A major bottleneck in the aquaculture of abalone is feeding during the nursery stage of production, from larval settlement to approximately 10 mm in shell length (SL). Most commercial abalone nurseries settle larvae onto vertical plastic plates coated in a film of algae that acts as a settlement cue and an important postsettlement food source. As abalone grow, their food consumption increases exponentially, and it becomes increasingly difficult to maintain an adequate supply of algal food. Even grazing-resistant algae, like Ulvella lens, are often depleted when abalone reach 3–5 mm SL, requiring nurseries to provide additional algae or to wean the juveniles prematurely onto manufactured diets. Early weaning typically results in slower growth and higher mortality relative to live algal feeds. The current study tested various algal species to aid early weaning of the abalone Haliotis iris. Two experiments were conducted pairing nursery tanks of similar environmental conditions to test a total of three algal treatments: (1) the benthic diatom Nitzschia longissima, (2) a film of N. longissima and U. lens, and (3) a film of N. longissima and a naturally occurring mixture of green algal species that remained on weaning tank surfaces after a previous cohort of abalone had been harvested from the tank. Algae were established prior to the introduction of juvenile (SL, 2–7 mm) H. iris at a density of 15,000–30,000 abalone per tank (2.5 m3 water volume, 13 m2 surface area). The abalone were raised to approximately 15 mm SL with twice-weekly supplementary feeding of suspended N. longissima during the first 4 wk, and the addition of manufactured feed 3 times a day for the duration of the experiment. The N. longissima films were completely removed by grazing within 4–5 days whereas the green algal films persisted for 60–120 days. Despite the difference in resilience of algal films, there was no significant difference (P > 0.05) in abalone performance between treatments 1 (98.7% survival, growth of 85 µm/day) and 2 (98.3% survival, growth of 92 µm/day). In a second experiment, treatment 2 provided slightly greater growth than the mixed algal film of treatment 3(101 µm/day vs. 96 µm/day, P = 0.034), but survival rates were similar (98.2% vs. 98.3%, P = 0.86). All 3 algal treatments offer practical and effective means of weaning H. iris onto manufactured feeds at an SL of more than 3 mm. However, both treatments 1 and 3 can be established more rapidly than U. lens and are therefore likely to be more efficient for commercial weaning of H. iris and potentially for other species of abalone.
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Vol. 29 • No. 3