Seasonal Changes in the Nutrition of Oreochromsniloticus Linn, (Pisces: Cichlidae) in Lake Ziway; Ethiopia
No Thumbnail Available
Date
1990-01
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
The quality and digestibility of the natural food of Oreochromis
niloticus in Lake ZiHay, Ethiopia, ~/aS studied for a period of one year,
October, 1988 to September, 1989. The stomach and rectal contents of 956
fishes I'/ere analyzed for total organic matter, protein, lipid, carbohydrate
and energy. Different forms of inorganic nitrogen and or tho-phosphate in the
I-later 11ere also determined to assess if there is any relationship I-lith the
composition of the diet.
Total organic matter (55.7% D.\<I.), protein (4.6% D.W.), lipid (5.3%
D.I'1.) and energy (8.7KJ/g D.w.) Here consistently lO~1 for most parts of the
year, Hhile carbohydrate (21.5% D.~/') ~ms relatively high. Protein, lipid and
carbohydrate accounted for 57.0% of the ash free dry Height (AFDI'Il. Detritus
is assumed to contribute most of the unaccountable pOl:tion of the AFDI>I. All
nutrients shoHed significant monthly variation (ANOVA, P < 0.0001), hOHever,
the variation of nutrients bet~leen sexes Has not significant (ANOVA, P >
0.05).
Estimates of assimilation efficiency using ash as a reference marker
revealed that 36.7% of the total organic matter I'las absorbed. Protein, lipid,
carbohydrate and energy !lad dic;jestibility values of 73.3%, 13.3%, 39.1% and
37.3%, respectively. Assimilation efficiency values ~Iere also estimated for
three months using three indigenous markers, ash, hydrolysis resistant ash
(HRA), and hydrolysiS resistant organic matter (HROB). Results shol1ed that
ash and HRA gave higher values in tHO (August and November) of the three
months considered. HROH gave higher values only in one month (Hay).
The quality of food expressed as the ratio of digestible protein to Kilo
Joule of digestible energy varied significantly over the 12 months considered,
and ranged from 6.0 to 117.0. Although the qual! ty of the food appears to be
sufficient to support gro~lth during most of the year, 101'1 amount of digestible~
organic matter in the diet seems to restrain the maximum grol1th possible.
Condi tiol} of Q. nl.loticus Has variable betl'leen months but not betl'leen seXes. :
Honthly food quality and the corresponding condition of fish had no
significant correlation (r = 0.012) indicating that fish condition might not
be sensitive eno\lgh to detect changes in food q\lality over a short period of
time. The overall condition of O. lliloticus in Ln)<e Zi\-my I'las found to be
lO~ler than that of Lake lmassa, and this is probably due to inferior quality
of the diet and 10l'ler feeding rate.
The length-weight relationships of O. niloticus that range from 11. 2 to
31.0 em in size ~Iere fou\\d to be, ~l == 0.028 L2.37I
" r2 = 0.906, P < 0.0001 for
males and \q = 0.106 L2 •448 , r2 = 0.852, P < 0.0001 for the females.
There Has no relationship betl~een the composi tiOll of the diet of O.
nilotious of Lake Zi\omy and the nuti:ients (nitrogen and phosphorus) in the
lake water.
Description
Keywords
Biology