46 JUNE 2014 • WORLD AQUACULTURE • WWW.WAS.ORG to I. galbana, as larval development progressed and total feed amount was provided twice daily. The single-species diet of D. tertiolecta and the mixed-species diet of D. tertiolecta and I. galbana supported satisfactory growth (65 percent) and survival (69 percent) of larval California sea cucumbers over 18 days, with more than 65 percent of larvae reaching the doliolaria stage. The single-species diet of I. galbana resulted in poor survival (<50 percent) and larvae failed to metamorphose to doliolaria. As sea cucumber larvae develop to doliolaria and pentactula stages (Figs. 4 and 6), their bodies start to constrict and behaviour changes from swimming to exploration of settlement surfaces. To induce settlement and metamorphosis, suitable surfaces must be provided for mass production of juveniles. In Japan, the benthic diatoms Nevicula, Achnanthes, Amphora and Nitzschia are cultured to induce settlement and metamorphosis and for mass juvenile production of the sea cucumber A. japonicus (Ito and Kitamura 1997). Asha and Muthiah (2002) examined the effectiveness of various settlement cues (Algamac®, powdered Sargassum, powdered Spirulina, periphytic diatoms and dead algae) for induction and metamorphosis of the sea cucumber Holothuria spinifera and reported that larval settlement can be better induced by Algamac® and periphytic diatoms than by Sargassum, Spirulina or dead algae. In the present study, larvae were induced to settle and metamorphose successfully using settlement plates coated with Spirulina or laboratory-cultures of the live, benthic diatom Amphora salina. Powdered Spirulina was diluted with freshwater and settlement plates were painted with the slurry and air dried overnight before immersion in larval rearing tanks. Many studies have reported larval settlement of sea cucumbers and other marine invertebrates using natural biofilms, but the use of such biofilms was avoided to reduce the risk of contamination of culture vessels with biofouling organisms such as copepods, ciliates, barnacles and mussels. Copepods can be very harmful in hatchery production systems and a sudden infestation may destroy entire batches of sea cucumber larvae or early juveniles (Fig. 7). Copepods can survive in filtered and UV-treated seawater systems, but infestations may be controlled by rinsing all screens and other rearing materials with fresh water before and after use and storing them in a container with chlorinated water (Agudo 2006). Two nursery phases were used for juvenile production of California sea cucumbers. Both phases were carried out in static UVS seawater at ~14 °C, with 50-60 percent of culture water exchanged daily. During the first phase, juveniles were grown on settlement plates in larval rearing tanks for 4-5 weeks. In this phase, juveniles were weaned from the larval diet by providing a slurry of Spirulina and C. muelleri ad libitum daily. Dried Spirulina was mixed with seawater until completely emulsified and held overnight to increase its density before feeding to juveniles. For the second nursery phase, juveniles (Fig. 8) were detached from settlement plates or tank surfaces and transferred to trough tanks (300 cm long × 80 cm wide × 40 cm deep). Sea cucumber juveniles at this age were characterised by large size variation and were difficult to detach from settlement plates and tank surfaces. In a hatchery system, Agudo (2006) used a gentle water jet to Delta Hy and co aquacultu complet enginee Ou Ga Ai Po Pla Te Ele Co Hy Delta pre for cus Optima Op Office: 7 ww ydronics provides c ooling solutions for ure applications or te design/build ser ring, equipment a r Product Offering as Fired Boilers/He r Cooled Chillers & olypropylene Heat ate & Frame Heat emperature Contro ectric Boilers & W ombined Heat/Pow ybrid Solar System ‐plumbs and skid‐ stomer installation al Water Te Means ptimal Produ 27‐938‐2421 I Fax ww.deltahyd custom heating r your specific r needs. We offer rvices including nd installation. gs Include: eaters Heat Pumps Exchangers Exchangers ols ater Heaters wer Turbines ms mounts systems n and export. mperature uction x: 727‐938‐2311 dro.com LEFT, FIGURE 7. A copepod (top) roaming on a juvenile California sea cucumber. RIGHT, FIGURE 8. Early juvenile California sea cucumbers of various sizes.
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