Overview of the fish assemblage through the small-scale fishing analysis in the Betsiboka delta and estuary, northwestern Madagascar

WIOMSA 12th symposium, poster presentation, October 13th, 2-3pm

THEME XX: Fish ecology and biodiversity


Tsirilaza Benjamin (Univ. Tuléar),

Andriambeloson Johary Andriamihaja (IOGA) 

Rasoloariniaina Jean Robertin (Institut d’Enseignement Supérieur d’Antsirabe) 

Andriamirado Rabarison Guy Arthur (CNRE)


The estuary and delta is a transition zone between the continental and oceanic environment. Studies on fish population in deltaic and estuarine areas have a social and economic importance because these specific estuarine systems are under threats linked to the expansion of human activities. The fish assemblage is explored by fishing practices in the Betsiboka delta and estuary, to complete the previous studies on sedimentology, biochemistry and mangrove ecosystem. The study on estuary fish assemblage requires knowledge of salinity gradient due to a change in salinity will influence the fish distribution and their habitats.

64 stations measuring electrical conductivity were carried out to categorize the habitat. Field observations were made to determine the fishing practices in the delta. The characteristics of the fish population, such as species richness and size, were compared to the habitat characteristics by daily monitoring the small-scale fishery during the dry season (May - October 2021). After processing the data with QGIS by Inverse Distance Weighting, the Betsiboka water conductivity was mapping into freshwater (FW), brackish water (BW) and marine water (MW) zones. 8 types of fishing gear operate in this area, including 1 type in the FW zone, 5 in the BW zone and 4 in the MW zone. Some gear types are found in two observations zones. 48 species of fish and 4 species of crustaceans have been inventoried in the delta, of which 13 species are found in the FW zone, 18 in the BW zone and 24 in the MW zone. Two fish species are present in these 3 types of habitats.

Physico-chemical parameters of the water @ Benjamin Tsirilaza

The survey permitted to discuss the demography of the fish population in the Betsiboka Delta. The majority of the fish caught in the BW zone do not reach adulthood. The fish inventory in Betsiboka estuary showed a close and almost similar specific richness to the South African estuaries. Furthermore, monitoring during the raining season should be necessary to conclude on the fish population of the Betsiboka delta and estuary.


water electrical conductivity, traditional fishing, fish population, Betsiboka estuary