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|1. Lates niloticus||2. S. niloticus||3. Elizabeth. argentii|
|4. Haplochromis||5. P. aethiopicus||6. Clarias sp.|
|7. Alestes sp.||8. M. frenetus||9. Synodontis sp.|
|10. Labeo sp.||11. Mormyrus sp.||several. Bivalves|
|13. Gastropods||14. Odonata nymphs||fifteen. Chironomid larvae|
|sixteen. Ephemeroptera nymphs||17. Corixid people||18. Chaoborus larvae|
|19. Caridina nilotica||20. Crabs||21. Cladocerans|
|22. Ostracods||23. Copepods|
step 3.step one. Predator proportions, prey-species dating
The results of the present study indicate a significant size related shift in the feeding behaviour of Lates. As it grows, its diet changes from mostly invertebrates to almost entirely fish. The findings made using percentage occurrence analysis of prey categories with respect to the size of the predator are presented in Fig.1. The results reveal that up to a predator size of 70cm (TL), crustacea were numerically the principle consituent of the diet, accounting for 44.2% of the food items eaten, followed by fish which made up 34.3% of the diet. In Lates larger than 70cm, fish was the dominant food item, contributing 69.2% whereas the number of crustacea in the diet declined to 20%. Hunter (1970) observed that juvenile Lates feed predominantly on invertebrates whereas the adults prey mainly on fish. Change in diet as a fish increases its size has been recorded in many species and Hellawell (1972) noted variation with age in the composition of the diet in Rutilus rutilus. In the present investigation, the number of large prey items tended to be larger than the the number of small items found in the stomachs of Lates. The maximum number of food items reported in a single stomach was 7 Oreochromis niloticus, 21 juvenile Lates and 105 Rastrionebola argentii (in a Lates in the 8990 cm size group) and 628 Caridina nilotica in a specimen from the 4050cm size group.
2. Analysis of the sizes of three fish prey-species (Lates niloticus, Oreochromis niloticus and Haplochromis spp.) recovered from Lates stomachs reveals an increase in prey size with increase in predator size. The figure further shows that most of the prey species selected by the predator were less than one third of its size. Another point Fig. 2 shows is that, whereas the maximum size of prey ingested increased with predator size, the minimum size of prey barely increased. Moore and Moore (1976), studying Anguilla anguilla, found that the maximum length of frequently ingested organisms increased from 3cm in fish of 1525cm to 6.5cm in specimens measuring 45. 155cm.
Significant changes were observed in the composition of the diet of Lates from the five depth strata sampled. Fig. 3 shows that, with increase in depth, the occurrence of both insects and fish items (Lates of all lengths combined) declined from 17.6% to 5.2% and from 37.3% to 17.1% respectively. Crustacea, of which Caridina nilotica was the most important, constituted 23.1% of diet of Lates from the shallow waters increasing to 71.6% in specimens from the deeper zones. Molluscs made a small contribution to the diet but showed a slight increase within the intermediate depth stratum. Hunter (1970), when working on Lake Albert, indicated that Lates niloticus of less than 20cm in length preyed mainly on Odonata nymphs within the shallow water and in lagoons, whereas in the offshore areas, Caridina nilotica formed the bulk of the diet of juvenile Lates. Lock (1975) found that although Bagrus bayad preyed upon a variety of https://datingranking.net/pl/tgpersonals-recenzja/ fish species, their relative importance in the diet varied with depth. Hopson (1972) made similar observations among Lates found in the inshore and offshore areas of Lake Chad.