University of Khartoum

Some Aspects Of Fishery At Jelekag (White Nile).

Some Aspects Of Fishery At Jelekag (White Nile).

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Title: Some Aspects Of Fishery At Jelekag (White Nile).
Author: Jackson, E. Muso
Abstract: From the physical and chemical characteristics of the water studied, temperatures was low (14 o C) in December (winter or late Autumn) and high up to 30 o C in summer (June) and during the flood peak (September). Turbidity was lower in March (16cm) and higher in December (172cm). Likewise, conductivity was lo w in March (140umhos/cm) and high up to 650umhos/cm in December. The pH showed that the water was almost alkaline with its pH ranging between 7.6 to 8.0. The water remains well aerated throughout the year due to the favorable climatic conditions , keeping dissolved oxygen values between 7.6mg/L to 8.0mg/L. However, alkalinity was low in December (88mg/L) and was found increasing in summer (June) to 101mg/L were it attain its maximum value of 116mg/L in September . Nitrate level was lower in September (2.0mg/L) with marked increase in March through to June when it was higher (4.0mg/L). Whereas phosphate was low reaching 0.12mg/L in March and a high value was recorded in September (0.27mg/L). Silicate showed low reading in March (14.7mg/L) and reaches its high value in December (29.5mg/L). Sulphate however, was low in September (6.0mg/L) and reached a value of 11.0mg/L in June. Chlori de oscillated to attain a high value in December (6.2mg/L) and a low value of 2.0mg/L was reached in March. From the phytoplankton studies , Oscillatoria was the prominent algae of the flood season. While Microcystis, Navicula and Surrella showed high records during the dry season. The high volume of phytoplankton was encountered in June of which up to 492, 000 cells/L was reached, while the low volume was in September 54,300 cells/L. Zooplankton however, attained 124,200 cells/L in March and 4 in the catch almost throughout the year. Other species found have their seasonal occurrence. If the environmental factors remain unchanged and right mesh sizes are employed then; January, May and August are the best catching months. However, the whole of the rainy and flood seasons could have been the best fishing period, but the prevailing environmental factors such as; floating grass, heavy winds, long raining time and the bright moon light adversely affects fishing. The preference taste merit of the fish species in the study area include: Lates niloticus, Gymnarchus niloticus, Clarias species, Heterotis niloticus and Tilapia species. Of the five gill nets under questioning, mesh size 5(10cm), 6(12cm), 7(14cm), and 8(16cm) are the best sustainable catching nets in the area . Biological studies showed that operculum and scales are the best tools for age determination. Six distinctive sexual maturity stages from stage I to stage VI were recognized. The sex ratio showed the number of males always lesser than females. Analysis of food and feeding habits of the dominant fish species studied showed no specialized feeding habit. This work was executed during the period December 2000- November 2001 at Jelekag (White Nile) a volume of 6,600 cells/L was reached in June. The dominant species encountered during flood was Limnocaluns . Whereas Daphnia, Diaptomus , Cyclops, Paragordius and Keratella were most found during the dry season. Ichthyomass studies showed that Distichodus and Tilapia species were present
URI: http://khartoumspace.uofk.edu/handle/123456789/11294
Date: 2015-05-24


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