Sea cucumbers fisheries becoming commercially exploited due to the increasing demand in Asian markets. The resulting unregulated exploitation has led to the collapse of several natural stocks . In this context, aquaculture represents an alternative to meet the demand, reducing pressure on wild stocks and at the same time allowing the restocking of local populations. Sea cucumbers have great potential to be reared in aquaculture and have been shown to have a valuable application in i ntegrated multi-trophic aquaculture systems (IMTA). Holothuria arguinensis Koehler & Vaney, 1906 is a potential species for aquaculture in Europe. H owever, there are very few studies o n nutrition during the larval development of this species. The present study was undertaken in order to examine the effect of three diets in the larval development, growth, survival and settlement success of H. arguinensis
Holothuria arguinensis broodstock were maintained in a recirculating aquaculture system (RAS) with sediment. To induce the spawning, individuals were first transferred and maintained for 24 hr in substrate-free spawning tank, to void their gut contents , followed by thermal stimulation to induce gamete release . Larvae were fed with three diets: Rhodomonas baltica and Phaedactylum tricornutum (Diet A); R. baltica and Skeletonema marinoi (Diet B) ; R. baltica and Chaetoceros calcitrans (Diet C). The experiment was conducted in 50 L fiberglass tanks, 3 tanks were used for each diet . Water samples were taken daily after the first day to monitor larval development. The mean length and width of 15 larvae were register during the planktonic phase and after settlement. J uveniles number was estimated by counting the juveniles in three substrates: pvc tubes, transparent plastic plates and ceramic tile .
H. arguinensis l arvae increased in size, reaching the mid auricularia stage on day 7 post fertilization, with a higher mean length and width in larvae fed with the Diet C, 543.24 µm and 301.06 µm, respectively (p < 0.001). Doliolaria stage presented a significantly higher length (699.64 µm) and width (475.78 µm) in individuals fed with Diet B (p < 0.05). Pentactula stage followed the same pattern, significantly higher lengths and widths were observed in larvae fed with Diet B and at this stage, s urvival was also higher in animals fed with Diet B (6.25%) than with the Diet A (2.76%) or Diet C (2.76%). Although, no significan t differences were observed in the mean length of juveniles (p ˃0.05) fed with the three diets, width was significantly higher in H. arguinensis juveniles fed the Diet A (263.74 µm ; p < 0.001). The highest juvenile number was observed with the Diet A (54.19%), mainly in the pvc tube, followed by Diet B (31.46%) with also a higher number of juveniles in this subtracte. Diet C presented the lowest number of juveniles (14.35%). In t his study, new mixtures of microalgae were used to rear H. arguinensis larvae until the juvenile stage . Diet B, R. baltica and S. marinoi , appear to be advantageous during the latest stages of larval development and Diet A lead to a higher number of settled juveniles. Considering high commercial value, ecological role and its potential use in IMTA, we assume that the development of effective diets for the different stages of H. arguinensis larval development would be extremely valuable to the aquaculture industry.