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Ruakaka, New Zealand

Roberts R.D.,Cawthron Institute | Roberts R.D.,OceaNZ Blue Ltd | Watts E.,Cawthron Institute
Journal of Shellfish Research | Year: 2010

Haliotis australis is a medium-size New Zealand abalone with aquaculture potential. H. australis can be readily ripened and spawned, but larval settlement has proved difficult. The current study addressed aspects of larval settlement (i.e., attachment and metamorphosis) in laboratory experiments and small-scale hatchery trials. Competence to metamorphose was first seen weakly in larvae at 8 days old at 14.5°C, but larval metamorphosis rates increased progressively up to at least 12 days of age. In laboratory experiments, larvae showed a dose-dependent response to dissolved -aminobutyric acid (GABA), with settlement peaking at 1 M (57% metamorphosis 4 days after settlement induction) and declining at higher and lower doses. Across a range of cues, metamorphosis was highest on crustose coralline algae (97 ± 4% metamorphosis after 4 days), intermediate on 1 M GABA (55 ± 14%), and low on diatom films (<20%). GABA combined additively with diatom film to give strong metamorphosis (81 ± 6%). Metamorphosis induction by a diatom film was doubled if the film was pregrazed by juvenile H. australis (76% vs. 35%, P < 0.0001), but the grazing effect appeared to be species specific, because pregrazing by Haliotis iris had no effect (41% vs. 35%, P = 0.720). The species-specific response to trail mucus appears to preclude GABA as being the main inducer of metamorphosis in this case. On hatchery plates, settlement on pregrazed biofilms was approximately 4-fold higher when the plates were horizontal rather than vertical (41 % vs. 10% metamorphosis, P = 0.003). Settlement on ungrazed horizontal plates remained low even if those plates had been held in water with adult conspecifics, but without contacting the abalone. We conclude that tanks offering sloped or horizontal surfaces will be more effective than vertical plates for settlement of H. australis, and that pregrazed biofilms and/or GABA are promising settlement cues. Source

Roberts R.D.,Cawthron Institute | Roberts R.D.,University of Otago | Roberts R.D.,OceaNZ Blue Ltd | Barker M.F.,University of Otago | Mladenov P.,University of Otago
Journal of Shellfish Research | Year: 2010

Abalone larvae settle (attach and metamorphose) in response to crustose coralline algae (CCA), but it is not known whether the settlement cues arise from the CCA or from microbes on their surface. The CCA Phymatolithon repandum induced close to 100% metamorphosis of Haliotis iris larvae. Pebbles and shells with a biofilm but without visible macroalgae induced, on average, 58% metamorphosis on H. iris larvae within 2 days, and biofilms are commonly used to cue settlement in H. iris hatcheries. This suggests that settlement on P. repandum might be triggered by the surface biofilm rather than the CCA itself. Treatment of P. repandum with antibiotics, germanium dioxide, and scrubbing did not significantly reduce settlement of H. iris larvae. Diatom strains isolated from P. repandum induced little attachment or metamorphosis at the low diatom densities (103104 cells/cm2) found on P. repandum, but induced moderate attachment (3085% after 4 days) and metamorphosis (240%) at high densities (5 × 104-1 × 106 cells/cm2). Nine bacterial strains isolated from P. repandum induced low-percent attachment (045% after 7 days) and metamorphosis (020%) if assayed in the presence of antibiotics. Parallel assays without antibiotics had higher attachment (4080% after 7 days) and metamorphosis (550%), but this activity may have arisen from bacteria introduced with the larvae. Although bacteria and diatoms did induce some attachment and metamorphosis of H. iris larvae, they were less effective than P. repandum (95% within 2 days). Treatments that greatly reduced the biofilm on P. repandum had no effect on its settlement-inducing activity. This evidence supports the view of CCA as an especially potent source of inducers for temperate abalone larval settlement. Source

Dyck M.,University of Auckland | Roberts R.,OceaNZ Blue Ltd | Jeffs A.,University of Auckland
Journal of Shellfish Research | Year: 2010

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 35 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, 27 mm) H. iris at a density of 15,00030,000 abalone per tank (2.5 m 3 water volume, 13 m 2 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 45 days whereas the green algal films persisted for 60120 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 m/day) and 2 (98.3% survival, growth of 92 m/day). In a second experiment, treatment 2 provided slightly greater growth than the mixed algal film of treatment 3(101 m/day vs. 96 m/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. Source

Dyck M.,University of Auckland | Roberts R.,OceaNZ Blue Ltd | Jeffs A.,University of Auckland
Aquaculture | Year: 2011

Feeding during the nursery stage of abalone aquaculture, from larval settlement to 10. mm in shell length (SL), is a major challenge in the intensification of abalone aquaculture. Commercial abalone nurseries typically settle larvae onto vertical plastic plates coated with algae that act as a settlement cue and an important post-settlement food source. It becomes increasingly difficult to maintain an adequate algal food supply as the abalones grow and for this purpose many nurseries use the alga, Ulvella lens, as it is a very effective settlement cue as well as offering a resilient food source for the developing abalones. However, juvenile abalones can deplete a film of diatoms on the plates before they are capable of ingesting U. lens, and once abalone reach ~. 5. mm SL the high grazing pressure may exceed even what U. lens can support, requiring nurseries to provide additional cultured algae or prematurely wean the juveniles onto manufactured diets. Three prospective microfilamentous algal species isolated from the tanks of a commercial abalone facility, were selected as potentially suitable nursery algae as they demonstrated resistance to intensive juvenile grazing pressure, displayed rapid vegetative growth, and could be triggered to mass sporulate as a means of rapidly coating nursery tanks. The current study involved two experiments and assessed the suitability of each species as a live algal feed for juvenile abalones compared to U. lens. These experiments measured: (1) ingestibility and grazing resistance of each alga against juvenile abalone 1-8. mm SL, and (2) the ability of each species to recover once grazers had been removed. Two algae (Ulvophyceae sp. 1 and 3) demonstrated the desirable properties of being easily grazed by abalones of a smaller size (average SL 2.33. mm and 2.20. mm respectively) than U. lens (2.89. mm) yet provide an algal film that is likely to be resilient and durable under grazing pressure. These algae also displayed significantly greater rates of recovery following grazing than U. lens (p < 0.01), an important attribute for restoring algal films in nursery systems between grazing events or between batches of juvenile abalones. The results of this study indicate that these novel algae have a combination of desirable characteristics for use in commercial abalone nurseries. Further experiments in commercial scale nursery systems should be pursued to assess the food value and performance of these species as a feed for juvenile abalones. © 2011 Elsevier B.V. Source

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