Broodstock conditioning and larval rearing of the geoduck clam (Panopea generosa Gould, 1850)

• Main Author: Marshall, Robert
• Language: English
• Published: University of British Columbia 2012
• Online Access: http://hdl.handle.net/2429/41531

The aim of this thesis was to identify conditions that optimize Panopea generosa broodstock conditioning and larval growth and survival in a hatchery setting. A series of experiments subjected broodstock (adults) to various levels of key factors [i.e. temperature (Ch. 2), salinity (Ch. 3) and nutrition [ration (Ch. 4) and feed type (Ch. 5)]. A larval experiment examined the effects of stocking density and feed level combinations on growth and survival (Ch. 6). Broodstock responses were quantified using gravimetric (condition and gonadosomatic indices) and histological techniques (development classification, volume fractions and oocyte diameter). Survival and spawning rates were also examined. Of the temperatures tested (7, 11, 15 and 19˚C) 11˚C had the highest spawning rates (% individuals) and more oocytes follicle⁻¹, than 15 and 19˚C. At 7˚C gonadosomatic indices were highest but this temperature did not produce spawning clams. Gonads degenerated at 19˚C. Among salinities of 17, 20, 24, and 29 gonad sheath thickness and area occupied by gametes increased at 29 but not at 24. Salinities of 17 and 20 were associated with fungal infection and had high mortality rates after 26 d exposure. With higher ration treatments (up to 7.2 × 10⁹ cells clam⁻¹ d⁻¹ [Isochrysis sp. (TISO) and Chaetoceros muelleri, 50:50 by cell count] clams became more spawned. Very high rations (10.0 × 10 ⁹ cells clam⁻¹ d⁻¹) increased mortality. Algal type [Dunaliella tertiolecta, (TISO), C. muelleri and TISO + C. muelleri) had no measurable impact on gonad development based on any of the response variables used. The larval experiment showed that there was a significant interaction between stocking density and feed level with respect to growth and survival. The most efficient treatment was 10 larvae ml⁻¹ fed 5,000 cells larva⁻¹ (TISO) as it had among the highest growth (3.75 μm day⁻¹) and survival (42%) rates but low algal requirements. These findings illustrate reproductive responses of P. generosa that can be applied to a hatchery management strategy.