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Title: Sex Ratio, Length-Weight Relationship,Condition Factor and the Food Habit of Catfish, Clarias Gariepinus (Burchell) in Lake Langeno, Ethiopia
???metadata.dc.contributor.*???: Dr. Demeke Adtnassu
Teka, Leul
Issue Date: Jun-2001
Publisher: Addis Ababa University
Abstract: Sex-ratio, length-weight relationship, condition factor (n = 859) and the food habit (n = 764) of C. gariepinus were studied in Lake Langeno from monthly samples collected using hook and lines between April 2000 and October 2000. Female to male sex-ratio was in favour of females in the total sample (1.41:1) and in both seasons of low water-level (1.29:1 ) and high water-level (1.53:1). Sex-ratio was not significantly different from 1:1 in five of the eight length classes used for the study. In three of the length classes (between 25 cm and 54 cm, TL), females were at least 1.53 times more numerous than males. The relationship between total length (range: 28 to 104 cm) and total weight ( range: 150 to 8000g) was found to be curvilinear and statistically significant (R2=0.955, P<0.05) with a slope (b =2.91) very close to the cube. Monthly mean Fulton condition factor (FCF) ranged from 0.55 to 0.65 for male and from 0.61 to 0.66 for female C. gariepinus. Monthly mean relative condition factor (RCF) ranged from 0.91 to 1.09 for males and from 0.99 to 1.10 for females. Generally, females had seasonally higher FCF and RCF than males. On the average, large values of FCF and RCF were recorded in May,and low values in June for both sexes. There was no significant difference (ANOVA, P=0.1334) in FCF and RCF between the low water and high water seasons. Mean FCF and mean RCF of females were larger than those of males in all length-classes except in the smallest class (25 to 34cm TL) in which case males had larger values. Stomach contents of C. gariepinus were composed of organisms belonging to six taxa or groups,detritus, sand grains and unidentified plant and animal remains. The identified taxa/groups were algae ( Microcystis sp. and unidentified filamentous species), Macrophytes (shoots , roots, fruits and seeds), Crustacea, Insecta, Hydracarina and Pisces. Crustaceans were represented by Ceriodaphnia sp., Diaphanosoma sp. andMesocyclops sp., and by unidentified Ostracod species. Insects were represented by various developmental stages of Trichoptera, Hemiptera, Diptera, Ephemeroptera, Odonota, Coleoptera, Plecoptera and Hymenoptera. O. niloticus was the only fish species ingested by C. gariepinus. The presence of sand and benthic organisms (insect larvae and pupae) was considered as indicative of a bottom feeding habit The frequency of occurrence, the numerical abundance and gravimetric methods each suggested that crustaceans, insects and fish were the most important food of C. gariepinus in Lake Langeno. Numerically, crustaceans were most important (93%) but in terms of frequency of occurrence (75%) and weight (93%) insects were most important items in the diet of C. gariepinus. Fish were the least important (below 10% by each method) food as compared to crustaceans and insects Cladocera and Copepoda were found to be the dominant Crustacean members in the diet of C.gariepinus. Diptera, Hemiptera and to some extent Odonata were the most important whereas Plecoptera and Hymenoptera were least important insects in the diet of C. gariepinus The relative contribution of each food item varied with the size of C. gariepinus. Thus, frequency of occurrence was relatively high for Crustacea (about 60%) in C. gariepinus between 45 and 64 cm TL, for insects (> 80%) in those below 54 cm TL, and for fish (20-60%) above 65 cm TL. Numerically, crustaceans contributed more than 90% for each length group but their contribution was below 90% for C. gariepinus above 84 cm TL. The numerical contribution of insects and fish increased for C. gariepinus above 84 cm. Gravimetric contribution of crustaceans was relatively high (10-15%) for C. gariepinus between 45 and 74 cm TL, and that of fish (about 10%) for large (>84 cm TL) C. gariepinus. The weight contribution of insects was about similar for all size groups of C. gariepinus caught in the study. The results suggested that as C. gariepinus grows larger it consumes progressively more fish . The ratio between prey (O. niloticus ) length and predator (C. gariepinus) length varied greatly.About 50% of the C. gariepinus had ingested tilapia whose length was between 1/10,h and 1/30 of their own length. A few individuals had ingested tilapia whose length was either above 1/5 or below 1/30th of their length Frequency of C. gariepinus with empty stomach was quite low (0 to 2.2 %) in samples taken between April and June, which was coincident with period of low water level. In contrast, the frequency was high (9.5 to 20%) in July, August and October. In general, about 95% of the total number of empty stomachs were recorded during the season of high water level. This coincided with the period when C. gariepinus ingested more fish as compared to the other period The relative importance of fish to the diet of C. gariepinus was more pronounced during the season of high water level. Crustaceans and insects, however, were equally important throughout the study period .
Description: A thesis presented to the School of Graduate Studies Addis Ababa University In partial fulfillment of the requirements for the degree of Master of Science in Biology
Appears in Collections:Thesis - Biology

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