Precise identification of reef fishes caught in Toliara and Ranobe Bays, southwestern Madagascar
Creators: name: VOLANANDIANA, Jean Jubrice Anissa
name: PONTON, Dominique
name: RABERINARY, Daniel
name: JAONALISON, Henitsoa
name: LEOPOLD, Marc
name: BEHIVOKE, Faustinato
name: RANDRIATSA, Roddy Michel
name: DURAND, Jean-Dominique
Publisher: name: Zenodo
Year: 2022
Subjects: biodiversity
fish
identification
Madagascar
DNA Barcoding

description: Poster presented at the 12th WIOMSA Scientific Symposium, 10-15 october 2022, Port Elizabeth, South Africa

Abstract

Although reef fishes are the main targets of the small-scale fishery in southwestern Madagascar, precise names of the species caught by the different fishing gears remain largely unknown. However, signs of fisheries overexploitation such as decrease in fish size landed and the overall biomass of catches is more and more evident. The state assessment of the reef fisheries in southwestern Madagascar remains difficult due not only to the lack of regular monitoring data on landings, but also to the difficulty of precise identification of species. In order to improve the knowledge and typology of the species caught by the different fishing gears, a monthly monitoring of the catches by fishing gear was carried out in Toliara Bay and is ongoing in Ranobe Bay.  In order to provide identifications to the species as precise as possible, a double approach was adopted, including the characterization of the different morphospecies observed from morpho-anatomical characters and clearly explained coloration patterns, and on the other hand, the genetic variability of a fragment of cytochrome oxidase 1 (COI), i.e. the DNA barcode. This study aims  to improve the efficiency of reef fishes identification caught by different gears in Toliara and Ranobe Bays.

The study was based on the  images and caudal fin tip collection from fishers catches using the five main gears used in this region: gillnets, handlines, fishing guns, beach seines and bottom mosquito trawl nets. Images allowed to save time in the field for the description of anatomical characters; and fin tips were used as a DNA source for barcoding analyses. Sampling was done from May 2018 to April 2019 (Toliara Bay), and from October to December 2020 (Ranobe Bay). The collected images were coded and stored in Adobe Lightroom software. For each family, the individual images that were morphologically similar were grouped into a morphospecies. Each morphospecies was characterized by the external morphology and color patterns of the individuals. Morphospecies were then associated to a species name using images of barcoded individuals and from Fishbase; the obtained scientific names were called “hypothetical species”. The DNA sequences (COI) of at least one tissue per morphospecies were analyzed in the laboratory of the University of Montpellier.

A total of 2,193 individuals images were obtained and  classified in 64 families, 530 morphospecies and 452 hypothetical species. Fisher catches from both bays are dominated by Labridae. Beach seines and gillnets had the most common families (4), while gillnet and handline had the most common hypothetical species (23). Of the five gears, gillnets were the most diverse in terms of families (49), morphospecies (202) andhypothetical species (182). Preliminary results, based on 82 tissues samples, indicate that 55 sequences present less than or equal to 1% divergence with sequences present in Genbank. We found that 21 out of 55 hypothetical names matched the assigned names through DNA barcoding. These findings indicate the importance of molecular tool and the inefficiency of identification-based morpho-anatomical characters for some species.

Upon completion of DNA barcoding analyses, this study will be served as a diversity baseline of fish species characterizing each fishing gear in southwestern Madagascar. It will allow be used as a guideline to the good procedures that need to be implemented elsewhere in the Western Indian Ocean.