Sargassum sp. meal is a plant ingredient that has not been used properly, and its potential has not fully realized as an herbivorous fish diet. This experiment aims to determine the potential use of sargassum meal in the grow-out of the rabbitfish diet. Rabbitfish (initial weight of 51.76 ± 0.11 g ind−1) those were cultivated in fifteen floating net cages sized 1×1×1.5 m3 at 20 fish cage−1 stocking density lasted for 90 days. This experiment was designed as Completely Randomized Design with five treatments of sargassum meal dosages in diets, which were 0.0, 7.5, 15.0, 22.5, and 30.0%, with three replications each. The results showed that no significant effect (P>0.05) of different sargassum meal dosages on the specific growth rate and survival rate of rabbitfish. However, feed intake increased with increasing sargassum meal, where the highest was obtained at 22.5% (275.6±9.2 g fish−1) and 30.0% (270.8±8.4 g fish−1) dosages which were significantly higher (P<0.05) than the other dosages. At the same time, sargassum meal dosages were significantly different (P<0.05) on feed efficiency and protein efficiency ratio, where they both seem to decrease with the increase of sargassum meal. The highest feed efficiency was obtained at the dosage of 0.0% (68.6±3.6%) that had no significant effect (P>0.05) with 7.5% (63.7±2.2%) and for protein efficiency ratio was obtained at 0.0% (2.29±0.12) that had no significant effect (P>0.05) with 7.5% (2.20±0.08) and 15.0% (2.12±0.05) dosages. The use of sargassum meal as much as 30.0% caused a lower crude lipid and higher crude protein contents in the nutritional body composition of rabbitfish, and was significantly different (P<0.05) compared to 0.0% dosage. Based on the growth rate of fish, the optimum dosage of sargassum meal in rabbitfish grow-out diet was estimated at 19.46%, but only 7.5% of sargassum meal could be used in the diet based on feed efficiency.

Ulva lactuca is a green seaweed with a high potency to be used as fish diet. The feeding trial aimed to evaluate the use of U.lactuca as fresh diet for the nursery of golden rabbitfish Siganus guttatus. Five treatments were evaluated, namely 100% fresh Ulva (FU), the combination of fresh Ulva and dry pellet with the ratio of 75:25% (UP1), 50:50% (UP2), 25:75% (UP3), and 100% dry pellet (DP) with three replicates. Golden rabbitfish with a mean initial weight of 6.2 g were stocked into fifteen rearing tanks at a density of 20 fish tank−1. After 90 days, growth responses differed significantly amongst dietary groups. Fish fed DP had similar weight gain (219.86%) to UP3 (232.21%), and its specific growth rate (1.29%/day) was similar to UP2 (1.11%/day) and UP3 (1.33%/day), but significantly different (p<0.05) from FU (SGR -0.25%/day; WG -19.97%). The survival rate of fish fed UP2 (98.33%) was significantly different (p<0.05) from FU (80.00%). The fish body color fed FU had bright yellowish color and high carotenoids (14.69 µg g−1) compared to DP. The combination of fresh Ulva with pellet at the same ratio of 50% and 25:75% similar to the 100% pellet diet can support the fish growth.