Papers by Akonkwa Balagizi
Mechanisms of sex determination and differentiation are extremely labile in fish, as demonstrated... more Mechanisms of sex determination and differentiation are extremely labile in fish, as demonstrated by the numerous sex reversal experiments performed on teleosts. In Nile tilapia, sex reversal processes using exogenous sex steroids allow to produce individuals with atypical sexual genotypes that constitute major tools to investigate the mechanisms of sex determination and differentiation, from gonad differentiation to sexual differentiation of brain and behavior. The aim of this study was to assess the influence of sexual genotype and the role of circulating sex steroids on the expression of agonistic behaviors in Nile tilapia breeders. Observations were carried out on fights staged between one male (M) and one female (F) acclimatized in 250-L aquaria at 27°C. Agonistic behaviors were recorded (for 25 min) in five crosses (6 repetitions with different pairs): MXY×FXX (control), MXY×FXY, MXY×FYY, MXX×FXX and MYY×FXX. Quantified behaviors were: fin raising, throat swelling, chasing, la...
POSTER De 1960 a 2012, le niveau des eaux du lac Kivu avait connu une baisse de 0,58 m, situation... more POSTER De 1960 a 2012, le niveau des eaux du lac Kivu avait connu une baisse de 0,58 m, situation imputable aux variations climatiques des dernieres decennies (Balagizi et al . 2015). En plus, l’usage des engins de peche non conformes a la conservation des ressources aquatiques a ete constate dans la pecherie de ce lac (Akonkwa et al ., sous presse). Ainsi, cette etude se focalise sur l’evaluation des impacts de la peche et des variabilites climatiques sur le peuplement de poissons du lac Kivu. Les effectifs et biomasses par espece de poisson, issus des differentes pratiques de peche, les degres de maturation des gonades des poissons, les valeurs de facteur de condition K de l’espece Limnothrissa miodon , les stations et habitats de peche, les donnees sur l’evolution du niveau des eaux, ont ete consideres. Dans ce lac, la communaute des poissons de la partie sud-ouest apparait comme la plus stressee a cause des pratiques de peche utilisant des filets a petites mailles dont les tulle...
The climate change, its variability and impact on fish catches in Lake Kivu, were verified from t... more The climate change, its variability and impact on fish catches in Lake Kivu, were verified from the analysis of climate variables and fisheries statistics. The results show qualitative and quantitative disturbances in the variation of rainfall, significant increase in temperature of 1.57°C, 0.63°C and 0.66°C at Kamembe, Gisenyi and Lwiro, respectively around Lake Kivu watershed. The relative humidity decreased significantly by 4.5% and 7% at Gisenyi and Kamembe, respectively; the wind speed decreased by 3 m/s. These changes resulted in a decrease of 0.58 m in water level of the lake, followed by periods of declines in catches of Limnothrissa miodon, the major lake’s commercial fish. Predictions show a decline in Catch per Unit Effort of 2.92 kg for approximate reduction of 0.01 m water level by 2025. Strategic policies should be made and adaptation measures be taken to prevent the climate change, in order to conserve the aquatic resources and avoid advert conditions in fisheries sec...
Journal of Experimental Zoology Part A: Ecological and Integrative Physiology, 2017
In Nile tilapia Oreochromis niloticus, phenotypic males and females with different sexual genotyp... more In Nile tilapia Oreochromis niloticus, phenotypic males and females with different sexual genotypes (XX, XY, YY) have particular behavioral and physiological traits. Compared to natural XX females and XY males, XY and YY females and XX males expressed higher level of aggressiveness that could be related to higher levels of 17-estradiol and 11-ketotestosterone, respectively. Our results suggest that the presence of a Y chromosome increases aggressiveness in females. However, since the same relationship between aggressiveness and the Y chromosome is not observed in males, we can hypothesize that the differences in aggressiveness are not directly dependent on the genotype but on the sex reversal procedures applied on young fry during their sexual differentiation to produce these breeders. These hormonal treatments could have permanently modified the development of the brain and consequently influenced the behavior of adults independently of their genotype. In both hypotheses (genotype or sex reversal influence), the causes of behavioral modifications have to be searched in an early modification of the brain sexual differentiation.
European Scientific Journal, ESJ, 2017
This study was focused on the description of fishing gears on Lake Kivu. Data were collected from... more This study was focused on the description of fishing gears on Lake Kivu. Data were collected from March 2012 to February 2014 in Goma, Bukavu, and Kibuye fishing stations. The study findings indicate that gill nets, beach seine, lift net, trammel net composed of two panels of small and larger meshes (mosquito net attached to lift net parts), mosquito net, longline, single line, pots, and cast net were identified as fishing gears used on Lake Kivu. Longline was more selective (2 species) in terms of species selection. The lift net presented the best catch (19.4 ± 11 kg), while the trammel net showed the highest CPUE (7.9 ± 6.1 kg/h). The large dimensions of gears and the long netting duration characterized gillnets (1023.2 ± 620.1 m2 ) and longline (10.3 ± 4.6 hours) respectively. Cast-nets (20mm) showed the largest mesh size, while mosquito nets (1 ± 0.3 mm) were the smallest.
Journal of Fish Biology, 2020
Haplochromis pharyngalis and H. petronius, two endemic cichlids from the Lake Edward system (Ugan... more Haplochromis pharyngalis and H. petronius, two endemic cichlids from the Lake Edward system (Uganda, DR Congo), are very similar in general morphology, but have been reported to differ in pharyngeal jaw morphology and distribution. We analysed 51 morphometrics and various qualitative characteristics of 48 specimens from different localities. The morphological traits of both species strongly overlap and differences in the pharyngeal jaw morphology correspond to a geographic morphocline. We conclude that all specimens belong to one valid species, H. pharyngalis, and consider H. petronius to be a synonym.
In Nile tilapia Oreochromis niloticus, phenotypic males and females with different sexual genotyp... more In Nile tilapia Oreochromis niloticus, phenotypic males and females with different sexual genotypes (XX, XY, YY) have particular behavioral and physiological traits. Compared to natural XX females and XY males, XY and YY females and XX males expressed higher level of aggressiveness that could be related to higher levels of 17í µí»½-estradiol and 11-ketotestosterone, respectively. Our results suggest that the presence of a Y chromosome increases aggressiveness in females. However, since the same relationship between aggressiveness and the Y chromosome is not observed in males, we can hypothesize that the differences in aggressiveness are not directly dependent on the genotype but on the sex reversal procedures applied on young fry during their sexual differentiation to produce these breeders. These hormonal treatments could have permanently modified the development of the brain and consequently influenced the behavior of adults independently of their genotype. In both hypotheses (genotype or sex reversal influence), the causes of behavioral modifications have to be searched in an early modification of the brain sexual differentiation.
This study was focused on the description of fishing gears on Lake Kivu. Data were collected from... more This study was focused on the description of fishing gears on Lake Kivu. Data were collected from March 2012 to February 2014 in Goma, Bukavu, and Kibuye fishing stations. The study findings indicate that gill nets, beach seine, lift net, trammel net composed of two panels of small and larger meshes (mosquito net attached to lift net parts), mosquito net, longline, single line, pots, and cast net were identified as fishing gears used on Lake Kivu. Longline was more selective (2 species) in terms of species selection. The lift net presented the best catch (19.4 ± 11 kg), while the trammel net showed the highest CPUE (7.9 ± 6.1 kg/h). The large dimensions of gears and the long netting duration characterized gillnets (1023.2 ± 620.1 m 2) and longline (10.3 ± 4.6 hours) respectively. Cast-nets (20mm) showed the largest mesh size, while mosquito nets (1 ± 0.3 mm) were the smallest.
The climate change, its variability and impact on fish catches in Lake Kivu, were verified from t... more The climate change, its variability and impact on fish catches in Lake Kivu, were verified from the analysis of climate variables and fisheries statistics. The results show qualitative and quantitative disturbances in the variation of rainfall, significant increase in temperature of 1.57°C, 0.63°C and 0.66°C at Kamembe, Gisenyi and Lwiro, respectively around Lake Kivu watershed. The relative humidity decreased significantly by 4.5% and 7% at Gisenyi and Kamembe, respectively; the wind speed decreased by 3 m/s. These changes resulted in a decrease of 0.58 m in water level of the lake, followed by periods of declines in catches of Limnothrissa miodon, the major lake’s commercial fish. Predictions show a decline in Catch per Unit Effort of 2.92 kg for approximate reduction of 0.01 m water level by 2025. Strategic policies should be made and adaptation measures be taken to prevent the climate change, in order to conserve the aquatic resources and avoid advert conditions in fisheries sector of Lake Kivu.
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Papers by Akonkwa Balagizi