Length – Weight Relationship, Condition Factor and the Food of Juvenile Nile Tilapia (Oreochromis Niloticus L.) in Lake Hawassa and Lake Zwai, Ethiopia
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Date
2017-06-05
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Addis Ababa University
Abstract
Length - weight relationship, condition factor and the food of juveniles of O. niloticus in lakes Hawassa and Zwai were studied from monthly samples taken during March to August 2016. Total length (TL, cm) and total weight (TW, g) of both juvenile populations were curvilinearly related (ANOVA, P<0.005) with high coefficient of determination (R2≥ 0.86). The equation was TW = 0.0322*TL2.72 for the Lake Hawassa population whereas TW = 0.0558*TL2.54for the Lake Zwai population. The length – weight coefficient (b) value suggested isometric growth for the juveniles in Hawassa (b=2.72) whereas allometric growth for those in Zwai. Mean ± SE fulton condition factor (FCF) was 1.74 and 1.65 for juveniles in Lake Hawassa and Lake Zwai, respectively. Mean FCF did not vary significantly (ts, p>0.05) between the two populations. Mean ± SE relative condition factor (RCF) was 1.02 and 1.01 respectively, for Hawassa and Zwai populations. Mean RCF value (>1) suggested that both juvenile populations are in good growth condition. Stomach content analysis (Hawassa n=185, Zwai n=200) revealed that both populations feed on a variety of organisms belonging to phytoplankton, zooplankton, insects, nematodes and unidentified animals. Both frequency of occurrence and numerical abundance method showed that zooplankton were the most important food of both juvenile population and the least nematodes, in that order were the most important food items categories frequency of occurrence and numerical abundance showed that the relative importance of animals decrease whereas that of phytoplankton increases as the size (TL) of the juveniles increases (TL: 4cm to14.5cm).
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Condition Factor, Food, Juvenile Oreochromis Niloticus, Lakes Hawassa and Zwai