Different aspects of Holothuria scabra larval production, including feeding regimen and water treatment, were investigated under experimental conditions. This study highlights the optimization of techniques and simplification of the requirements of sea cucumber larval rearing. The growth performance, development, and survivorship of H. scabra larvae were measured to assess which treatment provides optimum results. Chaetoceros gracilis (Cgr) and Chaetoceros calcitrans (Cc) were administered singly and in combination (Cgr-Cc) to sea cucumber larvae. Growth was highest in combined Cgr-Cc feed with mean final length of 2088µm, followed by Cc with 1855 µm and Cgr with 1800 µm, but with no significant difference (p>0.05). Similarly, survival rates among treatments were not statistically different (Cgr-Cc = 2.23%; Cgr = 1.6%; Cc = 1.3%) (p>0.05). However, larval development was better in combined Cgr-Cc and Cc single diet, with 90% and 100% composition of early juveniles on Day 30. Slower development was observed in Cgr single feed, with only 90% early juveniles observed later on Day 35. Different microalgal concentration of Cgr-Cc (10,000, 30,000 and 50,000 cells.mL-1) were also tested. Juveniles (~3 mm) yielded from 50,000 cells.mL-1 microalgal concentrations were five times larger than when fed at 10,000 cells.mL-1 microalgae. Development of larvae was also faster in 50,000 cells.mL-1 , yielding harvestable juveniles in 25 days. However, water replenishment in tanks with high microalgal density should also be regularly done at 50-70% rate in two days interval to mitigate fouling. In addition, sand-filtered, chlorinated, and UV-treated seawater were also tested for their efficiency as culture media. Growth rates were significantly highest in sand-filtered seawater (68.3 µm.d-1), followed by UV-treated seawater (52.4 µm.d-1), and by chlorinated seawater (34.8 µm.d-1) (p<0.05). Larval development did not differ in sand-filtered and UV-treated seawater, yielding ~1 mm juveniles as early as Day 25. Likewise, sand-filtered seawater rendered highest survival of larvae (10.24%) followed by UV-treated seawater (6.24%); chlorinated seawater yielded lowest (2.60%) (p<0.05). Although a sterilization process is advised, findings on sand-filtered seawater as a rearing medium were notable.
This study explored the feasibility of Laurencia papillosa, Sargassum spp, and Gracilaria bailinae crude extracts as feeds for the juvenile sea cucumber Holothuria scabra in a tank-based system. Post-metamorphic juveniles (~1 mm) were harvested from larval tanks and were reared until the late juvenile stage in indoor tank systems at 300 ind./tank stocking density for 45 days. Growth and survival rates of H. scabra juveniles were monitored to assess the performance of each seaweed treatment. L. papillosa consistently yielded the best growth (SGR: 7.63-11.32%.d-1) and highest survival rates (54.6–56.8%) of H. scabra juveniles. The performance of L. papillosa did not differ from that of Sargassum spp., while G. bailinae yielded poor growth (SGR of 5.01–9.38%.d-1) and low survivorship of juveniles (8.77–19.77%). Growth and survival rates were similar between fresh and dried seaweeds (p>0.05), suggesting dried seaweeds' applicability as feeds for juvenile H. scabra. Moreover, increased feed rations resulted in better growth of juveniles, but survival rates among feed rations (4.5, 6.0, 7.5, and 9.0 L.d-1) did not differ significantly (p>0.05). The monthly mean water temperature ranged from 26.6°C to 28.8°C, salinity of 33.2–35.1 ppt, dissolved oxygen of 6.1–8.3 mg/L, and pH of 8.1–8.3. High yields of sea cucumber juveniles were observed during the dry season, while low survival rates (<20%) were observed during wet months. The success of this study could set forth the application of tank-based nursery systems for H. scabra, especially during the season of high rainfall and extreme weather conditions that heavily affects cage rearing in the open-sea setting.
Decatopecten radula is highly sought for its shell meat making it as a source of food and income for local shellfish gatherers in Guiuan, Eastern Samar. This study provides biological information for future conservation and management. Data were obtained monthly in the three selected sites within coastal waters of Guiuan, Eastern Samar from January 2016 to December 2016. These scallops were distributed at shallow areas of Trinidad Tubabao Island, Kamandag Reef, and Magluto Reef in depths of approximately 1-5 meters throughout the sampling period. Scallops are abundant in Kamandag reef where the site is characterized by its rocky area and mainly composed of a sandy bottom. Scallops were found on the surface of the sediment, attached to rocks or hard elements, hidden in a seagrass and seaweed. Physico-chemical parameters were observed within a narrow and normal range. Water temperature did not vary widely from 28°C to 30°C while salinity, pH, and dissolved oxygen ranged from 33-34, 8.2-8.7, and 3.4-4.8 mg/L respectively. The results from the 825 scallops showed that D. radula is dioecious species with four gonad stages (developing, mature, spawning, spent) based on the histological examination and calculation of gonadosomatic index (GSI). The spawning period of the species is protracted and spawning peaks occur from August to November with a male-female sex ratio of 1:1.24. Size at sexual maturity reached 55 mm shell height (SH) in males and 60 mm SH in females. Thus, the collection of scallop should be limited to individuals >60 mm shell height.
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