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This study assessed potential improvement of sandfish (Holothuria scabra) culture using supplemental feeding with seaweed to explore its potential to support short-cropping. Three phased experiments evaluated juvenile growth and survival performance by: offering two types of seaweed-based supplemental feeds (Sargassum sp. and Gracilaria verrucosa) both processed by fermentation and pulverisation (Experiment 1); evaluating three stocking densities (25, 35 and 45 individuals per m2) using the best-performing diet from Experiment 1 (Experiment 2); and upscaling to commercial-level culture in three 400 m2 earthen ponds (Experiment 3). Fermented diets were prepared using a probiotic mixture (Saccharomyces boulardii, Lactobacillus acidophilus and Bacillus subtilis) added to ground, dried seaweed; while the pulverised diets were offered as a ground powder (350–450 µm particle sizes). Sandfish offered fermented Sargassum and Gracilaria reached 35.0% and 29.7% heavier mean final weights (18.18 ± 0.19 g and 16.81 ± 0.08 g, respectively), compared to their pulverised equivalents (11.82 ± 1.09 g across both seaweed species, p 0.05). Valuable new information has been generated for further development of supplemental feeding of sandfish, and results here demonstrate high technical feasibility to support short cropping, with optimisation of this culture model required.

The potential for integration of sandfish (Holothuria scabra) and snubnose pompano (Trachinotus blochii) culture was assessed in two experiments. Experiment 1 examined the effect of varying pompano:sandfish stocking density ratios (1:0.5, 1:1, 1:1.5 and pompano monoculture control) on growth, survival and sediment quality (measured by Total Organic Matter: TOM and Sediment Total Nitrogen: STN content) over 75 days. Experiment 2 applied the best density (1:1) determined from Experiment 1 to commercial-scale co-culture in 2 × 500 m2 earthen ponds over 8 months. Mean pompano weight gain during Experiment 1 was 11.9% higher on average in co-culture across all treatments (70.5 ± 5.2 g cf. control: 59.7 ± 4.8 g), while sandfish performed better (11.6% increase) at density ratios of 1:0.5 and 1:1. Survival remained high (>91%) in all treatments. Absolute growth rates were 14.9% higher in co-culture for pompano, whereas fastest sandfish growth occurred at density ratios of 1:0.5 and 1:1 (10.3% and 11.2% higher cf. control, respectively). Sediment TOM and STN content reduced with increasing sandfish density (TOM: 55.6–46.1% and STN:62.3–34.5% lower cf. control). During Experiment 2 pompano and sandfish reached 494.5 ± 1.8 g and 393.0 ± 20.9 g, respectively; over 8 months from initial sizes of 2.53 ± 0.02 g and 5.49 ± 0.05 g. Specific growth rates averaged 2.20 ± 0.02 and 1.75 ± 0.03%/day. Sediment TOM and STN increased over the culture period. Results demonstrate high feasibility for co-culture of these species with improved pond sediment quality.