Dietary Composition and Biometric Characteristics of the Giant African Threadfin, Polydactylus quadrifilis (Cuvier, 1829) from, Nigeria

Abstract

The giant African threadfin, Polydactylus quadrifilis (Cuvier, 1829) is a commercially important marine and brackish water fish. The dietary composition, feeding intensity, growth pattern and condition factor of the fish from Lagos Lagoon, Nigeria was investigated for a period of six months to provide additional information toward the development of fisheries in Lagos Lagoon system. A total of eighty eight fish samples were purchased from Artisanal fisherman using cast net along side with other fish species from Lagos Lagoon between January and June 2014.The regression coefficient “b” exhibit positive allometric growth in Lagos Lagoon. The value of exponent “b” was found to be 3.14 and condition factor (k) of the fish was 1.44 respectively, which was an indication that the fish were thriving very well in the Lagoon. During the study period 94% fish showed active feeding; 12.5% stomachs were found full, 21.6% stomachs were three-quarter full, 20.5% stomachs were half full, 39.8% stomachs were quarter full and 5.7% stomachs were empty. The fish fed on varieties food items such as shrimp, fish and crab with 56.9, 36.9 and 6.3 percent in average respectively. The presence of crab and shrimp was attestation to its carnivorous tendency, while occurrence of bony fish was an indication of its piscivorous habit.  Variations in the Index of Relative Importance (IRI %) and GII among the prey groups showed that shrimp were the most important component in the Giant African threadfin.

Keywords: Polydactylusquadrifilis, diet, length-weight relationship, condition factor