Growth, Development and Survival of Holothuria scabra Larvae in Different Microalgal Regimens and Water Rearing Media

Abstract

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.