Grow-out culture of tropical abalone, Haliotis asinina (Linnaeus) in suspended mesh cages with different shelter surface areas

This study investigated the effects of shelter surface area (SSA) on the feeding, growth and survival of the donkey-ear abalone, Haliotis asinina reared in mesh cages (0.38x 0.38x 0.28 m) suspended in flow-through tanks (water volume =6 m(3)). Cages had sections of polyvinylchloride (PVC) that provided shelters with surface area of 0.22 m(2), 0.44 m(2) and 0.66 m(2). Hatchery-produced abalone with initial shell length of 32 +/- 1 mm and wet weight of 7.5 g were stocked at 50 individuals cage(-1) that corresponded to stocking densities of ca. 227, 113 and 75 abalone m(-2) of SSA. The ratios of shelter surface area to cage volume (SSA: CV) were 5.5, 11 and 16.5. Abalones were provided an excess red seaweed Gracilariopsis bailinae (= Gracilaria heteroclada) at weekly intervals over a 270-day culture period. Feeding rates (18-20% of wet weight), food conversion ratio (26-27) and percent survival (88-92%) did not differ significantly among treatments (p > 0.05). Body size at harvest ranged from 56 to 59 mm SL and 52 to 57 g wet body weight with significant differences between abalone reared at SSA 0.22 m(2) and 0.66 m(2) (p < 0.05). Abalone reared in cages with 0.66 m(2) SSA grew significantly faster at average daily growth rates of 132 μm and 188 mg day(-1). Stocking densities of 75-113 m(-2) SSA in mesh cages suspended in flow-through tanks resulted in better growth of abalone fed red seaweed.