Search

Copyright of African Journal of Ecology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Crustaceana is the property of Brill Academic Publishers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Crustaceana is the property of Brill Academic Publishers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The purpose of this work was to investigate the physical and chemical dynamics of Lake Nokoué for its efficient management. For this purpose, two sampling campaigns per month from five stations (North, South, Central, East and West) were conducted for a period of one year (November 2020 to November 2021). Physic and chemical parameters (temperature, salinity, depth, water transparency, pH, dissolved oxygen and total dissolved solids) were measured and wet substrate samples were collected to study the granulometry. Data analysis revealed that Lake Nokoué is mainly affected by two regimes: flooding and low water. Flooding, which is not directly related to rainfall, did not begin until one month after the major rainy season in June. The sources that contributed to the flooding of Lake Nokoué were the freshwater tributaries coming mainly from the Ouèmé River and the flow of the Sô River from August to November. The inflow of fresh water contributed to the decrease in salinity and transparency of the lake from the east to the south. During the low water period (from December to July), Lake Nokoué is characterized by an increase in salinity and transparency from the south to the northeast due to the massive intrusion of sea water into the lake. The highest dissolved oxygen levels are observed in the south and center (5.92 ± 0.46 mg/L) while it varies greatly in the north and west (Eichhornia crassipes concentration zone) during flooding. The average annual depth of Lake Nokoué was 1.47 ± 0.66 m with an average annual pH of 6.85 ± 0.56. [ABSTRACT FROM AUTHOR]

Two experiments were conducted in order to determine the appropriate age and stocking density of vundu catfish Heterobranchus longifilis at the weaning time. In the first experiment, five triplicate groups of 100 larvae (initial mean weight=3.4 mg) per aquaria were stocked from first feeding [day 3 post-hatch (p.h.)] to day 30 p.h., and then weaned, on days 3 (W3), 5 (W5), 8 (W8) and 14 (W14), and an unweaned group (An). Significant differences were observed in growth, survival, cannibalism, coefficient of weight variation and body composition among larvae weaned at different ages and the control group. The later the larvae were weaned, the better were the growth performances [final mean weight: from 65.1 to 201.1 mg and specific growth rate (SGR): from 11.0 to 15.2% day−1] and the survival (from 36.5% to 74.3%). The experiment with stocking densities of 5, 10, 25 and 50 larvae L−1 showed that increasing the stocking density decreased growth performances and weight variation but improved the survival rate of larvae. The best growth performances (SGR=13.4 and 11.4% day−1) with the lowest survival rates (70.3% and 77.3%) were observed in larvae stocked at densities of 5 and 10 larvae L−1 respectively. [ABSTRACT FROM AUTHOR]

The effects of the use of Azolla filiculoides Lam., as an alternative source of protein, on growth performances and production of Nile tilapia, Oreochromis niloticus, reared in wetland ponds was evaluated. Three isonitrogenous (27% CP) and isocaloric (4019.14 kcal/g) diets A0, A10, and A20 containing three levels of Azolla 0, 10, and 20, respectively, as a partial substitution of fish meal, were fed to three triplicate ponds of male O. niloticus (initial mean weight = 15.5 g). The Azolla-free diet (0% Azolla) served as a control. The growth performances and production are good in all treatments after 90 days of experiment. No significant differences among dietary treatment (P > 0.05) were noticed for daily growth rate (1.15 g/day-1.26 g/day), specific growth rate (2.27-2.35%/day), survival (74.78-77.43%), annual fish production (31.01-32.75 kg/are/year), and feed conversion ratio (1.06-1.13). Thus, similar growth and production performances were observed with fishes fed with A0 and those fed with A20. Therefore, up to 20%of Azolla in the ration of O. niloticus has no negative effect on either growth or production. The cost-benefit analysis showed a considerable reduction in the production costs of one kilogram of fish with increasing Azolla levels in diet, amounting to US$0.09 between A0 and A10 (P > 0.05) and US$0.14 between A0 and A20 (P < 0.05). These results indicate that, on an isonitrogenous and isocaloric basis, using Azolla at up to 20% in a diet can constitute a viable alternative source of protein for O. niloticus in tropical wetlands. [ABSTRACT FROM AUTHOR]

Four feeding experiments were conducted to estimate the optimal daily food ration of Eurasian perch at different stages of its development under optimum rearing temperature (23 °C). Mean initial weights of 0.22-, 0.73-, 1.56- and 18.9-g fish, previously habituated to a dry diet, were used in experiments lasting between 14 and 30 days, depending on initial body weight. Daily feeding levels ranged from 2% to 20% of biomass in 0.22-g fish, from 1% to 8% in 0.73-g fish, from 1% to 10% of biomass in 1.56-g fish and from 0.3% to 3% of biomass for 18.9-g fish. Feeding levels significantly affected survival of perch, except in experiment 4 with large juveniles (18.9). In experiments 2 and 3 (with 0.73- and 1.56-g fish, respectively), cannibalism was significantly higher at the lowest feeding level (1% biomass day−1), while starvation seemed to be the major cause of death in experiment 1 with 0.22-g fish. Values of specific growth rate (SGR) plotted against daily food ration allowed the maintenance, optimum and maximum feeding levels to be determined, according to the Brett and Grove''s model. Optimum feeding level for Eurasian perch decreased from 7.4% to 5.1%, 4.5% and 2.2% biomass day−1 for fish of 0.22, 0.73, 1.56 and 18.9 g initial body weight, respectively. [Copyright &y& Elsevier]