Juvenile Oreochromis Niloticus Research Articles

The Seasonal Food Habits of Oreochromis niloticus (Osteichthys: Siluriformes) in the Ikpoba Reservior, Benin City, Nigeria

Stomach contents of 424 adult and juvenile Oreochromis niloticus netted from the Ikpoba Reservoir were analysed. Phytoplankton formed the dominant food items of the fish during the dry and wet months of the sampling period. Zooplankton population in the fish diet was more pronounced during the wet months. Blue green algae were found most frequently in the stomach of the fish followed by Diatoms and Green algae. Zooplankton (Cladocera and Copepoda) occurred less frequently in the diet of adults than juvenile fish. There was significant difference (P < 0.05) between the volume of food recorded in the fish stomachs during the dry and wet months of the year. Food abundance and feeding activity was heaviest during the dry than the wet months. The predominance of a wide variety of planktonic organisms in the fish stomachs suggested planktiphagous feeding habits. Journal of Aquatic Sciences Volume 14, April 1999, pp. 33-36 KEY WORDS: Oreochromis niloticus, Ikpoba Reservoir, Stomach Contents.

A statistical power analysis of the ‘internal reference’ technique for comparing growth and growth depensation of tilapia strains

Experiments were conducted to compare the growth and growth compensation of three strains of juvenile Oreochromis niloticus. Ten full sib families (10 replicates) per strain were split and grown under crowded and uncrowded conditions for 3 weeks (the treatment). Both treatments were then grown an additional 12 weeks under less crowded conditions (the compensation). Standard length measurements were made at the end of crowding and the end of compensation. Each replicate included a size‐matched control population of a fourth (red) reference strain. ANCOVA with the reference strain used as a cofactor revealed significant strain effects on specific growth throughout the experiment. The reference strain removed most of the random among‐replicate error variance as shown by an increase of r 2 from 0.06 to 0.91 when it was included in the statistical models. If the reference fish had not been used, approximately 450 replicate families would have been needed to achieve the sensitivity of the present experiment (a difference of 7% among strains significant at P=0.05). We conclude that the CLSU strain grows significantly more slowly than the Israel and NIFI strains under the experimental conditions, that the crowding effect was essentially eliminated after 12 weeks of compensation, and that the reference strain greatly improved the resolution of the strain‐testing experiment.

Acute toxicity of cadmium to juveniles ofClarias gariepinus(Teugels) andOreochromis niloticus(Trewavas)

Abstract The acute toxicity of cadmium was determined for juveniles of Clarias gariepinus (Teugels) and Oreochromis niloticus (Trewavas) in 96‐h static bioassays. Symptoms of toxicosis in both species showed that cadmium causes subacute effects such as loss of equilibrium, copious accumulation of mucus and air gulping. C. gariepinus, LC50 10.850 (10.097 ‐ 11.659) mg/1 was more susceptible to cadmium than O. niloticus LC50 19.319 (18.376 ‐ 20.310) mg/1. Possible ‘reasons for the difference in susceptibility of these two species to cadmium are suggested.

Nutritive value of diet containing dried lactic acid fermented fish silage and soybean meal for juvenileOreochromis niloticusandClarias gariepinus

Resume Fagbenro O., K. Jauncey, G. Haylor. Aquat. Living Resour., 1994, 7, 79-85. Dry diets containing varying levels of dried fermented fish silage and soybean meal blend (FS: SBM) as replacement for 25,50 or 75 % of fish meal protein were fed to juvenile Oreochromis niloticus (8.210.1 g) and Clarias gariepinus (10.8k0.3 g) at 5 % body weight per day for 70 days. Diets containing CO-dried FS: SBM supported weight gains and growth rates similar to those in the control treatment without significant differences @>0.05). Feed conversion, protein efficiency ratio and protein productive values followed a similar trend with growth performance values. Apparent protein digestibility decreased in both fish species with increasing dietary level of CO-dried FS: SBM. Carcass composition of experimental fish were not affected by the diets and morphological defects were not observed. Results indicate that CO-dried FS: SBM can partially replace fish meal protein as well as establish the potential of utilizing wastehndersized tilapias as a protein feedstuff in dry aquaculture diets.

Oesophagus structure during adaptation to salinity inoreochromis niloticus(Perciformes, pisces) juveniles

Abstract Fifteen days old Oreochromis niloticus juveniles were gradually adapted to 10, 20, 30 and 35‰ sea water. The morphology of the oesophagus epithelium was observed at different intervals after transfer to higher salinities. At 10‰, no changes are evident compared to fresh water controls. Regions of single columnar epithelium, reported to play a role in ion trasport, appear within the normal pluristratified one at 20, 30 and 35‰ four weeks after transfer from fresh water. These modifications widen in individuals left for longer at high salinities.

Fish communities in the eastern, seasonal-floodplain of the Sudd, Southern Sudan

Annual flooding of the permanent Sudd swamps innundates large areas of Oryza longistaminata grasslands. Fish migration into a southeast section of the seasonal floodplain was led by Clarias gariepinus, Polypterus senegalus and several small species which were intent on spawning. Channa obscura and juveniles of Oreochromis niloticus were prominent among later entrants. From a total of 23 species caught in seasonal habitats, 7 contributed over 97% of total estimated numerical and biomass densities. The latter ranged from 435–580 kg ha−1. In the 1982–83 flood-season entry to the floodplain was essentially restricted to species tolerant of oxygen-deficient waters and thereby able to penetrate the papyrus and Typha swamps of the permanent wetland. Migrants became stranded in temporary pools and subject to heavy cropping by birds.