Ontogenetic variation in the diet of Chrysichthys nigrodigitatus (Lacepede 1808) in a tropical estuarine ecosystem in Nigeria
The ontogenetic variation in the diet of Chrysichthys nigrodigitatu (Lacepede 1808) was investigated. The study was carried out for a period of 15months (Feb.-Sept. 1996 and March - Sept. 1997) based on 660 specimens of the fish. It was aimed at a detailed analysis of the diet composition of C. nigrodigitatus and the variation in diet with size class. The diet composition was analysed using the occurrence, numerical and gravimetric methods. These were combined into a composite Index of Relative Importance (IRI) which formed the basis of determining the importance of each food category. C. nigrodigitatus is a benthic omnivorous feeder subsisting on a variety of benthic food items, with significant ontogenetic shifts in diet composition. The size classes 0-30.00cm and 31-60.00cm adult had preference for plankton, 61-90.00cm preferred fish and crabs while 91-120.00cm had preferential diet of shrimps. Index of Relative Importance (IRI) was as follows: fish -31.8%, Crustaceans -23.6%, bivalves -10.61%, as major food items. The minor food items included plankton, polychaetes, palmfruits, plant materials and detritus. Variation of condition factor (C.F) with fish length was studied with highest C.F value of 1.86 for size group 10-19cm and lowest C.F value of 0.71 for size group 40-49cm.This study has not only identified C. nigrodigitatus as a benthic predator in the estuary, but has also provided data that can make significant inputs into the trophic modeling and multispecies management of the estuary.
| Main Authors: | , , |
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| Format: | conference_item biblioteca |
| Language: | English |
| Published: |
Fisheries Society of Nigeria
2010
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| Subjects: | Ecology, Chrysichthys nigrodigitatus, Nigeria, Cross River Estuary, brackishwater environment, Feeding behaviour, Food composition, Food conversion, |
| Online Access: | http://hdl.handle.net/1834/38191 |
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| Summary: | The ontogenetic variation in the diet of Chrysichthys nigrodigitatu (Lacepede 1808) was investigated. The study was carried out for a period of 15months (Feb.-Sept. 1996 and March - Sept. 1997) based on 660 specimens of the fish. It was aimed at a detailed analysis of the diet composition of C. nigrodigitatus and the variation in diet with size class. The diet composition was analysed using the occurrence, numerical and gravimetric methods. These were combined into a composite Index of Relative Importance (IRI) which formed the basis of determining the importance of each food category. C. nigrodigitatus is a benthic omnivorous feeder subsisting on a variety of benthic food items, with significant ontogenetic shifts in diet composition. The size classes 0-30.00cm and 31-60.00cm adult had preference for plankton, 61-90.00cm preferred fish and crabs while 91-120.00cm had preferential diet of shrimps. Index of Relative Importance (IRI) was as follows: fish -31.8%, Crustaceans -23.6%, bivalves -10.61%, as major food items. The minor food items included plankton, polychaetes, palmfruits, plant materials and detritus. Variation of condition factor (C.F) with fish length was studied with highest C.F value of 1.86 for size group 10-19cm and lowest C.F value of 0.71 for size group 40-49cm.This study has not only identified C. nigrodigitatus as a benthic predator in the estuary, but has also provided data that can make significant inputs into the trophic modeling and multispecies management of the estuary. |
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