Konan et al. J. Appl. Biosci. 2013. Caractérisation de la reproduction de Thysochromis ansorgii dan la foret des marais, Cote d'Ivoire
5716Reproductive characteristics of Thysochromis ansorgii (Pisces, Cichlidae) in the Tanoe-Ehy swamp forest (Côte d'Ivoire) Abstract: Objectives: The study investigates the reproductive traits of Thysochromis ansorgii (Boulenger, 1901) in the Tanoe-Ehy swamp forest (Côte d'Ivoire) which is characterized by acute seasonal variations of some environmental variables. Methodology and results: Fish capture, using fyke nets and fish traps, and environmental variable (temperature, dissolved oxygen, and water depth) measurements as well were done monthly from March 2012 through February 2013. Sex ratio for all fishes (1:0.9) was slightly in favour of female and size at first maturity was 68.5 and 80.9 mm SL for females and males respectively. The main breeding seasons determined (April-July and October-December) coincided with the rainy seasons (or sampling site flooded seasons) in which females produced more oocyts comparatively to the dry months. Conclusion and application of results: This study showed that temperature, dissolved oxygen and hydrological conditions have direct impact on both length of breeding period and the amount of oocyts produced by females. These data help suggest a closure of T. ansorgii capture by fishermen during April-June period in order to allow the majority of mature fishes to reproduce. In addition, the choice of fish capture gears (mainly gillnets) might refer to the maturity size determined for T. ansorgii.
22%). Based on advanced sexual maturity stages, 14 species in spawning period, were captured at the 11 sampling sites. Results of sediment analysis indicated a predominance of sand (> 60%) in spawning sites and optimal values of temperature (28.52°C), pH (6,53), conductivity (36,50 μS/cm) and dissolved oxygen (5,37 mg/l).
Conclusion and application of results:The present study showed that sites sampled in Lake Buyo located within the Tai National Park are characterized by sandy sediments and constitute spawning areas for several fish species. The location of these spawning areas therefore is an important tool for managers in conserving fish diversity of Taï National Park.
Aims: Information on ichthyoplankton is an important tool in determining reproduction periods that if associated to environmental variables. The abundance and distribution of ichthyoplankton and their relationships to some environmental variables of the water in Lake Buyo were analyzed. Preferred microhabitats for spawning, dispersion and nursery were also verified.
Place and Duration of Study: The study was conducted monthly from April 2019 through September 2019 in lake Buyo.
Methodology: Acylindro-conical net (500 µm in mesh opening size, 50 cm in mouth diameter) and stream net (7 mm in mesh opening size) were used.
Results: During the study period, the very lowest densities of eggs (1-2 ind/10 m3) and larvae were recorded in sites (S3 and S8) located relatively far from shoreline and the highest (186-724 ind/10 m3) in sites located near shoreline. The sites closed to littoral were identified as spawning areas by fish species during study period and sites located in deep water are not spawning sites. No significant difference between seasons was observed for each sampling site.
Conclusion: Eggs and larvae distribution in Lake Buyo was strongly influenced by water depth, water temperature, dissolved oxygen, percentage of gravel, percentage of coarse sand and proportion of very fine sand.
Sectors IV and V of the Ebrié lagoon are increasingly experiencing fish mortality. The abundance biomass comparison (ABC) is graphical method use to assess the level of environmental disturbance in this area. The aim of the study were to detect the environmental changes caused by anthropogenic activities using ABC curve of benthic macroinvertebrate assemblages presented in the studied areas. Results of the ABC analyses indicated that stations L, K and M are less stressed with biomass curve above abundance curve. Stations N and A recorded a stressed environment with abundance curve above biomass curve. The ABC plots showed that N and A stations could be classified as moderately disturbed and polluted. The Clarke's W index to the benthic macroinvertebrates data, confirmed this situation; it ranged from -0,129 (N) to 0,224 (L). The results of the present study can be extrapolated to other tropical wetland systems to predict the levels of disturbance and to identify characteristic organisms to predict the environmental conditions in the wetland health assessment program.
The study evaluated some population parameters of Polydactylus quadrifilis within Ebrié lagoon (Potou sector). Samples were obtained using artisanal gillnet fishery from April 2004 to March 2006. A total of 741 individuals of P. quadrifilis ranged from 11 to 70 cm were examined. Population parameters were estimated where asymptotic length (L∞) was found 60 cm, growth rate (K) 0.33 per year, the longevity (T max) 9.09 years, and growth performance index (Φ′) 3.06. The length at first capture (Lc50 = 10.60 cm) was lower than the length at first maturity (Lm50 = 40 cm). Total mortality rate (Z) was calculated as 1.10 per year including natural mortality and fishing mortality. The exploitation rate (E=0.36) was found to be less than the maximum exploitation rate (E max = 0.44) and indicated that P. quadrifilis is not overexploited. The current exploitation rate should be maintained by sustainable fisheries measures including monitoring of fishing effort.
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