Metamorphic success and production cost of Holothuria scabra reared on microalgal concentrates compared with live microalgae

Abstract

Larval food is a bottleneck in the culture of Holothuria scabra. Whether larval metamorphic success and juvenile production can be improved using microalgae concentrates was investigated. Larvae were reared under a fixed daily feeding ration of 20,000 cells mL-1 using three commercial concentrates (Instant Algae®, Reed Mariculture Inc.): TW1200 (Thalassiosira weisflogii; TW), TISO1800 (Isochrysis sp.; TISO), and Shellfish1800 (mixed diatom; SHELL) and compared with live Chaetoceros calcitrans (CC). The diet efficacy was evaluated based on larval development rate, sizes and survival to late auricularia (LA) with hyaline spheres (HS), and post settlement. Larvae in TW did not progress beyond LA. The average size during LA in TISO (855.7 ± 62.67µm) was significantly higher compared with SHELL. Larvae fed CC reached LA stage earlier, attained significantly larger sizes (1028.43 ± 19.38 µm), and have significantly higher incidence and size of HS. Better metamorphic and settlement performance in CC and SHELL may be related to the higher carbohydrate content in these feeds. The average number of post-settled juveniles in CC (9,268 ± 2,183.79) was over three times more than in SHELL, and an order of magnitude for TISO. Because of the low juvenile yield and longer feeding duration, the estimated cost of producing each juvenile using SHELL is PhP 2.00 and PhP 11.77 for TISO, compared to PhP 0.52 using CC. Development of local microalgal concentrates can enable more hatcheries to undertake sandfish culture, and access to more affordable supplemental feed to promote higher post settlement success.