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Thermal and dietary optimization in the hatchery culture of juvenile Pacific geoduck clams (Panopea generosa, Gould 1850) Arney, Bianca Danielle


This research is the first to examine thermal and dietary optimization in the hatchery culture of juvenile Pacific geoduck (Panopea generosa). Chapter 2 investigated temperature and feed ration optimization; chapter 3 examined live algae substitution with the spray-dried species, Schizochytrium spp. or Spirulina (Arthrospira platensis). Geoduck growth and survival were measured to quantify treatment success. The temperature trial tested four temperatures (7, 11, 15, 19 °C) in juvenile and post-larval culture. Temperature promoted a significant growth effect in both sizes. The 19 °C culture elicited a delayed growth benefit in juveniles, and suppressed ash-free dry weight (AFDW), which recommends utilization of 15 °C. In contrast, geoduck post-larvae displayed immediate (post 7 d) shell growth acceleration at 19 °C. The 19 °C temperature shortened the rearing period by 2.9 d, suggesting its application in post-larval culture. The ration experiment examined the feed ration requirements of four geoduck juvenile size classes. Ration quantities between 0.0 - 128.0x10⁶ equivalent Isochrysis cells individual⁻¹ day⁻¹ were tested. All treatments received Chaetoceros muelleri and Isochrysis sp. mixed by AFDW. Following shell length/wet weight optimization, the following rations (10⁶ equivalent Isochrysis cells individual⁻¹ day⁻¹) should be applied between week 1 and 4 of the tested geoduck culture: 4.0 (1); 8.0 (2); 16.0 or 32.0 (shell length or wet weight optimum, respectively; 3); and 32.0 (4). The algae substitution trial replaced the above bi-algae diet with variant levels (0, 25, 50, 75, 100%) of Schizochytrium or Spirulina in two size classes. Between spray-dried diets, Spirulina treatments enhanced geoduck growth. However, overall growth displayed a general decline with elevated spray-dried inclusion and maximal growth occurred between 0 – 25% substitution. The superior bi-algae diet contained a polyunsaturated fatty acid Σn – 3/n – 6 ratio of 2.9, a value conserved in the bivalve literature. This may indicate its importance in future bivalve studies. Tissue analysis suggested potential limited digestion of spray-dried derived protein or carbohydrate, but indicated general lipid/fatty acid sequestration. These findings do not recommend dietary incorporation of Schizochytrium or Spirulina, but culture refinement may enhance juvenile geoduck hatchery production.

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