Effect of Stocking Density and Rearing Facility on Growth and Profitability of Tilapia rendalli Fry
A study was conducted to compare the growth potential of Tilapia rendalli at three different stocking densities, using different rearing facilities. T. rendalli fry of 0.9±0.1g average weight were stocked in tanks and hapa-in-ponds at the stocking density of 30, 60 and 90 fry/m 3 . Locally made feed (CP-18%) was administered at 5% body weight three times a day for three months. Monthly sampling was conducted to assess growth by measuring weight and length for specific growth rate (SGR), average daily gain (ADG), weight gain (WG), and biomass (BM). The results of the study showed a significantly higher (P 0.05) as well as within the stocking densities (P > 0.05). The results of this study have a significant contribution towards stocking densities as well as rearing facilities used by hatchery operators. It is recommended that hapas mounted in pond fry rearing for T. rendalli fingerling production is most ideal. The results of the present study suggested that production of good quality fingerlings at stocking densities of 30 fry/m 3 must be adopted in the culture of T. rendalli as fish grows faster than the other stocking densities of 60 and 90 fry/m 3 as demonstrated in this study.
Some aspects of biology and aquaculture potentials of Tilapia guineensis (dumeril) in Nigeria
The paper emphasizes on the several attempts made to raise the brackish water tilapia species, Tilapia guineensis both on an experimental and production basis by researchers and fish farmers in Nigeria. Besides, the aquaculture potentials of Tilapia guineensis have been reported by several authors. However, problems exist which are not found with the culture of other tilapia species. Even under most favourable conditions (e.g. the monosex culture of Tilapia guineensis), a poor growth rate and a mediocre feed conversion do not presage profitable aquaculture exploitation. The present review therefore throws light on areas of further research to enhance the growth performance of Tilapia guineensis with emphasis on fish larvae nutrition and first feeding (development of bio-encapsulated feed for larval fish based on nutritionally enriched nematodes and Calanoid copepods), digestibibilty of the feed ingredients, elucidation of the dietary protein requirements, improved culture technique through the use of the Recirculating Aquaculture Systems and the adoption of the most recent technology (The YY Male technology) that produces Genetically Male Tilapia through genetic manipulation. Specific recommended areas for further research are also proffered.
Serum Profiles of Luteinizing Hormone, Oestradiol and Cholesterol and Ovarian Functions in Layer Poultry Birds (Gallus domesticus) Fed Diets Containing Furazolidone
This study was carried out to assess the serum profiles of luteinizing hormone (LH), oestradiol, cholesterol and ovarian functions in layer poultry birds (Rhode Island Red;Gallus domesticus) fed a diet containing various concentrations of furazolidone (FZ). A total of 40 birds were randomly assigned to receive FZ 0, 200, 400 or 800 mg/kg feed (ppm) daily during the pre-laying age, i.e. 13–18 weeks (for 5 weeks). Blood samples were collected at weekly intervals. Concentrations of LH and oestradiol in serum were estimated at alternate weeks using radioimmunoassays. Serum cholesterol levels were analysed by an enzymatic calorimetric method. Furazolidone administration was terminated at the 18th week of age. The birds were sacrificed at 22nd week of age and ovarian tissues were processed for morphometric studies. Serum LH, oestradiol and cholesterol levels were affected by age (p<0.001) and FZ dose (p<0.001). Serum LH and oestradiol levels were lower (p<0.05) in birds receiving FZ 800 mg/kg feed daily compared with the controls, whereas serum cholesterol profiles were lower (p<0.05) in all FZ-administered groups than in the control group. The mean weight of ovaries having no yolky follicles observed in the group receiving FZ 400 or 800 mg/kg feed per day was reduced (p<0.05) compared with the control group. Dosing FZ at 800 mg/kg feed per day reduced (p<0.05) the mean volume of ovaries having no yolky follicles compared with the control group. In birds receiving FZ 800 mg/kg feed per day, the mean length of the oviduct was reduced (p<0.05) as compared with the control group. Morphometric studies revealed that the mean number of oocytes with diameter in the range 401–800 μm decreased (p<0.05) in birds fed FZ 400 or 800 mg/kg feed per day. Initial egg production was affected by age (p<0.001) and dose (p<0.001) of FZ. The mean number of eggs laid by different groups revealed that egg production was reduced (p<0.05) in birds receiving FZ 800 mg/kg feed per day as compared with the controls. The present data suggest that FZ causes suppression in serum profiles of LH, oestradiol, cholesterol and ovarian functions in Rhode Island Red layer poultry birds. Therefore, great care must be taken with use of FZ in layer poultry birds (Gallus domesticus) with regard to dosage and duration of administration.