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Rotifers and brine shrimp (Artemia) are important prey items for rearing marine fish larvae. Their availability in the water column may be reduced when they are transferred to larval rearing tanks at lower temperature. In this study, Brachionus rotundiformis (SS-type) and Brachionus plicatilis (L-type) were semi-continuously cultured and fed on live microalgae (Isochrysis galbana) at 20°C. Upon hatching, Artemia nauplii were fed I. galbana for 24 h at 20°C before temperature shock and handling experiments took place. Temperature shock and handling stress experiments with prey were conducted to test prey availability for larval culture of Eastern Pacific rockfish (Sebastes) species. Prey was sampled in 1 mL aliquots in the water column from 10 L buckets at 10, 14, 18, and 20°C after 0, 2, 4, 6, 12, 24, and 48 h suspension and from four water levels (top, middle, 5 cm above bottom, and bottom). The concentration of suspended prey (initially 10 prey per ml) was significantly reduced for all species after temperature transfer occurred and recovery was correlated with handling and transfer temperature. Rotifers and Artemia should be cultured at similar or lower temperatures compared with those of larval cultures or subjected to an acclimation period before being added to larval tanks.
Rockfish culture remains at a preliminary stage due to difficulties in obtaining larvae and establishing optimal culture conditions. Attempts to obtain larvae from hook-and-line captured wild rockfish have failed due to high larval mortalities; however, maintaining mature reproducing rockfish in tanks is an alternative to obtaining viable larvae. Visibly gravid females were collected monthly from the Oregon Coast Aquarium in Newport and held in isolation until they naturally released live larvae. In this study, we evaluated optimal temperature (10, 14, and 18ºC), green-water techniques, and grow-out in static cultures with Sebastes caurinus and S. malinger larvae. Survival of Sebastes caurinus larvae at 18 ºC was <15%, while survival was >40% at 10 and 14 ºC. Nannochloropsis occulata (Nanno) and Isochrysis galbana, Tahitian strain (T-Iso) were tested in a green-water and enrichment study with S. malinger larvae. T-Iso was better than Nanno for green-water conditioner and as a food for rotifers and either newly hatched or enriched Artemia. An average growth rate of 0.13 mm per day was observed for all three broods from females of different sizes, 2.95, 0.86, and 0.77 kg. Survival and initial size of larvae were greater for larvae from the largest female. Results from these experiments will be helpful in optimizing rockfish larval culture conditions for possible restoration of threatened rockfish species of the Eastern Pacific and for aquaculture. |
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