Effect of ration on gonad development of the Pacific geoduck clam, Panopea generosa (Gould, 1850)

摘要

The effect of ration on Panopea generosa gonad development was tested over 52 days. Clams were fed Isochrysis sp. and Chaetoceros muelleri (50 : 50 cell count) at rations of 0.8 x 10(9), 2.4 x 10(9), 4.0 x 10(9), 5.6 x 10(9), 7.2 x 10(9) and 10.0 x 10(9) cells clam(-1) day(-1) (R-1, R-2, R-3, R-4, R-5 and R-6, respectively). The highest ration (R-6) caused a 25% die-off within 3 days and was discontinued. Ration did not significantly affect condition index, gonadosomatic index, connective tissue occupation index or oocyte diameter. Clams fed the R-5 ration (85% of which spawned from day 26 to 52) were more spent than clams in any other treatment with significantly fewer oocytes mm(-2) than those fed the R-1, R-2 and R-3 rations and significantly lower levels of sperm occupation than clams fed any other ration. Spawn percentages were low from day 26 to 52 in R-1, R-2 and R-4 (15, 0 and 0%, respectively). Clams in the R-3 treatment had a similar spawn percentage (100% from day 26 to 52) to those in the R-5 treatment yet maintained gonads in a more ripened condition with higher levels of gamete occupation, making R-3 the most likely ration to maximize gamete output over time.