Preliminary Study on the Use of Sargassum horneri as a Dietary Ingredient for Juvenile Rochia nilotica: Effects on Growth and Survival

Rochia nilotica is an economically important marine gastropod in Pacific Island countries, valued for its nacreous shell used in ornaments. The brown macroalga Sargassum horneri accumulates in large quantities along coastal regions, causing significant ecological and economic burdens. We evaluated the effects of S. horneri-based feed on the growth performance of juvenile R. nilotica under controlled tank conditions in Chuuk Lagoon, Micronesia. Juveniles (initial shell width ≈ 12.7 mm) were reared for 120 days and fed either a formulated diet (disc-shaped pellets, <1 cm in diameter) containing S. horneri or a traditional live-rock diet providing natural biofilms. Notable biological differences in shell width and height were observed after 2 months, with final mean values of 19.86 ± 1.76 mm and 15.92 ± 1.25 mm in the S. horneri group (94% survival), compared with 16.40 ± 1.26 mm and 13.14 ± 0.96 mm in the natural diet group (86% survival). Although greater growth and survival were observed in the tank receiving the formulated diet, fully replicated multi-tank experiments are required to definitively confirm whether these differences were caused directly by the dietary treatment. Given its abundance and environmental impact, recycling S. horneri biomass as a sustainable feed source could support trochid aquaculture and resource restoration and contribute to circular bioeconomy practices in Pacific Island countries.