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- The effects of stocking density on physiological traits in Holothuria forskali broodstockPublication . Sousa, João; Félix, Pedro M.; Brito, Ana C.; Venâncio, Eliana; Silva, Francisco Azevedo e; Simões, Tomás; Raposo, Andreia; Neves, Marta; Narciso, Luís; Melo, Ricardo; Pombo, AnaThe high demand of sea cucumbers in international markets, mostly based in Asia, has left a deep impact on the natural stock of many species, leading to an investment in aquaculture techniques in order to mitigate these impacts. This study aimed to determine the effects of stock density in rearing broodstock of Holothuria (Panningoturia) forskali Delle Chiaje, 1823, a common species in the Mediterranean Sea and eastern Atlantic with commercial value. To do so, two different density treatments were selected: 1 kg/m2 and 2 kg/m2. The trial took place over five months and individuals were fed a mixture of frozen microalgae (Tetraselmis sp. and Phaeodactylum tricornutum). At the end of the trial, the effects of stock density on the individuals’ condition were assessed by analysing different variables, namely their fresh and gutted weight, evisceration and mortality rates, gonadosomatic index and oocyte size and even biochemical content, such as protein and lipid content in muscle bands. No significant differences were found between density treatments regarding any of the parameters assessed, aside from mean oocyte diameter. Individuals from the lower-density treatment presented a smaller mean oocyte diameter, supplied with fewer oocytes, than individuals in both the higher-density treatment and the baseline group. Regardless of this one difference, all trial individuals were able to maintain their elevated gonadal developmental stage for a full period of five months past their reproductive peak, with female holothurians subjected to the higher-density treatment showing signs of increasing vitellogenic reserves, a considerable advantage in aquaculture broodstock rearing.
- Do broodstock diets influence viability and larval development of Holothuria mammata?Publication . Venâncio, Eliana; Félix, Pedro M.; Brito, Ana C.; Sousa, João; Silva, Francisco Azevedo e; Simões, Tomás; Narciso, Luís; Amorim, Ana; Dâmaso, Luísa; Pombo, AnaThe intensive exploitation of sea cucumbers, mainly exported to Asian seafood markets, has contributed to deplete natural populations of several species. In Europe, the aquaculture production of these echinoderms is minimal, reflecting the low scientific production on the topic. In Portugal, like in Mediterranean countries, there are native species with high commercial value, which can be potential candidates for aquaculture. The control over the reproductive cycle is an important tool for rearing success, which, in turn, decreases the pressure over natural stocks. However, there are very few studies on the larval development of European species and none on the broodstock maturation in captivity. The present work studied the influence of three diets on the gonadal maturation and larval viability and development of Holothuria mammata. After 120-days of captivity the broodstock groups fed with a mixture of live microalgae (Diet 2) and a mixture of live microalgae and extruded dry food (Diet 3) reached the spawning stage, in contrast to the group fed with a mixture of frozen microalgae (Diet 1). Spawning was induced by thermal shock. Larval rearing from broodstock fed on Diet 2, total mortality was observed on the 12th day, after the onset of mid auricularia stage. The stocks of larvae from the broodstocks fed diets 1 and 3 reached the stage of pentactula on the 27th day. The success in spawning induction and embryonic development suggest that H. mammata may accept different types of diets as frozen microalgae mixes or live microalgae and dry feeds and still produce viable offspring. However, it is essential to develop more studies on the reproductive biology of H. mammata to optimize the hatcheries techniques to broodstock conditioning and larval rearing in captivity.
- Modelling the distribution of a commercial NE-Atlantic Sea Cucumber, Holothuria mammata: demographic and abundance spatio-temporal patternsPublication . Félix, Pedro M.; Pombo, Ana; Silva, Francisco Azevedo e; Simões, Tomás; Marques, Tiago A.; Melo, Ricardo; Rocha, Cristina; Sousa, João; Venâncio, Eliana; Costa, José L.; Brito, Ana C.There is an increasing demand for sea cucumbers, for human consumption, mainly from Asian markets and, as a consequence, NE-Atlantic species are now new targets for exploitation and exportation. Holothuria mammata is one of the most valuable species in Europe. However, the lack of historical economic interest in this species in most European countries has also led to a lack of studies concerning biological and ecological aspects on wild populations and this is a major issue for stock management. This study aims to determine the temporal and spatial patterns of distribution of H. mammata, considering its abundance and demographic structure in a NE-Atlantic area, SW Portugal, as a function of environmental conditions. For that, a population from a marine protected area was followed for 1 year at 1.5-month intervals. Throughout the coastal area, six sites were selected and at each sampling campaign three random transects per site and substrate (rock and sand) in which all H. mammata individuals were counted and measured. For each site and survey several environmental parameters of interest, from the water column, the sediment and substrate cover, were also measured. Generalized Linear Models were used to model the spatial and temporal distribution of the species according to environmental conditions, to determine the species’ habitat preferences. The distribution models indicate that abiotic and biotic parameters of the water column are not the main drivers shaping the distribution of H. mammata. The species has a patchy distribution, and its habitat preferences depend on environmental stability, the presence of shelter and habitat complexity, which is more important for smaller, more vulnerable, individuals, while bigger size classes tend to venture more into less stable environments in an opportunistic fashion. The knowledge of these population traits is determinant to develop stock management measures, which are now urgent to prevent the depletion of commercial sea cucumber populations in the NE-Atlantic. Sustainable fisheries policies should be developed and start by considering to delimit fishing areas and periods, considering the species spatial and temporal distribution patterns.
- Reproductive biology of the sea cucumber Holothuria mammata (Echinodermata: Holothuroidea)Publication . Venâncio, Eliana; Félix, Pedro M.; Brito, Ana C.; Silva, Francisco Azevedo e; Simões, Tomás; Sousa, João; Mendes, Susana; Pombo, AnaHolothuria mammata is one of the most valuable species of sea cucumber, as well as one of the main target species harvested in the Mediterranean and NE-Atlantic regions. This study aims to describe the reproductive cycle of H. mammata in a coastal area of southwest Portugal. Monthly samplings were carried out for 19 months, with the concomitant collection of environmental data and biometric data. H. mammata had a sex ratio of 1:1.2 (male:female) and a size at first maturity of 142 mm for males and 167 mm for females. The gonadosomatic index (GI) peaked between April and May for both sexes. Gonad development started when days had a shorter photoperiod (9 to 13 h of sunlight) and lower seawater temperature (<15ºC), and spawning occurred later, with longer photoperiod (13 to 15 h of sunlight) and higher seawater temperature (>15ºC) and chlorophyll-a concentrations. The development of new studies to increase the biological and ecological knowledge of the populations of H. mammata is essential to create conditions for the domestication of broodstock in captivity, to allow the development of fishing regulations based on informed decisions and to create precise measures for the conservation of ecosystems.