ከፍተኛ ኢኮኖሚያዊ ጠቀሜታና የምርት መጠን (MEY) ወደሚያስገኘው የዓሣ መጠን ወይም ርዝመት (LMEY) ቢጨምር ከማህበራዊና ኢኮኖሚያዊ ጥቅሞች አንፃር የተሻለ እንደሚሆን ጥናቱ ያሳያል፡፡ Abstract The fishery resource in Lake Koka is very important for food and nutrition security, and the livelihoods of many riparian communities. Proper resource utilization is very essential to sustain the benefits of this natural capital for the present and future generations. So far little is known about the state of the fishery in Lake Koka. Therefore, the study aims at combining stock assessment of fishery target species of Lake Koka with an economic analysis to find out if current exploitation levels are biologically and economically sustainable or need adjustment. Biomass dynamic models (equilibrium and non-equilibrium), bioeconomic model, and the Thompson and Bell model were applied to estimate reference points related to Maximum Sustainable Yield (MSY), Maximum Economic Yield (MEY), and their corresponding efforts (fMSY & fMEY). While the reference points estimated using the length-based Thompson and Bell predictive model were not significantly different from the non-equilibrium model, the former model provided a more flexible estimate than the other models. As none of the models tested suggested overfishing of the target resources, I conclude that the general state of the Lake Koka fishery is healthy, but see scope for improvement in terms of socioeconomic benefits if the current minimum length of capture were increased toward the length of capture at MEY.

The study was conducted to estimate the maximum sustainable yield (MSY) and optimum level of fishing effort for Nile tilapia (Oreochromis niloticus) stock in Lake Chamo, Ethiopia. Data were collected from eight major landing sites of Lake Chamo for three days in a week for ten months (February to November, 2018). The total length, sample weight and total weight of O. niloticus caught by the fishermen and the fishing effort were the basic information collected from these sites. Totally, 7,570 O. niloticus samples were collected in 120 days. The FiSAT software was used to determine von Bertalanffy growth and mortality parameters. Jones length based cohort analysis model and length-based Thompson and Bell yield prediction models were employed to estimate the maximum sustainable yield. The estimated growth parameters; asymptotic length that the fish attains at an older age(L∞) and growth constant(k)of O. niloticus were 55 cm and 0.37 yr-1, respectively. Overall about 11 million O. niloticus populations were estimated to exist in the lake. The estimated current annual yield was 290.1 tons per year for O. niloticus fisheries of the lake. However, the predicted value of MSY was 313 tons per year obtained at fMSY of 136,249 nets. The length at first maturity (L50) was 39.6 and out of the total annual catch 93.1% were below their respective size of maturity. Thus, the current yield reduction might be due to growth overfishing with reduced mesh sizes. As reported in the earlier studies and according to the finding of this investigation, the catch and yield of Lake Chamo is in the state of reduction through year. Unless the lake is properly managed, the future yields of Lake Chamo will be declining that may lead the resources depletion. Co-management practices, using the recommended mesh size and level of effort (number of nets) should be considered for the sustainability of the resources., Journal of Agriculture and Environmental Sciences, Vol 4 No 2 (2019)

Phosphorus uptake by plant roots and arbuscular mycorrhizae (AM) hyphae can be described based on morphological and physiological uptake characteristics and parameters affecting P transport in the soil to the uptake surface. The current study aimed to quantify the relative contribution of hyphae and roots to P uptake of onion and to investigate the associated mechanisms using a mechanistic simulation model. Onion was grown in a growth chamber under controlled conditions at five levels of P supply with (M) or without (NM) AM. Uptake by onion roots and AM hyphae was simulated separately using a nutrient-uptake model, which was developed for roots. Model parameters describing P transport in the soil, as well as morphological and physiological uptake characteristics of roots and hyphae were derived from soil and nutrient-solution experiments. The model fairly described P uptake of M and NM plants at the highest level of P supply (28 μM P in soil solution) where roots and hyphae contributed nearly equally to P uptake of M plants. However, at lower P levels (

Effective management is essential for small-scale fisheries to continue providing food and livelihoods for households, particularly in developing countries where other options are often limited. Studies on the population dynamics and stock assessment on fishery target species are thus imperative to sustain their fisheries and the benefits for the society. In Lake Koka (Ethiopia), very little is known about the vital population parameters and exploitation status of the fishery target species: tilapia Oreochromis niloticus,common carp Cyprinus carpióand catfish Clarias gariepinus.Our study, therefore, aimed at determining the vital population parameters and assessing the status of these target species in Lake Koka using length frequency data collected quarterly from commercial catches from 2007-2012. A total of 20 097 fish specimens (distributed as 7 933 tilapia, 6 025 catfish and 6 139 common carp) were measured for the analysis. Von Bertalanffy growth parameters and their confidence intervals were determined from modal progression analysis using ELEFAN I and applying the jackknife technique. Mortality parameters were determined from length-converted catch curves and empirical models. The exploitation status of these target species were then assessed by computing exploitation rates (E) from mortality parameters as well as from size indicators i.e., assessing the size distribution of fish catches relative to the size at maturity (L m),the size that provides maximum cohort biomass (Lopt) and the abundance of mega-spawners. The mean value of growth parameters L x, Kand the growth performance index 0' were 44.5 cm, 0.41/year and 2.90 for O. niloticus,74.1 cm, 0.28/year and 3.19 for C. carpioand 121.9 cm, 0.16/year and 3.36 for C. gariepinus,respectively. The 95 % confidence intervals of the estimates were also computed. Total mortality (Z) estimates were 1.47, 0.83 and 0.72/year for O. niloticus, C. carpioand C. gariepinus,respectively. Our study suggest that O. niloticusis in a healthy state, while C. gariepinusshow signs of growth overfishing (when both exploitation rate (E)and size indicators were considered). In case of C. carpio,the low exploitation rate encountered would point to underfishing, while the size indicators of the catches would suggest that too small fish are harvested leading to growth overfishing. We concluded that fisheries production in Lake Koka could be enhanced by increasing Etoward optimum level of exploitation (E opt)for the underexploited C. carpioand by increasing the size at first capture (Lc)toward the L opt range for all target species. Un manejo pesquero eficiente es fundamental para que las pesquerías artesanales puedan continuar proveyendo alimento y sustento para los hogares, particularmente en los países en vía de desarrollo, en donde otras opciones a menudo son limitadas. Estudios sobre la dinámica poblacional de las especies objetivo de las pesquerías son, por lo tanto, imperativos para mantener las pesquerías y los beneficios para las sociedades. Esto también es válido para los recursos del Lago Koka (Etiopia) en donde hasta ahora se sabe muy poco sobre los parámetros poblacionales vitales y el estatus de las especies objetivo como la tilapia Oreochromis niloticus,la carpa Cyprinus carpioy el bagre Clarias gariepinus.El estudio aquí presentado tiene como objetivo determinar estos parámetros y evaluar el estado de la pesquería de estas especies en el lago Koka, utilizando los datos de frecuencia de tallas obtenidas de capturas trimestrales en el periodo 2007-2012. Un total de 20 097 especímenes fueron medidos (7 933 de tilapia, 6 025 de bagre y 6 139 de carpa). Los parámetros de crecimiento de von Bertalanffy fueron derivados del análisis de progresión de las modas usando ELEFAN I y aplicando la técnica de jackknife. Las tasas de mortalidad fueron estimadas de curvas de capturas basadas en longitudes y usando modelos empíricos. La tasa de explotación (E), se estimó con los parámetros de mortalidad y también considerando indicadores del tamaño a través de la distribución de tallas en las capturas y su relación con la talla de la primera madurez (L m),el tamaño que provee la biomasa máxima del cohorte (L opt)y la abundancia de los "mega-desovantes". Los valores calculados para los parámetros de crecimiento L m, Ky el índice de la capacidad de crecimiento 0' fueron: 44.5 cm, 0.41 año-1 y 2.90 para O. niloticus,74.1 cm, 0.28 año-1 y 3.19 para C. carpióy 121.9 cm, 0.16 año-1 y 3.36 para C. gariepinus,respectivamente. La tasa de mortalidad total (Z) fue estimada en 1.47, 0.83 y 0.72 año-1 para O. niloticus, C. carpioand C. gariepinus,respectivamente. Nuestros resultados sugieren que la población de O. niloticusse encuentra en un estado saludable, mientras C. gariepinusya muestra signos de sobrepesca por crecimiento. En el caso de C. carpiolas tasas de explotación tan bajas (E

In Ethiopia, the tilapia, Oreochromis niloticus, is an extremely important fish from ecological, economic and social point of view. Information on biological parameters like the size at first maturity (L50), Fulton’s condition factor (K) and length – weight relationship are very crucial for the sustainable management of the fishery. Therefore, the present study aims at providing information on the length-weight relationship, condition factor and size at first maturity (L50) of Oreochromis niloticus in Lakes Koka, Ziway and Langano. Fish samples were collected on monthly basis from October 2005 to February 2006. Length-weight relationships (total length (L) in cm; total weight (W) in g were calculated for O. niloticus in Lakes Koka (W = 2.61*10-2L2.89; n = 205; r2W = 1.04* 10−2L3.19; n = 279; r2 = 0.97) and Langano (W = 1.64*10−2L3.04; n = 525; r2 = 0.88). The average K value of O. niloticus from Lake Koka (1.87) is slightly higher than Ziway (1.81) and Langano (1.84). The size at first maturity (L50) of O. niloticus is smaller in Lake Ziway (Female =18.1cm, male=19.6cm) and Langano (both sexes 19.5cm) than Lake Koka (both sexes 23.5cm) which is contrary to the generally accepted principle that fish mature earlier in smaller water bodies than larger ones. Hence, the nutritional status and the level of fishing pressure appear to be important factors for the variations observed in the present study.Keywords/phrases: Condition factor; Lakes Koka, Ziway, Langano; L50; Length-weight relationship; O. niloticusEthiop. J. Biol. Sci., 7(2): 139-157, 2008