Growth performance of the rabbitfish Siganus sutor raised at outdoor rearing ponds in Toliara, SouthWestern Madagascar

In Madagascar, decrease of fish stock and poverty lead small scale fishermen to deploy destructive fishing gear. At Toliara Reef, fishermen using mosquito seine net catch up to 50% of juvenile fish and up to 42% of these juveniles belong only to the rabbitfish Siganus sutor species.This prohibited fishing practice disturbs the structure of adult fish populations and aquaculture may be one of the effective solutions to alleviate the problem of stock depletion. Rabbitfishes possess most of the desirable characteristics for aquaculture (e.g. herbivory and responsive to artificial food, high survival in high rearing densities) and the culture of several Siganus species have been tested in various countries. However, no study has been conducted on the rearing of S. sutor in Madagascar. Here, we investigated such a possibility regarding the growth performances and survival rate of S. sutor. Juveniles (initial mean body weight of 6.06g ± 2.43 and length of 6.23cm ± 0.8) were successfully retrieved from fishermen catches and we applied fish grow-out experiments in outdoor rearing pond (16m3) for a duration of five months. The rearing density was 8 fish/m3 and the performance of different diets were tested. A locally produced industrial fish food (composed of corn, soya flour, wheat, vitamins, oil…) at a feed ration of8% of fish biomass were compared with cooked rice at a feed ration of 25% of fish biomass. Dissolved oxygen, temperature, salinity, turbidity and pH were recorded three times a day along the experiment. Fish fed with industrial fish food had a significant higher growth (p<0.05) with a final mean body weight of 68.11g ± 26.71 and a final mean length of13.91cm ± 1.69. At the end of the experiment, fish fed with cooked rice displayed a mean body weight of 34.81g ± 15 and a mean length of 11.15cm ± 1.76. Feed conversion ratio is 2.99 for industrial food while it reaches up to 20.67 for the cooked rice. Surprisingly, fish fed with industrial food showed a significant lower survival rate (p<0.05) of 47.2%, compared to 95.7% for the cooked rice. Our study highlights the possibility of rearing juvenile rabbitfish in outdoor rearing pond using essentially locally produced industrial food. Controlling the rearing of juvenile rabbitfishes can be suggested as a practical approach to improve the survival rate of these juveniles through sea ranching and for improving livelihood of local communities through alternative activity

The potential nursery areas and recruitment seasons of Siganus sutor in Madagascar

editorial reviewedBackground Seagrass beds support the productivity of coastal fisheries by ensuring the survival of juvenile fishes and securing their recruitment in adult populations. This habitat is a preferred fishing area targeted by small-scale fishermen in developing countries, using Mosquito seine nets as observed in SW Madagascar. Previous studies revealed that seines nets caught large proportions of juveniles, especially dominated by Siganus sutor up to 42% of catches. In a conservation perspective, recruitment monitoring of this highly affected species is needed to provide key information related to their spatial and temporal distribution along the coastal habitats. This research aims at understanding recruitment patterns of S. sutor in critical habitats of SW Madagascar. The specific objectives are (a) to detect the recruitment seasons of S. sutor; (b) to identify their potential nursery areas; and (c) to understand why S. sutor select specific zones as a nursery area. Methods Catches from small scale fishers from mangroves, seagrass meadows, intermediate areas (i.e. sandy bottoms between seagrass patches and coral reefs) and seagrass associated to coral reefs were sampled with three stations per habitat and three days per month from July 2021 to June 2022. In meantime, ecological data related to surface temperature and salinity were recorded In the laboratory, all individuals were identified, photographed in order to automatically measure their size with ImageJ software. Another survey was carried out to address biological data (food availability) and habitat characteristics (depth, seagrass cover and diversity) in order to understand their influence on nursery areas selection for S. sutor. Results The catch of 5714 individuals shows that the abundance and size of rabbitfish exhibited a spatial and seasonal variability pattern. Rabbitfish size increased from habitats located near the coast compared to those near the reef. The smallest S. sutor size only occurred in the mangroves and seagrass meadows with 2.2 ±1.46 cm, against 4.2±1.48 for the intermediate areas and 5.1±1.47 seagrass associated with coral reefs. Considering abundance, juveniles of S. sutor is significantly more abundant in seagrass meadows (with 59.4%) while this species appeared to be rare in mangroves (<1%). This is indicated that this species did not colonize mangroves at an early stage. The small sized S. sutor were most abundant in seagrass meadow, suggesting this habitat could be the main nursery area for this species. Two recruitment seasons corresponding to the smallest mean size and the most abundant occurred in August 2021 and in January 2022 so far. This highlights the seasonality of S. sutor recruitment in SW Madagascar during warm and cool seasons. Conclusion To conclude, seagrass meadows constitutes the main nursery areas for S. sutor. Their massive settlement occurred in January (warm season) and August (cool season). Madagascar is characterized by two main recruitment season so far. As sampling will be completed in June 2022, results explaining why S. sutor choose seagrass meadows as a potential nursery will be available by August 2022 and will be presented. Such information will be useful for the decision making to develop management measures for the sustainable use of S. sutor resources and coastal habitats.Fish juvenile recruitment in coastal habitats of Western Indian Ocean14. Life below water11. Sustainable cities and communitie

Overview and progress of consortium research related to the biology, ecology and aquaculture of rabbitfish

editorial reviewedCoastal habitats support global fisheries by ensuring the survival of juvenile fishes. These habitats constitute one of the fishing areas targeted by small-scale fishermen in the least developed countries, including Madagascar. The accessibility of these habitats at low tides makes it an ideal fishing area for mosquito seine nets as observed for instance in SW Madagascar and beach seining in Kenya. However, this practice negatively impacts fisheries production due to catches of high numbers of juveniles, in Madagascar and Kenya mostly composed of shoemaker spinefoot rabbitfish (Siganus sutor). Despite Malagasy laws that forbid the deployment of mosquito seine nets, fishermen continue with their use. In Kenya, the beach seines have been outlawed but enforcement remains a challenge. This context highlights the need for management measures and alternative sources of income for a sustainable use of marine resources and for improving the fishermen livelihood. The ongoing consortium research entitled “Fish juvenile recruitment in coastal habitats of western Indian Ocean” was funded by MASMA program administered by WIOMSA. It is an interdisciplinary research program intending to understand recruitment patterns of shoemaker spinefoot rabbitfish (Siganus sutor) in coastal habitats of Kenya and Madagascar. It explores evidence-based solutions for improving the welfare of coastal communities and sustainable use of marine resources. Research activities were divided into four work packages. In WP1, Siganus sutor recruitment patterns in coastal habitats were targeted to identify the nursery ground and recruitment periods. It is based on juvenile fish sampling at four coastal habitats (mangroves, seagrass meadows, intermediate areas and seagrass associated with the coral reef) in Madagascar during twelve months. In WP2, sampling for the analysis of the population connectivity of S. sutor for detecting the sources of juveniles in the coastal habitats at five sites along the western coast of Madagascar was completed. In WP3, ecological models for predicting the arrival of newly settled S. sutor will be based on historical and newly collected data (WP1) using the random forests algorithm. Predictors are composed of remotely sensed oceanic conditions and a post-larval supply index calculated from post-larval sampling in the coastal habitats using light-traps. Like juvenile sampling, post-larval sampling was performed three nights per month which will cover all the juvenile sampling periods. In WP4, fish feeding behavior is studied and experiments on capture-based juvenile fish grow-out are ongoing at the Belaza aquaculture facilities (Toliara, Madagascar). Eight fish grow-out treatments focusing on three stocking densities, three fish diets, and pond dimensions are being tested. In WP1, about 5,720 juvenile individuals were obtained from 120 juvenile fish samples. The standard length of each of these individuals were measured for analyzing the spatial distribution of S. sutor. The nursery ground and recruitment seasons for S. sutor emerged from our research. The findings will be presented orally by PhD student Helga Berjulie Ravelohasina during the symposium. In addition, about 360 epifaunal community samples were obtained between July 2021 and April 2022. The spatial distribution of abundance, diversity and richness of epifauna associated with seagrass will be presented in a poster by MSc student Mory Justino. In WP2, at each location, 45 individuals were sampled, for a total of 225 adults for Madagascar and 180 from Kenya. Genotyping is in progress. In WP3, monitoring of the newly settled fish, in parallel with post-larval sampling, is in progress and should be completed by June 2022. In meantime, the extraction of remotely sensed oceanic conditions covering the sampling periods is being processed with R programming for the period. In WP4, preliminary results on fish grow-out identified the best fish diet and the most optimal stocking density at the smallest size (about 2 cm of standard length). More details related to these findings will be presented in a poster by master student Nandrianina Maminantenaina. In addition, the gut content and stage isotopes of three ontogenetic stages (i.e. post-larvae, juvenile, and adult) of S. sutor were analysed the natural trophodynamics. The findings are based on 1160 gut contents and muscle tissue samples collected during the warm (October 2021 to February 2022) and cool season (May to August 2022). The potential nursery areas and the main recruitment seasons of Siganus sutor were identified. The oral presentation entitled “The potential nursery areas and recruitment season of S. sutor in Madagascar” by Helga Berjulie Ravelohasina will provide further details of our findings. The variability of food availability related to epifauna concentration will be known in the poster on Mory Justino. The most optimal fish diet as well as the optimal stocking density will be presented in a separate poster entitled “Density and fish diet effect on rabbitfish growth in controlled systems” presented by Nandrianina Maminantenaina.Biology, ecology and aquaculture of rabbitfish14. Life below water2. Zero hunger11. Sustainable cities and communitie

The early life stages of fish in SW Madagascar : elements for a better knowledge and a better management of exploited resources

Les écosystèmes marins qui fournissent de multiples services écosystémiques indispensables au bien-être de l’humanité sont actuellement menacés par la surexploitation des ressources et l’utilisation d’engins destructifs. Ceci conduit à une perte à l’échelle globale de 20% des mangroves, 19% des récifs coralliens et 110 km2 par an des herbiers. Les habitats côtiers qui soutiennent jusqu’à 20% de la production globale de la pêche sont les plus touchés, notamment dans les pays les moins avancés comme Madagascar. Dans ce pays, 87% des écosystèmes récifaux sont menacés, notamment dans le sud-ouest où les petits pêcheurs utilisent des engins prohibés capturant les juvéniles. Une meilleure connaissance de l’écologie des jeunes poissons est donc un point clé pour la mise en place des mesures de gestion efficaces et robustes. D’où l’objet de ce présent travail centré sur les jeunes stades de développement des poissons, identifiés en utilisant le barcoding ADN. Les identifications à l’espèce ont permis de prédire l’approvisionnement en post-larves et de découvrir la variabilité du recrutement en juvéniles qui semble liée à l’altération des apports en post-larves. Au total, 387 espèces ont été observées avec 9 nouvelles espèces pour Madagascar. L’intérêt et les limites du barcoding ADN sont largement discutés (chapitre 1). L’approvisionnement en post-larves a été mieux prédit par les conditions océaniques obtenues par télédétection avec une précision de 60% pour la richesse et 50% pour l’abondance. Pourtant, la performance des modèles pour prédire l’abondance semble influencée par les caractéristiques des masses d'eau qui sont différentes entre les deux sites, tandis que la performance pour prédire la richesse parait similaire entre ces deux sites (chapitre 2). Les conditions océaniques obtenues par télédétection expliquent mieux les assemblages de post-larves. Pourtant, ces conditions océaniques structurent davantage les assemblages de post-larves dans les masses d'eau présentant des caractéristiques d’eaux côtières que ceux dans les eaux présentant des caractéristiques océaniques (chapitre 3). La période de recrutement et les assemblages de juvéniles diffèrent entre les années. Ces variabilités interannuelles ont été aussi observées dans l’approvisionnement en post-larves qui semble conditionné par les variations des conditions océaniques. Ce qui suggère que les altérations des apports en post-larves influencent la distribution temporelle des juvéniles (chapitre 4). Le cas du recrutement des juvéniles de Siganidae, qui semble être fortement en lien avec les apports en post-larves, est développé dans la discussion générale. De même, la localisation des zones de nourriceries a permis de proposer des mesures de gestion tenant compte du contexte local qui sont aussi discutées.Marine ecosystems which provide multiple ecosystem services essential to human well-being are currently threatened by resources overexploitation and the use of destructive fishing gears. This leads to a global loss of 20% of mangroves, 19% of coral reefs, and 110 km2 per year of seagrass meadows. The coastal habitats that support up to 20% of global fisheries production are the most affected, particularly in least developed countries such as Madagascar. In this country, 87% of coral reef are threatened, particularly in the southwestern part of the island where small-scale fishermen practice juveniles fishing. A better knowledge of the ecology of young fishes is thus a key point for the implementation of effective and robust measures. The present work was centred on early developmental stages of fish identified using DNA barcoding. Identifications to the species level were used to predict the post-larvae supply and to discover the variability in juveniles recruitment that appears to be related to the alteration of post-larvae supply. In total, 387 species have been observed with nine new species for Madagascar. The interests and limitations of DNA barcoding are widely discussed in Chapter 1. Post-larvae supply was better predicted by the remotely sensed oceanic conditions with an accuracy of 60% for species richness and 50% for abundance. However, the performance of models for predicting abundance appears to be influenced by the characteristics of water masses that are different among sites, while the performance of models for predicting species richness appears similar between the sites (discussed in Chapter 2). The remotely sensed oceanic conditions better explained the post-larval fish assemblages. However, these oceanic conditions structure mostly the post-larval fish assemblages in water masses with coastal water characteristics than those in waters with ocean characteristics (discussed in Chapter 3). The period of juvenile recruitment as well as juvenile assemblages differ among years. These interannual variabilities were also observed on post-larvae supply which were conditioned by the interannual variation of oceanic conditions. This suggests that alterations in post-larvae supply influence the temporal distribution of juvenile fish, which is a subject discussed in Chapter 4. The case of Siganidae recruitment, which seems to be strongly linked to post-larvae supply, is developed in the final discussion of this thesis. Likewise, the identification of nursery areas allows to propose management measures to deal with the local context that are also discussed

Les premiers stades de vie des poissons dans le SO de Madagascar : éléments pour une meilleure connaissance de la biodiversité et une meilleure gestion des ressources exploitées

Marine ecosystems which provide multiple ecosystem services essential to human well-being are currently threatened by resources overexploitation and the use of destructive fishing gears. This leads to a global loss of 20% of mangroves, 19% of coral reefs, and 110 km2 per year of seagrass meadows. The coastal habitats that support up to 20% of global fisheries production are the most affected, particularly in least developed countries such as Madagascar. In this country, 87% of coral reef are threatened, particularly in the southwestern part of the island where small-scale fishermen practice juveniles fishing. A better knowledge of the ecology of young fishes is thus a key point for the implementation of effective and robust measures. The present work was centred on early developmental stages of fish identified using DNA barcoding. Identifications to the species level were used to predict the post-larvae supply and to discover the variability in juveniles recruitment that appears to be related to the alteration of post-larvae supply. In total, 387 species have been observed with nine new species for Madagascar. The interests and limitations of DNA barcoding are widely discussed in Chapter 1. Post-larvae supply was better predicted by the remotely sensed oceanic conditions with an accuracy of 60% for species richness and 50% for abundance. However, the performance of models for predicting abundance appears to be influenced by the characteristics of water masses that are different among sites, while the performance of models for predicting species richness appears similar between the sites (discussed in Chapter 2). The remotely sensed oceanic conditions better explained the post-larval fish assemblages. However, these oceanic conditions structure mostly the post-larval fish assemblages in water masses with coastal water characteristics than those in waters with ocean characteristics (discussed in Chapter 3). The period of juvenile recruitment as well as juvenile assemblages differ among years. These interannual variabilities were also observed on post-larvae supply which were conditioned by the interannual variation of oceanic conditions. This suggests that alterations in post-larvae supply influence the temporal distribution of juvenile fish, which is a subject discussed in Chapter 4. The case of Siganidae recruitment, which seems to be strongly linked to post-larvae supply, is developed in the final discussion of this thesis. Likewise, the identification of nursery areas allows to propose management measures to deal with the local context that are also discussed.Les écosystèmes marins qui fournissent de multiples services écosystémiques indispensables au bien-être de l’humanité sont actuellement menacés par la surexploitation des ressources et l’utilisation d’engins destructifs. Ceci conduit à une perte à l’échelle globale de 20% des mangroves, 19% des récifs coralliens et 110 km2 par an des herbiers. Les habitats côtiers qui soutiennent jusqu’à 20% de la production globale de la pêche sont les plus touchés, notamment dans les pays les moins avancés comme Madagascar. Dans ce pays, 87% des écosystèmes récifaux sont menacés, notamment dans le sud-ouest où les petits pêcheurs utilisent des engins prohibés capturant les juvéniles. Une meilleure connaissance de l’écologie des jeunes poissons est donc un point clé pour la mise en place des mesures de gestion efficaces et robustes. D’où l’objet de ce présent travail centré sur les jeunes stades de développement des poissons, identifiés en utilisant le barcoding ADN. Les identifications à l’espèce ont permis de prédire l’approvisionnement en post-larves et de découvrir la variabilité du recrutement en juvéniles qui semble liée à l’altération des apports en post-larves. Au total, 387 espèces ont été observées avec 9 nouvelles espèces pour Madagascar. L’intérêt et les limites du barcoding ADN sont largement discutés (chapitre 1). L’approvisionnement en post-larves a été mieux prédit par les conditions océaniques obtenues par télédétection avec une précision de 60% pour la richesse et 50% pour l’abondance. Pourtant, la performance des modèles pour prédire l’abondance semble influencée par les caractéristiques des masses d'eau qui sont différentes entre les deux sites, tandis que la performance pour prédire la richesse parait similaire entre ces deux sites (chapitre 2). Les conditions océaniques obtenues par télédétection expliquent mieux les assemblages de post-larves. Pourtant, ces conditions océaniques structurent davantage les assemblages de post-larves dans les masses d'eau présentant des caractéristiques d’eaux côtières que ceux dans les eaux présentant des caractéristiques océaniques (chapitre 3). La période de recrutement et les assemblages de juvéniles diffèrent entre les années. Ces variabilités interannuelles ont été aussi observées dans l’approvisionnement en post-larves qui semble conditionné par les variations des conditions océaniques. Ce qui suggère que les altérations des apports en post-larves influencent la distribution temporelle des juvéniles (chapitre 4). Le cas du recrutement des juvéniles de Siganidae, qui semble être fortement en lien avec les apports en post-larves, est développé dans la discussion générale. De même, la localisation des zones de nourriceries a permis de proposer des mesures de gestion tenant compte du contexte local qui sont aussi discutées

Variation of the trophic ecology in two teleost species associated to seagrass beds at Toliara Reef (Madagascar)

editorial reviewedSmall scale fishermen in Toliara (South West of Madagascar) extensively use small mesh seine nets in the seagrass zones and this practice may affect the structure of seagrass-associated fishes by catching small fish, juvenile and even post-larvae. The general objective of the present study is to evaluate the trophic ecology of two dominant teleost species (the rabbitfish Siganus sutor and the goby Oplopomus oplopomus) from catches of local fishermen using bottom seine nets. More specifically, this study aims to evaluate the temporal and spatial variation of the trophic ecology of those species by using stable isotopes and stomach contents. The sampling was carried out in seagrass beds in front of two villages: Ankilibe on December 2017 and 2018, and in Sarodrano on December 2018. To assess variation in diet, stomach content analyses were performed on 40 specimens/species/village/year. Preys were identified to the level of class and then assigned to different food groups. Stable isotope analyses were performed on muscles to complete information on variation in feeding habits. The combination of these methods revealed that the diet of species varies according to the year and the site of collection. This probably results from plasticity and accommodation to the availability of food sources and changes in environmental factors. In both species, the type of food consumed remains the same but the difference is observed in the frequency and the abundance of prey. Trophic variation is also observed over relatively long period of time as it is confirmed by stable isotope analyses. This study clearly demonstrates the trophic ecology of these two seagrass-associated fishes vary across time and space but additional works are now needed to understand which factors drive this variation.2. Zero hunger1. No povert

Spatial trophic plasticity of two dominant seagrass-associated fishes in Toliara lagoon (SW Madagascar)

In the seagrass zone of Toliara (South West of Madagascar), the local fishermen deployed seine nets with small mesh size that likely affect the structure of seagrass meadow systems and associated fishes. Nevertheless, the responses of fish communities living in this ecosystem to these threats are currently unknown for the WIO region. This present study aims to evaluate the trophic diversity of fishes living in seagrass beds and to assess their trophic plasticity. More specifically, along this work, we compare the diet of two dominant species (the rabbitfish Siganus sutor and the goby Oplopomus oplopomus) found in the catches of local fishermen on seagrass beds and we evaluate a potential variation in their trophic ecology. The sampling of fishes was achieved by collecting the catches of traditional fishermen using bottom seine nets. Fish sampling occurred in front of the Ankilibe fisherman village in December 2017 and 2018, and in front of the village of Sarodrano (December 2018). This sampling strategy allowed us to make spatial and temporal comparisons. In order to assess the diet of these two fish species, stomach content analyses was performed on 40 specimens/species/village/year. Using a binocular microscope, animal preys were identified to the level of class and assigned to the planktonic or the benthic compartment. Plant items are classified as either phytoplankton, fragments of algae, or seagrasses. The trophic niche of each fish populations was quantified in two ways: as a percentage of occurrence and as a mean percent composition of each item in the gut content. The rabbitfish has gut filled by 50% of detritus, 40% of fragments of seagrass, and 10% of phytoplankton. The diet of the goby was more diversified and composed of 40% of detritus, 25% of copepods, 20% of operculum, 10% of gastropods and 5% of ostracods. There was no significant difference between the two sites along the two years of campaign. An isotopic analyses will be effectuated soon to know the trophic position of the studied fishes

Annotated checklist of the fishes of Madagascar, southwestern Indian Ocean, with 158 new records

International audienceAn annotated checklist of the fish species of the Madagascar EEZ (southwestern Indian Ocean) comprises a total of 1,798 species in 247 families. 158 species are recorded from Madagascar for the first time. The majority of the species is autochthonous; 28 species have been introduced, mainly in freshwater habitats. The fish fauna is mostly marine (95.4% of the total number of native fish species), with the Gobiidae, Labridae, Serranidae, Pomacentridae and Apogonidae being the families with most representatives; among the 90 native freshwater fish species (adults mainly occurring in freshwater), the Cichlidae are the dominating family, but there are also two endemic families, the Bedotiidae (16 species) and Anchariidae (6 species). The fish fauna at Madagascar is typical for offshore, high islands in the southwestern Indian Ocean. Zoogeographically, the main element of the marine fish fauna of Madagascar consists of widespread tropical Indo-Pacific species (978 species, 58.3% of the total native marine species). A total of 13 species (3.3%) are found worldwide, either circumtropical or circumtropical including warm temperate zones. A total of 215 species (12.8%) are found worldwide, either circumtropical or circumtropical including warm temperate zones. An additional 453 species (27.0%) are Indian Ocean endemics, including 233 western Indian Ocean endemics (13.9%), 73 southwestern Indian Ocean endemics (4.4%), 16 species endemic to Madagascar and Mascarenes (1.0%), 4 species endemic to Madagascar and Comoros (0.2%), 3 species endemic to Madagascar and Madagascar Ridge(0.2%), and 37 marine species endemic to Madagascar (2.2%). Most of the autochthonous freshwater fishes are endemic to Madagascar (87 species, 96.7% of the native freshwater species)

Spatial and interannual variability of presettlement tropical fish assemblages explained by remote sensing oceanic conditions

Understanding the interannual effect of various environmental factors on biodiversity distribution is fundamental for developing biological monitoring tools. The interannual variability of environmental factors on presettlement fish assemblages (PFAs) has been so far under investigated, especially in Madagascar. Numerous explanatory variables including local hydro-dynamic conditions recorded during the sampling night, characteristics of the benthic substrate and remotely sensed oceanic conditions (RSOC) were used to explain the spatio-temporal variability of PFAs in southwestern Madagascar. Gradient forest analyses were used to hierarchically classify the effect of these explanatory variables on the PFAs for two sites and during two different recruitment seasons. RSOC variables appeared to better explain the PFAs than the local variable and the characteristics of the benthic substrate. The PFAs caught in water masses with coastal characteristics were better explained than those with open water characteristics. This spatial variability is hypothesised to be linked to differences in feeding conditions among water masses. The gradient forest analyses also highlighted the complexity of predicting PFAs as the species for which abundances were better explained by RSOC variables varied between years. This interannual variability was mainly explained by the interannual variation of chlorophyll a (Chl a) concentration, wind and surface current, with better prediction obtained during the year with high Chl a values associated with high averaged sea surface temperature. These findings suggest the importance of forecasting Chl a concentrations, taking into account the impact of tropical storms and climate variability in order to predict PFAs in the future

Application of DNA Barcoding for Monitoring Madagascar Fish Biodiversity in Coastal Areas

Madagascar is a marine biodiversity hotspot. A recent checklist recorded 1689 marine or transitional water fish species, 2.5% being endemic. To date, studies in this country were mostly focused on adult fishes using morphological-based identification. The early life stages of fishes remain largely understudied. The present work aimed to improve knowledge of fish biodiversity in Madagascar by focusing on post-larval reef fishes and settled juveniles in seagrass meadows of southwest Madagascar by using either species identification keys or DNA barcoding. Up to 119,500 individuals were collected, and 1096 individuals were successfully barcoded. We identified 387 species—85 through their morphology (with 58 unsuccessfully sequenced) and 302 by using CO1 barcoding corresponding to 302 barcode index numbers (BINs). This study added 27 new BINs for the BOLD database, 120 new for Madagascar, but only 159 were assigned a precise species name. By referring to the updated checklist of Madagascar fishes, 10 new species were detected for Madagascar. This number will probably increase when all the barcoded specimens become assigned to precise species names. These preliminary findings stress our poor knowledge of marine fish biodiversity in Madagascar and demonstrate the relevance of DNA barcoding in improving this knowledg