Caractérisation De La Pêche Au Lac Kivu

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

Do sex reversal procedures differentially affect agonistic behaviors and sex steroid levels depending on the sexual genotype in Nile tilapia?

peer reviewedIn Nile tilapia Oreochromis niloticus, phenotypic males and females with different sexual genotypes (XX, XY, YY) have particular behavioural 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 17β-oestradiol 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 behaviour of adults independently of their genotype. In both hypotheses (genotype or sex reversal influence), the causes of behavioural modifications have to be searched in an early modification of the brain sexual differentiation

Influence of sexual genotype on agonistic behaviors and sex steroid levels of phenotypic males and females in the Nile tilapia (Oreochromis niloticus)

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, lateral attack, frontal display, tail beating, mouth fighting and biting. For steroid assay, blood was sampled on 10 individuals of each phenotype/genotype combination. Testosterone (T), 17beta-estradiol (E2) and 11-ketotestosterone (11KT) were measured by radioimmunoassay. Expression of aggressive behaviors was significantly higher in couples with a XY or YY female than in MXY×FXX. The mean durations (in % of total time) of threatening behavior expression were respectively 41 ± 3 and 8 ± 1 %; and the mean frequencies of attacking behaviors were 110 ± 7 and 25 ± 5 n h-1. Expression level of agonistic behaviors in MXY staged with FXY or FYY seems to be adjusted to the aggressiveness level of females. Aggressiveness level was low and similar in MXY×FXX, MXX×FXX and MYY×FXX crosses. When comparing males together in these 3 crosses, only MXX showed a slightly but significantly higher expression of aggressive behaviors. Compared to normal MXY, MXX had significantly higher levels of circulating 11KT (16.0 ± 4.1 and 26.5 ± 4.2 ng mL-1 respectively), that could be related to their higher aggressiveness. However, no similar difference was reported between females. E2 concentrations were similar between males (mean: 4.0 ± 0.4 ng mL-1) and increased in females with the presence of Y chromosome(s) (FXX: 6.5 ± 1.4, FXY: 9.5 ± 1.7 and FYY: 14.1 ± 2.2 ng mL-1). These results raised the question of an involvement of E2 in the control of agonistic behaviors in females. No influence of the genotype was observed on T levels. 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, in which the level of aggressiveness is paradoxically higher in XX, we can hypothesize that the differences in aggressiveness are not directly dependant on the genotype but on the sex reversal procedures which young fry were exposed to during their sexual differentiation. These hormonal treatments could have permanently modified the development of the brain and consequently influenced the behavior of adults independently to their genotype. The role of endogenous steroids in agonistic behaviors needs further clarification

Need for harmonized long-term multi-lake monitoring of African Great Lakes

To ensure the long-term sustainable use of African Great Lakes (AGL), and to better understand the functioning of these ecosystems, authorities, managers and scientists need regularly collected scientific data and information of key environmental indicators over multi-years to make informed decisions. Monitoring is regularly conducted at some sites across AGL; while at others sites, it is rare or conducted irregularly in response to sporadic funding or short-term projects/studies. Managers and scientists working on the AGL thus often lack critical long-term data to evaluate and gauge ongoing changes. Hence, we propose a multi-lake approach to harmonize data collection modalities for better understanding of regional and global environmental impacts on AGL. Climate variability has had strong impacts on all AGL in the recent past. Although these lakes have specific characteristics, their limnological cycles show many similarities. Because different anthropogenic pressures take place at the different AGL, harmonized multi-lake monitoring will provide comparable data to address the main drivers of concern (climate versus regional anthropogenic impact). To realize harmonized long-term multi-lake monitoring, the approach will need: (1) support of a wide community of researchers and managers; (2) political goodwill towards a common goal for such monitoring; and (3) sufficient capacity (e.g., institutional, financial, human and logistic resources) for its implementation. This paper presents an assessment of the state of monitoring the AGL and possible approaches to realize a long-term, multi-lake harmonized monitoring strategy. Key parameters are proposed. The support of national and regional authorities is necessary as each AGL crosses international boundaries

Need for harmonized long-term multi-lake monitoring of African Great Lakes

To ensure the long-term sustainable use of African Great Lakes (AGL), and to better understand the functioning of these ecosystems, authorities, managers and scientists need regularly collected scientific data and information of key environmental indicators over multi-years to make informed decisions. Monitoring is regularly conducted at some sites across AGL; while at others sites, it is rare or conducted irregularly in response to sporadic funding or short-term projects/studies. Managers and scientists working on the AGL thus often lack critical long-term data to evaluate and gauge ongoing changes. Hence, we propose a multi-lake approach to harmonize data collection modalities for better understanding of regional and global environmental impacts on AGL. Climate variability has had strong impacts on all AGL in the recent past. Although these lakes have specific characteristics, their limnological cycles show many similarities. Because different anthropogenic pressures take place at the different AGL, harmonized multi-lake monitoring will provide comparable data to address the main drivers of concern (climate versus regional anthropogenic impact). To realize harmonized long-term multi-lake monitoring, the approach will need: (1) support of a wide community of researchers and managers; (2) political goodwill towards a common goal for such monitoring; and (3) sufficient capacity (e.g., institutional, financial, human and logistic resources) for its implementation. This paper presents an assessment of the state of monitoring the AGL and possible approaches to realize a long-term, multi-lake harmonized monitoring strategy. Key parameters are proposed. The support of national and regional authorities is necessary as each AGL crosses international boundaries