Current Status And Trends Of Fishes And Fishery Of A Shallow Rift Valley Lake Lake Ziway Ethiopia

Lake Ziway is an economically important lake in the country. However, the physico-chemicalrnparameters of the lake seem to be threatened by anthropogenic and climatic factors, which inrnturn affect biotic factors as reflected in fish catch. A study was made to assess the status andrntrends of fishes and fishery during October 2012 to September 2014 in Lake Ziway.rnConductivity and pH showed more or less no change during the last two decades as the meanrnvalues ranged from 361.5±9.7 to 484.51±15.3 μS/cm and 8.03±0.2 to 8.37±0.1, respectively.rnDissolved oxygen content has higher values around the northern part of the lake at the inlet ofrnMeki River (5.71±0.6) and Ketar River (6.01±0.5).rnTen fish species were identified with low species diversity for the lake (H′ value of 1.67). Therncomposition of the fishes has undergone some changes as compared to the last few decades.rnFor instance, Carassius auratus and Labeobarbus microterolepis were not cought in this study.rnInaddition, Cyprinus carpio, which was never reported inearlier catch earlier, attained thernhighest relative frequency (25.19 %) in this study, next to Oreochromis niloticus (27.88 %),rnand then followed by Carassius carassius (20.71%) and Clarias gariepinus (20.51%).rnCanonical Correspondence Analysis (CCA) showed that the average abundance of C. carpio,rniirnC. carassius and C. gariepinus were positively correlated with nutrients, whereas thernabundance of Labeobarbus ethiopicus and Labeobarbus intermedius had negative correlationrnwith most of the physico-chemical variables.rnSome biometric measurements (length-weight relationship, condition factor, and sex ratio)rnwere examined for the fishes. The length-weight relationship in Barbus paludinosus, C.rncarassius, C. carpio, L. intermedius, C. gariepinus, Tilapia zillii and O. niloticus wererncurvilinear and statistically highly significant (P < 0.05). Fulton Condition Factor values (meanrn± SD) of the fishes were 1.26±0.19 (B. paludinosus), 1.52±0.14 (C. carpio), 2.13±0.57 (C.rncarassius), 1.73±0.38 (L. intermedius), 0.76±0.21 (C. gariepinus), 1.9±0.35 (T. zillii) andrn1.83±0.21 (O. niloticus) for both sexes. Females were more numerous than males for allrncommercially important fish species except C. gariepinus, and the ratio was significantlyrndifferent from the hypothetical distribution of 1:1 (X2 > 4).rnThe frequency of ripe C.carpio as well as GSI values were generally high during Februaryrnthrough to June and peaking between March and May sugesting that fish resources werernintensivelly in breeding condition. Fecundity, for C. carpio of fork length from 32 cm to 46rncm, ranged from 75,645 and 356,743 eggs with a mean of 210,538. Fecundity was significantlyrn(P < 0.05) related to fork length to total weight as well as to gonad weight. The relationshiprnbetween fecundity and fork length was curvilinear whereas that between fecundity and totalrnweight and that between fecundity and gonad weight were linear.rnThe fish catch of Lake Ziway currently declined from 3180 tons in 1997 to 1157.14 tons inrn2014. Most of the threats resulted from the anthropogenic impacts on the lake. Increasedrnpressure in fishing was a problem in the lake. Currently, plenty of pumps are abstracting freshrniiirnwater from the lake by state and private commercial farms throughout the year that arerncritically impacting the water level of Lake Ziway. As a result, the lake ecosystem is beingrnaffected by catchment degradation and siltation. The study suggested that if nutrient levelsrncontinue to increase and water levels continue to decline, further changes in fish compositionrncan be expected in the lake, especially with a shift towards fish that are mainly turbiditytolerantrnspecies such as C. carpio.rnThe study showed that the fishery sector has been of critical importance to the economy and tornthe social well-being of the fishermen in the study area. However, current harvest trends andrnfishery conditions put these attributes of the production at risk. It is threatened with problemsrnof open access to the resources, pollutions, marketing, and lack of technology. Hence,rnappropriate management is an urgent requirement that could assist in sustainable exploitationrnof the resources, so that the resource could contribute to food security in the study area inrnparticular and in the country in general

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