Seasonal food selection by three-sized <i>Oreochromis niloticus niloticus</i> (Trewavas) in a polycultured earthen pond

Abstract

Pooled gut contents of 486 fish, were analysed weekly from February – July (26 weeks). The juveniles fed intensively (5.1 – 10 cm SL) 77 – 100% followed by the fry (1.1 - 5.0 cm SL) 58 - 90.5% and adults (10.1 - 15.0 cm SL) 57 - 94%. The condition factor (k) had values that ranged from 3.55 - 17.4 confirming the active feeding habit of this fish. Temperature readings in the morning (0900 h) ranged from 18 – 35^OC for atmosphere while the afternoons (1500 h) ranged from 20 – 35^OC morning water column was between 10 – 25^OC while afternoon was 18 – 28^OC. Dissolved oxygen for morning was between 6.0 and 11.0 mgl^-1. While dissolved oxygen values of afternoon was between 8.8 and 12.0 mgl^-1. Free carbon dioxide ranged from 0.0 to 2.8 mgl^-1 in the morning that afternoon that for was between 0.0 – 0.9 mgl^-1. The rainfall was from April – July with a mean of 147.540 + 0.04 mm. There was seasonal variation (P < 0.05) in the gut contents between the dry and wet seasons. Contents were found to compose mainly of algae in all the three different sizes of fish sampled. Chlorophyceae were most preferred (40%) next were sand particles (but not regarded as food) (11.5%), Myxophyceae (11%), Detritus (6.8%), Fragments of higher vegetation (6.7%), Bacillarophyceae (6.5%), Zooplankton (5.4%), Euglenophyceae (4.4%), supplemental food (4.4%), chrysophyceae (0.56%) and least were Xanthophyceae 0.33%.

Key words: Food selection, Oreochromis, earthen pond.

Journal of Aquatic Sciences Vol.20(1) 2005: 47-51