Seaweed farming offers a sustainable solution to malnutrition and economic challenges in southwestern Madagascar. This study assessed the seasonal performance of 12 edible seaweed species and optimized cultivation parameters for Gracilaria corticata and Gracilaria salicornia using long-line aquaculture. Environmental factors, including temperature, light intensity, salinity, and current speed, were monitored across warm and cool seasons. G. corticata, G. salicornia, and Hormophysa cuneiformis exhibited the highest retention rates (>50 %) and growth performance, with G. corticata demonstrating significant superior growth in both seasons. Smaller cuttings (0–50 g) achieved higher retention and specific growth rates, particularly in the first 30 days. Growth was significantly influenced by light intensity (4209.35 ± 3274.72 lux in the warm season; 3107.77 ± 3194.22 lux in the cool season) and temperature (30.20 ± 1.26 °C in the warm season; 24.83 ± 0.35 °C in the cool season), with optimal conditions occurring in the warm season. These findings highlight the potential of G. corticata and G. salicornia for sustainable aquaculture, contributing to species diversification and food security. Optimizing environmental conditions and cutting sizes is crucial for maximizing seaweed productivity in Madagascar.

The spatial and temporal distribution of macroalgal assemblages at 10 sites in the Baie de Ranobe and Baie de Toliara in southwestern Madagascar were investigated during warm (February to March) and cool (July to August) seasons. Algal species were identified and coverage estimated at six habitats between the shore and 15 m depth, based on surveys with 0.5 m x 0.5 m quadrats along transects of 30 m long by 5 m broad. Ninety eight taxa (53 red, 24 green, 21 brown) were identified of which 42 were edible. Species dominance varied by bay and season, with Sargassum latifolium dominating during the warm season, and Hypnea musciformis and Ulva lactuca prevalent during the cool season. Algal cover did not differ significantly between bays, but cover differed significantly between habitats. S. latifolium, U. lactuca, and H. musciformis were prominent on the algal shelf, Ulva reticulata on the inner shelf, and Amansia rhodantha on the outer shelf. Edible seaweed proportions increased during the cool season, particularly at algal and inner-shelf habitats. Generalized Linear Model analysis confirmed significant differences in edible algal cover across habitats and seasons. The potential of sustainably using macroalgae for aquaculture and human consumption in southwestern Madagascar is highlighted.

We present the first open-access, island-wide isotopic database (IsoMad) for modern biologically relevant materials collected on Madagascar within the past 150 years from both terrestrial and nearshore marine environments. Isotopic research on the island has increasingly helped with biological studies of endemic organisms, including evaluating foraging niches and investigating factors that affect the spatial distribution and abundance of species. The IsoMad database should facilitate future work by making it easy for researchers to access existing data (even for those who are relatively unfamiliar with the literature) and identify both research gaps and opportunities for using various isotope systems to answer research questions. We also hope that this database will encourage full data reporting in future publications.

Since the pioneering work in 70’, relatively few studies looked at the trophic niches of teleost reef fishes in Madagascar. The lagoon of Toliara (SW Madagascar) is facing threat from the use of mosquito net trawls, often practiced in seagrass and fringing reef habitats. These practices have the potential to induce alterations in the ecological dynamics of the species and in their feeding behaviors. The primary objective of this study is to investigate the dietary preferences and their potential interannual and spatial variation in two teleost fish species frequently found in mosquito net trawl: the rabbitfish Siganus sutor as juveniles and the goby Oplopomus oplopomus as adults. Sampling was conducted at two distinct sites, Ankilibe and Sarodrano, over a two-year period, in December of both 2017 and 2018. The diet composition of these two species was assessed through the examination of their stomach contents and the analysis of stable isotopes (δ13C and δ15N) from a sample of 40 individuals during each field campaign. A total of 22 different food items were identified in the stomach of young S. sutor, with seagrass and benthic mobile prey items being predominant. In adult O. oplopomus, 21 food items were identified, with a high representation of mobile benthic prey and zooplankton. Analyses of stomach contents and stable isotopes revealed significant variations in diet composition across different years and spatial locations. In addition, the results indicated a significant variation in diet according to the size of the individuals studied. The present study is one of the few documenting trophic variations in reef fishes, highlighting some feeding plasticity which could be highly valuable for a rapid adaptation in changing environments.

Worldwide, there exist fewer than 10 large-scale hatcheries dedicated to the production of the sea cucumber Holothuria scabra. Most of the existing hatcheries operate at a pilot scale or receive financial support from research programs. Large-scale hatcheries are defined as private industries that annually produce a minimum of 500,000 juveniles and engage in the exportation of several tons of dried product. Here, we present, for the first time, an analysis of the embryo and larval productions from a large-scale hatchery that annually exports over 5 tons of H. scabra trepang. Utilizing this data, we assessed the impact of isolating broodstock in tanks with elevated temperatures for 10 days, referred to as "maturation tanks," on ovarian maturation. Furthermore, we conducted a comparative analysis to assess the effectiveness of thermal shock and in vitro fertilization (IVF) in obtaining embryos and larvae. The analyzed data originated from Indian Ocean Trepang, a private aquaculture company located in Madagascar. Between August 2017 and December 2018, a total of 291 fertilization trials were conducted, involving 6154 females and 2173 males. Over these 17 months, the total number of embryos obtained was 225 million through IVF and 147 million through thermal shock. The number of 3-day-old auricularia larvae obtained at 11 months was 95 million for IVF trials and 51 million for thermal shock trials. The incubation of broodstock in maturation tanks has been found to enhance ovarian maturity, resulting in a notable 1.3 to 1.5-fold increase in the number of ootids. The combined implementation of IVF and thermal shock methods demonstrated a substantial increase in the productivity of the H. scabra hatchery. Thermal shock is comparatively simpler to implement than IVF and yields higher embryo production per trial. However, it is characterized by greater unpredictability and leads to a higher degree of variability in outcomes. IVF offers superior control over fertilization parameters and furnishes valuable insights into the sexual maturity of the broodstock. During challenging periods, such as the cold season or copepod infestations, the implementation of in vitro fertilizations becomes essential for ensuring hatchery profitability.

This study explored the local knowledge, utilisation and consumption of seaweeds (lomotsy in Malagasy) among coastal communities in southwestern Madagascar. Primary data were collected in eight villages, through a survey questionnaire (with a total of 629 respondents) and daily focus group discussions, conducted between May and December 2022. The findings reveal widespread familiarity with seaweed, used predominantly for farming, cleaning fishing equipment, and shading fish during transport. A smaller proportion of respondents (9%) had experimented with seaweed as a food source, notably incorporating species like Kappaphycus alvarezii and Hydroclathrus clathratus into soups and sauces. Despite the coastal inhabitants' recognition of seaweed, the potential of the seaweed resource has not been fully developed, with utilisation restricted mainly to limited traditional practices. An interest in incorporating seaweed into a person's future diet or in seaweed cultivation was expressed by 58% and 45% of the respondents, respectively. This study underscores the importance of enhanced and sustainable use of the seaweed resource in Madagascar's coastal communities, presenting opportunities for economic development and ecological conservation.

In the seagrass zone of Toliara (southwestern Madagascar), the local small-scale fishermen deploy seine mosquito nets that likely affect the structure of seagrass meadow systems and associated fishes. Nevertheless, the responses of these associated fishes communities to the intense marine resource exploitation using such destructive fishing gear remain unknown for the WIO region, especially in southwestern Madagascar. The present study aims to evaluate the trophic diversity of fishes living in seagrass beds and to assess their trophic plasticity. More specifically, we compared the diet of two dominant species in the catches of local fishermen (the rabbitfish Siganus sutor and the goby Oplopomus oplopomus) and we evaluated the potential variation in their trophic ecology. The sampling of fishes was achieved by collecting the catches of two small-scale fishermen using seine mosquito nets off Ankilibe only in December 2017, off Ankilibe and Sarodrano in December 2018. This sampling strategy allowed us to make spatial and temporal comparisons. In order to assess the diet of these two dominant fish species, stomach content analyses were performed on 40 specimens/species/village/year. Using a binocular microscope, animal preys were identified at class level and assigned to planktonic or benthic compartment. Plant items were classified as either phytoplankton, fragments of algae, or seagrass. The trophic niche of each fish population 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, 30% of gastropods (body or just operculum) and 5% of ostracods. The results of isotopic analyses (in progress), will improve our knowledge of the diet of these two fish species, which are decreasing progressively in small-scale fishermen catches due to heavy fishing pressure.

The present work analyzes data from Madagascar Holothurie Societe Anonyme to determine the effect of water temperature on the survival and growth of Holothuria scabra juveniles in ponds, and tests a system for heating pond water during the cold season (April–August). Our study shows that while water temperature does not affect the survival of endobenthic juveniles of H. scabra it greatly affects their growth. We strongly recommend using a system to shade farming ponds during the hot season (September–March), and a water heating system such as greenhouses during the cold season.

The effect of sediment quality and stocking density on the survival and growth of the sea cucumber Holothuria scabra reared in nursery ponds and in pens was studied at Aqua-Lab Farm in Toliara, south west Madagascar. Three types of sediment (micro-atoll, mangrove and seagrass bed) were tested for their food quality properties. Experiments were carried out in ponds at juvenile stocking densities of 10, 20, 30 and 40 individuals m -2 (juveniles size: 0.24 to 15 g) and in sea pens at juvenile stocking densities of 3, 6, 9 and 12 individuals m -2 (juveniles size: > 15 g). The results showed that the nature of the sediment did not affect the survival or growth of H. scabra . High survival (>95 %) and good growth rates (>0.22 g d -1 ) were observed during eight weeks of rearing in ponds. However, stocking density clearly influenced its growth. Highest growth rates of 0.23 g d -1 and 0.64 g d -1 were respectively obtained at low stocking densities in the ponds (stocking density: 10 individuals msup>-2; rearing time: 10 weeks) and sea pens (stocking density: 3 individuals m -2 ; rearing time: 9 months). Regardless of stocking density, juvenile growth ceased above a maximum biomass of 160 g m -2 in outdoor ponds and 692 g m -2 in sea pens. In order to optimize the farming of H. scabra , we suggest (i) the use of sediment collected from seagrass beds for nursery ponds, although sediments from other sources may be used, and (ii) the stocking biomass should not exceed 160 g m -2 in nursery ponds and 650 g m -2 in sea pens or at natural ranching sites. Keywords: Holothuria scabra , endobenthic sea cucumber juveniles, rearing, survival, growth.

Oocyte maturation in sea cucumbers is stopped during the meiosis at prophase I. Maturation naturally concludes just before spawning leading to a mature oocyte ready to be fertilized. Although thermal shocks applied on mature individuals can induce spawning, it is currently not possible to perform reliably in vitro fertilization of sea cucumber oocytes. The present paper reports the discovery of a new and highly effective oocyte maturation inducer (OMI), called MIF (for maturation inducing fractions). MIF's effects on oocytes of the marketable species Holothuria scabra were analysed and compared to that of the few OMIs described in literature. MIF induces the maturation and fertilization of more than 90% of oocytes while other OMIs [1-methyladenine, dithiothreitol (DTT), dimercapto-propanol (BAL) and L-cysteine] induces 28-90% of oocytes to mature depending on the tested inducer. Moreover the use of the other OMIs result in fertilization rates that never exceed 40%, and the obtained larvae often present developmental abnormalities. MIF's action on H. scabra oocytes is efficient yearlong even outside the spawning period of H. scabra. MIF is effective on the oocytes of all aspidochirote species tested so far but only when it is prepared from spawns of regular female sea urchin.

dagascar (Laroche et Ramananarivo 1995; Conand et al. 1997; Rasolofonirina et Conand 1998; McVean et al. 2005) et les populations naturelles sont actuellement surexploitées (Conand 1998; Conand et al. 1997). En 1999, un projet de mariculture des holothuries a vu le jour à Madagascar (Jangoux et al. 2001). Les travaux ont été financés par la Coopération Universitaire belge au développement (CUD) et les autorités de Malagasy. Y ont également participé les universités de Bruxelles et de Mons (Belgique), ainsi que l’Université de Malagasy, à Toliara (Jangoux et al. 2002). Les premiers travaux ont consisté à construire une écloserie sur le site de l’Institut halieutique et des sciences marines de Toliara (IHSM). L’écloserie a commencé ses activités en 2003 et produit actuellement des dizaines de milliers de juvéniles de l’espèce d’holothurie ayant la plus forte valeur marchande, Holothuria scabra. La partie principale comprend un bâtiment climatisé de 120 m2 renfermant six pièces dévolues à la culture d’algues, à l’élevage larvaire, à la maintenance des géniteurs, à l’analyse microscopique et au traitement informatique. Les aquariums de l’écloserie sont reliés à une station de pompage d’eau de mer dont le réservoir est alimenté à marée haute. L’eau de mer se déverse dans un bassin de décantation de 30 m3. L’eau stockée dans ce bassin est ensuite filtrée de façon répétée avant d’être utilisée dans les bacs d’élevage larvaire.

Different problems related to Holothuria scabra farming were observed at the sea cucumber aquaculture project Madagascar Holothurie S.A. (Toliara, Madagascar). In this paper, those problems are presented, their impact on sea cucumber production is characterised and solutions permitting to avoid or to minimise their impact are proposed. A drastic salinity drop occurred during low tides in one period of the year and after cyclones. This provoked behaviour troubles in the H. scabra: individuals stayed burrowed in sediment even at night, a period when they are usually at the surface. However, that did not affect their growth. When possible, we suggest choosing a site far from areas where salinity is apt to drop. Isopods Cymodoce sp. infested sea cucumbers in outdoor ponds during the hot season, provoking a high mortality rate (average 8% week -1 ) in cultivated H. scabra. The introduction of the carnivorous fish Terapon jarbua in the ponds proved successful in preventing this problem. The fish eat isopods and can eliminate them within 10 days. Infections induced by isopods totally disappeared within two weeks. The crabs Thalamita crenata were abnormally abundant in the pens during some periods of the year. They are the most redoubtable sea cucumber predators in the region and may provoke the mortality of the entire stock within one month. The crabs attack principally the newly transferred juveniles. The adults whose weight was more than 250 g were never affected. The elimination of the crabs in the surrounding area is to be carried out before the transfer of the juveniles and a daily watch of the pens is necessary in order to limit the impact of predation on production.

Different problems related to Holothuria scabra farming were observed at the sea cucumber aquaculture project Madagascar Holothurie S.A. (Toliara, Madagascar). In this paper, those problems are presented, their impact on sea cucumber production is characterised and solutions permitting to avoid or to minimise their impact are proposed. A drastic salinity drop occurred during low tides in one period of the year and after cyclones. This provoked behaviour troubles in the H. scabra: individuals stayed burrowed in sediment even at night, a period when they are usually at the surface. However, that did not affect their growth. When possible, we suggest choosing a site far from areas where salinity is apt to drop. Isopods Cymodoce sp. infested sea cucumbers in outdoor ponds during the hot season, provoking a high mortality rate (average 8% week -1 ) in cultivated H. scabra. The introduction of the carnivorous fish Terapon jarbua in the ponds proved successful in preventing this problem. The fish eat isopods and can eliminate them within 10 days. Infections induced by isopods totally disappeared within two weeks. The crabs Thalamita crenata were abnormally abundant in the pens during some periods of the year. They are the most redoubtable sea cucumber predators in the region and may provoke the mortality of the entire stock within one month. The crabs attack principally the newly transferred juveniles. The adults whose weight was more than 250 g were never affected. The elimination of the crabs in the surrounding area is to be carried out before the transfer of the juveniles and a daily watch of the pens is necessary in order to limit the impact of predation on production.

The abundance of echinoderm larvae, in particular sea cucumber larvae, was assessed in the lagoon of To- liara Great Reef in southwest Madagascar from December 2000 to May 2002. More than 9000 echinoderm larvae were collected, 33% of which came from sea cucumbers. Mean larval density varied greatly de- pending on the season. Sea cucumber larvae were most abundant during the hot season (November to April) with an average of 77 larvae per 350 m 3 as compared to 1 larva per 350 m 3 during the cool season (May to October). Sea cucumber larvae were found in large numbers at the time temperatures dropped, ac- counting for 50% of the total number of echinoderm larvae observed. Sea cucumber larvae were not found in the plankton from June to October. Three different families of sea cucumbers were observed: Holothuri- idae, Stichopodidae and Synaptidae. Holothuriidae were the most numerous, accounting for 86% of all sea cucumber larvae collected.

Various types of calcareous structures have been observed in Holothuria scabra sea cucumber larvae and epibiont juveniles at various ages and stages of development. An unpaired calcareous body can be observed as early as the dipleurula stage (less than two days after fertilisation); it is located in the posterior part of young larvae (36 h), grows, changes appearance (from a star, it becomes a half-sphere) and can still be found in epibiont juveniles. The madreporite appears in older auricularia (10 days) in the form of a curved stalk located at the base of the water ring canal; it develops to form a screened sphere in pentactulae and juveniles. Tables are recognisable in doliolaria larvae (15 days) and the initial formation of the peripharyngeal calcareous ring can been observed in pentactulae (17 days). The first podia rods and perforated disks appear in 20-day-old juveniles and anal plates from day 22 onwards, but button spicule only develop at the end of the epibiont life stage (45 days).

Richard Rasolofonirina, Devarajen Vaïtilingon, Igor Eeckhaut and Michel Jangoux Institut Halieutique et des Sciences Marines, Université de Toliara, BP 141, Toliara 601, Madagascar; Laboratoire de Biologie Marine (CP 160/15), Université Libre de Bruxelles, 50 Av. F. D. Roosevelt, B-1050 Bruxelles, Belgique; Laboratoire de Biologie Marine, Université de Mons-Hainaut, 20 Place du Parc, 7000 Mons, Belgique.

Les éléments calcaires du tégument, des tentacules buccaux et des podia des holothuries constituent d’importants caractères taxonomiques. Ces éléments toutefois se modifient en cours de croissance et pourront être très différents chez les juvéniles et les adultes d’une même espèce (Féral, 1980; Cutress, 1996; Massin et al., 2000). Ces différences concernent surtout la taille et/ou l’architecture des éléments (plus grand, plus petit, plus complexe, plus simple), mais elles peuvent aussi être liées à la disparition précoce et/ou l’apparition tardive de certains d’entre eux. Massin et al. (2000) ont décrit en détail la diversité des spicules présents chez les juvéniles de Holothuria scabra. Toutefois, hormis celles que l’on trouve parmi les travaux généralistes et assez anciens de Mortensen (1921, 1937, 1938), il n’y a guère d’informations disponibles sur les structures calcaires que présentent les larves d’holothuries (voir, e.g., Hamel et al. 2002, Sewell et McEuen 2002). Le présent travail s’intéresse à ces structures chez les stades préet immédiatement post-métamorphiques de l’espèce H. scabra. Il a pour but de déceler leur moment d’apparition, de les décrire et d’en suivre la croissance de la jeune larve au juvénile épibionte.

Holothuria scabra est l'holothurie comestible a haute valeur marchande la plus distribuee et la plus exploitee dans l'Indo-Pacifique tropical. Des lors, et a cause de la demande croissante des pays importateurs et consommateurs, les stocks naturels de l'espece sont confrontes actuellement un probleme de surexploitation. A Madagascar, les situations economique, sociale et politique difficiles ainsi que l'insuffisance d'un plan efficace pour l'amenagement de cette exploitation, rendent la situation plus delicate encore. La surexploitation se traduit par la diminution de la production, la rarefaction de certaines especes, la degradation de la qualite du produit et entraine une forte concurrence entre les exploitants et le non respect de la legislation existante. Un plan d'amenagement de cette exploitation est propose dans ce travail. Celui-ci concerne la gestion de la peche, la restauration et la perennisation des stocks naturels, et la valorisation des produits. L'holothuriculture est consideree comme la solution d'avenir pour pallier une demande sans cesse croissante en trepang, restaurer les stocks naturels et sauver les especes d'holothuries menacees d'extinction.