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

• Main Author: Arney, Bianca Danielle
• Language: English
• Published: University of British Columbia 2013
• Online Access: http://hdl.handle.net/2429/45170

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.