Overview And Progress Of Consortium Research Related To The Biology, Ecology And Aquaculture Of Rabbitfish

BackgroundCoastal habitats support global fisheries by ensuring the survival of juvenile fishes.These habitats constitute one of the fishing areas targeted by small-scale fishermenin the least developed countries, including Madagascar. The accessibility of thesehabitats at low tides makes it an ideal fishing area for mosquito seine nets asobserved for instance in SW Madagascar and beach seining in Kenya. However, thispractice negatively impacts fisheries production due to catches of high numbers ofjuveniles, in Madagascar and Kenya mostly composed of shoemaker spinefootrabbitfish (Siganus sutor). Despite Malagasy laws that forbid the deployment ofmosquito seine nets, fishermen continue with their use. In Kenya, the beach seineshave been outlawed but enforcement remains a challenge. This context highlightsthe need for management measures and alternative sources of income for asustainable use of marine resources and for improving the fishermen livelihood. Theongoing consortium research entitled “Fish juvenile recruitment in coastal habitats ofwestern Indian Ocean” was funded by MASMA program administered by WIOMSA.It is an interdisciplinary research program intending to understand recruitmentpatterns of shoemaker spinefoot rabbitfish (Siganus sutor) in coastal habitats ofKenya and Madagascar. It explores evidence-based solutions for improving thewelfare of coastal communities and sustainable use of marine resources.MethodResearch activities were divided into four work packages. In WP1, Siganus sutorrecruitment patterns in coastal habitats were targeted to identify the nursery groundand recruitment periods. It is based on juvenile fish sampling at four coastal habitats(mangroves, seagrass meadows, intermediate areas and seagrass associated withthe coral reef) in Madagascar during twelve months. In WP2, sampling for theanalysis of the population connectivity of S. sutor for detecting the sources ofjuveniles in the coastal habitats at five sites along the western coast of Madagascarwas completed. In WP3, ecological models for predicting the arrival of newly settledS. sutor will be based on historical and newly collected data (WP1) using the randomforests algorithm. Predictors are composed of remotely sensed oceanic conditionsand a post-larval supply index calculated from post-larval sampling in the coastalhabitats using light-traps. Like juvenile sampling, post-larval sampling was performedthree nights per month which will cover all the juvenile sampling periods. In WP4,fish feeding behavior is studied and experiments on capture-based juvenile fishgrow-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.ResultsIn WP1, about 5,720 juvenile individuals were obtained from 120 juvenile fishsamples. The standard length of each of these individuals were measured foranalyzing the spatial distribution of S. sutor. The nursery ground and recruitmentseasons for S. sutor emerged from our research. The findings will be presentedorally by PhD student Helga Berjulie Ravelohasina during the symposium. Inaddition, about 360 epifaunal community samples were obtained between July 2021and April 2022. The spatial distribution of abundance, diversity and richness ofepifauna associated with seagrass will be presented in a poster by MSc studentMory Justino. In WP2, at each location, 45 individuals were sampled, for a total of225 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 inprogress and should be completed by June 2022. In meantime, the extraction ofremotely sensed oceanic conditions covering the sampling periods is beingprocessed with R programming for the period. In WP4, preliminary results on fishgrow-out identified the best fish diet and the most optimal stocking density at thesmallest size (about 2 cm of standard length). More details related to these findingswill be presented in a poster by master student Nandrianina Maminantenaina. Inaddition, 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 collectedduring the warm (October 2021 to February 2022) and cool season (May to August2022).ConclusionThe potential nursery areas and the main recruitment seasons of Siganus sutor wereidentified. The oral presentation entitled “The potential nursery areas and recruitmentseason of S. sutor in Madagascar” by Helga Berjulie Ravelohasina will providefurther details of our findings. The variability of food availability related to epifaunaconcentration will be known in the poster on Mory Justino. The most optimal fish dietas 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 byNandrianina Maminantenaina.

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