Studies on the "biology of the Family Schilbeidae (Osteichthyes : Siluriformes) in Lake Kainji, Nigeria.

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Date
1977-10
Authors
OLATUNDE, AKINOLA A.
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Abstract
The biology of the Family Schilbeidae (Osteiehthyes : Siluriformes) in Lake Kainji, Nigeria was investigated. Eleven sampling stations located within the central basin of the lake were sampled monthly with static gill nets of various stretched mesh sizes, supplemented by netting in Shagunu creek with smallmesh nets. Five schilbeid species were found. Eutropius niloticus RUPPELL and Physailia pellucida BOULENGER were the commonest and most abundant. Schilbe mystus LINNAEUS was less abundant, but was far more abundant than Siluranodon auritus (GEOFFROY ST. HILLAIRE) and Schilbe uranoscopus RUPPELL which were very r a r e. All species were found in a variety of habitats in the lake and adjacent in lets; but P. pellucida is pelagic and S. mystus is riverine. The pectoral spines display rings which are shown to be annual so can be used to determine the age and growth of E. niloticus and S. mystus. Females grow faster, attain greater maximum s i z e, live longer and attain maturity at a greater length than the males. Sex ratio varied seasonally with more females in the population than males. Sex ratios and gonad cycles provided evidence of breeding pattern for all the species except S. uranoncopus. P. pellucida spawned several times during a prolonged breeding season while others spawned once during a short breeding season from June to November. Stomach contents showed that although every species would take a variety of food, Siluranodon auritus is phyto-plonktonivorous; Physailia pellucida feeds mainly on zooplankton, both species of Scbilbe are mainly piscivorous and Eutropius niloticus is omnivorous. Food selection was influenced by age or size of the fish and seasonal availability of food items. Digestive enzymes showed a correlation with the dets of the species studied. The biochemical and nutritive values of the three common schilbeids were determined and suggestions are irrade for more effective harvesting of schilbeids for consumption
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Dissertation submitted for the degree of DOCTOR OF PHILOSOPHY in Department of Zoology
Keywords
biology,, Family Schilbeidae,, Osteichthyes,, Siluriformes),, Lake Kainji, Nigeria.
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